龙门山南西段一个不成峰的飞来峰构造

DAPTANYA NAPPE OUTLIER TN THE SOUTHWEST LONGMENSHAN MOUNTAINS

大偏崖飞来峰是一个产于河谷中的飞来峰,其中产Pseudo fusulina kraffli。属海相早二叠世早期(隆林期)的生物,与上扬子地台梁山期的海陆交互相共处在一地。据此化石和参考龙门山相近地区飞来峰的(竹蜓)化石及其他化石组合,推断飞来峰是来自川西-藏东地区。根据大偏崖飞来峰的产出形态、构造地质特征与地貌的关系,确定龙门山前山带的上古生界是一个不生根的大飞来峰,其生物化石组合与近邻的龙门山后山及上扬子地台不相同,与川西-藏东-带确可对比。据此推断上扬子地台在印支晚期发生过逆掩推覆构造运动,其后在燕山—喜马拉雅期,上扬子地台驮负着龙门山向北东方向作左旋运动,同时向北西俯冲形成龙门山。

Dapianya nappe outlier is located in a river valley and contains Pseudofusulina kraff ti in the Early Permian (Longlin age). From the Pseudo fusulina Krffii and the correlation with the Fusulinids in the neighbourhood in the Longmenshan Mountains it is deduced that it was napped form west Sichuan-east Tibet region. From the occurrence, tectonic regime and relationship between structures and landfrom of the Dapianya nappe oullier it is concluded that the Upper Palaeozoic Erathem in the front range of the Longmenshan Mountains is a great thrust outlier, the fossil assemblage in which differs from that in the rear range of the Longmenshan Mountains and that in the Upper Yangtze paraplatform whereas may be correlated with that in west Sichuan-east Tibet region. Accordingly, it is inferred that a nappe tectonic movement took place in the Upper Yangtze paraplatform in the Late Indo-Chinese epoch, subsequently, in the Yanshan-Himalayan period, the Upper Yangtze paraplatform moved left-laterally (notheastwards), simultaneously, subducted northwestwards forming the Longmenshan Mountains.