南秦岭勉略古缝合带非史密斯地层和古海洋新知

NEW RECOGNITION OF NON SMITH STRATIGRAPHY AND PALEOCEANOGRAPHY OF MIANXIAN LUEYANG PALEOSUTURE IN SOUTHERN QINLING, CHINA

南秦岭勉略古缝合带是一个构造混杂岩型非史密斯地层区，由不同时代的原地地层系统和异地地层系统的构造岩片构成。泥盆纪—石炭纪硅质岩的常量元素、稀土元素分析结果指示了勉略小洋盆的存在。区域背景分析表明晚震旦世到早寒武世，南秦岭为扬子板块北部边缘的一部分，中、晚寒武世以后开始分裂形成南秦岭裂陷槽。该海槽于中、晚志留世萎缩但未关闭，泥盆纪又进一步开裂逐渐形成大陆边缘裂谷盆地，晚泥盆世后期到早石炭世早期形成一开放小洋盆。早石炭世后期出现洋壳俯冲，从而转化为活动大陆边缘盆地。该洋盆可能持续到二叠纪，并于印支期最终关闭、碰撞和造山。

Mianxian Lueyang paleosuture in southern Qinling is built up of non Smith strata of structural melange type. These Non Smith strata are dissected into autochthonous and allochthonous stratigraphic systems guided by the theory of non Smith stratigraphy. On the basis of the analysis of major elements and rare earth elements of Devonian Early Carboniferous silicalite, the authors suggest that Mianxian Lueyang zone existed a continental margin rift in Devonian, formed a little ocean from the late Late Devonian to early Early Carboniferous, occurred subducting of oceanic crust and was transformed into an active continental margin in late Late Carboniferous. Mianxian Lueyang little ocean was an inheritable basin. From the Late Sinian to the Early Cambrian, southern Qinling was a part of northern edge of the Yangtze Plate. The rift trough of southern Qinling formed from the Middle Cambrian to the Early Silurian. The rift trough shrank but was not closed in the Middle and Late Silurian. This relict rift trough was further opened in Devonian and gradually developed a little ocean. It is possible that this ocean existed in Permian, was closed in Triassic and affected by the collision of the Yangtze and North China plates.