Paper Number: 959
Petrogenesis Implications of Zoned Spinel from Northeastern Jiangxi Province Ophiolite (NEJXO), China
Guo, G.L.1,2, Liu, X.D.1 , Liu, C.D.1 , Zhou, W.T.1,3 , Duan, G.H.1
1Fundamental Science on Radioactive Geology and Exporation Technology Laboratory, East China University of Technology, Nanchang, Jiangxi, 330013, China
2CARMA, State Key Laboratory of Continental Tectonic and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijng 100037, China
3Team 209 of Yunnan Nuclear Industry, Kunming, Yunnan, 650000, China
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Spinel is a very important rock-forming mineral in peridotites, and can be used as a sensitive indicator of petrologic processes that occur in its host rock [1]. This study focus on zonal spinel in serpentines from Northeastern Jiangxi Province ophiolite (NEJXO), China. The northeastern Jiangxi Province ophiolite is located in SE margin of the Yangtze Block, and the original sequence of ophiolite has been structurally disrupted. NEJXO often represents a relic of the Huanan ocean between Yangtze and Cathaysia blocks [2]. Most of the dismembered peridotites of NEJXO are highly serpentinized, requiring care in applying geochemistry to distinguish their tectonic setting.
The structure and composition of those zonal spinels from NEJXO are responsive to changing conditions of regional geological processes. Those zonal spinel from NEJXO show granular structure with Cr# value between 45.36 to 49.53 wt.%, and FeOT, Ga, Co, Ni and Ti increasing from core to rim, whereas Cr and Mn decrease (Figure 1). The ferric iron of zonal spinel calculated using the charge balance equation shows that the rim has much higher ferric iron ratio than the core, which suggests the environmental oxygen fugacity has increased from core to rim [3]. Those characteristics indicate that the zonal spinel may form during a subduction metasomatic process, and re-ordering of trace element from core to rim. During the subduction process, oxidizing fluids infiltrated the pores in the spinel, and re-ordering of Fe2+ and Fe3+ into octahedral and tetrahedral sites, which promoted Ga, Co, Mn, Ni and Ti redistributed between tetrahedral and octahedral sites. It suggest that fluid played an important role in the formation of zonal spinel, in addition the source of fluid in the mantle peridotite is closely related to the tectonic environment. Therefore, the zonal spinel has recorded the geodynamic envronmenta evolution of the Northeastern Jiangxi Province ophiolite.
Acknowledgements
This study was financially supported by National Natural Science Foundation of China (No. 41262002)
References:
[1] Dick HJB and Bullen T (1984) CMP 86:54-76
[2] Li XH et al. (1997) PR, 81(1-2):129-144
[3] Dare SAS et al. (2009) CG 261(1-2):199-216