中天山南缘桑树园子剪切带早志留世韧性变形事件及其地质意义  

An Early Silurian ductile deformation event in the Sangshuyuanzi shear zone,the southern margin of the Central Tianshan belt,and its geological significance

作　　者：王盟[1] 张进江[1] 戚国伟[1] 郑勇[1] 刘凯[1] 

机构地区：[1]造山带与地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京100871

出　　处：《岩石学报》2014年第10期3051-3061,共11页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41121062);科技部重点基础研究项目(2014CB448000);中国地质局地质调查项目(12120113096500;12120113094000;1212011120135)联合资助

摘　　要：桑树园子剪切带位于中天山南缘,经历了多期韧性变形事件。对其变形样式和变形历史进行深入研究有利于加深对天山造山带构造演化的认识。本文对剪切带北部发生强烈韧性变形的岩石进行变形样式及相关年代学研究,识别出一期早志留世右旋剪切运动。该期走滑剪切事件造成部分前寒武纪斜长角闪岩发生深熔作用形成浅色脉体,使花岗闪长岩发生强烈的糜棱岩化石,并伴随同构造花岗质脉体的侵入。斜长角闪岩中浅色脉体中的锆石具弱的振荡环带或无环带,Th/U比值较低,具深熔作用中新生锆石的特点,其^206Pb/^238U加权平均年龄为430.1Ma。糜棱状花岗闪长岩样品锆石核部LAICPMS U-Pb年龄为496.3Ma,是中天山北缘古天山洋向南俯冲的记录。其锆石的变质增生边给出430.5Ma的年龄,记录了花岗闪长岩遭受后期糜棱岩化改造的时间。侵入花岗闪长岩中的同构造花岗质脉体也给出较为一致的432.9Ma的锆石结晶年龄。这一年龄范围与中天山北缘古天山洋盆闭合的时间一致,因此桑树园子剪切带北部在～430Ma的右旋走滑事件可能是吐哈地块与中天山碰撞事件的陆内响应。The Sangshuyuanzi ductile shear zone on the southern margin of the Central Tianshan belt experienced multiple deformation events. The formation of the shear zone might be related to the closure of the Paleo-Tianshan Ocean or the South Tianshan Ocean and /or subsequent intra-continental strike-slip movement. A detailed study on the deformation style and deformation history of the Sangshuyuanzi shear zone is vital to understand the tectonic evolution history of the Tianshan orogen. An Early Silurian right-lateral strike-slip event is identified in the northern part of the shear zone based on detailed field observation and tectonochronological study.Rocks involved in the shear zone include Precambrian basement rocks of the Central Tianshan belt,Early Paleozoic granitic intrusions and syn-shearing granitic dykes. The amphibolite is part of the basement rocks of the Central Tianshan belt,and consists of some leucosomes that occur along the foliation of the amphibolite. The leucosomes veins are isolated,rootless and occur widely in the amphibolite with different sizes ranging from several meters long and 10 ～ 20 cm wide to several centimeters long and 2 ～ 3mm wide. All the above features show the felsic veins formed during anatexis caused by regional shearing. Besides,there are some felsic veins occurred as structural lens,which might migrate from deep crust and intrude the amphibolite during shearing. The shapes of the structural lens show a sense of dextral shearing. The mylonitic granodiorite are characterized by well-developed foliation and lineation.They have a foliation of about 190°∠70°（ dip∠dip angle）. Felsic minerals like feldspar and quartz were elongated to form lineation.The lineation dips to the east（ 100°） with an angle of about 15°. Dynamic recrystallization of feldspar and quartz are common in the mylonitic granodiorite. The syn-shearing granitic dykes that intrude the mylonites vary in size from several tens of meters long and 20 ～30cm wide to several tens of centimeters long and

关 键 词：变形年代学 锆石 桑树园子剪切带 中天山 

分 类 号：P542[天文地球—构造地质学] P597.3[天文地球—地质学]