【摘要】 位于青藏高原东北缘的临夏盆地是一个挤压挠曲型的前陆盆地,褶皱和逆冲断裂带自7.8Ma开始由西向东向盆地内部扩展,形成生长地层和生长不整合,代表高原东北部持续的构造变形过程。这种同沉积的构造变形一直持续到大约1.8Ma左右东山组沉积结束,临夏盆地内部强烈褶皱变形,致使东山组及其以下的新生代地层均被卷入褶皱之中(与其上的最老黄河阶地——井沟砾石层为角度不整合接触),拉脊山断裂继续向北东方向扩展,银川背斜最终形成。随后黄河、大夏河出现,开始了发育河流阶地和堆积风成黄土的新阶段。由平衡地质剖面法得到临夏盆地西缘7.8Ma以来总的地壳缩短量为3.2~3.6km,缩短率为0.41~0.46mm/a。如果取从7.8到1.8Ma之间的大约6.0Ma作为临夏盆地的构造变形时段,其缩短速率则为0.5~0.6mm/a。从临夏盆地形成和演化过程来看,青藏高原东北缘的构造变形以沿北西西向断裂的逆冲和地壳缩短为主要特征,导致挤压挠曲型前陆盆地的逐渐隆升和消亡,最终使新生代前陆盆地的大部分并入青藏高原东北缘,成为青藏高原的最新组成部分。更多还原

【Abstract】 The Linxia Basin, located on the northeastern margin of the Qinghai-Tibet Plateau, is a compressional flexural foreland basin. At the boundary of the basin, the fold and thrust fault zone has expanded towards to the interior of the basin from west to east since 7.78 Ma, while growth strata and growth unconformities formed, reflecting a continuous process of tectonic deformation on the northeast edge of Qinghai-Tibet Plateau. This kind of tectonic deformation accompanying deposition persisted until the complete deposition of the Dongshan Formation at about 1.8 Ma. The strong folding of the strata includes the Dongshan Formation and lower older units in the Linxia Basin. The Dongshan Formation and the upper, oldest terrace of Yellow River, the Jinggou Formation of conglomerate, form an angular unconformity. Therefore, the Lajishan Mountain expanded continuously to the NE until the Yinchuan anticline formed. Then a new stage in the development of the Yellow River and Daxia River appeared, river terraces developed, and aeolian loess was deposited. The total crustal shortening is about 3.2-3.6 km on the western margin of the Linxia Basin since 7.8 Ma; thus, the average shortening rate has been about 0.41-0.46 mm/a calculated from the balanced cross-section. If we select a 6.0 Myr period between 7.8 Ma and 1.8 Ma as the period of tectonic deformation, then the shortening rate is about 0.5-0.6 mm/a. Both the style of development and the evolution of the Linxia Basin suggest that the tectonic deformation on the northeast margin of the Qinghai-Tibet Plateau is characterized by thrusting and crustal shortening with a WNW orientation. Such tectonic deformation led to the following evolution: the foreland basin gradually rose and sedimentation stopped, then most of the Cenozoic foreland basin merged into the northeast margin and became the newest part of the Qinghai-Tibet Plateau.更多还原