秦岭造山带泥盆纪的沉积体系与古地理格局演化

秦岭造山带以商丹断裂带为界分为南秦岭和北秦岭。南秦岭在早古生代是扬子板块的被动大陆边缘，在志留纪末曾因垂向隆升变为古陆。因其南缘长期处于地幔上涌的构造薄弱带，所以到泥盆纪首先从这里开始扩 张，并逐渐演化成有限洋盆，与扬子板块分离，成为独立的板块，内部也因拉张形成裂陷盆地与块断隆起相间的环境格局。其自南而北依次为安康古陆→旬阳-镇安盆地→小磨岭古陆→刘岭盆地。在盆地内堆积了从陆相到海相，从浅水到深水的各种沉积体系，组成向上变细和变深的充填序列。而在北侧，该板块仍在向华北板块下面俯冲。北秦岭南缘的弧前沉积体系记录了这种俯冲作用的演化。这种与早古生代十分不同的古地理格局标志秦岭造山带已进入了新的演化阶段。

DEVONIAN DEPOSITIONAL SYSTEM AND PALAEOGEOGRAPHIC EVOLUTION OF QINLING OROGENIC BELT

During the Early Palaeozoic, the South Qinling belonged to the passive continental margin of the Yangtze Plate. It changed to ancient land due to vertical movement in the end of the Silurian. Because its southern margin located in the structure weak zone caused by mantle bugle for a long time , during the Devonian extension first began to form here and a restricted oceanic basin was formed gradually while South Qinling separated from the Yangtze Plate and changed into an independent plate. The environmen-tal framework that fault-subsided basins alternated with block-faulted uplifts was formed by extension. They are Ankang Uplifl-Xunyang-Zhenan Basin-Xiaomoling Uplift-Liuling Basin from south to north, respectively. These basins were generally filled with upward fining and deepening sedimentary sequence that comprises nonmarine to marine, shallow marine to deep marine depositional systems. At the same time, this plate still subducted beneath the North China Plate. The forearc deposition system at the southern margin of North Qinling indirectly recorded this evolution of subduction. The much different palaeogeographic framework from the Early Palaeozoic indicates that Qinling orogenic belt has entered a new evolutionary stage.