摘要
在十余年野外考察的基础上，通过火山—沉积组合、高压变质带及俯冲杂岩带产出特征、花岗岩浆活动、同位素年龄值等综合分析研究，结合近年区调成果，提出北祁连中段地区早古生代的构造演化模式，认为该区是在古陆壳基底上由震旦纪打开经海底扩张生成的留有微陆块的微洋盆；寒武—奥陶纪，以黑河—八宝河为轴发生海底扩张，同时分别向南北两侧发生不对称双向俯冲，北侧以前进式的弧后扩张作用产生新生洋壳向北推进，相应早期的俯冲杂岩带也随之由南向北先后反弹回跳到地表，转化为汇聚过渡壳；南侧由早期被动陆缘的拉张过渡壳转为向南俯冲的阿拉斯加型活动大陆边缘，其后缘形成弧后盆地；志留纪俯冲作用停止，洋盆消失而转为岛链带及浊流海槽并存的构造格局；泥盆纪，北侧阿拉善地块与南侧中祁连地块最终汇聚而碰撞，形成以新陆壳为特征的造山带。
A tectonic evolution model of Early Paleozoic in the middle part of North Qilian Area is put forward based on the field investigation of more than ten years, and a series of comprehensive researches, including volcanic sedimentary association, the characteristics of the complex in high pressure metamorphism zone, subduction complex rock zone, granitic magmatism and isotopic age, etc. In Sinian, paleocontinental crust broke up, and micro ocean basin was formed with remnant fragmants of continental crust. In Cambrian Ordovician, asymmetric bisubduction took place southward and northward respectively with Heihe Babaohe Zone being a spreading ridge. During the northward subduction, progressive back arc extension gave rise to a new ocean crust. This type of events took place northward repeatedly, and their correspondant products, subduction complexes, were elevated back to the surface and transformed into convergent transitional crusts. During the southward subduction, the earlier extentional transition crusts were transformed to Alaska type active continental margins which subducted southward, and subsequently arc back extensional basin was formed . In Silurian, with subduction ended and the oceanic basin disappearing, a tectonic framework with the coexistence of island chains and turbidity trough was formed. In Devonian, an orogenic belt with new continental crust was formed as the result of the convergence and collision between the Alaskan massif and the Middle Qilian massif.
出处
《地球科学进展》
CAS
CSCD
1997年第4期315-323,共9页
Advances in Earth Science
基金
国家计委国地司科技找矿攻关项目"北祁连山西段镜铁山式铁铜金矿床成矿预测和定位研究"
关键词
双向俯冲
造山带
造山模式
构造演化
Northern Qilian Area, Extentional transition crust, Bisubduction, Subduction complex rock, Convergent transition crust, Orogenic belt.
