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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。
At the same time that the North China Plate and the Yangtze Plate collided along the Shangalite belt in the late Caledonian region, at the northern margin of the Yangtze Plate, the present-day South Qinling structural belt began to develop a stretching belt extending in the east-west direction, including extensional slip of the Wudang block The Paleozoic large-scale basic magmatic activity in the Wudang block and the Ziyang-Langao Paleozoic alkaline magmatic activity belt in the west, the Zhen’an-Xunyang shallow collapse basin and the Fuping uplift, etc. The extensional tectonic belt occurred between two collision events of Qinling Mountains in time and located between the two suture zones in the north and south. Therefore, it is a very important stage in the evolution of the Qinling orogenic belt. The beginning of extensional structure is likely to be related to the gravity collapse of the orogenic belt after the collision between the southern and northern Qinling Mountains. With the formation of the Late Paleozoic Mian Lueyang south of the extensional zone, the South Qinling Mountains gradually evolved into a passive continental margin to the south of the North China Plate, So that the extension of the South Qinling crust extends to early - Middle Triassic. Geochronology and lithogeochemical studies of the underlying mantle of the upweep in the Wudang block extensional slip system show that the metamorphic greenstone and metamorphic volcanic rocks in these basic rocks and the Miaoluo ophiolite assemblage Has a great similarity, so Mian Loyang is likely to be the result of this stretching action of South Qinling.