郯庐断裂带的演化及其对西太平洋板块运动的响应

EVOLUTION OF THE TAN-LU FAULT ZONE AND ITS RESPONSES TO PLATE MOVEMENTS IN WEST PACIFIC BASIN

首次从郯庐断裂带走滑糜棱岩中获得了白云母 1 2 7 62± 0 1 9Ma的40 Ar 39Ar年龄 ,其与糜棱岩的全岩40 Ar 39Ar年龄相吻合。这些年代学研究成果以及同走滑期岩浆活动 ,表明郯庐断裂带于早白垩世发生了大规模的左行平移。这一早白垩世构造—岩浆事件是伊泽纳崎板块突然发生高速、斜向俯冲的结果。晚白垩世 早第三纪郯庐断裂带转变成巨型的伸展构造 ,普遍控制发育了断陷盆地。太平洋板块的高角度正向俯冲使中国东部出现软流圈上涌、岩石圈拆沉 ,从而造成了郯庐断裂带与整个中国东部卷入了强烈的伸展活动。晚第三纪初期起动的挤压活动 ,使郯庐断裂带上的断陷盆地同步抬升和闭合 ;断裂带的逆冲活动则断续延至今日 ,成为中国东部最大的近代地震活动带。郯庐断裂带晚第三纪以来的挤压活动是西太平洋弧后扩张的响应 ,而印度板块碰撞的构造挤出起着辅助作用。

A muscovite 40 Ar 39 Ar age of 127.62±0.19 Ma was firstly obtained from strike slip mylonite in the Tan Lu fault, which was consistent with mylonite whole rock 40 Ar 39 Ar ages. The isotopic dating as well as syn strike slip magmatism showed that a large scale strike slip movement of the Tan Lu fault zone occurred in Early Cretaceous. The Early Cretaceous tectono magmatism event resulted from a suddenly high speed and oblique subduction of the Izanagi plate. The Tan Lu fault zone turned into a huge extensional structure during Late Cretaceous to Eogene, leading to a series of development of fault bounded basins. It was suggested that extensional activities of the Tan Lu fault zone might be related to asthenospheric upwelling and lithospheric delamination in East China caused by high angle, orthogonal subduction of the Pacific plate. The compressive activities from the earliest Neogene closed the above mentioned basins. The thrusting of the Tan Lu fault zone lasted to present days with several intervals. Therefore, the fault zone became the largest earthquake belt in East China. The post Eogene compressive activity was a response to backarc spreading in West Pacific area, and the extrusion from the Indian plate collision also played a partial role in the E W compression in East China.