摘要
造山带浅变质碎屑杂岩变质变形期次的建立有助于厘定增生杂岩的形成机制,约束洋壳俯冲带增生折返的构造过程。采用中小尺度构造解析的方法对羌塘中部玛依岗日地区的印支期增生杂岩进行剖析,发现其构造样式主要为三叠纪洋壳俯冲期E—W向单剪变形和汇聚期N—S向挤压变形的共轴叠加,并受到了新生代浅层次近南北向纵弯褶皱的轻微改造,岩石普遍发育三期构造面理,前两期伴随有浅变质作用。碎屑岩第一期剪切型流劈理S1在区域上表现为透入性的同构造压溶石英脉条带,利用流体包裹体显微测温实验,发现石英包含大量原生不混溶沸腾包裹体群,分为富CO_2三相包裹体和NaCl-H_2O气液两相包裹体,300~400℃的完全均一温度代表第一期变形的温度,非沸腾气液两相包裹体盐度-P/T等容线相图显示均值集中在0.3GPa左右,指示第一期变形的深度为~11km。增生杂岩的进变质作用不具有同一变质相系,P-T-t轨迹表现为折线式,俯冲通道浅部为中P/T变质相系,中深部为高P/T变质相系。高压变质岩折返的退变质作用具有冷却型P-T-t轨迹,晚三叠世(211~221 Ma)与浅变质杂岩发生构造拼贴,古特提斯洋同时发生关闭,羌北地块与羌南地块的短暂汇聚引起了第二期强挤压变形和同碰撞型岩浆侵入事件。
The establishment of the metamorphism and deformation stages of epimetamorphic clastic rock complex in orogenic belt will contribute to determining the forming mechanism of accretionary complex and constrain the accretion-exhumation process of oceanic crust subcution zone.Medium-or small-scale structure analyses on the Indosiniana ccretionary complex in the Mayigangri area of central Qiangtang suggest that the structural style is the coaxial superimposition of E W-trending simple shear deformation of Triassic subduction of oceanic crust and N Strending compressional deformation during convergent stage,which was reformed slightly by the Cenozoic nearly N S-trending buckle folding on shallow tectonic level.The complex developed three distinct foliations which correspond to the above three stages,with the two earlier ones usually accompanied with epimetamorphism.The C-type foliation S1 of the first stage（M1D1）in the clastic rock is showed as penetrative syntectonic pressolution quartz veins on the regional scale.The microscopic temperature-measuring experiment for fluid inclusions found that a large amount of primary immiscible boiling inclusion groups occurred in the quartz veins and can be grouped into CO2-rich three-phase inclusions and NaCl-H2 O solution two-phase（gas-liquid）inclusions.The both inclusions show a coincident complete homogenization temperature of 300 - 400℃ which represents the metamorphic temperature of the M1D1.The salinity-P/Tisochore diagram of non-boiling gas-liquid two-phase inclusions shows a mean trapping pressure of 0.28 GPa,indicating the depth of the M1D1is-11.3km.The prograde metamorphism of accretionary complex shows varied metamorphic facies series,with the shallow part of subduction channel characterized by mediumP/T metamorphic facies series and the middle deep part feature high P/T metamorphic facies series.The exhumation retrometamorphic P-T-t paths of high-pressure metamorphic rocks exhibit as cooling type.Blueschists and eclogites exhumed into the epimetamorphic complex at late Triassic（211-221Ma）,which was concurrent with the closure time of the paleo-Tethys ocean.After that,the transient convergence of North Qiangtang terrane and south Qiangtang accretionary terrane resulted in the second stage intense compressional deformation（M2D2）and syn-collision type intermediate-acid magmatism along the Longmu Co Shuanghu suture.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2017年第2期384-399,共16页
Acta Geologica Sinica
基金
中国地质调查局项目(编号1212011221081
12121010818014
1212011221115)
中国地质大学(北京)优秀教师基金项目(编号2-9-2014-004)
国家自然科学基金青年基金项目(编号41402177)联合资助成果
关键词
羌塘
石英脉
增生杂岩
变质变形
流体包裹体
Qiantang
quartz vein
accretionary complex
deoformation and metamorphism
fluid inclusion
作者简介
崔玉良，男，1989年生。硕士，构造地质学，主要从事区域地质调查工作。Email：814399394@qq．com.
通讯作者：梁晓，男，1984年生。博士，讲师，构造地质学专业，从事构造地质学的研究与教学。Email：liangxcugb@163．com.
