Nature and geochemical effects of fluids during ductile shearing of UHP eclogite

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	Nature and geochemical effects of fluids during ductile shearing of UHP eclogite
	Gao, LE (Gao LiE); Zeng, LS (Zeng LingSen); Hu, MY (Hu MingYue); Chen, J (Chen Jing); Jia, ZR (Jia ZeRong)
刊名	ACTA PETROLOGICA SINICA
	2011
卷号	27 期号:4 页码:1095-1115
关键词	Ductile shear zone UHP metamorphism Eclogite Aqueous fluid Rutile Sulu UHP belt
ISSN号	1000-0569
英文摘要	Ductile shear zone is a highly coupled system that involves both mechanical and chemical processes at the presence of aqueous fluids at relatively high temperature conditions. Presence of fluids is one of the major factors that lead to highly localized ductile deformation and the formation of shear fabric. Therefore, variations in mineral chemistry in highly strained rocks can be used to infer the geochemical nature of fluids involving in ductile deformation. Sample DH-2G, an intensively sheared eclogite, consists of garnet, omphacite, rutile, and minor phengite, zoisite, hornblende, plagioclase, quartz, zircon and apatite. There are great variations in garnet grain sizes across different strain domains. In porphyroblast-like domain, garnet grains are only half to one-fourth of the sizes of those within the sheared band. Omphacite and rutile show similar pattern. Electron microprobe and LA-ICP-MS analyses were performed on garnet, omphacite, and utile grains. These data are used to discuss how shearing strain affects the trace element geochemistry of garnet, omphacite, and rutile. In the following discussion, we call those omphacite grains coexisting with fine garnet (garnet-I) as omphacite-I, and those with coarse garnet (garnet-II) as omphacite-II. Our data show that (1) major and trace element contents in garnet-I and garnet-II are almost the same, except Ni; and (2) omphacite-I and omphacite-II also do not show substantial differences in major element composition; but they do have significant differences in trace element geochemistry, especially in REEs. As compared to those in omphacite-1, omphacite-II have (1) lower LREE by up to 25 40 times; (2) elevated HREE by up to 5 10 times; (3) higher contents of Ni, Zn, Co, Sc, Ba, Zr, Y, Rb, Hf, but lower V, Sr, U. Th, Pb, and (4) weak to strong positive Eu anomalies with Eu/Eu* =1. 0 similar to 1. 5; Furthermore, Nb/Ta ratio values of rutiles in sheared domains dramatically increase from the core toward the rim from <19. 0 to >20. 0. Petrography, element geochemistry, and P-T estimations indicate that fluids involved in the ductile shearing possiblby were internally buffered, and are highly enriched in V, Sr, U, Th, Pb, Zr, NI) and LREE. These fluids might derived from decompressional dehydration of normally anhydrous minerals (e. g. omphacite and ruffle). The fluids, the important carrier of mobile elements (LILE and LREE) and relatively immobile elements (HFSE), conspicuously affect the rheology of subduction crust and could contribute to the rapid exhumation of UHP slab.
学科主题	变质岩岩石学
WOS关键词	PRESSURE METAMORPHIC ROCKS ; SUBDUCTED CONTINENTAL-CRUST ; TRACE-ELEMENT FRACTIONATION ; SCIENTIFIC DRILLING PROJECT ; DABIE-SHAN CHINA ; EASTERN CHINA ; OXYGEN-ISOTOPE ; SULU OROGEN ; LU-HF ; MINERAL CHEMISTRY
WOS研究方向	Geology
语种	中文
出版者	SCIENCE CHINA PRESS
WOS记录号	WOS:000290080200016
内容类型	期刊论文
源URL	[http://119.78.100.197/handle/2HKVOGP0/39339]
专题	中国地质调查局
作者单位	Peking Univ, Sch Phys, Beijing 100871, Peoples R China
推荐引用方式 GB/T 7714	Gao, LE ,Zeng, LS ,Hu, MY ,et al. Nature and geochemical effects of fluids during ductile shearing of UHP eclogite[J]. ACTA PETROLOGICA SINICA,2011,27(4):1095-1115.
APA	Gao, LE ,Zeng, LS ,Hu, MY ,Chen, J ,&Jia, ZR .(2011).Nature and geochemical effects of fluids during ductile shearing of UHP eclogite.ACTA PETROLOGICA SINICA,27(4),1095-1115.
MLA	Gao, LE ,et al."Nature and geochemical effects of fluids during ductile shearing of UHP eclogite".ACTA PETROLOGICA SINICA 27.4(2011):1095-1115.