Hello Guest User, You are visiting this website from a computer with an IP address of 172.71.223.147 with the name of '?' since Fri Mar 29, 2024 at 4:08:47 AM PT for approx. 0 minutes now.
The Sheahan Diamond Literature Reference Compilation - Scientific and Media Articles based on Major Keyword - Coesite
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.
Coesite is a form of silicon dioxide formed under ultra high pressure and temperature conditions (greater than 2.5 GPa and 700 degrees C which occurs at a depth of 70 km). It has been found in meteor impact craters and as eclogitic xenoliths in kimberlites. Eclogite evolves through the metamorphism created by subduction and continental collisions. Eclogitic diamonds are distinguished from peridotitic diamonds by including a greater range of carbon isotopes, including C13 which is never present in peridotitic diamonds whose carbon source was never exposed to sunlight whose radiation is critical to the C13 isotope. Peridotitic diamonds are Archean aged, whereas eclogitic diamonds can be younger. Articles about coesite are relevant to diamonds because coesite occurs in eclogitic xenoliths that are the source rocks for eclogitic diamonds.
Butler, J.P., Jamieson, R.A., Steenkamp, H.M., Robinson, P.
Discovery of coesite eclogite from the Nordyane UHP domain, Western Gneiss region, Norway: field relations, metamorphic history and tectonic significance.
Journal of Metamorphic Geology, in press available
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.
Earth and Planetary Science Letters, Vol. 412, pp. 42-51.
Mantle
Coesite
Abstract: Compressional and shear wave velocities of coesite have been measured using ultrasonic interferometry in a multi-anvil apparatus up to 12.6 GPa at room temperature for the first time. While the P wave velocity increases continuously with pressure, the S wave exhibits an anomalous softening and the velocity decreases continuously with pressure. Finite strain analysis of the data yielded KS0=103.6(4) GPaKS0=103.6(4) GPa, G0=61.6(2) GPaG0=61.6(2) GPa and View the MathML sourceK0?=2.9(1), View the MathML sourceG0?=0.3(1) for the bulk and shear moduli and their pressure derivatives, respectively. The anomalous elastic behavior of coesite results in large velocity and impedance contrasts across the coesite–stishovite transition, reaching ?39% and ?48% for P and S wave velocity contrasts, and ?70% and 78% for P and S wave impedance contrasts, respectively, at pressure ?8 GPa, with P and S wave velocity perturbations showing no apparent dependence on depths (i.e., View the MathML sourcedln?V(PorS)/dh?0) within 8–12 GPa. These unusually large contrasts and depth independent characteristics render the transition between the two silica polymorphs one of the most plausible candidates for the cause of the seismically observed X-discontinuity. The current P and S wave velocity perturbation dependences on the SiO2 content, d(ln?VP)/d(SiO2)?0.43 (wt%)?1d(ln?VP)/d(SiO2)?0.43 (wt%)?1 and d(ln?VS)/d(SiO2)?0.60 (wt%)?1d(ln?VS)/d(SiO2)?0.60 (wt%)?1, can serve as a geophysical probe to track ancient subducted eclogite materials to gain insights on the geodynamics of the mantle.
Earth and Planetary Science Letters, Vol. 446, pp. 137-148.
Mantle
Coesite, subduction
Abstract: The ability to accurately constrain the secular record of high- and ultra-high pressure metamorphism on Earth is potentially hampered as these rocks are metastable and prone to retrogression, particularly during exhumation. Rutile is among the most widespread and best preserved minerals in high- and ultra-high pressure rocks and a hitherto untested approach is to use mineral inclusions within rutile to record such conditions. In this study, rutiles from three different high- and ultrahigh-pressure massifs have been investigated for inclusions. Rutile is shown to contain inclusions of high-pressure minerals such as omphacite, garnet and high silica phengite, as well as diagnostic ultrahigh-pressure minerals, including the first reported occurrence of exceptionally preserved monomineralic coesite in rutile from the Dora -Maira massif. Chemical comparison of inclusion and matrix phases show that inclusions generally represent peak metamorphic assemblages; although rare prograde phases such as titanite, omphacite and corundum have also been identified implying that rutile grows continuously during prograde burial and traps mineralogic evidence of this evolution. Pressure estimates obtained from mineral inclusions, when used in conjunction with Zr-in-rutile thermometry, can provide additional constraints on the metamorphic conditions of the host rock. This study demonstrates that rutile is an excellent repository for high- and ultra-high pressure minerals and that the study of mineral inclusions in rutile may profoundly change the way we investigate and recover evidence of such events in both detrital populations and partially retrogressed samples.
Abstract: Intergranular coesite is extremely rare in, and bears crucial information on the formation and preservation of, ultrahigh-pressure (UHP) rocks. Here, we report the first occurrence of intergranular coesite in a metasedimentary rock, which occurs in the Ganjialing area in the Dabie Shan, east-central China, and contains abundant coesite inclusions in both garnet and dolomite. We investigated the content of structural water in these minerals with Fourier transform infrared spectroscopy. Our new results undermine the ubiquity of the “pressure-vessel” model and highlight the role of reaction kinetics in preserving coesite due to the availability of water in UHP rocks.
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: Three types of polyphase solid-inclusions (PSIs) with distinct mineral assemblages and micro-structures were found in garnet of an ultrahigh-pressure (UHP) eclogite-vein system from the Dabie Shan, east-central China. Type-1 PSI contains variable volumes of quartz, K-feldspar, plagioclase ± other phases, whereas Type-2 PSI contains variable volumes of quartz, calcite ± other phases. Both types display shapes that are compatible with those of euhedral coesite inclusions. Type-3 PSI always contains a rutile core that is surrounded by plagioclase ± quartz and generally displays the morphology of the rutile core. Variable amounts of K-feldspar are embedded within the plagioclase of Type-3 PSIs. The three PSI types developed fluid-mediated microstructures that include wedge-like offshoot and protrusion textures and inclusion-garnet interfaces controlled by the crystallographic structure of garnet. PSIs in peak minerals of UHP rocks have been previously thought to represent primary supercritical fluid or melt inclusions. Here we propose that the studied PSIs were formed under high-pressure (HP) eclogite-facies conditions during exhumation and represent reaction products between an enclosed mineral, such as coesite and rutile, and external fluids infiltrating the host garnet along fractures that have been healed later on. Two immiscible aqueous fluids (i.e., a siliceous and a carbonaceous) were involved in the formation of these PSIs. The siliceous fluid was rich in various large ion lithophile elements like Cs, Rb, Ba, K, Pb, Li, and Sr, whereas the carbonaceous fluid was rich in Pb and Sr. The new PSI formation mechanism proposed in this study brings significant implications for tracing fluid evolution and post-entrapment modifications of mineral inclusions in HP and UHP metamorphic rocks.
Journal of Metamorphic Geology, https://doi.org/10.1111/jmg.12470
China
coesite
Abstract: To understand the preservation of coesite inclusions in ultrahigh?pressure (UHP) metamorphic rocks, an integrated petrological, Raman spectroscopic and focused ion beam (FIB) system-transmission electron microscope (TEM) study was performed on a UHP kyanite eclogite from the Sulu belt in eastern China. Coesite grains have been observed only as rare inclusions in kyanite from the outer segment of garnet and in the matrix. Raman mapping analysis shows that a coesite inclusion in kyanite from the garnet rim records an anisotropic residual stress and retains a maximum residual pressure of approximately 0.35 GPa. TEM observations show quartz is absent from the coesite inclusion-host kyanite grain boundaries. Numerous dislocations and sub?grain boundaries are present in the kyanite, but dislocations are not confirmed in the coesite. In particular, dislocations concentrate in the kyanite adjacent to the boundary with the coesite inclusion, and they form a dislocation concentration zone with a dislocation density of ~109 cm?2. A high?resolution TEM image and a fast Fourier transform?filtered image reveal that a tiny dislocation in the dislocation concentration zone is composed of multiple edge dislocations. The estimated dislocation density in most of the kyanite away from the coesite inclusion-host kyanite grain boundaries is ~108 cm?2, being lower than that in kyanite adjacent to the coesite. In the case of a coesite inclusion in a matrix kyanite, using Raman and TEM analyses we could not identify any quartz at the grain boundaries. Dislocations are not observed in the coesite, but numerous dislocations and stacking faults are developed in the kyanite. The estimated overall dislocation density in the coesite?bearing matrix kyanite is ~108 cm?2, but a high dislocation density region of ~109 cm?2 is also present near the coesite inclusion-host kyanite grain boundaries. Inclusion and matrix kyanite grains with no coesite have dislocation densities of ?108 cm?2. Dislocation density is generally reduced during an annealing process, but our results show that not all dislocations in the kyanite have recovered uniformly during exhumation of the UHP rocks. Hence, one of the key factors acting as a buffer to inhibit the coesite to quartz transformation is the mechanical interaction between the host and the inclusion that lead to the formation of dislocations in the kyanite. The kyanite acts an excellent pressure container that can preserve coesite during the decompression of rocks from UHP conditions. The search for and study of inclusions in kyanite may be a more suitable approach for tracing the spatial distribution of UHP metamorphic rocks.
Journal of Metamorphic Geology, Vol. 37, 3, pp. 401-414.
China
coesite
Abstract: To understand the preservation of coesite inclusions in ultrahigh?pressure (UHP) metamorphic rocks, an integrated petrological, Raman spectroscopic and focussed ion beam (FIB) system-transmission electron microscope (TEM) study was performed on a UHP kyanite eclogite from the Sulu belt in eastern China. Coesite grains have been observed only as rare inclusions in kyanite from the outer segment of garnet and in the matrix. Raman mapping analysis shows that a coesite inclusion in kyanite from the garnet rim records an anisotropic residual stress and retains a maximum residual pressure of ~0.35 GPa. TEM observations show quartz is absent from the coesite inclusion-host kyanite grain boundaries. Numerous dislocations and sub?grain boundaries are present in the kyanite, but dislocations are not confirmed in the coesite. In particular, dislocations concentrate in the kyanite adjacent to the boundary with the coesite inclusion, and they form a dislocation concentration zone with a dislocation density of ~109 cm?2. A high?resolution TEM image and a fast Fourier transform?filtered image reveal that a tiny dislocation in the dislocation concentration zone is composed of multiple edge dislocations. The estimated dislocation density in most of the kyanite away from the coesite inclusion-host kyanite grain boundaries is ~108 cm?2, being lower than that in kyanite adjacent to the coesite. In the case of a coesite inclusion in a matrix kyanite, using Raman and TEM analyses, we could not identify any quartz at the grain boundaries. Dislocations are not observed in the coesite, but numerous dislocations and stacking faults are developed in the kyanite. The estimated overall dislocation density in the coesite?bearing matrix kyanite is ~108 cm?2, but a high dislocation density region of ~109 cm?2 is also present near the coesite inclusion-host kyanite grain boundaries. Inclusion and matrix kyanite grains with no coesite have dislocation densities of ?108 cm?2. Dislocation density is generally reduced during an annealing process, but our results show that not all dislocations in the kyanite have recovered uniformly during exhumation of the UHP rocks. Hence, one of the key factors acting as a buffer to inhibit the coesite to quartz transformation is the mechanical interaction between the host and the inclusion that lead to the formation of dislocations in the kyanite. The kyanite acts as an excellent pressure container that can preserve coesite during the decompression of rocks from UHP conditions. The search for and study of inclusions in kyanite may be a more suitable approach for tracing the spatial distribution of UHP metamorphic rocks.
Abstract: As reported in our prior work, we have recovered microdiamonds and other unusual minerals, including pseudomorph stishovite, moissanite, qingsongite, native elements, metallic alloys, and some crustal minerals (i.e., zircon, quartz, amphibole, and rutile) from ophiolitic peridotites and chromitites. These ophiolite-hosted microdiamonds display different features than kimberlitic, metamorphic, and meteoritic diamonds in terms of isotopic values and mineral inclusions. The characteristic of their light carbon isotopic composition implies that the material source of ophiolite-hosted diamonds is surface-derived organic matter. Coesite inclusions coexisting with kyanite rimming an FeTi alloy from the Luobusa ophiolite show a polycrystalline nature and a prismatic habit, indicating their origin as a replacement of stishovite. The occurrence in kyanite and coesite with inclusions of qingsongite, a cubic boron nitride mineral, and a high-pressure polymorph of rutile (TiO2 II) point to formation pressures of 10-15?GPa at temperatures ?1300?°C, consistent with depths greater than 380?km, near the mantle transition zone (MTZ). Minerals such as moissanite, native elements, and metallic alloys in chromite grains indicate a highly reduced environment for ophiolitic peridotites and chromitites. Widespread occurrence of diamonds in ophiolitic peridotites and chromitites suggests that the oceanic mantle may be a more significant carbon reservoir than previously thought. These ophiolite-hosted diamonds have proved that surface carbon can be subducted into the deep mantle, and have provided us with a new window for probing deep carbon cycling.
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.
Journal of Metamorphic Geology, doi.org/10/111/jmg.12566
Mantle
coesite
Abstract: Ultrahigh?pressure (UHP) metamorphism observed in continental terranes implies that continental crust can subduct to ~40 kbar before exhuming to the surface. This process is one of the least understood and widely debated parts of the orogenic cycle. The dominantly felsic composition of UHP continental terranes means that many petrology?based techniques for determining peak pressures and temperatures are often not possible. In such cases, the detection of UHP conditions depends on the preservation of coesite, a rarely preserved mineral in exhumed UHP terranes as it rapidly transforms to quartz on decompression. Consequently, the qualitative identification of palisade quartz microstructures that form during the retrograde transformation of coesite to quartz is often used to identify UHP terranes. In this study, we conduct EBSD and misorientation analysis of palisade quartz inclusions in the coesite?bearing pyrope quartzite from the Dora Maira massif in the Alps, and matrix?scale palisade quartz in the Polokongka La granite from Tso Morari in the Ladakh Himalaya, in order to quantitatively define crystallographic characteristics of quartz after coesite. The repeatability of our observations in two unrelated occurrences of UHP rocks supports our interpretation that the following features provide a systematic and predictable set of criteria to identify the coesite to quartz transition: (1) Quartz crystallographic orientations define spatially and texturally distinct subdomains of palisade quartz grains with ‘single crystal’ orientations defined by distinct c?axis point?maxima. (2) Adjacent subdomains are misorientated with respect to each other by a misorientation angle/axis of 90°/. (3) Within each subdomain, palisade quartz grain boundaries commonly have intra? and inter?granular misorientations of 60°/[0001], consistent with the dauphiné twin law. Our observations imply that the coesite?to?quartz transformation is crystallographically controlled by the epitaxial nucleation of palisade quartz on the former coesite grain, specifically on potential coesite twin planes such as (101) and (021).