摘要
在南苏鲁地区,大陆造山带根部主要由5种不同化学成分的岩石类型组成,分别以石榴石橄榄岩、榴辉岩、片麻岩、石英岩和大理岩为代表。它们的原岩是古老的花岗质侵入岩、表壳岩和基性—超基性侵入岩,并一起经历了超高压变质作用。正变质的花岗质片麻岩是超高压变质带的主要组成部分,构成了花岗质和奥长花岗质岩石组合,不同于典型的TTG岩系。变质火山岩具有双峰式火山岩地球化学特征,很可能形成于大陆裂谷环境。除幔源石榴石橄榄岩以外,其他各种岩石都具有可变的、但均低于正常变质岩的氧同位素值,表明其原岩曾在地壳浅部发生了不同程度的水-岩交换作用,并在整个超高压变质过程中保持其米级尺度的不均匀性。新的温、压计算结果表明,石榴石橄榄岩的形成条件可能是1100～1200℃和6.5～8.0GPa,地热梯度等于或小于5℃/km,即以前认为变质作用不可能达到的“禁区”。
The root of the continental orogenic belt in the southern Sulu area consists of five rock types with different chemical compositions.Their representative rocks are garnet peridotite,eclogite,gneiss,quartzite and marble.Their protoliths are old granitic intrusive,supracrustal and mafic-ultramafic intrusive rocks,which have all been subjected to ultrahigh-pressure(UHP )metamorphism.The granitic orthogneiss-es constitute the main part of the UHP belt in the southern Sulu area;they form a granitic and trond-hjemitic rock association,which is different from the typical TTG magmatic series.The metavolcanic rocks in the supracrustal rocks show the geochemical characteristics of bimodal volcanic rocks,indicating a tec-tonic continental rift environment.Except the mantle-derived garnet peridotites,all of the rocks have vari-able,lowerδ 18 O values than those of normal metamorphic rocks.This indicates that the protoliths of UHP rocks had undergone various degrees of fluid-rock interaction in the shallow level of the crust,and their meter-scale heterogeneity was preserved during the formation and exhumation of the UHP metamorphic rocks.Recent temperature-pressure(pT)calculations suggest that the pT conditions of garnet peridotites were probably1100～1200℃and6.5～8.0GPa with a geothermal gradient of than5℃/km or less,i.e.in the forbidden-zone of metamorphism in the Earth.
出处
《地质通报》
CAS
CSCD
北大核心
2002年第10期609-616,共8页
Geological Bulletin of China
基金
国家"九五"重大科学工程--中国大陆科学钻探工程项目
中国地质调查局1:25万连云港幅区域地质调查项目(0199209051)
国家自然科学基金(49772142)
国土资源部大陆动力学开放研究实验室的研究成果。
关键词
大陆造山带根部
超高压变质作用
物质组成
pT条件
南苏鲁地区
the root of the continental orogenic belt
ultrahigh-pressure metamorphism
material compo-sition
pT conditions
southern Sulu area
