扬子地块西缘新生代造山作用与前陆盆地构造演化

THE CENOZOIC OROGENESIS AND TECTONIC EVOLUTION OF THE FORELAND BASIN IN THE WESTERN MARGIN OF YANGTZE MASSIF

地貌学、第四纪地质学。同位素及构造。沉积的综合分析表明，扬子地块西缘造山带的主体隆升时期发生于新生代特别是第四纪以来，其隆升幅度可达2000～4000m，中新世以来至少有5～6km地层被剥蚀，上升速率约达0．6mm／a；与其伴生的前陆盆地新生代沉积可分为老第三纪继承性萎缩拗陷盆地阶段和新第三纪─第四纪前陆盆地改造阶段。前者具有山间和山前磨拉石盆地特征，后者具有类磨拉石盆地性质。深部资料的进一步分析表明第四纪时期岩石图具四层结构，中地壳为一区域性韧性流壳层，是处于岩石图加厚后的均衡调整和区域伸展时期，盆山关系的分析也表明，造山带与前陆盆地在形成、演化和改造上具有统一的区域构造背景。

A synthetical study of geomorphology, Quaternary, isotopic geochronology, tectonics and sedimentology shows that the orogenic belt in the western margin of Yangtze massif has been mainly risen since Cenozoic, especially the Quaternary, with a rising height of 2, 000-4, 000 m.Strata with a thickness of 5, 000-6, 000 m has been denuded since Miocene, the rising velocity is about 0. 6 mm/a. The foreland basin of Longmenshan-Jinpingshan orogenic belt in Cenozoic may be divided to two stages, i. e, the succedent sag down-warped basin during Paleogene when intermountain and piedmont molasse basins were formed, and transformed foreland basin from Neogene to Quaternary when molasse basin was formed. The further analysis of deep-seated information indicates that the lithosphere includes four layers during Quaternary, and the middle crust is a regional ducticle fluid layer, so it is time of lithosphere isostatic adjustment and regional extension after its thicking. The study of relationship between the basins and the mountains also shows that the formation, evolution and transformation of the orogenic belt and the foreland basin have the same regional tectonic setting, i. e, the compression stress field resulting from the collision between Qiangtang-Qamdo massif and Yangtze massif during Indosinian- Yanshanian movement.