Comparison of Redox States between the Ultramafic Bodies of Xigaze and Luobusha Ophiolites, Tibet, China

作     者：ZHU Xiangkun HE Yuan SHE Yuwei WAN Hongqing 

作者机构：MNR Key Laboratory of Deep-Earth DynamicsMNR Key Laboratory of Isotope GeologyInstitute of GeologyChinese Academy of Geological SciencesBeijing 100037China 

出 版 物：《Acta Geologica Sinica(English Edition)》 (地质学报（英文版）)

年 卷 期：2020年第94卷第S1期

页      面：93-93页

核心收录：

学科分类：0709[理学-地质学] 0819[工学-矿业工程] 081803[工学-地质工程] 08[工学] 0818[工学-地质资源与地质工程] 0708[理学-地球物理学] 0816[工学-测绘科学与技术] 

基　　金：granted by the China Geological Survey(Grant No.121201102000150069) 

主　　题：ultramafic bodies redox states tectonicsetting Xigaze ophiolite Luobusha ophiolite 

摘      要：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.