Structural characteristics and genetic mechanism of transfer zones in an extensional rift zone: An example from the Xihu Sag, East China Sea Basin

Abstract

The Xihu rift zone within the East China Sea Shelf Basin (ECSSB) is governed by NE-striking segmented extensional faults, which were formed by Cenozoic orthogonal NW-SE extension. However, the segmentation of the NE-striking faults has up to now received only limited attention. Here, we employ seismic data, information about pre-existing faults, the Cenozoic fault system, and fault activity rate to analyze the structural characteristics and genetic mechanism of the transfer zones in the Xihu sag. Our results demonstrate that: (1) The Cenozoic structures and evolution of the Xihu sag are fundamentally controlled by the NE-striking extensional faults, while showing influence from the pre-existing NW-striking basement structures. (2) The transfer zones are preliminarily recognized on the fault system map along the bottom of the Pinghu Formation (T40 surface, ∼43 Ma), which is segmented by the NE-striking faults. The cross faults are identified in the transfer zones, which are commonly truncated by the T30 (∼33.9 Ma) surface and above the T100 (∼66 Ma) surface. These faults are generally composed of strike-slip structures. In addition, the transfer zones are primarily developed above the pre-existing NW-striking basement faults. (3) A hybrid genetic model is proposed to interpret the formation of the NW-striking strike-slip transfer zones in the Xihu sag, including the influence of the pre-existing NW-striking basement faults, and the different extensions along the rifts. Finally, six genetic-mechanism-structural models are established for general cases, based on whether the pre-existing faults are developed and the different extensions existed or not. This study may have significant implication for future study on the transfer zones in this area.