摘要
华北板块与扬子板块于加里东晚期沿商丹带发生碰撞的同时,在扬子板块北缘,即现今南秦岭构造带,开始发育一条近东西向延伸的拉伸带,其中包括武当地块伸展滑脱构造、武当地块古生代大规模基性岩浆活动及其西侧紫阳-岚皋古生代碱性岩浆活动带、镇安-旬阳浅层塌陷盆地以及佛坪隆起等。该伸展构造带主体在时间上发生在秦岭两期碰撞事件之间,空间上位于南北两个缝合带之间,因此,是秦岭造山带演化过程中的一个非常重要的阶段。该伸展构造的开始很可能与南、北秦岭碰撞后的造山带重力塌陷有关,随着该伸展带南侧晚古生代勉略洋的形成,南秦岭逐渐演化为华北板块南侧的被动大陆边缘,从而使南秦岭的地壳伸展一直延续到早—中三叠世。武当地块伸展滑脱系统中顺层侵位的基性岩席群的年代学与岩石地球化学的研究表明,这些基性岩与勉略蛇绿岩组合中的变辉绿岩及变基性火山岩具有很大的相似性,因此勉略洋很可能也是南秦岭这次拉伸作用的结果。
Simultaneously with the colliding of the North China plate and Yangtze plate along the Shang-dan suture zone in the late Caledonian,a nearly east-west-trending extensional belt was initiated on the northern margin of the Yangtze plate,i.e.the present South Qinling tectonic belt.The belt is composed of the extensional tectonics of the Wudang block,Paleozoic basic sheet swarms in the Wudang block and Ziyang-Langao Paleozoic alkaline magmatic zone,Zhen'an-Xunyang Devonian shallow rift basin and Fop-ing uplift.This extensional belt formed between two collision events in terms of time and between the north and south sutures of the Qinling orogen in terms of space;so the extension represents a very im-portant evolutional stage.The authors propose that the initiation of the extension is very likely to be relat-ed to the gravitational collapse of the orogenic belt caused by collision of the South Qinling and North Qinling belts.Along with the formation of the Late Pale ozoic Mianlue ocean south of this extensional belt,South Qinling gradually evolved into a passive continent margin on the south side of the North China plate.Therefore the crustal extension of the South Qinling lasted to the Early -Mid Triassic.The geochronology and geochemistry of the basic sheets intruded along the bedding into the extensional detach-ment system of the Wudang block during the extension suggest that they have many similarities to those of metadiabase and metabasic volcanic rocks of the Mianlue ophiolite;so it is very possible that the Mianlue ocean is the result of this extension of the South Qinling.
出处
《地质通报》
CAS
CSCD
北大核心
2002年第8期471-477,共7页
Geological Bulletin of China
基金
国家自然科学基金(49972066
40072076)
博士后基金资助。
