郯庐断裂带肥东段早白垩世中期走滑运动的年代学证据

郯庐断裂带肥东段西韦地区和桃花源地区出露了大规模的北北东向韧性剪切带。桃花源地区韧性剪切带显示出2期构造变形的叠加。野外构造和显微构造分析皆指示为左行走滑韧性剪切带。糜棱岩中石英与长石的变形行为指示其变形温度分别为400~450℃和500℃。通过对这两处走滑剪切带内糜棱岩化花岗岩脉的锆石LA-ICP-MS定年,获得了3个样品的侵位年龄分别为(133.2±1.9)Ma,(131.3±2.0)Ma,(130.3±2.0)Ma。再结合已有的研究成果,认为在128~124Ma(早白垩世中期)郯庐断裂带发生过左行走滑活动。综合分析表明,郯庐断裂带在晚侏罗世和早白垩世中期分别经历了2期左行走滑活动,而期间和之后的早白垩世则处于伸展活动之中。伸展活动持续较长,控制发育了西侧的合肥盆地及断裂带内一系列岩浆活动;而区域挤压背景下出现的走滑活动则相对短暂。这些演化规律显示该断裂带在晚侏罗世—早白垩世呈现为交替式的走滑和伸展活动。新发现的早白垩世中期走滑活动,与太平洋区伊泽纳崎板块板块运动方向的调整相对应,是大洋板块运动方向短暂调整的构造响应。

Geochronological Evidence for the Middle Early Cretaceous Strike-slip Movement from the Feidong Segment of the Tan-Lu Fault Zone

A large-scale NNE-striking ductile shear belts are exposed inXiwei and Taohuayuan areasfrom the Feidongsegment of the Tan-Lu Fault zone. There is two phases of deformation in the ductile shear belt from Taohuayuan areas. Field structures and microstructures indicate sinistral ductile shear sense. Deformation behaviors of quartz and feldspar in mylonites from the shear belts demonstrate that deformation temperatures are 400~450 ℃ and ca. 500 ℃, respectively. Three mylonitized granite dikes in the ductile shear zone were dated by the zircon LA-ICP-MS method, and obtained weighted mean ages of (133.2±1.9) Ma,(131.3±2.0) Ma, and (130.3±2.0) Ma, respectively. Combined with previous research results, a sinistralstrike-slip of 128~124 Ma（middle Early Cretaceous）was identified. These results furtherimply that the strike-slip movement of the Tan-Lu Fault Zone took place in Late Jurassic and middle Early Cretaceous respectively since collision of the North and South China plates, and the fault zone was under the setting of extension in earlier and later Early Cretaceous. Extensional movement of the fault zone controlled the development of the Hefei basin to the west and magmatism along the fault zone, and the extensional movement lasted longer than the strike-slip movement. The Tan-Lu Fault Zone presented alternative the strike-slip and extensional movement from the late Jurassic to Early Cretaceous. The middle Early Cretaceous sinistralstrike-slip is a tectonic response to short-term adjustment of the Izanagi Plate motion directions and has a close relationship.