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The Sheahan Diamond Literature Reference Compilation - Scientific and Media Articles based on Major Keyword - UHP
The Sheahan Diamond Literature Reference Compilation is compiled by Patricia Sheahan who publishes on a monthly basis a list of new scientific articles related to diamonds as well as media coverage and corporate announcements called the Sheahan Diamond Literature Service that is distributed as a free pdf to a list of followers. Pat has kindly agreed to allow her work to be made available as an online digital resource at Kaiser Research Online so that a broader community interested in diamonds and related geology can benefit. The references are for personal use information purposes only; when available a link is provided to an online location where the full article can be accessed or purchased directly. Reproduction of this compilation in part or in whole without permission from the Sheahan Diamond Literature Service is strictly prohibited. Return to Diamond Keyword Index
Sheahan Diamond Literature Reference Compilation - Scientific Articles by Author for all years
Each article reference in the SDLRC is tagged with one or more key words assigned by Pat Sheahan to highlight the main topics of the article. In an effort to make it easier for users to track down articles related to a specific topic, KRO has extracted these key words and developed a list of major key words presented in this Key Word Index to which individual key words used in the article reference have been assigned. In most of the individual Key Word Reports the references are in crhonological order, though in some such as Deposits the order is first by key word and then chronological. Only articles classified as "technical" (mainly scientific journal articles) and "media" (independent media articles) are included in the Key Word Index. References that were added in the most recent monthly update are highlighted in yellow.
UHP refers to ultra high pressure metamorphism of rocks within the crust involving pressures that theoretically exist deeper than the 80-90 km thickness of crustal rocks. Ultra high pressure conditions emerge in subduction settings, which is relevant to diamonds because eclogite, a major source rock for diamonds, originated as an oceanic slab.
Phase and melting relations of peridotite H2O and basalt H2O systems to the top of the lower mantle and implications for slab subduction and hot mantle plume.
18th. International Mineralogical Association Sept. 1-6, Edinburgh, abstract p.75.
Olivine pyroxene H2O system as a practical analogy for estimating the elastic properties of fluid bearing mantle rocks at high pressures and temperatures.
Geophysical Research Letters, Vol. 29,9,May 1, p. 39-
Carboniferous and Triassic eclogites in the Western Dabie Mountains east central Chin a: evidence for protracted convergence of the North and South Chin a Blocks.
Journal of Metamorphic Geology, Vol. 20, 9, pp. 873-886.
Ultra high pressure metamorphism in western Tianshan, China: part I. Evidence from inclusions of coesite pseudomorphs in garnet and from quartz exsolution lamellae i
Limiting effect of UHP metamorphism on length scales of oxygen, hydrogen and argon isotope exchange: an example from the Qinglongshan UHP eclogites, Sulu Terrain.
International Geology Review, Vol. 47, 7, pp. 716-749.
High pressure/ultrahigh pressure eclogites from the Hongan Block, east central China: geochemical characterization, isotope disequilibrium, geochronology
Contributions to Mineralogy and Petrology, Vol. 149, 5, pp. 499-526.
High pressure ultrahigh pressure eclogites from the Hong an Block, east central China: geochemical characterization, isotope disequilibrium and geochronological controversy.
Contributions to Mineralogy and Petrology, On line
An Early Cretaceous intrusive complex in the Dabie Shan ultrahigh pressure metamorphic terrane, East China. Evidence for the beginning of post orogenic collapse.
GAC Annual Meeting Halifax May 15-19, Abstract 1p.
Epidote rich talc kyanite phengite eclogites, Sulu terrane, eastern China: P T fo2 estimates and the significance of epidote talc assemblage in eclogite.
Quartz exsolution in clinopyroxene is not proof of ultra high pressures: evidence from phase equilibration temperatures and eclogite from the eastern Blue Ridge, southern Appalachians.
Geological Society of America Annual Meeting ABSTRACTS, Nov. 7-10, Paper 195-3, Vol. 36, 5, p. 453.
SIMS analyses on trace and rare earth elements in coexisting clinopyroxene and mica from minette mafic enclaves in potassic syenites crystallized under high pressure.
Contributions to Mineralogy and Petrology, Vol. 148, 6, pp. 675-688.
Song, S., Zhang, L., Chen, J., Liou, J.G., Niu, Y.
Sodic amphibole exsolutions in garnet from garnet-peridotite, North Qaidam UHP belt, NW China: implications for ultradeep origin and hydroxyl defects in mantle garnets.
Wang, Q., Shaocheng, J., Salisbury, M.H., Xia, B., Pan, M., Xu, Z.
Shear wave properties and Poisson's ratios of ultrahigh pressure metamorphic rocks from the Dabie Sulu orogenic belt, China: implications for crustal composition.
Journal of Geophysical Research, Vol. 110, B8, pp. B08411 10.1029/2004 JB003435
Eclogitic and ultrahigh pressure crustal garnets and their relationship to Phanerozoic subduction diamonds, Bingara area, New England Fold Belt, eastern Australia.
Vendian Early Ordovician geodynamic evolution and model for exhumation of ultrahigh and high pressure rocks from the Kokchetav subduction collision zone.
Russian Geology and Geophysics, Vol. 47, 4, pp. 424-440.
Ferrando, S., Frzzotti, M.L., Dallai, L., Compagnoni, R.
Multiphase solid inclusions in UHP rocks ( Su-Lu, China): remnants of supercritical silicate rich aqueous fluids released during continental subduction.
Chemical Geology, Vol. 223, 1-3, Nov. 22, pp. 68-81.
Mantle derived UHP garnet pyroxenite and eclogite in the Moldanubian Gfohl Nappe, Bohemian Massif: a geochemical review, New PT and tectonic interpretations
International Geology Review, Vol. 48, 9, pp. 765-777.
Perraki, M., Proyer, A., Mposkos, E., Kaindl, R., Hoinkes, G.
Raman micro spectroscopy on diamond, graphite and other carbon polymorphs from the ultrahigh pressure metamorphic Kimi Complex of the Rhodope metamorphic province.
Earth and Planetary Science Letters, Vol. 241, 3-4, pp. 672-685.
Ratschbacher, L., Franz, L., Enkelmann, E., Jonckheere, R., Porschke, A., Hacker, B.R., Dong, S., Zhang, Y.
The Sino-Korean Yangtze suture, the Huwan detachment and the Paleozoic Tertiary exhumation of ultra high pressure rocks along the Tongbai Xinxian Dabie Mtns.
Geological Society of America, Special Paper, No. 403, pp. 45-76.
Evidence for diamond grade ultra high pressure metamorphism and fluid interaction in the Svartberget Fe Ti garnet peridotite websterite body, western Gneiss region, Norway.
Mineralogy and Petrology, Vol. 88, 1-2, pp. 381-405.
Vrijmoed, J.C., Van Roermund, H.L.M., Davies, G.R.
Evidence for diamond grade ultra high pressure metamorphism and fluid interaction in the Svartberget Fe Ti garnet peridotite websterite body, Western Gneiss
Wawrzenitz, N., Romer, R.L., Oberhansli, R., Dong, S.
Dating of subduction and differential exhumation of UHP rocks fromn the Central Dabie Complex ( E-China): constraints from microfabrics, Rb-Sr and U-Pb isotope systems.
49 Ar 39 Ar thermochronology of the Sulu terrane: Late Triassic exhumation of high and ultrahigh pressure rocks -implications for Mesozoic tectonics East Asia.
Geological Society of America, Special Paper, No. 403, pp. 77-92.
SHRIMP U Pb zircon dating of the Rongcheng eclogite and associated peridotite: new constraints for UHP metamorphism of mantle derived mafic ultramafic bodies
Geological Society of America Special Paper, No. 403, pp. 115-126.
Isotopic constraints on age and duration of fluid assisted high pressure eclogite facies recrystallization during exhumation of deeply subducted continental crurs
Journal of Metamorphic Geology, Vol. 24, 8, pp. 687-702.
Partitioning of FeO between magnesiwustite and liquid iron at high pressures and temperatures: implications for the composition of the Earth's outer core.
Earth and Planetary Science Letters, Vol. 257, 3-4, May 30, pp. 435-449.
Jianxin, Z., Jingsui, Y., Fabcong, M.,Yusheng, W., Huimin, Li., Cailai, W.
U Pb isotopic studies of eclogites and their host gneisses in the Xitishan area of the North Qaidam mountains, western China: new evidence HP-UHP belt.
Journal of Asian Earth Sciences, Vol. 28, 2-3, Nov. 15, pp. 143-150.
Identification of UHP and non-UHP orthogneisses in the Sulu UHP terrane, eastern China: evidence from SHRIMP U-Pb dating of mineral inclusion bearing zircons.
International Geology Review, Vol. 48, 12, pp. 1067-1086.
Melting relations in the chloride carbonate silicate systems at high pressure and model for formation of alkalic diamond forming liquids in the upper mantle.
Earth and Planetary Science Letters, in press available
Wang, Q., Wyman, D.A., Xu, J., Jian, P., Zhao, Z., Li, C., Xu, W., Ma, J., He, B.
Early Cretaceous adakitic granites in the northern Dabie Complex, central China: implications for partial melting and delamination of thickened lower crust.
Geochimica et Cosmochimica Acta, Vol. 71, 10, May 15, pp. 2609-2636.
Yin, A., Manning, C.E., Lovera, O., Menold, C.A., Chen, X., Gehrels, G.
Early Paleozoic tectonic and thermomechanical evolution of ultrahigh pressure (UHP) metamorphic rocks in the northern Tibetan Plateau, northwest China.
International Geology Review, Vol. 49, 8, pp. 681-716.
Velocity conductivity relationships for mantle mineral assemblages in Archean cratonic lithosphere based on a review of laboratory dat a and Hashin-Shtrikman extremal bonds.
Chemical composition and ultrahigh P metamorphism of garnet peridotites from the Sulu UHP terrane, China: investigation of major, trace elements and Hf isotopes
Chemical composition and ultrahigh P metamorphism of garnet peridotites from the Sulu UHP terrane, China: investigation of major trace elements and Hf isotopes.
Chemical Geology, Vol. 255, 1-2, Sept. 30, pp. 250-264.
Fluids in deeply subducted continental crust: petrology, mineral chemistry and fluid inclusion of UHP metamorphic veins from the Sulu Orogen, eastern China.
Geochimica et Cosmochimica Acta, Vol. 72, 13, July 1, pp. 3200-3228.
The effect of oxygen fugacity on the olivine to wadsleyite transformation: implications for remote sensing of mantle redox state at the 410 km seismic ...
Two stage collision related extrusion of the western Dabie HP-UHP metamorphic terranes, centra China: evidence from quartz c-axis fabrics and structures.
Differential subduction and exhumation of crustal slices in the Sulu HP-UHP metamorphic terrane: insights from mineral inclusions, trace elements, U-Pb and Lu Hf isotope analyses of zircon in orthogneiss
Journal of Metamorphic Geology, Vol. 27, 9, pp. 805-825.
Perraki, M., Korsakov, A.V., Smith, D.C., Mposkos, E.
Raman spectroscopic and microscopic criteria for the distinction of microdiamonds in ultrahigh-pressure metamorphic rocks from diamonds in sample preparation materials.
Zhang, Z.M., Schertl, H.P., Wang, J.L., Shen, K., Liou, J.G.
Source of coesite inclusions within inherited magmatic zircon from Sulu UHP rocks, eastern China, and their bearing for fluid rock interaction and SHRIMP dating.
Journal of Metamorphic Geology, Vol. 27, 4, pp. 317-333.
An AEM study of garnet clinopyroxenite from the Sulu ultrahigh pressure terrane: formation mechanisms of oriented ilmenite, spinel, magnetite, amphibole and
Contributions to Mineralogy and Petrology, in press available, 14p.
Zircon as the best mineral for P-T time history of UHP metamorphism: a review on mineral inclusions and U-Pb SHRIMP ages of zircons from the Dabie Sulu UHP rocks.
Journal of Asian Earth Sciences, Vol. 40, 1, pp. 1-39.
Saha, L., Pant, N.C., Pati, J.K., Upadhyay, D., Berndt, J., Bhattacharya, A., Satynarayanan, M.
Neoarchean high pressure margarite phengite muscovite chlorite corona mantle corundum in quartz free high Mg, Al phlogopite chlorite schists from the Bundelkhand
Contributions to Mineralogy and Petrology, in press available, 20p.
Episodic growth of zircon in UHP orthogneisses from the North Dabie Terrane of east central China: implications for crustal architecture of a collisional orogen.
Journal of Metamorphic Geology, In press available,
U-Pb zircon geochronology of coesite bearing eclogites from the southern Dulan areas of the North Qaidam UHP terrane, northwestern China: spatially and temporally
Journal of Metamorphic Geology, Vol. 28, 9, pp. 955-978.
Metamorphic growth and recrystallization of zircons in negative delta 18 O metamorphic rocks: a combined study of U-Pb dating, trace elements and O-Hf isotopes.
Ultra high pressure metamorphism and multistage exhumation of eclogite of the Luotian dome, North Dabie Complex Zone: evidence from mineral inclusions -texture
Journal of Asian Earth Sciences, Vol. 42, 4, pp. 607-617.
Mysen, B.O., Kumamoto, K., Cody, G.D., Fogel, M.L.
Solubility and solution mechanisms of C-O-H volatiles in silicate melt with variable redox conditions and melt composition at upper mantle temperatures and pressures.
Geochimica et Cosmochimica Acta, Vol. 75, 9, pp. 6183-6199.
Experimental study of partition of rare elements between minerals and melts of diamond forming eclogite carbonatite and peridotite carbonatites systems.
Comparison of the compositions of olivines and clinopyroxenes from mantle and crustal peridotites of collisional high pressure/ultrahigh pressure zones.
Comparison of the compositions of olivines and clinopyroxenes from mantle and crustal peridotites of collisional high pressure ultrahigh pressure zones.
Partial melting and element transfer during continental subduction zone metamorphism: geochemical insights from leucosome within UHP eclogite in the Dabie Orogen.
Oxygen isotope variations of garnets and clinopyroxenes in a layered Diamondiferous calcsilicate rock from Kokchetav Massif, Kazakhstan: a window into geochemical
Contributions to Mineralogy and Petrology, Vol. 162, 5, pp.1079-1092.
Zhang, Z.M., Dong, X., Liou, J.G., Liu, F., Wang, W., Yui, F.
Metasomatism of garnet periodite from Jiangzhuang, Sulu UHP belt: constraints on the interactions between crust and mantle rocks during subduction of cont. lithosphere
Journal of Metamorphic Geology, in press available
Zhang, Z.M., Dong, X., Liou, J.G., Liu, F., Wang, W., Yui, F.
Metasomatism of garnet peridotite from Jiangzhuang, southern Sulu UHP belt: constraints on the interactions between crust and mantle rocks during subduction of continental
Journal of Metamorphic Geology, Vol. 29, 9, pp. 917-937.
Delamination and ultradeep subduction of continental crust: constraints from elastic wave velocity and density measurement in ultrahigh pressure metamorphic rocks
Journal of Metamorphic Geology, Vol. 29, 7, pp. 781-801.
Delamination and ultra deep subduction of continental crust: constraints from elastic wave velocity and density measurement in ultra high pressure metamorphic rocks
Journal of Metamorphic Geology, Vol. 29, 7, pp. 781-801.
Zhao, Z., Niu, Y., Christensen, N.I., Zhou, W., Hou, Q., Zhang, Z.M., Xie, H., Zhang, Z.C., Liu, J.
Delamination and ultradeep subduction of continental crust: constraints from elastic wave velocity and density measurement in ultrahigh pressure met. rocks
Journal of Metamorphic Geology, Vol. 29, 7, pp. 781-801.
Multistage growth of garnet in ultrahigh pressure eclogite during continental collision in the Dabie Orogen: constrained by trace elements and U Pb ages.
Liou, J.G., Zhang, R., Liu, F., Zhang, Z., Ernst, W.G.
Mineralogy, petrology, U-Pb geochronology, and geologic evolution of the Dabie Sulu classic ultrahigh pressure metamorphic terrane, east-central China.
American Mineralogist, Vol. 97, no. 10, pp. 1533-1543.
Malaspina, N., Langenhorst, F., Fumagalli, P., Tumiati, S., Poli, S.
Fe 3+ distribution between garnet and pyroxenes in mantle wedge carbonate bearing garnet peridotites ( Sulu, China) and implications for their oxidation state.
Malaspina, N., Langenhorst, F., Fumagalli, P., Tumiati, S., Poli, S.
Fe 3 + distribution between garnet and pyroxenes in mantle wedge carbonate bearing garnet peridotites ( Sulu China) and implications for their oxidation state.
Martin, A.M., Laporte, D., Koga, K.T., Kawamoto, T., Hammouda, T.
Experimental study of the stability of a dolomite + coesite assemblage in contact with peridotite: implications for sediment-mantle interaction and diamond formation during subduction.
Comparison of the compositions of clinopyroxenes, garnets and spinels from mantle and crustal peridotites of collisional high pressure/ultrahigh pressure zones.
Trace element composition of continentally subducted slab-derived melt: insight from multiphase solid inclusions in ultrahigh pressure eclogite in the Dabie Orogen.
Journal of Metamorphic Geology, Vol. 31, 4, pp. 453-468.
Guarino, V., Wu, F-Y., Lustrino, M., Melluso, L., Brotzu, P., Barros Gomes, C.de, Ruberti, E., Tassarini, C.C.G., Svisero, D.P.
U-Pb ages, Sr, Nd isotope geochemistry, and petrogenesis of kimberlites, kamafugites and phlogopte-picrites of the Alto Paranaiba Igneous Province, Brazil.
Guo, S., Ye, K., Wu, Y., Chen, Y., Yang, Y., Zhang, L., Liu, J., Mao, Q., Ma, Y.
A potential method to confirm the previous existence of lawsonite in eclogite: the mass imbalance of Sr and LREEs in multi stage epidote ( Ganghe, Dabie UHP terrane).
Journal of Metamorphic Gology, Vol. 31, 4, pp. 415-435.
Tectonic relationships between E-type cratonic and ultra-high-pressure (UHP) diamonds: implications for craton formation and stabilization.
Proceedings of the 10th. International Kimberlite Conference, Vol. 1, Special Issue of the Journal of the Geological Society of India,, Vol. 1, pp. 45-58.
Kovach, V.,Salnikova, E., Wang, K-L., Jahn, B-M., Chiu, H-Y., Reznitskiy, L., Kotov, A., Lizuka, Y., Chung, S-L.
Zircon ages and Hf isotopic constraints on sources of clastic metasediments of the Slyudyansky high grade complex, southeastern Siberia: implication for continental growth and evolution of the Central Asian orogenic belt.
Journal of Asian Earth Sciences, Vol. 62, pp. 18-36.
Common Pb isotope mapping of UHP metamorphic zones in Dabie orogen, central China: implication for Pb isotopic structure of subducted continental crust.
Geochimica et Cosmochimica Acta, Vol. 143, pp. 115-131.
The architecture of the HP-UHP Dabie Massif: new insights from geothermobarometry of eclogites and implication for the continental exhumation processes.
Journal of Asian Earth Sciences, Vol. 86, pp. 38-58.
Two fresh types of eclogites in the Dabie Sulu UHP metamorphic belt, China: implications for the deep subduction and earliest stages of exhumation of the continental crust.
Journal of Earth Science ( Chinese pub in english), Vol. 23, no. 6, pp. 775-785.
Metamorphic evolution of medium temperatire ultra high pressure ( MT-UHP) eclogites from the South Dabie orogen, central China: an insight from phase equilibration temperatures modelling.
Journal of Metamorphic Geology, Vol. 31, 7, pp. 755-774,
Multiphase solid inclusions in zoisite bearing eclogite: evidence for partial melting of ultrahigh pressure metamorphic rocks during continental collision.
Godard, G., Frizzotti, M-L., Palmeri, R., Smith, D.C.
Origin of high pressure disordered metastable phases ( Lonsdaleite and incipiently amorphized quartz) in metamorphic rocks: geodynamic shock or crystal-scale overpressure?
In: Ultrahigh Pressure Metamorphism: 25 years after discovery of coesite and diamond. Eds. Dobrzhinetskaya, L., Cuthbert, S., Faryad, W., Elsevier Publ. Pp. 125-148.
First finding of microdiamond, coesite and other UHP phases in felsic granulites in the Moldanubian Zone: implications for deep subduction and a revised geodynamic model for Variscan Orogeny in the Bohemian Massif.
Prencipe, M., Bruno, M., Nestola, F., De La Pierre, M., Nimis, P.
Toward an accurate ab initio estimation of compressibility and thermal expansion of diamond in the (0, 3000K) temperature and (0,30 Gpa) pressure ranges, at the hybrid HF/DFT theoretical level.
The architecture of the HP-UHP Dabie massif: new insights from geothermobarometry of eclogites, and implication for the continental exhumation processes.
Journal of Asian Earth Sciences, Vol. 86, I, pp. 38-58.
Continental orogenesis from ocean subduction, continent collision/subduction, to orogen collapse, and orogen recycling: the example of the North Qaidam UHPM belt, NW China.
Deep subduction of continental crust in accretionary orogen: evidence from U-Pb dating on diamond-bearing zircons from the Qinling orogen, central China.
Abstract: The Late Neoproterozoic assembly of western Gondwana played an important role in the subduction of oceanic and continental lithospheres. Such event was also a source of arc magmatism, reworking of cratonic margins and development of ultra-high pressure (UHP) suture zones. In the Borborema province, NE Brazil, we have described for the first time UHP rocks enclosed within gneiss migmatite and calc-silicate rocks. They bear coesite included in atoll-type garnet from metamafic rocks, identified by petrographic study and Raman microspectroscopy analysis. U-Pb zircon dating of the leucosome of the migmatites and the calc-silicate rock displays, concordant ages of 639 ± 10 Ma and 649.7 ± 5 Ma, respectively, here interpreted as the minimum age of the eclogitization event in the region. U-Pb zircon dating of the coesite-bearing rock defined a concordia age of 614. 9 ± 7.9 Ma that comprised the retrograde eclogitic conditions to amphibolite facies. The UHP rocks, mostly retrograded to garnet amphibolites, occur enclosed in the Paleoproterozoic continental block composed of calc-silicate rocks, migmatized sillimanite gneiss, mylonitic augen gneiss and granitic and tonalitic gneiss along a narrow N-S oriented belt between the Santa Quitéria magmatic arc and the Transbrasiliano lineament. This block was involved in the subduction to UHP eclogite depths, and was retrogressed to amphibolite during its exhumation and thrusting. Our data indicate an important Neoproterozoic transcontinental suture zone connecting the Pharusian belt with Borborema Province, and probably with the Brasília belt in central Brazil.
Abstract: We have found >10 in situ microdiamonds in thin sections of eclogites from the Dabie and Su-Lu regions of central eastern China since the first occurrence of microdiamond in eclogites from the Dabie Mountains (DMT) reported in 1992. The microdiamonds are found not only in the central part but also in the northern part of the DMT. Several free crystals have been recovered from the crushed eclogites from the central DMT. Most in situ microdiamonds are inclusions in garnets but a few larger ones are intergranular. Most of the diamondiferous eclogites in the central part of the DMT are associated with coesite. Most importantly, the observation of microdiamonds in northern Dabie lead us to question the supposition that this is a low-P metamorphic terrane. All the diamondiferous eclogites from both the north and central DMT are of continental affinity as demonstrated by their negative ?Nd values. Therefore, both the north and central eclogite belts in the DMT are considered to be from the deep subducted terrane. Five in situ microdiamonds and two free crystals are first reported in this paper. The dimensions of the in situ microdiamonds are 30-80 ?m and the free crystals are up to 400–-00 ?m across. All the microdiamonds are confirmed as such by Raman spectroscopy. The results of an infrared spectroscopic investigation on two larger free crystals and two in situ microdiamonds show that all the microdiamonds from both the Dabie and Su-Lu regions are mixed types IaA and IaB diamonds and there is no indication of any synthetic microdiamonds in our samples because such synthetic microdiamonds are always rich in type Ib.
Petrik, I., Janak, M., Froitzheim, N., Georgiev, N., Yoshida, K., Sasinkova, V., Konecny, P., Milovska, S.
Triassic to Early Jurassic ( c. 200Ma) UHP metamorphism in the Central Rhodopes: evidence from U-Pb dating of monazite in diamond bearing gneiss from Chepelare ( Bulgaria).
Journal of Metamorphic Geology, Vol. 34, 3, pp. 265-291.
Abstract: The Barchi-Kol terrain is a classic locality of ultrahigh-pressure (UHP) metamorphism within the Kokchetav metamorphic belt. We provide a detailed and systematic characterization of four metasedimentary samples using dominant mineral assemblages, mineral inclusions in zircon and monazite, garnet zonation with respect to major and trace elements, and Zr-in-rutile and Ti-in-zircon temperatures. A typical diamond-bearing gneiss records peak conditions of 49 ± 4 kbar and 950-1000 °C. Near isothermal decompression of this rock resulted in the breakdown of phengite associated with a pervasive recrystallization of the rock. The same terrain also contains mica schists that experienced peak conditions close to those of the diamond-bearing rocks, but they were exhumed along a cooler path where phengite remained stable. In these rocks, major and trace element zoning in garnet has been completely equilibrated. A layered gneiss was metamorphosed at UHP conditions in the coesite field, but did not reach diamond-facies conditions (peak conditions: 30 kbar and 800-900 °C). In this sample, garnet records retrograde zonation in major elements and also retains prograde zoning in trace elements. A garnet-kyanite-micaschist that reached significantly lower pressures (24 ± 2 kbar, 710 ± 20 °C) contains garnet with major and trace element zoning. The diverse garnet zoning in samples that experienced different metamorphic conditions allows to establish that diffusional equilibration of rare earth element in garnet likely occurs at ~900-950 °C. Different metamorphic conditions in the four investigated samples are also documented in zircon trace element zonation and mineral inclusions in zircon and monazite. -Pb geochronology of metamorphic zircon and monazite domains demonstrates that prograde (528-521 Ma), peak (528-522 Ma), and peak to retrograde metamorphism (503-532 Ma) occurred over a relatively short time interval that is indistinguishable from metamorphism of other UHP rocks within the Kokchetav metamorphic belt. Therefore, the assembly of rocks with contrasting P-T trajectories must have occurred in a single subduction-exhumation cycle, providing a snapshot of the thermal structure of a subducted continental margin prior to collision. The rocks were initially buried along a low geothermal gradient. At 20-25 kbar they underwent near isobaric heating of 200 °C, which was followed by continued burial along a low geothermal gradient. Such a step-wise geotherm is in good agreement with predictions from subduction zone thermal models.
Abstract: The mechanisms that result in the formation of high-pressure (HP) and ultrahigh-pressure (UHP) rocks are controversial. The usual interpretation assumes that pressure is close to lithostatic, petrological pressure estimates can be transferred to depth, and (U)HP rocks have been exhumed from great depth. An alternative explanation is that pressure can be larger than lithostatic, particularly in continental collision zones, and (U)HP rocks could thus have formed at shallower depths. To better understand the mechanical feasibility of these hypotheses, we performed thermomechanical numerical simulations of a typical subduction and collision scenario. If the subducting crust is laterally homogeneous and has small effective friction angles (and is thus weak), we reproduce earlier findings that <20% deviation of lithostatic pressure occurs within a subduction channel. However, many orogenies involve rocks that are dry and strong, and the crust is mechanically heterogeneous. If these factors are taken into account, simulations show that pressures can be significantly larger than lithostatic within nappe-size, mechanically strong crustal units, or within a strong lower crust, as a result of tectonic deformation. Systematic simulations show that these effects are most pronounced at the base of the crust (at ?40 km), where pressures can reach 2-3 GPa (therefore within the coesite stability field) for millions of years. These pressures are often released rapidly during ongoing deformation. Relating metamorphic pressure estimates to depth might thus be problematic in mechanically heterogeneous crustal rock units that appear to have been exhumed in an ultrafast manner.
Abstract: Establishing the history of HP and UHP metamorphic rocks is important for quantifying Earth dynamics. The history of these rocks defines, among other things, paleo-subduction rates, P-T paths, and the kinematics of continent-continent collision. Although the appearance of certain minerals, such as coesite, stishovite, or diamond, provides unequivocal evidence of an HP or UHP component to the history of a rock, they cannot provide details of the P-T-t path a rock has experienced. However, complex solid solutions can. This reflects the fact that solid solutions have the potential to provide a continuous thermodynamically controlled response to evolving P-T conditions. To the extent that such solid-solution characteristics are preserved unmodified in a mineral throughout its history, a detailed description of the trajectory of the rock during burial …
Abstract: To study the kinetics of the spinel-to-garnet transformation in peridotite, we conducted reaction experiments in the garnet peridotite stability field (3.2 GPa, 1020-1220 °C, for 0.6-30 h) using a single spinel crystal embedded in monomineralic orthopyroxene powder or in a mixture of powdered orthopyroxene and clinopyroxene. The growth textures observed in the reaction rim between the spinel crystal and the polycrystalline pyroxenes show that the reaction rim grew in both the spinel and pyroxenes directions, suggesting mobility of both SiO2 and R2O3 components (where R is a trivalent cation). Olivine grains formed only in the presence of monomineralic orthopyroxene and were present in some domains without forming reaction rims. Based on a diffusion-controlled growth model, the growth kinetics of the garnet reaction rim can be described by [x(t)]2 = k0 exp(?H*/RT)t, where x(t) is the rim width at time t, R is the gas constant, T is the absolute temperature, and H* is the activation enthalpy of reaction; k0 and H* are, respectively, k0 = 10?19.8 ± 4.9 m2/s and H* = 171 ± 58 kJ/mol. The development of a garnet reaction rim around a spinel core has been observed in alpine-type peridotitic rocks and mantle xenoliths. The reaction rims experimentally produced in this study are characteristic of corona textures observed in natural rocks, and the experimentally measured growth rate of the rims places important constraints on dynamic transformation processes involving spinel and garnet in peridotite. However, to reconstruct the P-T-t history of the corona texture based on these elementary processes, additional detailed studies on the textural evolution and quantitative kinetics of the garnet-rim growth stage are required.
Abstract: Among orogenic peridotites, dunites suffer the weakest crustal metasomatism at the slab-mantle interface and are the best lithology to trace the origins of orogenic peridotites and their initial geodynamic processes. Petrological and geochemical investigations of the Lijiatun dunites from the Sulu ultrahigh-pressure (UHP) terrane indicate a complex petrogenetic history involving melt extraction and multistage metasomatism (carbonatitic melt and slab-derived fluid). The Lijiatun dunites consist mainly of olivine (Fo = 92.0-92.6, Ca = 42-115 ppm), porphyroblastic orthopyroxene (En = 91.8-92.8), Cr-spinel (Cr# = 50.4-73.0, TiO2 < 0.2 wt.%) and serpentine. They are characterized by refractory bulk-rock compositions with high MgO (45.31-47.07 wt.%) and Mg# (91.5-91.9), and low Al2O3 (0.48-0.70 wt.%), CaO (0.25-0.44 wt.%) and TiO2 (< 0.03 wt.%) contents. Whole-rock platinum group elements (PGE) are similar to those of cratonic mantle peridotites and Re-Os isotopic data suggest that dunites formed in the early Proterozoic (~ 2.2 Ga). These data indicate that the Lijiatun dunites were the residues of ~ 30% partial melting and were derived from the subcontinental lithospheric mantle (SCLM) beneath the North China craton (NCC). Subsequent carbonatitic metasomatism is characterized by the formation of olivine-rich (Fo = 91.6-92.6, Ca = 233-311 ppm), clinopyroxene-bearing (Mg# = 95.9-96.7, Ti/Eu = 104-838) veins cutting orthopyroxene porphyroblasts. Based on the occurrence of dolomite, mass-balance calculation and thermodynamic modeling, carbonatitic metasomatism had occurred within the shallow SCLM (low-P and high-T conditions) before dunites were incorporated into the continental subduction channel. These dunites then suffered weak metasomatism by slab-derived fluids, forming pargasitic amphibole after pyroxene. This work indicates that modification of the SCLM beneath the eastern margin of the NCC had already taken place before the Triassic continental subduction. Orogenic peridotites derived from such a lithospheric mantle wedge may be heterogeneously modified prior to their incorporation into the subduction channel, which would set up a barrier for investigation of the mas
Abstract: Chromitites (aggregates of chromite or chromian spinel) inform us of various mantle processes, including magmatism, magma/peridotite reaction and mantle dynamics [1]. They typically form as magmatic cumulates from chromiteoversaturated melt within conduits in the mantle peridotite [2]. They are usually enveloped by replacive dunite [1]. In Oman, both concordant and discordant chromitites are of low-P (upper mantle) magmatic origin [3, 4]. Their chromite grains contain inclusions of pargasite, aspidolite and pyroxenes, which suggest low P. Mineral chemistry suggests involvement of MORB for the concordant chromitite, and of arc-related magma for the discrodant one. This is consistent with the switch of tectonic setting, from MOR to SSZ, for the Oman ophiolite magmatism. Only the concordant chromitite shows metamorphic characters, i.e. exsolution of diopside in chromite and outward diffusion of Ni (< 30 cm) in the dunite envelope [5], indicating its longer residence in the mantle. Ultra-high pressure (UHP) chromitites have been reported from the Tibetan and Polar Ural ophiolites [6, 7]. Most of their petrographic characteristics can be explained by UHP "metamorphism" of low-P magmatic chromitites above [8]. This may suggest recycling of low-P chromitite as deep as the transion-zone mantle [9]. The UHP chromitite is, however, still highly enigmatic: some characteristics, e.g., the amount and origin of carbon as diamond, are difficult to explain. High-T aqueous fluids containing Cl, S and C, can mobilize Cr and precipitate chromite in the mantle [10]. Chromite was dissolved and precipitated in/from high-T fluids which formed diopsidites in Oman. Chromite was concentrated to form thin "hydrothermal chromitite". Sub-arc metasomatized peridotites contain secondary chromite closely associated with fluid inclusions, indicating Cr mobility via fluids within the mantle wedge. Hydrothermal chromitites are expected in the mantle where fluid circulation is available.
Abstract: Raman spectral characteristics of a range of diamond-based abrasives (powders and sprays) and drilling and cutting tools, originating from preparation laboratories worldwide, are presented. Some abrasives show strong broadening of the main diamond band [FWHM (full width at half band-maximum) > 5 cm? 1] accompanied by strong band-downshift (View the MathML source?˜ = 1316-1330 cm? 1). Others are characterised by moderate band broadening (FWHM = 1.8-5 cm? 1) at rather regular band position (View the MathML source?˜ = 1331-1333 cm? 1). In addition we found that a "fresh" abrasive and its used analogue may in some cases show vast differences in their Raman spectra. The Raman parameters of diamond-based abrasives overlap widely with Raman parameters of UHP (ultra-high pressure) microdiamond. It is hence impossible to assign diamond detected in a geological specimen to either an introduced artefact or a genuine UHP relict, from the Raman spectrum alone. Raman is an excellent technique for the detection of minute amounts of diamond; however it does not provide conclusive evidence for the identification of UHP microdiamond. The latter requires thorough verification, for instance by optical microscopy or, if doubts cannot be dispelled, transmission electron microscopy.
Proceedings of National Academy of Science USA, Vol. 113, no. 40, pp. 11127-11130.
Mantle
UHP
Abstract: We performed laser-heated diamond anvil cell experiments combined with state-of-the-art electron microanalysis (focused ion beam and aberration-corrected transmission electron microscopy) to study the distribution and valence of iron in Earth's lower mantle as a function of depth and composition. Our data reconcile the apparently discrepant existing dataset, by clarifying the effects of spin (high/low) and valence (ferrous/ferric) states on iron partitioning in the deep mantle. In aluminum-bearing compositions relevant to Earth's mantle, iron concentration in silicates drops above 70 GPa before increasing up to 110 GPa with a minimum at 85 GPa; it then dramatically drops in the postperovskite stability field above 116 GPa. This compositional variation should strengthen the lowermost mantle between 1,800 km depth and 2,000 km depth, and weaken it between 2,000 km depth and the D" layer. The succession of layers could dynamically decouple the mantle above 2,000 km from the lowermost mantle, and provide a rheological basis for the stabilization and nonentrainment of large low-shear-velocity provinces below that depth.
Journal of Metamorphic Geology, in press available
Europe, Sweden, Norway
UHP
Abstract: Metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust. Here we present a new occurrence of diamond within the Seve Nappe Complex of the Scandinavian Caledonides, on Åreskutan in Jämtland County, Sweden. Microdiamond is found in-situ as single and composite (diamond + carbonate) inclusions within garnet, in kyanite-bearing paragneisses. The rocks preserve the primary peak pressure assemblage of Ca,Mg-rich garnet + phengite + kyanite + rutile, with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite. Calculated P-T conditions for this stage are 830-840 °C and 4.1-4.2 GPa, in the diamond stability field. The ultrahigh-pressure (UHP) assemblage has been variably overprinted under granulite facies conditions of 850-860 °C and 1.0-1.1 GPa, leading to formation of Ca,Mg-poor garnet+biotite+ plagioclase+K-feldspar+sillimanite+ilmenite+quartz. This overprint was the result of nearly isothermal decompression, which is corroborated by Ti-in-quartz thermometry. Chemical Th-U-Pb dating of monazite yields ages between 445 and 435 Ma, which are interpreted to record post-UHP exhumation of the diamond-bearing rocks. The new discovery of microdiamond on Åreskutan, together with other evidence of ultrahigh-pressure metamorphism (UHPM) within gneisses, eclogites and peridotites elsewhere in the Seve Nappe Complex, provide compelling arguments for regional (at least 200 km along strike of the unit). UHPM of substantial parts of this far-travelled allochthon. The occurrence of UHPM in both rheologically weak (gneisses) and strong lithologies (eclogites, peridotites) speaks against the presence of large tectonic overpressure during metamorphism.
Abstract: Diamonds are renowned as the record of Earth’s evolution history. Natural diamonds on the Earth can be distinguished in light of genetic types as kimberlitic diamonds (including peridotitic diamonds and eclogitic diamonds), ultrahigh-pressure metamorphic diamonds and ophiolitic diamonds. According to the inclusion mineralogy, most diamonds originated from continental lithospheric mantle at depths of 140–250 km. Several localities, however, yield ultradeep diamonds with inclusion compositions that require a sublithospheric origin (>~250 km). Ultradeep diamonds exhibit distinctions in terms of carbon isotope composition, N-concentration, mineral inclusions and so on. The present study provides a systematic compilation concerning the features of ultradeep diamonds, based on which to expound their genesis affinity with mantle-carbonate melts. The diamond-parental carbonate melts are proposed to be stemmed from the Earth’s crust through subduction of oceanic lithosphere. Ultradeep diamonds are classified into a subgroup attaching to kimberlitic diamonds grounded by formation mechanism, and present connections in respect of carbon origin to eclogitic diamonds, ultrahigh-pressure metamorphic diamonds and ophiolitic diamonds.
Journal of Metamorphic Geology, Vol. 35, 5, pp. 541-564.
Europe, Sweden
UHP
Abstract: Metamorphic diamond in crustal rocks provides important information on the deep subduction of continental crust. Here we present a new occurrence of diamond within the Seve Nappe Complex of the Scandinavian Caledonides, on Åreskutan in Jämtland County, Sweden. Microdiamond is found in-situ as single and composite (diamond + carbonate) inclusions within garnet, in kyanite-bearing paragneisses. The rocks preserve the primary peak pressure assemblage of Ca,Mg-rich garnet + phengite + kyanite + rutile, with polycrystalline quartz surrounded by radial cracks indicating breakdown of coesite. Calculated P-T conditions for this stage are 830-840 ºC and 4.1-4.2 GPa, in the diamond stability field. The ultrahigh-pressure (UHP) assemblage has been variably overprinted under granulite facies conditions of 850-860 ºC and 1.0-1.1 GPa, leading to formation of Ca,Mg-poor garnet + biotite + plagioclase + K-feldspar + sillimanite + ilmenite + quartz. This overprint was the result of nearly isothermal decompression, which is corroborated by Ti-in-quartz thermometry. Chemical Th-U-Pb dating of monazite yields ages between 445 and 435 Ma, which are interpreted to record post-UHP exhumation of the diamond-bearing rocks. The new discovery of microdiamond on Åreskutan, together with other evidence of ultrahigh-pressure metamorphism (UHPM) within gneisses, eclogites and peridotites elsewhere in the Seve Nappe Complex, provide compelling arguments for regional (at least 200 km along the unit) UHPM of substantial parts of this far-travelled allochthon. The occurrence of UHPM in both rheologically weak (gneisses) and strong lithologies (eclogites, peridotites) speaks against the presence of large tectonic overpressure during metamorphism.
Abstract: Mechanisms of Precambrian orogeny and their contribution to the origin of ultrahigh temperature granulites, granite-greenstone terranes and net crustal growth remain debatable. Here, we use 2D numerical models with 150 °C higher mantle temperatures compared to present day conditions to investigate physical and petrological controls of Precambrian orogeny during forced continental plates convergence. Numerical experiments show that convergence between two relatively thin blocks of continental lithosphere with fertile mantle creates a short-lived cold collisional belt that later becomes absorbed by a long-lived thick and flat ultra-hot accretionary orogen with Moho temperatures of 700–1100 °C. The orogen underlain by hot partially molten depleted asthenospheric mantle spreads with plate tectonic rates towards the incoming lithospheric block. The accretionary orogeny is driven by delamination of incoming lithospheric mantle with attached mafic lower crust and invasion of the hot partially molten asthenospheric wedge under the accreted crust. A very fast convective cell forms atop the subducting slab, in which hot asthenospheric mantle rises against the motion of the slab and transports heat towards the moving orogenic front. Juvenile crustal growth during the orogeny is accompanied by net crustal loss due to the lower crust subduction. Stability of an ultra-hot orogeny is critically dependent on the presence of relatively thin and warm continental lithosphere with thin crust and dense fertile mantle roots subjected to plate convergence. Increased thickness of the continental crust and subcontinental lithospheric mantle, pronounced buoyancy of the lithospheric roots, and decreased mantle and continental Moho temperature favor colder and more collision-like orogenic styles with thick crust, reduced magmatic activity, lowered metamorphic temperatures, and decreased degree of crustal modification. Our numerical modeling results thus indicate that different types of orogens (cold, mixed-hot and ultra-hot) could be created at the same time in the Early Earth, depending on compositional and thermal structures of interacting continental blocks.
Abstract: “Super-deep” diamonds are thought to crystallize between 300 and 800 km depth because some of the inclusions trapped within them are considered to be the products of retrograde transformation from lower mantle or transition zone precursors. In particular, single inclusion CaSiO3-walstromite is believed to derive from CaSiO3-perovskite, although its real depth of origin has never been proven. Our aim is therefore to determine for the first time the pressure of formation of the diamond-CaSiO3-walstromite pair by “single-inclusion elastic barometry” and to determine whether CaSiO3-walstromite derives from CaSiO3-perovskite or not. We investigated several single phases and assemblages of Ca-silicate inclusions still trapped in a diamond coming from Juina (Brazil) by in-situ analyses (single-crystal X-ray diffraction and micro-Raman spectroscopy) and we obtained a minimum entrapment pressure of ~ 5.7 GPa (? 180 km) at 1500 K. However, the observed coexistence of CaSiO3-walstromite, larnite (?-Ca2SiO4) and CaSi2O5-titanite in one multiphase inclusion within the same diamond indicates that the sample investigated is sub-lithospheric with entrapment pressure between ~ 9.5 and ~ 11.5 GPa at 1500 K, based on experimentally-determined phase equilibria. In addition, thermodynamic calculations suggested that, within a diamond, single inclusions of CaSiO3-walstromite cannot derive from CaSiO3-perovskite, unless the diamond around the inclusion expands by ~ 30% in volume.
Abstract: Exhumed ultrahigh-pressure (UHP) terranes, involving slices of deeply subducted crustal rocks, provide unique material for studying material transfer in subduction zones. Diamond-bearing UHP rocks with sedimentary protoliths allow for tracing melting processes at both UHP and UHT including carbon cycling in the Earth. We studied microdiamonds and associated phases in two contrasting lithologies, (1) acid, quartzofeldpathic UHP gneiss composed of garnet, kyanite, feldspar, quartz and biotite, with a high ASI characteristic of sedimentary rocks, and (2) intermediate garnet-clinopyroxene rock containing quartz, feldspar, minor kyanite and biotite, which is metaluminous. Whereas rock (1) contains exclusively single octahedral diamonds with perfect crystal shape in garnet, kyanite (more common) and zircon, the microdiamonds in the rock (2) occur mostly as clusters of cuboid shape in garnet and zircon. Micro-Raman and FIB TEM data document presence of graphite, quartz and rutile at diamond/host interface or in separate multiple solid inclusions (MSI) whereas carbonates are practically absent. The morphology and lack of inclusions reflect relatively slow growth of the octahedral diamonds (rock 1) at lower fluid supersaturation. Individual deep and symmetrical negative trigons (AFM) on the (111) plane suggest dissolution by a residual silicate-carbonate melt. In contrast, polycrystallline character of diamond cuboids (rock 2) along with their common dissolution and formation of numerous tetragonal etch pits reflect relatively rapid growth of these grains from highly supersaturated fluid/melt. Peak P-T conditions for the UHP rocks of ? 1100ºC at 4.5 GPa are located above the phengite dehydration melting curve, where silicate melts are produced and may coexist with carbonate melts. In view of the light carbon isotope composition and lack of carbonates, we suggest that the diamonds crystallized from the graphitized primordial organic matter under reducing conditions at presence of silicate melt.
Abstract: Despite the advanced stage of diamond thin-film technology, with applications ranging from superconductivity to biosensing, the realization of a stable and atomically thick two-dimensional diamond material, named here as diamondene, is still forthcoming. Adding to the outstanding properties of its bulk and thin-film counterparts, diamondene is predicted to be a ferromagnetic semiconductor with spin polarized bands. Here, we provide spectroscopic evidence for the formation of diamondene by performing Raman spectroscopy of double-layer graphene under high pressure. The results are explained in terms of a breakdown in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix. Ab initio calculations and molecular dynamics simulations are employed to clarify the mechanism of diamondene formation, which requires two or more layers of graphene subjected to high pressures in the presence of specific chemical groups such as hydroxyl groups or hydrogens.
Geochemical Perspectives Letters, Vol. 4, pp. 19-23.
China
UHP
Abstract: Multiphase inclusions represent microenvironments where the interaction between fluid and host mineral is preserved during the rock geological path. Under its peculiar chemical-physical constraints, the entrapped solute-rich fluid might follow a crystallisation mechanism which is not predictable through simple equilibrium arguments. In this letter, by the modelling of solid-solution equilibrium and the application of principles of mass conservation, we demonstrate that cavities in mantle garnet filled with slab-derived fluids can re-equilibrate to a pyrope + spinel + chlorite assemblage at the same high P-T of their formation. The basis of this occurrence is a dissolution-reprecipitation mechanism, triggered by a dilute, non-equilibrated slab fluid.
Journal of Raman Spectroscopy, Vol. 48, 11, pp. 1566-1573.
Russia
UHP - Kokchetav
Abstract: CO2-bearing fluid inclusions coexisting with diamonds were identified in zircons from diamondiferous gneiss in the Kokchetav Massif. This discovery provides evidence for the presence of CO2 in UHP fluids and diamond formation in moderately oxidized conditions in the Kokchetav gneiss. Fluid and multiphase solid inclusions coexisting in zircons represent immiscible melt and fluid captured close to the peak metamorphic conditions for the Kokchetav UHP gneiss. Most of CO2-bearing inclusions are CO2+H2O mixtures except for some cases when they also contain daughter phases (e.g. muscovite, calcite and quartz) tracing the presence of aqueous and solute-rich fluids at different phases of UHP metamorphism. Decrease of pressure and temperature may have been responsible for the reduction of solutes in the CO2-bearing fluid. The lack of CO2-bearing inclusions in garnet porphyroblasts from diamond-bearing gneiss, as well as the common coexistence of aqueous CO2-bearing inclusions with calcite, testify that most likely all CO2 in fluid was consumed by the calcite-forming reaction and hydrous melt was the only remaining growth medium during retrograde metamorphism of the Kokchetav UHPM gneisses. Neither K-cymrite nor kokchetavite was identified among daughter phases in the hydrous melt inclusions in garnet, which indicates that they hardly could originate in a metapelitic system.
Journal of Metamorphic Geology, in press available
China
UHP
Abstract: Coesite is typically found as inclusions in rock-forming or accessory minerals in ultrahigh-pressure (UHP) metamorphic rocks. Thus, the survival of intergranular coesite in UHP eclogite at Yangkou Bay (Sulu belt, eastern China) is surprising and implies locally ‘dry’ conditions throughout exhumation. The dominant structures in the eclogites at Yangkou are a strong D2 foliation associated with tight-to-isoclinal F2 folds that are overprinted by close-to-tight F3 folds. The coesite-bearing eclogites occur as rootless intrafolial isoclinal F1 fold noses wrapped by a composite S1-S2 foliation in interlayered phengite-bearing quartz-rich schists. To evaluate controls on the survival of intergranular coesite we determined the number density of intergranular coesite grains per cm2 in thin section in two samples of coesite eclogite (phengite absent) and threee samples of phengite-bearing coesite eclogite (2-3 vol.% phengite), and measured the amount of water in garnet and omphacite in these samples, and also in two samples of phengite-bearing quartz eclogite (6-7 vol.% phengite, coesite absent). As coesite decreases in the mode, the amount of primary structural water stored in the whole rock, based on the nominally anhydrous minerals (NAMs), increases from 107/197 ppm H2O in the coesite eclogite to 157-253 ppm H2O in the phengite-bearing coesite eclogite to 391/444 ppm H2O in the quartz eclogite. In addition, there is molecular water in the NAMs and modal water in phengite. If the primary concentrations reflect differences in water sequestered during the late prograde evolution, the amount of fluid stored in the NAMs at the metamorphic peak was higher outside of the F1 fold noses. During exhumation from UHP conditions, where NAMs became H2O saturated, dehydroxylation would have generated a free fluid phase. Interstitial fluid in a garnet-clinopyroxene matrix at UHP conditions has dihedral angles >60°, so at equilibrium fluid will be trapped in isolated pores. However, outside the F1 fold noses strong D2 deformation likely promoted interconnection of fluid and migration along the developing S2 foliation, enabling conversion of some or all of the intergranular coesite into quartz. By contrast, the eclogite forming the F1 fold noses behaved as independent rigid bodies within the composite S1-S2 foliation of the surrounding phengite-bearing quartz-rich schists. Primary structural water concentrations in the coesite eclogite are so low that H2O saturation of the NAMs is unlikely to have occurred. This inherited drier environment in the F1 fold noses was maintained during exhumation by deformation partitioning and strain localization in the schists, and the fold noses remained immune to grain-scale fluid infiltration from outside allowing coesite to survive. The amount of inherited primary structural water and the effects of strain partitioning are important variables in the survival of coesite during exhumation of deeply subducted continental crust. Evidence of UHP metamorphism may be preserved in similar isolated structural settings in other collisional orogens.
Progress in Earth and Planetary Science, Vol. 5.6, 18p. Available
Mantle
UHP - spectroscopy
Abstract: Understanding what governs the speciation in the C-O-H-N system aids our knowledge of how volatiles affect mass transfer processes in the Earth’s interior. Experiments with aluminosilicate melt?+?C-O-H-N volatiles were, therefore, carried out with Raman and infrared spectroscopy to 800 °C and near 700 MPa in situ in hydrothermal diamond anvil cells. The measurements were conducted in situ with the samples at the desired temperatures and pressures in order to avoid possible structural and compositional changes resulting from quenching to ambient conditions prior to analysis. Experiments were conducted without any reducing agent and with volatiles added as H2O, CO2, and N2 because both carbon and nitrogen can occur in different oxidation states. Volatiles dissolved in melt comprise H2O, CO32-, HCO3-, and molecular N2, whereas in the coexisting fluid, the species are H2O, CO2, CO32-, and N2. The HCO3-/CO32- equilibrium in melts shift toward CO32- groups with increasing temperature with ?H?=?114?±?22 kJ/mol. In fluids, the CO2 abundance is essentially invariant with temperature and pressure. For fluid/melt partitioning, those of H2O and N2 are greater than 1 with temperature-dependence that yields ?H values of ??6.5?±?1.5 and ??19.6?±?3.7 kJ/mol, respectively. Carbonate groups, CO32- are favored by melt over fluid. Where redox conditions in the Earth’s interior exceed that near the QFM oxygen buffer (between NNO and MW buffers), N2 is the stable nitrogen species and as such acts as a diluent of both fluids and melts. For fluids, this lower silicate solubility, in turn, enhances alkalinity. This means that in such environments, the transport of components such as high field strength cations, will be enhanced. Effects of dissolved N2 on melt structure are considerably less than on fluid structure.
Abstract: Ophiolitic peridotites represent variously depleted residues of the primitive mantle after multiple episodes of partial melting, melt extraction, and melt-rock interactions. They display a wide range of compositional and geochemical heterogeneities at different scales, and their incompatible bulk-rock compositions and mineral chemistries are commonly inconsistent with their evolution through simple partial melting processes at shallow mantle depths. Approaching these issues from different perspectives, the papers in this volume concentrate on (1) melt evolution and magmatic construction of ophiolites in various tectonic settings, and (2) the occurrence of microdiamonds, ultrahigh-pressure (UHP) minerals, and crustal material as inclusions in ophiolitic chromitites and peridotites. Crustal and mantle rock units exposed in different ophiolites show that the mantle melt sources of ophiolitic magmas undergo progressive melting, depletion, and enrichment events, constantly modifying the melt compositions and the mineralogical and chemical makeup of residual peridotites. Formation and incorporation of microdiamonds and UHP minerals into chromite grains occurs at depths of 350-660 km in highly reducing conditions of the mantle transition zone. Carbon for microdiamonds and crustal minerals are derived from subduction-driven recycling of surface material. Host peridotites with their UHP mineral and diamond inclusions are transported into shallow mantle depths by asthenospheric upwelling, associated with either slab rollback-induced channel flow or superplumes. Decompression melting of transported mantle rocks beneath oceanic spreading centers and their subsequent flux melting in mantle wedges result in late-stage formation of podiform chromitites during the upper mantle petrogenesis of ophiolites. Future studies should demonstrate whether diamonds and UHP minerals also occur in peridotites and chromitites of nonsubduction-related ophiolites.
Abstract: We present Microsoft Excel spreadsheets for calculation of thermodynamic functions and P-V-T properties of MgO, diamond and 9 metals, Al, Cu, Ag, Au, Pt, Nb, Ta, Mo, and W, depending on temperature and volume or temperature and pressure. The spreadsheets include the most common pressure markers used in in situ experiments with diamond anvil cell and multianvil techniques. The calculations are based on the equation of state formalism via the Helmholtz free energy. The program was developed using Visual Basic for Applications in Microsoft Excel and is a time-efficient tool to evaluate volume, pressure and other thermodynamic functions using T-P and T-V data only as input parameters. This application is aimed to solve practical issues of high pressure experiments in geosciences and mineral physics.
Abstract: The dynamics of formation and exhumation of high-pressure (HP) and ultra-high pressure (UHP) metamorphic orogens in double subduction-collision zones remain enigmatic. Here we employ two-dimensional thermo-mechanical numerical models to gain insights on the exhumation of HP-UHP metamorphic rocks, as well as their deformation during the collision of a micro-continent with pro- and retro-continental margins along two subduction zones. A three-stage collisional process with different convergence velocities is tested. In the initial collisional stage, a fold-and-thrust belt and locally rootless superimposed folds are developed in the micro-continent and subduction channel, respectively. In the second (exhumation) stage of HP-UHP rocks, a faster convergence model results in upwelling of the asthenosphere, which further leads to a detachment between the crust and lithospheric mantle of the micro-continent. A slower convergence model results in rapid exhumation of HP-UHP rocks along the north subduction channel and a typical piggy-back thrusting structure in the micro-continent. A non-convergence model produces a slab tear-off, leading to the rebound of residual lithosphere of the micro-continent. In the third and final stage, a series of back and ramp thrusts are formed in the micro-continent with the pro-continent re-subducted. Based on an analogy of our numerical results with the Western Dabie Orogen (WDO), we suggest that: (1) slab tear-off results in a rebound of residual lithosphere, which controls the two-stage syn-collisional exhumation process of HP-UHP rocks in the WDO; and (2) in contrast to the single subduction-collision system, the exhumation range of the partially molten rocks with lower viscosity and density is restricted to a specific region of the micro-continent by the Mianlue and Shangdan subduction zones, which generated the complex deformation features in the WDO.
Geochimica et Cosmochimica Acta, Vol. 232, pp. 303-328.
Africa, Morocco, Europe, Spain
UHP
Abstract: We present an integrated geochemical study of ultra-high pressure (UHP) garnet pyroxenites from the Ronda and Beni Bousera peridotite massifs (Betic-Rif Belt, westernmost Mediterranean). Based on their Sr-Nd-Pb-Hf isotopic systematics, we classify UHP garnet pyroxenites into three groups: Group A pyroxenites (Al 2 O 3 : 15-17.5 wt. %) have low initial 87 Sr/ 86 Sr, relatively high ? Nd , ? Hf and 206 Pb/ 204 Pb ratios, and variable 207 Pb/ 204 Pb and 208 Pb/ 204 Pb. Group B pyroxenites (Al 2 O 3 < 14 wt. %) are characterized by high initial 87 Sr/ 86 Sr and relatively low ? Nd , ? Hf and 206 Pb/ 204 Pb ratios. Group C pyroxenites (Al 2 O 3 ~ 15 wt. %) have depleted radiogenic signatures with relatively low initial 87 Sr/ 86 Sr and 206 Pb/ 204 Pb, high ? Nd and ? Hf , and their 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios are similar to those of Group B pyroxenites. The major and trace element and isotopic compositions of UHP garnet pyroxenites support their derivation from ancient (1.5-3.5 Ga) oceanic crust recycled into the mantle and intimately stirred with peridotites by convection. However, the genesis of these pyroxenites requires also the involvement of recycled continental lower crust with an isotopic composition akin to the lower crustal section of the lithosphere where these UHP garnet pyroxenites now reside in. These oceanic and continental crustal components were stirred in different proportions in the convective mantle, originating pyroxenites with a more marked geochemical imprint of either oceanic (Group A) or continental lower crust (Group B), or hybrid compositions (Group C). The pyroxenite protoliths likely underwent several melting events, one of them related to the formation of the subcontinental lithospheric mantle and continental crust, generating restitic UHP garnet pyroxenites now preserved in the Ronda and Beni Bousera orogenic peridotites. The extent of melting was mostly 3 controlled by the bulk Mg-number (Mg#) of the pyroxenite protoliths, where protoliths with low Mg# experienced higher degrees of partial melting than sources with higher Mg#. Positive Eu and Sr anomalies in bulk rocks, indicative of their origin from cumulitic crustal gabbros, are preserved mostly in high Mg# pyroxenites due to their higher melting temperatures and consequent lower partial melting degrees. The results of this study show that the genesis of UHP garnet pyroxenites in orogenic peridotites requires a new recipe for the marble cake mantle hypothesis, combining significant recycling and stirring of both oceanic and continental lower crust in the Earth's mantle. Furthermore, this study establishes a firm connection between the isotopic signatures of UHP pyroxenite heterogeneities in the mantle and the continental lower crust.
Journal of Metamorphic Geology, Vol. 36, 2, pp. 173-194.
Mantle
UHP
Abstract: Coesite is typically found as inclusions in rock?forming or accessory minerals in ultrahigh?pressure (UHP) metamorphic rocks. Thus, the survival of intergranular coesite in UHP eclogite at Yangkou Bay (Sulu belt, eastern China) is surprising and implies locally “dry” conditions throughout exhumation. The dominant structures in the eclogites at Yangkou are a strong D2 foliation associated with tight?to?isoclinal F2 folds that are overprinted by close?to?tight F3 folds. The coesite?bearing eclogites occur as rootless intrafolial isoclinal F1 fold noses wrapped by a composite S1-S2 foliation in interlayered phengite?bearing quartz?rich schists. To evaluate controls on the survival of intergranular coesite, we determined the number density of intergranular coesite grains per cm2 in thin section in two samples of coesite eclogite (phengite absent) and three samples of phengite?bearing coesite eclogite (2-3 vol.% phengite), and measured the amount of water in garnet and omphacite in these samples, and also in two samples of phengite?bearing quartz eclogite (6-7 vol.% phengite, coesite absent). As coesite decreases in the mode, the amount of primary structural water stored in the whole rock, based on the nominally anhydrous minerals (NAMs), increases from 107/197 ppm H2O in the coesite eclogite to 157-253 ppm H2O in the phengite?bearing coesite eclogite to 391/444 ppm H2O in the quartz eclogite. In addition, there is molecular water in the NAMs and modal water in phengite. If the primary concentrations reflect differences in water sequestered during the late prograde evolution, the amount of fluid stored in the NAMs at the metamorphic peak was higher outside of the F1 fold noses. During exhumation from UHP conditions, where NAMs became H2O saturated, dehydroxylation would have generated a free fluid phase. Interstitial fluid in a garnet-clinopyroxene matrix at UHP conditions has dihedral angles >60°, so at equilibrium fluid will be trapped in isolated pores. However, outside the F1 fold noses strong D2 deformation likely promoted interconnection of fluid and migration along the developing S2 foliation, enabling conversion of some or all of the intergranular coesite into quartz. By contrast, the eclogite forming the F1 fold noses behaved as independent rigid bodies within the composite S1-S2 foliation of the surrounding phengite?bearing quartz?rich schists. Primary structural water concentrations in the coesite eclogite are so low that H2O saturation of the NAMs is unlikely to have occurred. This inherited drier environment in the F1 fold noses was maintained during exhumation by deformation partitioning and strain localization in the schists, and the fold noses remained immune to grain?scale fluid infiltration from outside allowing coesite to survive. The amount of inherited primary structural water and the effects of strain partitioning are important variables in the survival of coesite during exhumation of deeply subducted continental crust. Evidence of UHP metamorphism may be preserved in similar isolated structural settings in other collisional orogens.
Physics and Chemistry of Minerals, dor.org/10.1007/ d00269-018-0987-5 13p.
Russia, Kazakhstan, Alps
coesite, UHP
Abstract: The high-pressure silica polymorphs coesite and stishovite were synthesized under water-saturated conditions from a natural granitic composition doped with Li and B. Experiments were performed in a Multi-Anvil apparatus between 4 and 9.1 GPa and 900 and 950 °C, based on the conditions of a subducting continental crust as realistic for the ultrahigh-pressure metamorphic units Dora Maira and Kochetav massifs. Run products consisted of coesite/stishovite?+?kyanite?±?phengite?±?omphacite, and quench material. The synthesized silica polymorphs were successively analyzed by infrared spectroscopy, electron microprobe, and Secondary-Ion Mass Spectrometry (SIMS). No hydrous defects were observed in coesite synthesized at 4 GPa and 900 °C, whereas coesite grown at higher pressures revealed a triplet of infrared absorptions bands at 3575, 3523, and 3459 cm??1, two minor bands at 3535 and 3502 cm??1, and a small band at 3300 cm??1 that was only visible at 7.7 GPa. The total amount of Al was charge-balanced by H and the other monovalent cations. However, the band triplet could not be associated with AlOH defects, while the band doublet was inferred to BOH defects and the small band probably corresponded to interstitial H. Stishovite displayed one dominant band at 3116 cm??1 with a shoulder at 3170 cm??1, and a minor band at 2665 cm??1, probably all associated with AlOH defects. BOH defects were not observed in stishovite, and LiOH defects were neither observed in coesite nor stishovite, probably because of preferentially partition of Li in other phases such as omphacite. The total amount of defect protons increased with pressure and with metal impurity concentrations. The general increase in OH defects in silica polymorphs with increasing pressure (this study) contrasted the negative pressure trend of OH in quartz observed previously from the same starting material, and revealed an incorporation minimum of OH in silica polymorphs around the quartz/coesite phase transition.
Abstract: Only limited data are available at present on the viscosity of kimberlite magmas. We investigate viscosity of synthetic carbonate-bearing (silicate82?+?carbonate18, wt%, 100NBO/T?=?313) anhydrous haplokimberlite melts theoretically and in experiments. We use new experimental data on viscosity of anhydrous haplokimberlite melts and a physical-chemical model (Persikov and Bukhtiyarov 2009; Persikov et al. 2015) to compare basic viscosity features in kimberlitic and basaltic melts (100NBO/T?=?56). Viscosity of melts is determined by the falling sphere quenching method in a large range of temperatures from 1300 to 1950?°C and pressures up to 7.5?GPa. We use two types of high-pressure apparatuses: a high gas pressure apparatus and a high pressure split-sphere multi-anvil apparatus to study the viscosity of melts at moderate (100?MPa CO2 pressure) and high (5.5?GPa and 7.5?GPa) pressures, respectively. The measured viscosity ranges for anhydrous haplokimberlite melts are from 1.5 (±0.45) to 0.11(±0.03) Pa s. The temperature dependence of the viscosity of haplokimberlite and basaltic melts is consistent with the theoretical Arrhenian equation. At a constant temperature, viscosity of anhydrous haplokimberlite melts increases exponentially about ten-fold as pressure increases from 100?MPa to 7.5?GPa. The activation energy of viscous flow increases linearly with pressure increase from 100?MPa to 7.5?GPa for anhydrous haplokimberlite melts but decreases in the case of basaltic melts, with the minimum at ~5.5?GPa. At a moderate pressure (100?MPa), haplokimberlite melts are about twenty times less viscous than basaltic melts, but are about four times more viscous at a high pressure (7.5?GPa), the temperature being 1800?°C in both cases. The experimentally observed behavior of the viscosity of anhydrous haplokimberlite melts is consistent with predictions of the physical-chemical model within the range of uncertainties in both experimental and calculated data (±30% rel.). Thus, the physical-chemical model is used to discuss possible effects of volume percentages of crystals and bubbles on viscosity of kimberlitic and basaltic magmas at different pressures and temperatures during their origin, evolution, and ascent.
Abstract: First-principles calculations are performed to investigate vacancy formation and migration in the B2 phase of MgO. Defect energetics suggest the importance of intrinsic non-interacting vacancy pairs, even though the extrinsic vacancy concentration might govern atomic diffusion in the B2 phase of MgO. The enthalpies of ionic vacancy migration are generally found to decrease across the B1-B2 phase transition around a pressure of 500?GPa. It is shown that this enthalpy change induces a substantial increase in the rate of vacancy diffusion in MgO of almost four orders of magnitude (?104) when the B1 phase transforms into the B2 phase with increasing pressure. If plastic deformation is controlled by vacancy diffusion, mantle viscosity is expected to decrease in relation to this enhanced diffusion rate in MgO across the B1-B2 transition in the interior of Earth-like large exoplanets. Our results of atomic relaxations near the defects suggest that diffusion controlled creep viscosity may generally decrease across high-pressure phase transitions with increasing coordination number. Plastic flow and resulting mantle convection in the interior of these super-Earths may be therefore less sluggish than previously thought.
Physics and Chemistry of Minerals, Vol. 46, pp. 77-89.
Russia, Europe, Alps
UHP
Abstract: The high-pressure silica polymorphs coesite and stishovite were synthesized under water-saturated conditions from a natural granitic composition doped with Li and B. Experiments were performed in a Multi-Anvil apparatus between 4 and 9.1 GPa and 900 and 950 °C, based on the conditions of a subducting continental crust as realistic for the ultrahigh-pressure metamorphic units Dora Maira and Kochetav massifs. Run products consisted of coesite/stishovite?+?kyanite?±?phengite?±?omphacite, and quench material. The synthesized silica polymorphs were successively analyzed by infrared spectroscopy, electron microprobe, and Secondary-Ion Mass Spectrometry (SIMS). No hydrous defects were observed in coesite synthesized at 4 GPa and 900 °C, whereas coesite grown at higher pressures revealed a triplet of infrared absorptions bands at 3575, 3523, and 3459 cm??1, two minor bands at 3535 and 3502 cm??1, and a small band at 3300 cm??1 that was only visible at 7.7 GPa. The total amount of Al was charge-balanced by H and the other monovalent cations. However, the band triplet could not be associated with AlOH defects, while the band doublet was inferred to BOH defects and the small band probably corresponded to interstitial H. Stishovite displayed one dominant band at 3116 cm??1 with a shoulder at 3170 cm??1, and a minor band at 2665 cm??1, probably all associated with AlOH defects. BOH defects were not observed in stishovite, and LiOH defects were neither observed in coesite nor stishovite, probably because of preferentially partition of Li in other phases such as omphacite. The total amount of defect protons increased with pressure and with metal impurity concentrations. The general increase in OH defects in silica polymorphs with increasing pressure (this study) contrasted the negative pressure trend of OH in quartz observed previously from the same starting material, and revealed an incorporation minimum of OH in silica polymorphs around the quartz/coesite phase transition.
Abstract: The thermoelastic parameters of Ca3Cr2Si3O12 uvarovite garnet were examined in situ at high pressure up to 13 GPa and high temperature up to 1100 K by synchrotron radiation energy-dispersive X-ray diffraction within a 6-6-type multi-anvil press apparatus. A least-square fitting of room T data to a third-order Birch-Murnaghan (BM3) EoS yielded K0 = 164.2 ± 0.7 GPa, V0 = 1735.9 ± 0.3 Å3 (K’0 fixed to 4.0). P-V-T data were fitted simultaneously by a modified HT-BM3 EoS, which gave the isothermal bulk modulus K0 = 163.6 ± 2.6 GPa, K’0 = 4.1 ± 0.5, its temperature derivative (?K0,T/?T)P = -0.014 ± 0.002 GPa K?1, and the thermal expansion coefficients a0 = 2.32 ± 0.13 ×10?5 K?1 and b0 = 2.13 ± 2.18 ×10?9 K?2 (K’0 fixed to 4.0). Our results showed that the Cr3+ enrichment in natural systems likely increases the density of ugrandite garnets, resulting in a substantial increase of mantle garnet densities in regions where Cr-rich spinel releases chromium through a metasomatic reaction.
Journal of Metamorphic Geology, in press available
China
UHP
Abstract: Dating ultrahigh?pressure (UHP) metamorphic rocks provides important timing constraints on deep subduction zone processes. Eclogites, deeply subducted rocks now exposed at the surface, undergo a wide range of metamorphic conditions (i.e., deep subduction and exhumation) and their mineralogy can preserve a detailed record of chronologic information of these dynamic processes. Here we present an approach that integrates multiple radiogenic isotope systems in the same sample to provide a more complete timeline for the subduction?collision?exhumation processes, based on eclogites from the Dabie?Sulu orogenic belt in eastern China, one of the largest ultrahigh?pressure (UHP) terranes on Earth. In this study, we integrate garnet Lu?Hf and Sm?Nd ages with zircon and titanite U?Pb ages for three eclogite samples from the Sulu UHP terrane. We combine this age information with Zr?in?rutile temperature estimates, and relate these multiple chronometers to different P?T conditions. Two types of rutile, one present as inclusions in garnet and the other in the matrix, record the temperatures of UHP conditions and a hotter stage, subsequent to the peak pressure (“hot exhumation”), respectively. Garnet Lu?Hf ages (c. 238 to 235 Ma) record the initial prograde growth of garnet, while coupled Sm?Nd ages (c. 219 to 213 Ma) reflect cooling following hot exhumation. The maximum duration of UHP conditions is constrained by the age difference of these two systems in garnet (c. 235 to 220 Ma). Complementary zircon and titanite U?Pb ages of c. 235 ? 230 Ma and c. 216 ? 206 Ma provide further constraints on the timing of prograde metamorphism and the "cold exhumation", respectively. We demonstrate that timing of various metamorphic stages can thus be determined by employing complementary chronometers from the same samples. These age results, combined with published data from adjacent areas, show lateral diachroneity in the Dabie?Sulu orogeny. Three sub?blocks are thus defined by progressively younger garnet ages: western Dabie (243 ? 238 Ma), eastern Dabie?northern Sulu (238 ? 235 Ma,) and southern Sulu terranes (225 ? 220 Ma), which possibly correlate to different crustal slices in the recently proposed subduction channel model. These observed lateral chronologic variations in a large UHP terrane can possibly be extended to other suture zones.
Geophysical Research Letters, Vol. 46, 3, pp. 1348-1356.
Mantle
UHP
Abstract: Iron oxides are important end?members of the complex materials that constitute the Earth's interior. Among them, FeO and Fe2O3 have long been considered as the main end?members of the ferrous (Fe2+) and ferric (Fe3+) states of iron, respectively. All geochemical models assume that high oxygen concentrations are systematically associated to the formation of ferric iron in minerals. The recent discovery of O22? peroxide ions in a phase of chemical formula FeO2Hx stable under high?pressure and high?temperature conditions challenges this general concept. However, up to now, the valences of iron and oxygen in FeO2Hx have only been indirectly inferred from a structural analogy with pyrite FeS2. Here we compressed goethite (FeOOH), an Fe3+?bearing mineral, at lower mantle pressure and temperature conditions by using laser?heated diamond?anvil cells, and we probed the iron oxidation state upon transformation of FeOOH in the pressure-temperature stability field of FeO2Hx using in situ X?ray absorption spectroscopy. The data demonstrate that upon this transformation iron has transformed into ferrous Fe2+. Such reduced iron despite high oxygen concentrations suggests that our current views of oxidized and reduced species in the lower mantle of the Earth should be reconsidered.
Abstract: Kyanite gneiss from the “New Barchinsky” locality (Kokchetav Massif) was studied in detail. This rock is characterized by zonal distribution of the C and SiO2 polymorphs in kyanite porphyroblasts: (1) cores with graphite and quartz inclusions; (2) clean overgrowth zone with inclusions of cuboctahedral diamond crystals. The Raman mapping of SiO2 polymorphs originally showed the presence of an association of disordered graphite + coesite “prohibited” in HT diamond-bearing rocks. Graphitization of diamond is the only likely mechanism of the disordered graphite formation in HT diamond-bearing rocks. However, the absence of disordered graphite in association with diamond in kyanite porphyroblasts from kyanite gneiss from the “New Barchinsky” locality eliminates the process of diamond graphitization at the retrograde stage. Most likely, crystallization of disordered graphite occurred at the retrograde stage from the UHP C-O-H fluid.
Abstract: How the ultrahigh-pressure (UHP) terranes are exhumed to shallow levels but preserving intact relics of the UHP phase assemblages is among the most interesting but challenging topics in geosciences. We investigate all the paleolatitudes where the UHP terranes were exhumed. Our results show that all the UHP terranes in continental collision zones or oceanic accretionary wedges were exhumed within low latitudes (0°-30°), and the average paleolatitude for exhumations of the investigated 43 UHP terranes is ˜5.1° N. In contrast, those UHP xenoliths in mantle-derived igneous rocks could be brought to surface at higher paleolatitudes. Furthermore, the pattern of frequency for the UHP terranes exhumed at convergent boundaries is consistent with that of interglacial stages throughout the Earth history, indicating that the UHP exhumation is controlled by the climate and thus suggesting that the exhumed UHP terranes may be useful paleoclimate indicators.
Abstract: An experimental study, implicated in the revealing of the conditions for the origin for Fe3+-bearing magnesiowüstite in the lithospheric mantle, was performed using Mössbauer spectroscopy of pre-synthesized samples. Experiments were carried out using a multi-anvil high-pressure split-sphere apparatus at 6.3-7.5 GPa, in the range of 1100-1650 °C in carbonate-metal, carbonate-oxide-metal, carbonate-oxide, carbide-oxide and carbonate-metal- sulphur systems. In three experimental series, oxygen fugacity gradient in the samples was created, which enabled the study of the processes of magnesiowüstite formation under oxidizing and reducing conditions (?logfO2 (FMQ) values from ?1 to ?5). It was established that Fe3+-bearing magnesiowüstite can form both in assemblage with oxidized phases, such as carbonate or with reduced ones—metal, carbides, sulphides, graphite and diamond. According to the Mössbauer spectroscopy, the composition of synthesized magnesiowüstite varied within a range of Fe3+/?Fe values from 0 to 0.3, with IV and VI coordination of Fe3+ depending on P, T, fO2, x-parameters. It was established that Fe3+-bearing magnesiowüstite formation processes under upper mantle P,T-conditions include redox reactions, with magnesiowüstite being (1) reductant or (2) product of interaction, (3) crystallization processes of magnesiowüstite from an oxidized melt, where magnesiowüstite acts as a sink for ferric iron and (4) iron disproportionation.
Abstract: Local occurrences of coesite- and diamond-bearing rocks in the central Erzgebirge (northwestern Bohemian Massif, Germany) reveal ultrahigh-pressure (UHP) metamorphic conditions during the Variscan orogeny. Although UHP metamorphism supposedly affected a wider area, implying that rocks that equilibrated under UHP conditions occur dispersed in large volumes of high-pressure country-rock gneisses, mineralogical evidence is scarce. Here we have applied the new concept of capturing the distribution and characteristics of UHP rocks by analyzing inclusions in detrital garnet. Out of 700 inclusion-bearing garnets from seven modern sand samples from creeks draining the UHP area around the Saidenbach reservoir, we detected 26 garnets containing 46 mainly monomineralic coesite inclusions and 22 garnets containing 41 diamond inclusions. Combining these results with geochemical classification of the host garnets, we show (1) that coesite-bearing rocks are common and comprise eclogites as well as felsic gneisses, (2) that small inclusion size is a necessary precondition for the preservation of monomineralic coesite, and (3) for the first time, that diamond-bearing crustal rocks can be detected by analyzing the detrital record. Our results highlight the potential of this novel application of sedimentary provenance tools to UHP research, and the necessity of looking at the micrometer scale to find evidence in the form of preserved UHP minerals.
Abstract: The salt components of aqueous and aqueous-carbonic fluids are very important agents of metasomatism and partial melting of crustal and mantle rocks. The paper presents examples and synthesized data on mineral associations in granulite- and amphibolite-facies rocks of various composition in the middle and lower crust and in upper-mantle eclogites and peridotites that provide evidence of reactions involving salt components of fluids. These data are analyzed together with results of model experiments that reproduce some of these associations and make it possible to more accurately determine their crystallization parameters.
Abstract: This article is dedicated to the occurrence, relevance, and structure of minerals whose formation involves high pressure. This includes minerals that occur in the interior of the Earth as well as minerals that are found in shock-metamorphized meteorites and terrestrial impactites. I discuss the chemical and physical reasons that render the definition of high-pressure minerals meaningful, in distinction from minerals that occur under surface-near conditions on Earth or at high temperatures in space or on Earth. Pressure-induced structural transformations in rock-forming minerals define the basic divisions of Earth's mantle in the upper mantle, transition zone, and lower mantle. Moreover, the solubility of minor chemical components in these minerals and the occurrence of accessory phases are influential in mixing and segregating chemical elements in Earth as an evolving planet. Brief descriptions of the currently known high-pressure minerals are presented. Over the past 10 years more high-pressure minerals have been discovered than during the previous 50 years, based on the list of minerals accepted by the IMA. The previously unexpected richness in distinct high-pressure mineral species allows for assessment of differentiation processes in the deep Earth.
International Geology Review, Vol. 61, 4, pp. 504-519.
Russia, China
coesite, UHP
Abstract: The preservation of metastable diamond in ultrahigh-pressure metamorphic (UHPM) complexes challenges our understanding of the processes taking place during exhumation of these subduction zone complexes. The presence of diamonds in UHPM rocks implies that diamonds remained metastable during exhumation, and within thermodynamic stability of graphite for an extended period. This work studies the influence of pressure on the surface graphitization rate of diamond monocrystals in carbonate systems to understand the preservation of microdiamond during exhumation of UHP subduction complexes. Experiments were performed with 2-3 mm synthetic diamond monocrystals at 2-4 GPa in ????3 (1550°?) and ?2??3 (1450°?) melts using a high-pressure multi-anvil apparatus. The highest rate of surface graphitization took place at 2 GPa; diamond crystals were almost completely enveloped by a graphite coating. At 4 GPa, only octahedron-shaped pits formed on flat {111} diamond crystal faces. Our results demonstrate that the surface graphitization rate of diamonds in the presence of carbonate melts at 1450-1550°C increases with decreasing pressure. Decreased pressure alone can graphitize diamond regardless of exhumation rate. Metastable diamond inclusions survive exhumation with little or no graphitization because of excess pressure up to 2 GPa acting on them, and because inclusions are protected from interaction with C-O-H fluid.
Science Advances, doi. 10.1126/sciadv.aay5178 13p. Pdf
United States, Connecticut
UHT, HPG
Abstract: Diamond and coesite are classic indicators of ultrahigh-pressure (UHP; ?100-kilometer depth) metamorphism, but they readily recrystallize during exhumation. Crystallographically oriented pyroxene and amphibole exsolution lamellae in garnet document decomposed supersilicic UHP majoritic garnet originally stable at diamond-grade conditions, but majoritic precursors have only been quantitatively demonstrated in mafic and ultramafic rocks. Moreover, controversy persists regarding which silicates majoritic garnet breakdown produces. We present a method for reconstructing precursor majoritic garnet chemistry in metasedimentary Appalachian gneisses containing garnets preserving concentric zones of crystallographically oriented lamellae including quartz, amphibole, and sodium phlogopite. We link this to novel quartz-garnet crystallographic orientation data. The results reveal majoritic precursors stable at ?175-kilometer depth and that quartz and mica may exsolve from garnet. Large UHP terranes in the European Caledonides formed during collision of the paleocontinents Baltica and Laurentia; we demonstrate UHP metamorphism from the microcontinent-continent convergence characterizing the contiguous and coeval Appalachian orogen.
Science Advances, doi. 10.1126/sciadv.aay5178 13p. Pdf
United States, Connecticut
UHT, HPG
Abstract: Diamond and coesite are classic indicators of ultrahigh-pressure (UHP; ?100-kilometer depth) metamorphism, but they readily recrystallize during exhumation. Crystallographically oriented pyroxene and amphibole exsolution lamellae in garnet document decomposed supersilicic UHP majoritic garnet originally stable at diamond-grade conditions, but majoritic precursors have only been quantitatively demonstrated in mafic and ultramafic rocks. Moreover, controversy persists regarding which silicates majoritic garnet breakdown produces. We present a method for reconstructing precursor majoritic garnet chemistry in metasedimentary Appalachian gneisses containing garnets preserving concentric zones of crystallographically oriented lamellae including quartz, amphibole, and sodium phlogopite. We link this to novel quartz-garnet crystallographic orientation data. The results reveal majoritic precursors stable at ?175-kilometer depth and that quartz and mica may exsolve from garnet. Large UHP terranes in the European Caledonides formed during collision of the paleocontinents Baltica and Laurentia; we demonstrate UHP metamorphism from the microcontinent-continent convergence characterizing the contiguous and coeval Appalachian orogen.
Abstract: The first results on the interaction between an Fe-Ni melt and anthracene (?14?10) in the presence of olivine at 3 GPa and 1500°? and on the study of the component composition of the fluid generated in this process are presented. The stability of aliphatic hydrocarbons in the implemented conditions is confirmed experimentally. It is established that, under these conditions, crystallization of high-magnesian olivines occurs (Fo = 97-98 mol %). The composition of the fluid is similar to the composition of the fluid from inclusions in synthetic diamonds. The conditions implemented in the experiment might have occurred at the early stages of the Earth’s evolution.
Abstract: Data on the interaction of the Fe-Ni melt with CaCO3 and graphite at 5 GPa and 1400°? under the thermogradient conditions used in experiments on the growth of diamond on the BARS high-pressure apparatus are presented. The phase composition and component composition of the fluid captured by diamonds in the form of inclusions were studied by gas chromatography-mass spectrometry (GC-MS). Diamonds were synthesized from graphite. During the interaction of the Fe-Ni melt with CaCO3, Ca-Fe oxides and (Fe, Ni)3C carbide were formed. The stability of heavy hydrocarbons under the experimental conditions was confirmed. It was established that the composition of the fluid in synthesized diamonds is close to the composition of the fluid from inclusions in some natural diamonds. Nevertheless, it was concluded that crystallization of large diamonds under natural conditions is hardly possible due to the filling of the main crystallization volume with refractory oxide phases.
Earth-Science Reviews, Vol. 210, doi.org/10.1016 /j.earscirev.2020. 103356 27p. Pdf
Mantle
UHP, geodynamics
Abstract: Eclogites are witnesses of geodynamic processes that are commonly related to subduction of oceanic crust. Information on the part of these processes that refers to the burial of this rock type is rarely published but stored in the eclogitic garnet core and inclusions therein. To better understand general aspects of the burial process, a literature search on the chemical characteristics of garnet in worldwide occurrences of eclogite was undertaken. In most cases extended garnet cores show either a prograde growth zoning with increasing Mg, starting at a few percent of pyrope component, and decreasing Mn contents (type I eclogite) or a (nearly) constant chemical composition frequently with pyrope contents significantly above 10 percent (eclogites of types II and III). Only in minor cases, it is difficult to assign the reported garnet core to an eclogite type. The growth zoning of garnet was thermodynamically modelled for the chemical composition of a basalt following different burial paths. These paths are characterized either by a trajectory along a low geothermal gradient (type I eclogite), as expected for the subducting upper portion of oceanic crust, or a one characterized by nearly isothermal burial at temperatures above 500 °C reaching peak pressures up to 2.1 GPa (type III eclogite), as possibly due to crustal thickening during continent-continent collision, or more (type II eclogite) when basic rocks are tectonically eroded from the overriding continental plate before deep subduction. In addition, diffusion modelling was undertaken on mm-sized garnet demonstrating that the characteristics of the core zoning are not fully obliterated even during residence at temperatures of 800-850 °C within 10 million years. The scrutiny of more than 200 eclogites reported in the literature led to the following result: about half of them are type II eclogites; a third and a sixth can be related to type I and type III, respectively. Among type III are almost all of the few Proterozoic eclogites considered. To demonstrate the benefit of our study, we link the core zoning of eclogitic garnet from various (ultra)high-pressure terranes in Phanerozoic orogenic belts to the geodynamics shaping corresponding orogens. The eclogites in these belts are dominated by type II. Thus, we propose that some of the material of the lower portion of the overriding continental crust was tectonically eroded by a subducted oceanic plate and brought to great depth. Afterwards, this material was exhumed first in a deep subduction channel and then in an exhumation channel during continent-continent collision where a contact with the upper continental plate was re-established. Furthermore, we suggest that type II eclogite can also occur in extrusion wedges as far as oblique subduction took place.
Earth and Planetary Science Letters, Vol. 558, 115763, 6p. Pdf
Europe, Italy
UHP
Abstract: The stabilization of coesite is a diagnostic indicator of ultrahigh-pressure metamorphism and in many cases it implies that a rock has been subducted to a minimum depth of 80 km. Coesite typically occurs as rare relicts in rigid host minerals, but most commonly transforms into ?-quartz pseudomorphs during exhumation. The abundance of coesite-bearing rocks in orogens worldwide is a contentious issue in the petrological community, despite evidence from numerical modeling that suggests that coesite formation should be a common geological process during ultrahigh-pressure metamorphism. This knowledge gap must be addressed to improve the understanding of the geological aspects of subduction-zone geodynamics. Here we report that minuscule coesites (<20 ?m) occur as abundant inclusions in garnet-rich layers from the Italian Western Alps. The discovery of such intact inclusions may fill the gaps in the predicted and observed abundances of coesite worldwide. Through integrated approaches with resolutions down to the nano-scale, we show that these garnet-hosted inclusions are composed entirely of coesite. Our results suggest that common coesite-derived quartz pseudomorphs are less typical structures in ultrahigh-pressure metamorphic rocks and the minuscule coesite in many rocks may be overlooked because of its size. These findings open up new research directions for constraining the extent of deeply subducted rocks and their rheology.
PNAS, Vol. 118, no. 23, doi.org/10.1073/pnas .e2020680118 8p. Pdf
Mantle
deep source, genesis
Abstract: Globally distributed kimberlites with broadly chondritic initial 143Nd-176Hf isotopic systematics may be derived from a chemically homogenous, relatively primitive mantle source that remained isolated from the convecting mantle for much of the Earth’s history. To assess whether this putative reservoir may have preserved remnants of an early Earth process, we report 182W/184W and 142Nd/144Nd data for "primitive" kimberlites from 10 localities worldwide, ranging in age from 1,153 to 89 Ma. Most are characterized by homogeneous ?182W and ?142Nd values averaging ?5.9 ± 3.6 ppm (2SD, n = 13) and +2.7 ± 2.9 ppm (2SD, n = 6), respectively. The remarkably uniform yet modestly negative ?182W values, coupled with chondritic to slightly suprachondritic initial 143Nd/144Nd and 176Hf/177Hf ratios over a span of nearly 1,000 Mya, provides permissive evidence that these kimberlites were derived from one or more long-lived, early formed mantle reservoirs. Possible causes for negative ?182W values among these kimberlites include the transfer of W with low ?182W from the core to the mantle source reservoir(s), creation of the source reservoir(s) as a result of early silicate fractionation, or an overabundance of late-accreted materials in the source reservoir(s). By contrast, two younger kimberlites emplaced at 72 and 52 Ma and characterized by distinctly subchondritic initial 176Hf/177Hf and 143Nd/144Nd have ?182W values consistent with the modern upper mantle. These isotopic compositions may reflect contamination of the ancient kimberlite source by recycled crustal components with ?182W ? 0.
Mantle Convection and Surface Expressions, Geophysical Monograph, No. 263, Chapter 7, pp. 179- 14p. Pdf
Mantle
inclusions, subduction, CLIPPER
Abstract: Some rare diamonds originate below the lithosphere, from depths of 300-800 km and perhaps deeper. Ongoing sublithospheric or super-deep diamond research is providing new insight into the mantle and the hidden consequences of plate tectonics. Here we highlight several advances in the past decade, stemming from the discovery of inclusions from oceanic crust at lower mantle depths; inclusions having geochemical imprints of low-degree car-bonatitic melt, possibly from subducted slabs; hydrous ringwoodite and other signs of deep water; major mantle minerals preserved in their original crystal structure, including ringwoodite and CaSiO 3-perovskite; additional diamond varieties with a super-deep origin (CLIPPIR and type IIb diamonds), greatly increasing the known prevalence and diversity of super-deep diamonds; and consistent, recurring Fe-Ni-C-S metallic melt inclusions from depths of 360-750 km. Redox freezing of oxidized, slab-derived fluid/melt upon interaction with ambient metal-saturated mantle appears to be a phenomenon broadly recorded by many super-deep diamonds. Melting of car-bonate, as well as dehydration reactions, from subducted slabs are relevant mechanisms that may generate fluid/ melt contributing to diamond growth. Fe-Ni metal, with dissolved carbon, sulfur, and other elements is also indicated as a possible diamond-forming melt. These mobile and dynamic phases are agents of chemical mass-transfer in the deep mantle.
Abstract: The development of sophisticated sample environments to control temperature, pressure, and magnetic field has grown in parallel with neutron source and instrumentation development. High-pressure apparatus, with high- and low-temperature capability, novel designs for diamond cells, and large volume presses are matched with next-generation neutron sources and moderator designs to provide unprecedented neutron beam brightness. Recent developments in sample environments are expanding the pressure-temperature space accessible to neutron scattering experiments. Researchers are using new capabilities and an increased understanding of the fundamentals of structural and magnetic transitions to explore new territories, including hydrogenous minerals (e.g., ices and hydrates) and magnetic structural phase diagrams.
In: Mantle Convection and Surface Expressions, Geophysical Monograph, editors Marquarte, H., Ballmer, M., Vottaar, S., Konter, J., no. 263, 14p. Pdf
Mantle
Super-deep diamonds
Abstract: Some rare diamonds originate below the lithosphere, from depths of 300-800 km and perhaps deeper. Ongoing sublithospheric or super-deep diamond research is providing new insight into the mantle and the hidden consequences of plate tectonics. Here we highlight several advances in the past decade, stemming from the discovery of inclusions from oceanic crust at lower mantle depths; inclusions having geochemical imprints of low-degree car-bonatitic melt, possibly from subducted slabs; hydrous ringwoodite and other signs of deep water; major mantle minerals preserved in their original crystal structure, including ringwoodite and CaSiO 3-perovskite; additional diamond varieties with a super-deep origin (CLIPPIR and type IIb diamonds), greatly increasing the known prevalence and diversity of super-deep diamonds; and consistent, recurring Fe-Ni-C-S metallic melt inclusions from depths of 360-750 km. Redox freezing of oxidized, slab-derived fluid/melt upon interaction with ambient metal-saturated mantle appears to be a phenomenon broadly recorded by many super-deep diamonds. Melting of car-bonate, as well as dehydration reactions, from subducted slabs are relevant mechanisms that may generate fluid/ melt contributing to diamond growth. Fe-Ni metal, with dissolved carbon, sulfur, and other elements is also indicated as a possible diamond-forming melt. These mobile and dynamic phases are agents of chemical mass-transfer in the deep mantle.
Abstract: In this series of New Mineral Names, a thematic approach is used to help provide context for advances and discoveries in mineralogy. Planet Earth is ever-changing, and unique crystals are found in the tiniest of micro-geologic niches. With emerging analytical techniques, the formerly inaccessible becomes accessible. New minerals inspire creative approaches to overcoming chemical and technological challenges and can reveal what the Earth was like billions of years ago. In this issue, we look at recently described minerals that are associated with diamonds, dumps, and fumaroles: crowningshieldite, goldschmidtite, breyite, cardite, grimmite, hrabákite, freitalite, dioskouriite, dobrovolskyite, ferroefremovite, and vasilseverginite.
Abstract: Large, high-quality type IIa diamonds such as the Cullinan and the Koh-i-Noor are among the most elusive of mined gem diamonds. These are called CLIPPIR diamonds, an acronym reflecting the distinguishing physical characteristics of this variety of diamonds (Cullinan-like, Large, Inclusion Poor, Pure, Irregular, Resorbed) [1]. There is currently no reliable method to predict the occurrence of CLIPPIR diamonds in a deposit, which remains a hurdle for exploration and mining [2]. Mineral inclusions reveal that these are sublithospheric diamonds [1], which explains why their occurrence is effectively independent from more common eclogitic and peridotitic lithospheric diamonds and their associated indicator minerals. More recently, an analysis of iron isotopes in the metallic inclusions sometimes found in CLIPPIR diamonds has provided additional insight into their formation, which may provide clues for exploration. Three measurements of metallic Fe-Ni-C-S inclusions from two diamonds from the Letseng mine, Lesotho reveal remarkably heavy iron isotopic compositions, ?56Fe = 0.79-0.90‰ [3]. These measurements lie far outside the range of known mantle compositions (near 0‰) or expected reaction products at depth. Instead, the heavy signature is ascribed to subducted iron sourced from magnetite and/or Fe-Ni alloys precipitated during seafloor serpentinization of oceanic peridotite. These metallic inclusions provide physical evidence that traces serpentinite subduction into the mantle transition zone. This finding is a step toward a genetic model for CLIPPIR diamonds. Their formation requires input from deeply subducted serpentinized peridotite. Furthermore, this input may come specifically from cold subducting slabs, whose serpentinized mantle portions can bypass the shallow sub-arc dehydration activity and instead transport serpentinite-derived components such as hydrous minerals and iron-rich phases to the transition zone/uppermost lower mantle [4]. The results suggest that geochemical signatures related to deeply subducted serpentinites may eventually provide a basis for targeting CLIPPIR diamonds in volcanic deposits at surface.