大别山东北缘桐城高压-超高压变质带的构造解析及其对郯庐断裂带的制约

通过对郯庐断裂带南段桐城地区高压-超高压变质带详细的岩石学和构造学研究,将研究区从空间结构上划分为三个构造单元:上部低温-高压单元、中部中温-高压单元和下部超高压单元。根据研究区多期构造变形分析,共识别出了五期有区域构造地质学含义的事件(D_1-D_5):D_1代表高压-超高压变质岩中-晚三叠世同碰撞早期折返过程;D_2表征了高压-超高压变质岩晚三叠世同碰撞晚期折返过程;D_3记录了早白垩世中大别变质核杂岩的形成,也即整个中国东部晚中生代大规模伸展构造在研究区的表现;D_4可能标志着郯庐断裂走滑构造对高压-超高压造山带的叠加;D_5表现为脆性正断作用,控制了晚白垩世-古近纪潜山半地堑盆地的形成。这些结果表明了研究区所经历构造演化的复杂性,其构造几何形态很难用郯庐断裂左行平移南大别超高压变质岩来解释,也不支持桐城地区存在巨大走滑作用的证据。

Structural analysis of the Tongcheng HP-UHP metamorphic belt in the northeastern Dabieshan and its constraint on the Tan-Lu fault zone

According to detailed work of petrology and structural geology, the Tongcheng HP-UHP (high-pressure and ultrahigh-pressure) metamorphic belt in the southern segment of the Tan-Lu fault zone can be divided into three litho-tectonic units: upper low-temperature HP unit, middle medium-temperature HP unit and lower UHP unit upper. Structural analysis indicates that the Tongcheng massif has experienced polyphase deformation (D₁-D₅): D₁ represents the early stage of syn-collision exhumation process of the HP-UHP metamorphic rocks during the Middle-Late Triassic; D₂ represents the late stage of syn-collision exhumation process of the HP-UHP metamorphic rocks during the Late Triassic; D₃ corresponds to development of the Early Cretaceous central Dabieshan metamorphic core complex, which is also effect of the large-scale Late Mesozoic extensional tectonics in easterm China; D₄ might represent the strike-slip faulting of the Tan-Lu fault, superimposed on the HP-UHP metamorphic belt; D₅ is characterized by brittle faulting, and controled depvelopment of the Late Cretaceous-Paleogene Qianshan half-graben basin. These results suggest that the Tongcheng area experienced a complex tectonic history, which is difficult to explain by the model that the Tan-Lu fault dislocated the southern Dabieshan UHP metamorphic rocks to the northeast, and also does not support that there is robust evidence of huge strike-slip movement in the Tongcheng area.