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Comparison of redox states between the Ultramafic Bodies of Xigaze and Luobusha Ophiolites, Tibet, China

Acta Geologica Sinica(English Edition) 2020年第S1期94卷 93-93页

作者： ZHU Xiangkun HE Yuan SHE Yuwei WAN Hongqing MNR Key Laboratory of Deep-Earth Dynamics MNR Key Laboratory of Isotope GeologyInstitute of GeologyChinese Academy of Geological SciencesBeijing 100037China

The tectonic setting of podiform chromitite formation still remains highly debated. There is a close correlation between tectonic settings and oxygen fugacity(fO2)(e.g., Ballhaus, 1993;Dare et al., 2009;Parkinson and Arculus, 1999). Here we present results of fO2 of chromites determined by M?ssbauer spectroscopy from both the Luobusha and Dazhuqu areas along Yarlung Zangbo suture zone, Southern Tibet. The fO2 values(-1.02~0.04 log units against the FMQ buffer) and Cr#(22~54%) in chromites from lherzolites and harzburgites of both areas are similar to those of abyssal peridotites, indicating that they may be residues after partial melting at spreading centers. However, both dunite envelopes and chromitites from Luobusha have high fO2 values(0.04~2.25 log units) and Cr#(73~84%), showing an affinity to boninitic melts, and thus form in a suprasubduction zone. Dazhuqu dunites show diverse fO2 values(-0.22~2.19 log units) and Cr#(22~82%), indicating that they form in distinct settings. Chromitites and chromite dunites from Dazhuqu have low fO2 values(-0.3~0.71 log units) and Cr#(16~63%), both of which are similar to those of MORB-like basalts, inferring that they form in an extensional setting. Both high-Cr and high-Al chromitites from other typical podiform chromite ore deposits, such as Kempirsai, Oman, and Albania ophiolites, also show high fO2 values(e.g., Chashchukhin and Votyakov, 2009;Melcher et al., 1997;Quintiliani et al., 2006;Rollinson and Adetunji, 2015), while the distribution-limited small chromitites and chromite dunites from Dazhuqu exhibit low fO2 values. The phenomenon infers that the suprasubduction zone is more beneficial to the formation of podiform chromitites.

关键词： ultramafic bodies redox states tectonicsetting Xigaze ophiolite Luobusha ophiolite

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Major and Trace Element Characteristics of Apatites in Granitoids from Central Kazakhstan:Implications for Petrogenesis and Mineralization

Major and Trace Element Characteristics of Apatites in Grani...

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中国科学院地质与地球物理研究所2012年度（第12届）学术年会

作者： Mingjian CAO Guangming LI Kezhang QIN Eleonora Yusupovha SEITMURATOVA Yongsheng LIU Key Laboratory of Mineral Resources Institute of Geology and GeophysicsChinese Academy of Sciences Graduate University of Chinese Academy of Sciences

This paper presents abundances of major and trace elements of apatites in granitic rocks associated with different types of ore deposits in Central Kazakhstan on the basis of electron probe microanalysis and laser ablation inductively coupled plasma mass *** results demonstrate that the concentrations and ratios of elements in apatites from different granitoid rocks show distinct features,and are sensitive to magma evolution,petrogenetic and metallogenetic *** in the rocks associated with Mo-W deposits have high content of F and MnO,low content of Cl,which may be indicative of sedimentary sources,while apatites from a Pb-Zn deposit show relatively high content of Cl and low F content,which possibly suggest a high water content In these apatites,Sr contents decrease,while Mn and Y contents increase with magma *** relationship reflects that these elements in apatites are related with the degree of magmatic *** types of REE patterns in apatites are *** 1 character of highest(La/Yb) in apatites of Aktogai porphyry Cu-Mo deposit,Sayak-I skarn Cu deposit and Akzhal skarn Pb-Zn depposit is likely produced by the crystallization of heavy REE-enriched *** 2 character of upward-convex light REE in apatite of Aktogai porphyries likely results from La-enriched mineral *** 3 feature of Nd depletion in apatites of East Kounrad and Zhanet deposits both from Mo-W deposits primarily inherits the character of *** 4 apatites of Aktogai deposit and Akshatau W-Mo deposit with wide range of REE contents may suggest that apatites crystallize under a wide temperature *** types of apatite with distinct redox states are identified based on Eu *** Aktogai apatite with slight negative Eu anomaly displays the most oxidized state of the magma,and the apatites of other samples at Aktogai,East Kounrad and Akzhal with moderate negative Eu anomaly show moderate oxidizing conditio

关键词： apatite Central Kazakhstan granitoid magmatic differentiation metallogenetic processes redox states

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