On the basis of analyses on depositional patterns, fault activity, syn-eruption normal faults,dike arrangement, border fault kinematics and stress calculation from slip-data in the Hefei basin, detailed studies on evolution of extensional direction were conducted. The results show that the basin experienced an evolution from WNW -ESE extension of the earliest -middle Early Cretaceous, NW-SE extension of the latest Early Cretaceous to nearly N-S extension of Late Cretaceous-Paleo gene. Previous studies demonstrate that the Izanagi Plate moved WNW-wards during the earliest-middle Early Cretaceous and NNW-wards during latest Early Cretaceous while the Pacific Plate moved generally northwards during the Late Cretaceous to Paleogene. The synchronous clockwise rotation of the both extensional direction and oceanic plate motion suggests that destruction of the eastern North China Craton took place under the back-are extensional setting. The coupling variation between the extensional direction in the back-are region of the overriding continental plate and oceanic plate motion may be a result of change in trench retreating direction that leads to the change of extensional direction in the back-arc region.%本文通过白垩纪一古近纪期间合肥盆地沉积格局、断层活动性、同火山活动正断层、岩脉展布方位、盆缘断层运动学与断层擦痕应力场反演等多方面的综合分析,对伸展方向的演变进行了详细的研究.研究结果表明,早白垩世早一中期为NWW-SEE向拉伸.早白垩世晚期为NW-SE向拉伸,而晚白垩世至古近纪期间为近南北向拉伸.通过对比太平洋区大洋板块运动方向发现,早白垩世早一中期伊佐奈歧板块向NWW向运动,而早白垩世晚期转变为向NNW向运动,晚白垩世至古近纪期间出现的太平洋板块总体上是向正北运动,同样显示为顺时针的转变.两者演变规律的耦合,表明华北克拉通东部的破坏是发生在弧后拉张的动力学背景下.这一弧后大陆边缘的拉伸方向随着大洋板块运动方向的改变而变化,可能是海沟后退方向的改变具体驱动了弧后大陆边缘拉伸方向的改变.
展开▼
