青藏高原拉萨地块松多蓝闪石榴辉岩的变质演化:相平衡及变质作用P-T轨迹

CORC > 北京大学 > 地球与空间科学学院

	青藏高原拉萨地块松多蓝闪石榴辉岩的变质演化:相平衡及变质作用P-T轨迹; Metamorphic evolution of glaucophane eclogites from Sumdo, Lhasa block of Tibetan Plateau: Phase equilibria and metamorphic P-T path
	杨现力 ; 张立飞 ; 赵志丹 ; 朱弟成
刊名	岩石学报
	2014
关键词	榴辉岩相平衡 P-T轨迹拉萨地块青藏高原 Eclogite Phase equilibrium P-T path Lhasa block Tibetan Plateau Eclogite Phase equilibrium P-T path Lhasa block Tibetan Plateau
英文摘要	青藏高原拉萨地块松多蓝闪石榴辉岩主要矿物组合为石榴石、绿辉石、蓝闪石、绿帘石/斜黝帘石,及少量的金红石、石英、多硅白云母和普通角闪石.石榴石具有成分环带,从核到边Xpy升高,Xgr降低,部分石榴石外边缘受退变质改造影响,形成富Xgr的成分带.利用NCKMnFMASHTO体系中的P-T视剖面图,结合石榴石边部最大Xpy等值线和多硅白云母最大Si-含量值确定了松多榴辉岩的峰期变质条件为30±0.6kbar和610±6℃.石榴石核部到幔部成分环带记录的相对平缓的P-T轨迹反应了岩石早期经历了以加热升温为主、轻微加压的缓慢俯冲过程,地温梯度为7～8℃/km.石榴石幔部到边部成分环带,结合多硅白云母最大Si含量等值线模拟了以缓慢升温、快速增压为特征的P-T轨迹,反应了岩石由早期的缓慢俯冲进入到后期的快速俯冲阶段,地温梯度由7～8℃/km减小到5～6℃/km.峰期之后的榴辉岩经历了早期近等温减压的变质过程,以硬柱石和少量滑石的脱水反应生成蓝闪石和绿帘石(约22～ 23 kbar)为主要特征.其后的晚期退变质阶段以硬柱石消失后局部成分域内由富余流体的消耗形成冻蓝闪石(约16kbar)以及蓝闪石和绿辉石边部发育后成合晶为特征(11 ～12kbar),石榴石边部的韭闪石冠状体和金红石边部生成的榍石退变边也大致发生在该阶段.榴辉岩近等温减压的变质过程可能代表了早期的构造快速抬升过程.松多榴辉岩带可能代表了青藏高原拉萨地块内一条新的大洋型高压-超高压变质带,大约266Ma的榴辉岩相变质时代说明在拉萨地块内部可能存在过一个二叠纪的古特提斯洋盆.; The general mineral assemblage of glaucophane eclogite from Sumdo, Lhasa block of Tibetan Plateau is garnet + omphacite + glaucophane + epidote/clinozoisite, with minor rutile, phengite, hornblende and quaretz. Garnet porphyroblasts show compositional zonation with X-py increase and X-gr decease from the core to the rim. Part of garnet has an X-gr rich outer rim due to retrogression. We calculated the P-T pseudosection in the system of NCKMnFMASHTO, and estimated a peak metamorphic condition of 30 +/- 0.6kbar and 610 +/- 6 degrees C based on the isopleths of the maximum X-py of garnet and maximum Si content of phengite. The moderate slope of the P-T path recorded by the composition of garnet from the core to the mantle indicate that the rock experienced heating with less pressure increasing in the early stage of slow subduction. The geothermal gradient is about 7 similar to 8 degrees C/km. However, the composition of garnet from the mantle to the rim, combined with the Si content of phengite give out a slow heating but fast increasing pressure P-T path, which means it went into a fast subduction stage, and the geothermal gradient decreased to 5 similar to 6 degrees C/km. After peak metamorphism, the eclogite went into an early isothermal decompressional process, characterized by lawsonite + minor talc dehydrated to produce glaucophane and epidote (at about 22 similar to 23kbar). In the late retrogression period, lawsonite completely disappear and barrosite formed due to the enrichment in fluids in some area (about 16kbar). Symplectite generally occur at the rim of glaucophane and omphacite (about 11 similar to 12kbar), and pargasite corona in the rim of garnet, titanite overgrowing rutile also formed at such stage. The isothermal decompression of eclogite probably represent a fast tectonic exhumation. Above all, Sumdo eclogite maybe represent a new oceanic HP-UHP metamorphic belt in Lhasa block of Tibetan Plateau, and the metamorphic age of the eclogite which is about 266Ma suggest that there might be a palaeo-ocean in Permian in the central part of Lhasa block.; http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000337205700022&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701 ; SCI(E); 中文核心期刊要目总览(PKU); 中国科技核心期刊(ISTIC); 中国科学引文数据库(CSCD); 4; yangxljlu@126.com; lfzhang@pku.edu.cn; 5; 1505-1519; 30
语种	中文
内容类型	期刊论文
源URL	[http://ir.pku.edu.cn/handle/20.500.11897/212972]
专题	地球与空间科学学院
推荐引用方式 GB/T 7714	杨现力,张立飞,赵志丹,等. 青藏高原拉萨地块松多蓝闪石榴辉岩的变质演化:相平衡及变质作用P-T轨迹, Metamorphic evolution of glaucophane eclogites from Sumdo, Lhasa block of Tibetan Plateau: Phase equilibria and metamorphic P-T path[J]. 岩石学报,2014.
APA	杨现力,张立飞,赵志丹,&朱弟成.(2014).青藏高原拉萨地块松多蓝闪石榴辉岩的变质演化:相平衡及变质作用P-T轨迹.岩石学报.
MLA	杨现力,et al."青藏高原拉萨地块松多蓝闪石榴辉岩的变质演化:相平衡及变质作用P-T轨迹".岩石学报 (2014).