Evidence for palaeo-Tethyan oceanic subduction within central Qiangtang, northern Tibet

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	Evidence for palaeo-Tethyan oceanic subduction within central Qiangtang, northern Tibet
	Liu, Y (Liu, Yan); Santosh, M (Santosh, M.); Zhao, ZB (Zhao, Zhong Bao); Niu, WC (Niu, Wen Chao); Wang, GH (Wang, Gen Hou)
刊名	LITHOS
	2011
卷号	127 期号:1-2 页码:39-53
关键词	Garnet blueschist Petrology Metamorphic history Cold slab subduction Tethys Northern Tibet
ISSN号	0024-4937
英文摘要	The mechanism of formation of blueschist-eclogite belts and their space-time distribution are important in understanding the tectonics associated with convergent plate boundaries. Here we investigate the garnet-bearing blueschists from Rongma area of central Qiangtang in northern Tibet. The mineral assemblage in these rocks is characterized by porphyroblastic garnet set within a matrix of fine-grained amphibole, white mica, epidote, chlorite, albite and quartz with accessory rutile, titanite and apatite. The garnet porphyroblasts exhibit core and rim portions, and the cores carry abundant inclusions of Na amphibole, quartz and rutile, as well as rhomb-shaped inclusions of paragonite and epidote which are interpreted as pseudomorphs after lawsonite. The rims are characterized by coarse-grained inclusions of epidote as well as the absence of paragonite and epidote aggregates, clearly suggesting that the transition from garnet core to rim marks a metamorphic transformation from lawsonite- to epidote-stability field. The Mn content of the garnet porphyroblasts decreases from core to rim, whereas the Fe and Mg contents show an increasing trend. In the matrix, we identify two stages of Na amphibole rimmed by Na-Ca amphibole and albite. Retrograde chlorite is rimmed by fine-grained biotite. Based on microstructural observations and pseudosection modelling, we trace the P-T path for the Rongma garnet blueschist from 1.92 GPa and 490 degrees C ( lawsonite eclogite field) to about 1.68 GPa and 535 degrees C (epidote eclogite field), marking an initial increase in temperature and decrease in pressure. This stage is followed by a decrease of pressure through the blueschist facies down to P-T conditions of about 0.6 GPa and 530 degrees C. In combination with previous work including the available isotopic age data, the P-T path obtained in the present study suggests the deep subduction of palaeo-Tethyan oceanic crust between southern and northern Qiangtang blocks, supporting the model that the blueschist belt defines the location of the palaeo-Tethyan suture zone within northern Tibet. T-X(O) pseudosection modelling further reveals that the transformation of lawsonite to epidote occurred under high O contents. Our results provide important clues to better understand the subduction-related late Permian to early Triassic magmas in northern Tibet. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.
学科主题	构造地质学
WOS关键词	METAMORPHIC CORE COMPLEXES ; DEEP-CRUSTAL STRUCTURE ; P-T EVOLUTION ; TECTONIC EVOLUTION ; GEOLOGICAL SIGNIFICANCE ; THERMODYNAMIC MODEL ; MINERAL EQUILIBRIA ; PHASE-EQUILIBRIA ; LAWSONITE ; ECLOGITE
WOS研究方向	Geochemistry & Geophysics ; Mineralogy
语种	英语
出版者	ELSEVIER SCIENCE BV
WOS记录号	WOS:000298070600004
内容类型	期刊论文
源URL	[http://119.78.100.197/handle/2HKVOGP0/39391]
专题	中国地质调查局
作者单位	China Univ Geosci, Sch Earth Sci & Mineral Resources, Beijing 100083, Peoples R China
推荐引用方式 GB/T 7714	Liu, Y ,Santosh, M ,Zhao, ZB ,et al. Evidence for palaeo-Tethyan oceanic subduction within central Qiangtang, northern Tibet[J]. LITHOS,2011,127(1-2):39-53.
APA	Liu, Y ,Santosh, M ,Zhao, ZB ,Niu, WC ,&Wang, GH .(2011).Evidence for palaeo-Tethyan oceanic subduction within central Qiangtang, northern Tibet.LITHOS,127(1-2),39-53.
MLA	Liu, Y ,et al."Evidence for palaeo-Tethyan oceanic subduction within central Qiangtang, northern Tibet".LITHOS 127.1-2(2011):39-53.