贺兰山古元古代韧性剪切带变形历史及对华北孔兹岩带构造演化的约束

韧性剪切带是从变形构造动力学角度剖析大陆造山带的关键切入点。孔兹岩带记录了华北克拉通西部阴山与鄂尔多斯陆块俯冲-碰撞造山过程，带内显著发育一系列古元古代韧性剪切带。目前，这些韧性剪切带的变形特征、机制及时代等问题研究较少，制约了对孔兹岩带形成与演化的全面认识。本项目拟对孔兹岩带贺兰山古元古代多期韧性剪切带进行系统研究：1）通过宏观-微观构造解析、石英c轴组构EBSD分析、电子探针原位石英Ti温度-压力计和锆石Ti温度计等工作，定量化分析其几何学、运动学、动力学、变形机制及变形-变质温压条件；2）开展锆石与独居石原位微区U-Pb定年及云母Ar-Ar定年，厘清韧性剪切带活动时限和变形序列；3）结合前人研究，精细刻画贺兰山古元古代韧性剪切带变形历史，探讨阴山与鄂尔多斯陆块之间的俯冲极性及相互作用方式，揭示孔兹岩带高压麻粒岩折返过程，并为阐明孔兹岩带古元古代构造格局与演化提供重要的构造约束。

Ductile shear zones can serve as critical windows to understand the geodynamic origin of continental orogens. The Khondalite Belt has witnessed the orogenic processes involving the subduction and collision between the Yinshan and Ordos Blocks in the Western Block of the North China Craton. Meanwhile, a series of Paleoproterozoic ductile shear zones remarkably developed in the Khondalite Belt. However, their deformational features, mechanism and geochronology are still poorly known. It thus hampers a comprehensive understanding of the formation and evolution of the Khondalite Belt. This project will focus on the Paleoproterozoic ductile shear zones of the Helanshan Complex in the Khondalite Belt. An integrated study of macro- to micro-structural observations, electron backscatter diffraction (EBSD) analysis of quartz c-axis fabrics, titanium-in-quartz thermobarometer and titanium-in-zircon thermometer estimates will be conducted to quantitatively examine their geometry, kinematics, dynamics, deformational mechanism and pressure-temperature conditions. Additionally, in-situ zircon/monazite U-Pb dating and mica Ar-Ar dating will be performed to assess the timing of ductile shearing. Combined with previous studies, this project can allow us to reconstruct the deformation history of the Paleoproterozoic ductile shear zones in the Helanshan Complex. It further provides important structural constraints on the subduction polarity between the Yinshan and Ordos Blocks, the exhumation process of high-pressure granulites and the tectonic evolution of the Khondalite Belt.