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Comparison of Redox States between the Ultramafic Bodies of Xigaze and Luobusha Ophiolites, Tibet, China
Author(s) -
ZHU Xiangkun,
HE Yuan,
SHE Yuwei,
WAN Hongqing
Publication year - 2020
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.14492
Subject(s) - chromite , ophiolite , chromitite , geochemistry , geology , lithosphere , basalt , mineral redox buffer , prospecting , partial melting , ultramafic rock , tectonics , mantle (geology) , paleontology
Abstract The tectonic setting of podiform chromitite formation still remains highly debated. There is a close correlation between tectonic settings and oxygen fugacity ( f O 2 ) (e.g., Ballhaus, 1993; Dare et al., 2009; Parkinson and Arculus, 1999). Here we present results of f O 2 of chromites determined by Mössbauer spectroscopy from both the Luobusha and Dazhuqu areas along Yarlung Zangbo suture zone, Southern Tibet. The f O 2 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 f O 2 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 f O 2 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 f O 2 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 f O 2 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 f O 2 values. The phenomenon infers that the suprasubduction zone is more beneficial to the formation of podiform chromitites.