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Ophiolite-Hosted Diamond: A New Window for Probing Carbon Cycling in the Deep Mantle

Engineering 2019年第3期5卷 406-420页

作者： Dongyang Lian Jingsui Yang School of Earth Sciences and Engineering Nanjing University Nanjing 210023 China CARMA Key Laboratory of Deep-Earth Dynamics of MLR Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China

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℃, 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.

关键词： Ophiolite-hosted diamond Coesite Stishovite podiform chromitites Mantle transition zone

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Geochemical Characteristics of Zoned Chromites in Peridotites from the Proterozoic Miaowan Ophiolitic Complex, Yangtze Craton: Implications for Element Mobility and Tectonic Setting

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Journal of Earth Science 2020年第2期31卷 223-236页

作者： Yang Huang Hao Deng State Key Laboratory of Geological Processes and Mineral Resources Center for Global TectonicsSchool of Earth SciencesChina University of GeosciencesWuhan 430074China

The chrome spinel(chromite)in mantle peridotites from ophiolites can shed light on the formation and evolution process of *** chromites were found in the Late Proterozoic Miaowan ophiolitic complex(MOC),Yangtze *** to the metamorphism and intense deformation,most chromite grains in the MOC peridotites show typical chemical zoning(core-rim texture).The values of major and trace elements largely vary from core to rim within chromite grains,indicating that the chromites have undergone strong alteration and element *** and trace elements in the core parts of chromites are used to infer the tectonic origins and evolution of mantle peridotites in the *** chromites from the MOC peridotites have higher Cr#values and lower Ni and Ga contents with respect to those from Phanero-zoic mantle peridotites,indicating a higher degree of ***-situ major and trace elements(e.g.,Ga)characteristics of podiform chromites in the MOC show that chromites from both harzburgites and dunites have strong subduction-related signatures,indicating that the MOC has formed in a supra-subduction setting which is consistent with the geological and geochemical data presented in previous studies.

关键词： podiform chromite Miaowan ophiolitic complex trace elements Precambrian Yangtze Craton

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Occurrence and Emplacement of Chromite Ores in Sindhudurg District,Maharashtra,India

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Acta Geologica Sinica(English Edition) 2010年第3期84卷 515-527页

作者： Sridhar D.IYER Elapavalooru V.S.S.K.BABU Premchand G.MISLANKAR Anup R.GUJAR Navso V.AMBRE Victor J.LOVESON National Institute of Oceanography Council of Scientific and Industrial ResearchDona PaulaGoa 403004India National Geophysical Research Institute Council of Scientific and Industrial ResearchHyderabad 500007India Central Institute of Mining and Fuel Research Council of Scientific and Industrial ResearchDhanbad 828108India

In the present study,we present the occurrence and emplacement of chromite ore deposits from two abandoned mines（Kankavali[Janoli]and Wagda） in the Sindhudurg district of Maharashtra,*** ores,that occurred as lenses and are associated with metamorphic and ultrabasic rocks,consist of octahedral grains of chromite,while clinochlore is present between the interstices of these *** Kankavali（Janoli） and Wagda ores revealed a dominance of Cr_2O_3 followed by FeO and variable proportions of A1_2O_3,MgO,and SiO_*** former deposits have a slightly higher Cr_2O_3（average 52 wt%） and FeO（～18 wt%） than those from Wagda（Cr_2O_3～50 wt%,FeO～25 wt%）.The similar Cr~# values（0.73 for Kankavali[Janoli],0.74 for Wagda） correspond to those reported for typical podiform-type chromite *** suggest that the ores were emplaced as phacoliths in folded outcrops with a steep easterly dip and a northwest-southeast *** postulate the continuation of the fold structure from Janoli to Wagda（～4.5 km apart） and the probable （sporadic） occurrence of chromite along this *** possibility of the contribution of chromite grains from these areas to the coastal placer deposits cannot be ruled out.

关键词： chromite podiform formation placer Sindhudurg India

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Geochemistry of Chromitites in Eastern Part of Neyriz Ophiolite Complex (Southern Iran)

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Open Journal of Geology 2017年第3期7卷 213-233页

作者： Pedram Attarzadeh Mehrdad Karimi Mohammad Yazdi Kamal Nouri Khankahdani Department of Geology North Tehran Branch Islamic Azad University Tehran Iran Department of Geology Shiraz Branch Islamic Azad University Shiraz Iran Department of Geology Faculty of Earth Sciences Shahid Beheshti University Tehran Iran

The Neyriz ophiolite complex is a part of NW-SE thrust belt (Late Cretaceous) of Iran, which is over the Arabian plate margin. The complex is mainly composed of the upper mantle rocks. Our research was focused on the eastern part of Neyriz ophiolite complex so called as “Dowlat Abad-Tang e Hana”. Mantle sequence of this ophiolitic complex is comprising predominantly of harzburgite and minor lherzolite, dunitc sheaths and chromite pods. Harzburgite is the most abundant ultramafic rock and is associated with the less dunite masses. The chromites are known with Cr# 42 to 76 and Mg# 73 to 89. There is a negative correlation between Cr#-Mg# which is one of the features of podiform chromites. The geochemistry of these chromites is consistent with the overall composition of podiform chromites in terms of Cr#, Mg#, the amounts of Cr2O3 (13.35% - 54.47%), Al2O3 (0.43% - 8%), MgO (13.25% - 38.56%), TiO2 (0.003% - 0.206%) as well as the correlations between various oxides and all of them are high chromium types.

关键词： Ophiolite podiform Chromite Neyriz Iran

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