从前陆褶皱冲断带看大地构造相分析及其意义

 以浙西北为例,基于上二叠统长兴组(P₂c)和大隆组(P₂d)以及下三叠统政棠组(T₁z)深水浊积岩的发现,初步认为该区古生代至早三叠世具被动大陆边缘沉积楔特征。综合大地构造分析进一步表明研究区构造样式总体上以向北西逆冲的冲褶席(duplex)为特征,构造变形强度和密度自南东向北西呈递减趋势。自南东向北西具明显的分带性。该区大地构造相主要为前陆褶皱冲断带相,而上三叠统乌灶组(T₃w)为前陆磨拉石盆地相,二者可能是该区始于早中生代(T₁—T₃)造山作用的响应。大地构造相分析不仅较为圆满地解释了研究区的众多地质现象,为造山带模式提供新的制约,而且能为研究区提出新的战略目标。

THE SIGNIFICANCE OF THE TECTONIC FACIES ANALYSIS BASED ON THE STUDY OF THE FOREL AND FOLD-THRUST BELT

The NW Zhejiang was previously considered as "Caledonides" (Huang, 1980). Based on the discovery of the deep-water turbidites in the Upper Permian Dalong Fm. (P₂d), and Changxing Fro. (P₂c), and the Lower Triassic Zhengtang Fm. (T₁z), the authors think that the NW Zhejiang is of SE-dipping passive continental margin from the Paleozoic to the Early Triassic. Together with the foreland molasse basin during the Late Triassic (T₃w), the tectonics of the study area is characterized by a significant transition at some time between Early and Late Triassic period, when the study area experienced NW-ward deformation of folding and thursting. From SE to NW, the deformational style varies from multi-duplex, antiformal stack to hinterland-dipping duplex, and then to Jura Mountain-type fold zone with fold-style varying gradually from large-scale tight fold to mid-scale chevron fold, then to cylindrical fold. The zonation is shown as follows: 1) Northwest Zone; 2) Middle Zone; 3) Southeast Zone; 4) Chencai Zone. All the structural and sedimentary characteristics support the work hypothesis of Li jiliang (1989). By using the latest marine stratum involved in the deformation of the foreland fold and thrust belt and the oldest molasse basin as two significant constraints for the time of orogeny, the tectonic facies analysis provides a powerful tool for investigating tectonic evolution of orogenic belts.