天水盆地新近纪伸展构造——来自沉积与构造变形方面的证据

The Neogene extension of the Tianshui basin:Evidence from sedimentary and structural records

天水盆地位于青藏高原东北缘高海拔挤压隆升区与鄂尔多斯低海拔伸展区的过渡部位，新构造活动强烈。然而，新构造活动对天水盆地的影响尚不清楚。通过对盆地的沉积环境、构造沉降、构造变形等方面的研究，结果显示：①盆地由风成堆积、洪积扇、河湖相与湖泊相沉积组成，代表沉积中心的河湖相与湖泊相沿控盆断裂(西秦岭北缘断裂、西和断裂与礼县-罗家堡断裂)分布；②盆地经历了16~14Ma、9.2~7.4Ma和3.6~2.6Ma三次加速沉降期；③控盆断裂在同沉积期为正断层。沉积中心沿断裂分布、快速沉降事件及生长正断层表明，天水盆地至少在中新世晚期受控于走滑伸展构造，记录了青藏高原向北东方向的构造挤出作用。

Tianshui basin is located at the transition from the compressive high in northeastern Tibet to the extensional zone aroundOrdos, where Neo- tectonic deformation is strongly developed. However, the tectonics of Tianshui basin remains elusive. In thisstudy, the authors performed detailed analysis of sedimentation, tectonic subsidence and structural deformation, with some conclu?sions reached: ①Tianshui basin is filled with aeolian loess, pluvial fan, fluvial and lacustrine deposits, and lacustrine deposits which rep?resent depocenter occur along the major faults, like West Qinling northern fault, Xihe fault and Lixian-Luojiabao fault; ②the basinexperienced a three-phase subsidence, which happened at 16~14Ma, 9.2~7.4Ma and 3.6~2.6Ma respectively; ③the controlling faultsare normal faults formed during the synsedimentary phase. The lacustrine occurrence, increasing subsidence and growth of normalfaults indicate that Tianshui basin was controlled by extensional tectonics in at least Late Miocene and recorded the extrusion processof northeastern Tibet in the Late Cenozoic.