【摘要】 大别山的主要剪切带晚中生代时发生伸展拆离,整个构造体系以北大别变质杂岩为核心分为北部伸展构造体系和南部伸展构造体系。北部伸展体系中的晓天—磨子潭剪切带向北北东拆离;南部伸展体系中,水吼—五河剪切带和太湖—马庙剪切带向南南东拆离,而宿松—清水河剪切带则向南西拆离。系统的岩石有限应变测量分析显示:晓天—磨子潭剪切带的剪切位移量至少为56km,宿松—清水河剪切带的剪切距离至少为12km。在南部伸展体系中,福林参数K值从北到南的变化指示从纯剪切逐渐过渡到简单剪切,显示了北大别的岩浆侵入作用在南部伸展拆离体系中的主动作用。对大别山的4条剪切带中黑云母、白云母和角闪石的40Ar-39Ar同位素年代学分析表明,存在两组变形年龄,较早的一组年龄(约190Ma±)可能代表了造山带形成过程中超高压变质岩冷却和折返的时间;较晚的一组年龄(约125Ma±)则可能代表了碰撞造山带作用之后的伸展拆离作用的时间。应变测量分析、年代学分析和铂族元素的特征均表明北大别杂岩中的岩浆侵入作用是大别山晚中生代伸展拆离作用的主要诱因。更多还原

【Abstract】 The main shear zones of Late Mesozoic in the Dabie Mountains were characterized by extensional detachment structures. The entire tectonic system was divided by the northern Dabie metamorphic complex into the north and south extensional tectonic systems. In the north tectonic system, the Xiaotian-Mozitan shear zone displayed extentional detachment to the NNE. In the south tectonic system the displacement direction along the Shuihou-Wuhe and the Taihu-Mamiao shear zones was to the SSE, whereas displacement along the Susong-Qingshuihe shear zone was to the SW. Finite strain measurements showed that the shear displacement of the Xiaotian-Mozitan shear zone was more than 56 km, whereas that of the Susong-Qingshuihe shear zone was more than 12 km. From north to south in the south extensional tectonic system, the Flinn index (K) demonstrated a transition from pure shear to simple shear. Therefore, it might imply that the extensional environment in the south tectonic system could be controlled by magma intrusion in the North Dabie Mountains complex belt (NDMCB). The main shear zones in the Dabie Mountains displayed two deformation ages, ca.190 Ma and ca. 124 Ma (derived from mineral ~ 40 Ar-~ 39 Ar data). The earlier age (ca. 190 Ma) might be related to the ultra-high pressure(UHP)cooling and returning during the formation of the orogeny, and the later age (ca. 124 Ma) might represent the extensional detachment age after orogenesis. Strain analysis, chronology, and the mantle enrichment of platinum group elements all suggested that magma intrusion in the NDMCB could be the main cause of extensional detachment structures during the Late Mesozoic.更多还原