Interactions between large-scale strike-slip intersecting faults: Implication from the Tan–Lu and Xiangfan–Guangji fault zones in eastern China

The large-scale strike-slip Tan–Lu Fault Zone (TLFZ) and Xiangfan–Guangji Fault Zone (XGFZ) both terminate in the southeastern corner of the Dabie Orogen at an angle of almost 90°, and this corner therefore provides a very good natural laboratory for understanding the mechanism by which large-scale strike-slip faults terminate. We present new geochronological and structural data for the southeastern tip of the XGFZ and the southwestern tip of the TLFZ. The NW–SE-striking XGFZ records ductile shearing in its northwestern segment, characterized by discrete dextral shear zones that formed at temperatures of 350–400°C, as indicated by quartz c-axes fabrics and microstructures. In the southeastern segment of the XGFZ, WNW–ESE-trending thrusts are displayed. The NE–SW-striking TLFZ is characterized by discrete NE–SW-trending sinistral ductile shear zones in the Qianshan–Tongcheng segment, brittle left-lateral strike-slip faults in the Taihu–Qianshan segment, and thrusts to the south of Taihu. The trends of these thrusts change progressively southward from NE–SW to ENE–WSW and E–W. New zircon U–Pb dating results and previous cooling biotite 40Ar/39Ar ages constrain the timing of shearing in the XGFZ to 112–102 Ma (late Early Cretaceous), which is the same as the age of faulting in the TLFZ (110–102 Ma). The large-scale strike-slip TLFZ and XGFZ both terminate at their tips as thrusts. We suggest that interactions between the two faults led to the kinematic changing from strike-slip to thrusting, with this playing an important role in controlling the termination of these two large-scale intersecting strike-slip faults. The dextral shearing of the NW–SE-trending XGFZ, the sinistral shearing of the NE–SW-trending TLFZ, and the nearly E–W-trending thrust faults all indicate continental-scale N–S compression in eastern China during the late Early Cretaceous. This compression resulted from rapid NNW-ward oblique subduction of the Paleo-Pacific Plate.

大型走滑型郯庐断裂带（Tan–Lu Fault Zone, TLFZ）与襄樊-广济断裂带（Xiangfan–Guangji Fault Zone, XGFZ）均以近乎90°的夹角终止于大别造山带（Dabie Orogen）东南端，该区域因此成为探究大型走滑断裂终止机制的优质天然实验室。本文获取了襄樊-广济断裂带东南端与郯庐断裂带西南端的新年代学与构造地质学数据。走向北西-南东的襄樊-广济断裂带西北段记录了韧性剪切作用，其标志性特征为发育于350~400℃温度条件下的离散右旋剪切带，该结论可通过石英c轴组构与显微构造得以佐证。襄樊-广济断裂带东南段则呈现出北西西-南东东走向的逆冲断层。走向北东-南西的郯庐断裂带在潜山-桐城段表现为离散的北东-南西走向左旋韧性剪切带，在太湖-潜山段表现为脆性左旋走滑断层，太湖以南区域则发育逆冲断层。这些逆冲断层的走向自北向南逐渐由北东-南西向转变为北东东-南西西向乃至东西向。新获得的锆石U-Pb定年结果与已发表的黑云母40Ar/39Ar年龄数据，将襄樊-广济断裂带的剪切作用时代限定为112~102 Ma（早白垩世晚期），这一时代与郯庐断裂带的断裂活动时代（110~102 Ma）相一致。大型走滑型郯庐断裂带与襄樊-广济断裂带均以逆冲断层的形式终结于各自的端点位置。我们认为，两条断裂的相互作用引发了运动学方式从走滑向逆冲的转变，该过程对这两条大型相交走滑断裂的终止起到了关键控制作用。北西-南东走向的襄樊-广济断裂带右旋剪切、北东-南西走向的郯庐断裂带左旋剪切，以及近东西走向的逆冲断层，均指示早白垩世晚期中国东部发生了陆域尺度的南北向挤压作用。该挤压作用源于古太平洋板块快速向北北西方向的斜向俯冲。