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The Sheahan Diamond Literature Reference Compilation - Scientific and Media Articles based on Major Keyword - Boninites
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.
Boninites are an extrusive mafic rock rich in magnesium and silica whose magma is formed in "fore-arc" environments near island arcs where the "mantle wedge" above a subducting plate near the ocean trench undergoes partial melting. Boninites are more relevant to rare earths than diamonds.
Geochemistry of boninite type volcanic rocks in the Frotet Evans greenstone belt, Opawica subprovince Quebec: implications for the evolution of Archean belts
Precambrian Research, Vol. 115, No.1-4, pp. 349-71.
Geochemistry and petrogenesis of neoarchean high Mg low Ti mafic igneous rocks in an intracratonic setting, central India craton: evidence for boninite magmatism.
Journal of Asian Earth Sciences, Vol. 105, pp. 300-319.
India
Boninites
Abstract: High MgO volcanic rocks having elevated concentrations of Ni and Cr are potential hosts for platinum group elements (PGE) owing to their primitive mantle origin and eruption at high temperatures. Though their higher PGE abundance is economically significant in mineral exploration studies, their lower concentrations are also valuable geochemical tools to evaluate petrogenetic processes. In this paper an attempt has been made to evaluate the PGE geochemistry of high MgO volcanic rocks from two greenstone belts of western and eastern Dharwar Craton and to discuss different mantle processes operative at diverse geodynamic settings during the Neoarchean time. The Bababudan greenstone belt of western and Gadwal greenstone belt of eastern Dharwar Cratons are dominantly composed of high MgO volcanic rocks which, based on distinct geochemical characteristics, have been identified as komatiites and boninites respectively. The Bababudan komatiites are essentially composed of olivine and clinopyroxene with rare plagioclase tending towards komatiitic basalts. The Gadwal boninites contain clinopyroxene, recrystallized hornblende with minor orthopyroxene, plagioclase and sulphide minerals. The Bababudan komatiites are Al-undepleted type (Al2O3/TiO2 = 23-59) with distinctly high MgO (27.4-35.8 wt.%), Ni (509-1066 ppm) and Cr (136-3036 ppm) contents. These rocks have low ?PGE (9-42 ppb) contents with 0.2-2.4 ppb Iridium (Ir), 0.2-1.4 ppb Osmium (Os) and 0.4-4.4 ppb Ruthenium (Ru) among Iridium group PGE (IPGE); and 1.4-16.2 ppb Platinum (Pt), 2.8-19 ppb Palladium (Pd) and 0.2-9.8 ppb Rhodium (Rh) among Platinum group PGE (PPGE). The Gadwal boninites are high-Ca boninites with CaO/Al2O3 ratios varying between 0.8 and 1.0, with 12-24 wt.% MgO, 821-1168 ppm Ni and 2307-2765 ppm Cr. They show higher concentration of total PGE (82-207 ppb) with Pt concentration ranging from 13 to 19 ppb, Pd between 65 and 180 ppb and Rh in the range of 1.4-3 ppb compared to the Bababudan komatiites. Ir, Os and Ru concentrations range from 0.6 to 2.2 ppb, 0.2 to 0.6 ppb and 1.4 to 2.6 ppb respectively in IPGE. The PGE abundances in Bababudan komatiites were controlled by olivine fractionation whereas that in Gadwal boninites were influenced by fractionation of chromite and sulphides. The Al-undepleted Bababudan komatiites are characterized by low CaO/Al2O3, (Gd/Yb)N, (La/Yb)N, with positive Zr, Hf, Ti anomalies and high Cu/Pd, Pd/Ir ratios at low Pd concentrations suggesting the derivation of parent magma by high degrees (>30%) partial melting of mantle under anhydrous conditions at shallow depth with garnet as a residual phase in the mantle restite. The komatiites are geochemically analogous to Al-undepleted Munro type komatiites and their PGE compositions are consistent with Alexo and Gorgona komatiites. The S-undersaturated character of Bababudan komatiites is attributed to decompression and assimilation of lower crustal materials during magma ascent and emplacement. In contrast, the higher Al2O3/TiO2, lower (Gd/Yb)N, for Gadwal boninites in combination with negative Nb, Zr, Hf, Ti anomalies and lower Cu/Pd at relatively higher Pd/Ir and Pd concentrations reflect high degree melting of refractory mantle wedge under hydrous conditions in an intraoceanic subduction zone setting. Higher Pd/Ir ratios and S-undersaturation of these boninites conform to influx of fluids derived by dehydration of subducted slab resulting into high fluid pressure and metasomatism of mantle wedge.
International Geology Review, Vol. 58, 13, pp. 1596-1615.
India
Boninites
Abstract: Nd-isotope and lithogeochemistry of an early Palaeoproterozoic high-Si high-Mg boninite -norite (BN) suite of rocks from the southern Bastar craton, central India, are presented to understand their nature, origin, and tectonic setting of emplacement. Various types of evidence, such as field relationships, radiometric metamorphic ages, and the global distribution of BN magmatism, suggest emplacement in an intracratonic rift setting, commonly around 2.4 -2.5 Ga. On the basis of geochemistry these high-Si high-Mg rocks are classified as high-Ca boninites, high-Mg norites, and high-Mg diorites. Nd-isotope data indicate that the high-Mg norite and the high-Mg diorite samples are similar, whereas the high-Ca boninites have a different isotopic character. The high-Mg norite and the high-Mg diorite samples have younger TDM model ages than the high-Ca boninites. Geochemical and Nd-isotopic characteristics of the studied rocks indicate some prospect of crustal contamination; however, the possibility of mantle metasomatism during ancient subduction event cannot be ignored. Trace-element modelling suggests that the high-Ca boninites may have crystallized from a magma generated by a comparatively greater percentage of melting of a lherzolite mantle source than the source for the other two varieties. Furthermore, the high-Ca boninite rocks are most likely derived from an Archaean subduction process (the Whundo-type), whereas the other two types are the products of the interaction of subduction-modified refractory mantle wedge and a plume, around the Neoarchaean -Palaeoproterozoic boundary. The emplacement of the high-Mg norites and the high-Mg diorites may be linked to crustal thickening and associated cratonization at the end of the Archaean.
Abstract: Boninite is a volcanic rock derived from shallow melting of highly depleted hydrous mantle, fluxed with water from subducted slabs. The eruption of boninite early in the history of the Izu-Bonin-Mariana (IBM) arc (~ 48-45 Ma), suggests generation by melting of upper mantle material that was relatively unmodified by subducted components. Thus, the boninite composition should largely reflect that of the sub-arc mantle. For better understanding of the mantle sources of nascent arc settings and the contributions of different components to arc melts, we analyzed Os isotope ratios (187Os/188Os) of bulk rocks and mineral separates (euhedral Cr-spinel from boninites and euhedral Cr-spinel/magnetite mixtures from tholeiites younger than 45 Ma that erupted after boninites) from the Bonin Islands and Guam. The age-corrected (initial) Os isotope ratios of the whole-rock samples (0.1179-0.2050) were more radiogenic and variable than those of the mineral separates, possibly because of contamination with crustal materials during magma ascent or alteration after emplacement. The age-corrected Os isotope ratios of euhedral Cr-spinel in boninite from the Bonin Islands (0.1187-0.1254) and from Guam (0.1220-0.1269) are unradiogenic relative to primitive mantle, and those of the Cr-spinel/magnetite mixtures from the tholeiites from the Bonin Islands are similar to or slightly more radiogenic (0.1224-0.1382). The most depleted Os isotope ratio of the Cr-spinel from boninite yielded a model Re depletion (TRD) age of 1.4 Ga, suggesting that the mantle source of the boninite experienced melt extraction prior to 1.4 Ga. The source of the boninites is interpreted to be mostly highly depleted mantle with a small contribution of slab flux arising from altered oceanic crust that has radiogenic Os components, with or without contributions from components with relatively unradiogenic Os such as volcaniclastics of oceanic island basalt affiliation or very young mid-ocean ridge basalt.
Abstract: In this contribution, we present detailed field, petrography, mineral chemistry, and geochemistry of newly identified high-Si high-Mg metavolcanic rocks from the southern part of the ~3.3 Ga Holenarsipur greenstone belt in the western Dharwar craton, India. The rocks occur as conformable bands that were interleaved with the mafic-ultramafic units. The entire volcanic package exhibits uniform foliation pattern, and metamorphosed under greenschist to low grade amphibolite facies conditions. The rocks are extremely fine grained and exhibit relict primary igneous textures. They are composed of orthopyroxene and clinopyroxene phenocrysts with serpentine, talc, and amphibole (altered clinopyroxene). Cr-spinel, rutile, ilmenite, and apatite occur as disseminated minute grains in the groundmass. The mineralogical composition and the geochemical signatures comprising of high SiO2 (~53 wt. %), Mg# (~83), low TiO2 (~0.18 wt. %), and higher than chondritic Al2O3/TiO2 ratio (~26), reversely fractionated heavy rare earth elements (REE) (GdN/YbN ~ 0.8), resulting in concave-up patterns, and positive Zr anomaly, typically resembled with the Phanerozoic boninites. Depletion in the high field strength elements Nb, and Ti relative to Th and the REE in a primitive mantle normalized trace element variation diagram, cannot account for contamination by pre-existing Mesoarchean continental crust present in the study area. The trace element attributes instead suggest an intraoceanic subduction-related tectonic setting for the genesis of these rocks. Accordingly, the Holenarsipur high-Si high-Mg metavolcanic rocks have been identified as boninites. It importantly indicates that the geodynamic process involved in the generation of Archean boninites, was perhaps not significantly different from the widely recognized two-stage melt generation process that produced the Phanerozoic boninites, and hence provides compelling evidence for the onset of Phanerozoic type plate tectonic processes by at least ~3.3 Ga, in the Earth’s evolutionary history.
Abstract: Dunites in the mantle section of the Oman ophiolite contain olivines which show both a wide range of compositions (Fo86.2 to Fo94) and very high magnesium numbers. These data are combined with experimental liquidus olivine-melt data to show that the range of olivine compositions requires that the dunites formed from a range of melt compositions and that some of these melts were very magnesian, with MgO concentrations up to MgO?=?18-20?wt%. These observations are consistent with the finding of MgO-rich melt inclusions from chromitites in the mantle section of the Oman ophiolite (Rollinson et al., Lithos, 2018). It is proposed that the high Mg-olivines formed in equilibrium with high-Ca boninites, found in the upper section of the pillow lavas sequence of the ophiolite. A model is developed whereby high MgO boninites fractionated olivine through a process of melt-rock reaction/fractionation with the enclosing harzburgite to create a range of dunitic compositions and evolved boninitic lavas. Field evidence shows that the emplacement of boninites was late in the evolution of the Oman ophiolite indicating that the mantle dunites of boninitic origin formed late in the history of the ophiolite. High-Ca boninites form through the shallow, hydrous melting of the mantle wedge in a subduction setting and the presence of boninitic dunites and lavas further supports the view that the Oman ophiolite formed in a fore-arc setting through subduction-induced spreading.
Journal of Earth System Science, Vol. 128, 17p. Pdf
India
boninite
Abstract: The Dongargarh Supergroup along with the basal Amgaon Gneissic Complex constitutes the northwestern part of the central Indian Bastar craton. In the present study, we report a new finding of a boninite dyke intruded in the Amgaon gneisses of this area. The dyke composed of mainly pyroxenes, amphiboles and subordinate amount of plagioclase. The higher contents of SiO2 (51-54 wt.%), MgO (12-14 wt.%), Ni (375-473 ppm), Cr (1416-1580 ppm) and very low TiO2 (0.2-0.4 wt.%) are consistent with the boninite nature of the dyke as well as the unevolved primary nature of the source magma. The extraordinarily high CaO content (15.97-17.7 wt.%) with higher CaO/Al2O3 (3.13-3.96) ratios classifies it as high-Ca boninite. The trace element ratios including Zr/Ti, Ti/V, Ti/Sc and Ti/Yb further show its geochemical similarity with the Archaean boninite. The dyke also shows negative high-field strength element (Nb, Ta and Ti) anomalies which are the characteristics of the boninite rocks reported elsewhere and along with the enriched light rare earth element pattern, it shows more affinity particularly with the northern Bastar boninite dyke. The mineralogical and geochemical similarities of the boninite dykes from the Bastar craton indicate a widespread boninitic event during the Palaeoproterozoic having a similar origin. These boninite dykes indicate the preservation of subduction-related signatures in the lithospheric mantle beneath the Bastar craton at the time of its evolution or may be during the convergence of the Bastar and Bundelkhand cratons.
Journal of African Earth Sciences, Vol. 165, 18p. Pdf
Africa, Egypt
Boninite
Abstract: Peridotites of Abu Dahr represent the main litho-unit of a Neoproterozoic dismembered ophiolite sequence and are among the best-preserved and well-exposed mantle rocks in South Eastern Desert of Egypt. Here, we present new geochemical and mineral chemical data for peridotites and associated pyroxenites and for chromitites and their platinum-group minerals to constrain their petrogenesis and geotectonic setting. The Abu Dahr ophiolite mantle section consists mainly of harzburgites, cut by pyroxenite dykes and containing dunite-chromitite lenses. The harzburgites are composed of olivine, orthopyroxene, spinel and minor clinopyroxene (?1.0 vol %) and amphibole. Olivine from harzburgites is highly magnesian (Fo 91-93) and Cr-spinel shows a wide-range of Cr2O3 and Al2O3 contents. The enstatite component of orthopyroxene decreases from harzburgite (En = 90-91) to orthopyroxenite (En = 84-87). Amphiboles are represented by magnesiohornblende and tschermakite. The chromitites are massive to disseminated and composed of magnesiochromite with high Cr# (83-93) and Mg# (66-79), and low TiO2 (<0.1 wt%) content. Solid inclusions in chromite include olivine, orthopyroxene and hornblende. Laurite (RuS2) is the most common PGM detected in the investigated chromitite samples and forms micrometer-size inclusions in fresh chromite. Various Ni-sulfides are found both in fresh chromite and along serpentine veinlets. Harzburgites have a refractory composition with a very low Al2O3 (0.4-0.8 wt%) and CaO (0.2-1.6 wt%) contents and high bulk-rock Mg# (89-92). Geochemical data suggest that the Abu Dahr peridotites are highly depleted SSZ peridotites formed in a forearc mantle wedge setting by high degrees of hydrous partial melting and emplaced as a result of the collision of the intra-oceanic arc with the Beitan gneisses. The podiform chromitites and orthopyroxenites were formed due to impregnation of mantle wedge harzburgites by boninitic melt. The highly depleted nature of the harzburgite is responsible for the small reserves of chromite ore at Abu Dahr and in the South Eastern Desert in general.
