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Experimental Constraints on Formation of Low-Cr# Chromitite: Effect of Variable H2O and Cr2O3 on Boninitic-Magma and harzburgite Reactions

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Journal of Earth Science 2020年第4期31卷 709-722页

作者： Yage Zhao Yanfei Zhang Chao Wang Zhenmin Jin Qijin Xu College of Oceanography Hohai UniversityNanjing 210098China State Key Laboratory of Geological Processes and Mineral Resources China University of GeosciencesWuhan 430074China

Reactions between a boninitic or basaltic magma and harzburgite at shallow mantle depths are thought to be closely related to the formation of podiform chromitites,but little experimental data is available on these *** this study,a series of experiments were conducted at 1.5GPa and 1 000–1 400 oC to investigate the interactions between boninitic magma and harzburgite in homogenous mixed systems with varied bulk concentrations of water(~0.7 wt.%–10 wt.%)and Cr2O3(~0.2 wt.%–4 wt.%).In the experimental charges,chromite grains can be observed coexisting with orthopyroxene,clinopyroxene±olivine,and quenched melt in the Cr-bearing *** bulk concentration of Cr2O3 in the starting material has a slight effect on compositional changes in the chromites ***,the Cr#(Cr#=100×Cr/(Cr+Al))and Mg#(Mg#=100×Mg/(Mg+Fe))values for the chromites exhibit positive and negative correlations,respectively,with the bulk H2O *** 1 100 oC,chromite Cr#values range from^33–35 to^58–65,and chromite Mg#values range from^70–73 to^55–58when bulk H2O contents in the starting material are increased from^0.7 wt.%to^10 wt.%.The experimentally produced chromites have compositions(as expressed by Cr#,Mg#,and Ni O and Mn O contents)similar to natural chromites from low-Cr#chromitite *** suggest that the interactions between boninitic magmas with varied H2O contents and harzburgite in a shallow mantle wedge could be a possible mechanism that forms the low-Cr#chromitites found in *** emphasize here that H2O may play an important role in the compositional evolutions of natural chromitites.

关键词： low-Cr#chromitite boninitic magma harzburgite melt-rock reaction

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Thermal properties of harzburgite and dunite at 0.8–3 GPa and 300–823 K and implications for the thermal evolution of Tibet

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Geoscience Frontiers 2021年第2期12卷 947-956页

作者： Jianhua Ge Baohua Zhang Zili Xiong Lanfang He Heping Li Key Laboratory for High-Temperature and High-Pressure Study of the Earth’s Interior Institute of GeochemistryChinese Academy of SciencesGuiyang 550081China University of Chinese Academy of Sciences Beijing 100049China State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China

Thermal diffusivity(D)and thermal conductivity(κ)of harzburgite and dunite from Luobusha ophiolite were simultaneously measured up to 3 GPa and 823 K using the transient plane-source method in a multi anvil *** results show that the values of D andκof both samples systematically decrease with increasing temperature and increase with increasing *** combination of the thermal physical data of rocks and minerals and geophysical constraints,we performed numerical simulation on the thermal evolution of Tibet vary over depth,distance and geologic *** present results provide new constraints on occurrence of partial melting and its geophysical significance beneath Tibetan crust.

关键词： Thermal diffusivity Thermal conductivity harzburgite Dunite Thermal evolution Tibet

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Zircon Record of Ocean-Continent Subduction Transition Process of Dulan UHPM Belt, North Qaidam

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Journal of Earth Science 2015年第5期26卷 617-625页

作者： Jianzhou Yang Xiaochi Liu Yuanbao Wu Yanling Sun Department of Earth Sciences China University of GeosciencesWuhan State Key Laboratory of Lithospheric Evolution Institute of Geology and Geophysics Chinese Academy of Sciences

The North Qaidam UHPM（ultra-high pressure metamorphism） belt is a typical continental subduction-collision belt containing continental crust deep subduction metamorphic products and oceanic crust relics, And it is an ideal region to study the ocean-continent transition and exhumation mechanism of oceanic UHP rocks during continental deep subduction process. In this paper, we report integrated in situ U-Pb, Lu-Hf and O isotope analyses of zircons from a serpentinized harzburgite as well as U-Pb dating for zircons from a kyanite eclogite from the North Qaidam Dulan UHPM terrane, and use these data to discuss the ocean-continent transition and exhumation mechanisms of oceanic UHP rocks during continental deep subduction. The serpentinized harzburgite was dated at 448±9 Ma, consistent with 455±5 Ma age for the kyanite eclogite within analytical errors. Zircons from the serpentinized harzburgite have uniform 176Hf/177 Hf values ranging from 0.282 842 to 0.282 883 and εHf（t） values from 11.6 to 13.3. Zircon δ^18O values of the serpentinized harzburgite vary from 4.47‰ to 5.29‰, slightly lower than the value of 5.3‰±0.6‰ for the normal mantle zircon. These Hf-O isotopic features indicate that the protolith of the serpentinized harzburgite was derived from depleted-mantle source, and might have experienced high-temperature rock-water interaction. Therefore, the serpentinized harzburgite was possibly located in the lower part of an oceanic section. The serpentinized harzburgite and kyanite eclogite were both formed due to the subduction of oceanic crust. The UHP metamorphism occurred successively from the oceanic crust to continental crust rocks of the North Qaidam UHP terrane. Low-density serpentinized peridotite and continental rocks possibly have negative buoyancy and play a key effect on preservation and exhumation of high-density oceanic eclogite.

关键词： continental deep subduction ocean-continent transformation North Qaidam harzburgite eclogite

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Metasomatism of the peridotites from southern Mariana fore-arc:Trace element characteristics of clinopyroxene and amphibole

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Science China Earth Sciences 2007年第7期50卷 1005-1012页

作者： CHEN JunBing1,2 & ZENG ZhiGang1 1 Institute of Oceanology,Chinese Academy of Sciences,Qingdao 266071,China 2 Graduate University of Chinese Academy of Sciences,Beijing 100049,China 1. Institute of Oceanology Chinese Academy of Sciences Qingdao 266071 China 2. Graduate University of Chinese Academy of Sciences Beijing 100049 China

Modal composition and mineral composition of harzburgites from the southern Mariana fore-arc show that they are highly refractory. There are a few modals of clinopyroxene (0.7 vol %) in harzburgites. Two types of amphibole are found in these harzburgites: magnesiohornblende accompanied by clinopy-roxene with higher Al2O3 content (>7%) and lower Mg#; tremolite around orthopyroxene with lower Al2O3 content (harzburgites underwent two stages of metasomatism. The percolation of a hydrous melt led to mobility of Al,Ca,Fe,Mg,Na,and large amounts of trace element. LILE and LREE can be more active in hydrous melt than HREE and Ti,and the activities of most of the trace element except some of LILE are influ-enced by temperature and pressure.

关键词： trace element clinopyroxene amphibole harzburgite metasomatism Mariana

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Archean-Paleoproterozoic Lithospheric Mantle at the Northern Margin of the North China Craton Represented by Tectonically Exhumed Peridotites

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Acta Geologica Sinica(English Edition) 2017年第6期91卷 2041-2057页

作者： TIAN Wei WANG Shuangyue LIU Fenglin CHU Zhuyin WANG Bin CHEN Mimi Jennifer PRICHARD Key Laboratory of Orogenic Belts and Crustal Evolution MOESchool of Earth and Space SciencesPeking University State Key Laboratory of Lithospheric Evolution Institute of Geology and GeophysicsChinese Academy of Sciences Research School of Earth and Space Sciences the Australian National University

Tectonically emplaced peridotites from North Hebei Province, North China Craton, have retained an original harzburgite mineral assemblage of olivine （54%-58%）＋ orthopyroxene （40%-46%）＋minor clinopyroxene （〈1%）＋spinel. Samples with honinite-like chemical compositions also coexist with these peridotites. The spinels within the peridotites have high-A1 end-members with A1203 content of 30 wt%-50 wt%, typical of mantle spinels. When compared with experimentally determined melt extraction trajectories, the harzburgites display a high degree of melting and enrichment of SiO2, which is typical of cratonic mantle peridotites. The peridotites display variably enriched light rare earth elements （REEs）, relatively depleted middle REEs and weakly fractionated heavy REEs, which suggest a melt extraction of over 25% in the spinel stability field. The occurrence of are- and SSZ-type chromian spinels in the peridotites suggests that melt extraction and metasomatism occurred mostly in a subduction-related setting. This is also supported by the geochemical data of the coexisting boninite-like samples. The peridotites have lS7Os/lSSOs ratios ranging from 0.113-0.122, which is typical of cratonic iithospheric mantle. These lSTOs/ISSOs ratios yield model melt extraction ages （TRD） ranging from 981 Ma to 2054 Ma, which may represent the minimum estimation of the melt extraction age. The Ai203- lSTOs/lSSOs-proxy isochron ages of 2.4 Ga-2.7 Ga suggest a mantle melt depletion age between the Late Achaean and Early Paleoproterozoic. Both the peridotites and boninite-like rocks are therefore interpreted as tectonically exhumed continental lithospheric mantle of the North China Craton, which has experienced mantle melt depletion and subduction-related mantle metasomatism during the Neoarchean- Paleoproterozoic.

关键词： harzburgite boninite Re-Os isotopes lithospheric mantle Paleoproterozoic North China Craton

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