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    张八岭隆起早白垩世变质核杂岩的厘定——对郯庐断裂带的制约及其与成矿作用关系

    Determination of the Early Cretaceous metamorphic core complex in Zhangbaling Uplift: Constraints on the Tan-Lu fault and its relationship with metallogenesis

    • 摘要: 张八岭隆起广泛分布的平缓韧性剪切带与郯庐断裂带平移作用形成的陡立韧性剪切带明显不同。通过对平缓韧性剪切带的几何学、运动学分析,结合早白垩世盆地特征、中国东部变质核杂岩伸展拆离断层和同构造岩浆岩同位素定年结果,厘定出张八岭隆起早白垩世变质核杂岩。该变质核杂岩上盘由南华纪-奥陶纪沉积地层和早白垩世盆地组成,下盘为新元古代浅变质碎屑沉积岩、变海相火山岩(基底)以及早白垩世侵入岩,上下盘之间被一条主伸展拆离断层所分隔。变质核杂岩长轴为NE-SW向,指示构造反映上盘向SE剪切滑动,与中国东部变质核杂岩的伸展方向完全一致。通过本次变质核杂岩的厘定,结合野外地质事实,笔者认为管店-马厂断裂是郯庐断裂带的次级断裂,是对郯庐断裂带早白垩世末第三次左行平移的响应。在综合研究的基础上,建立了区域构造-岩浆-成矿关系模型,揭示了张八岭隆起早白垩世经历了早期伸展(变质核杂岩阶段)-挤压走滑(管店-马厂断裂形成阶段)-晚期伸展(闪长质脉岩侵位阶段)3个构造阶段,多期构造、岩浆的叠加作用下,形成了本区的金多金属矿产。

       

      Abstract: The gently dipping ductile shear zone widely distributed in the Zhan baling uplift is obviously different from the steeply dipping ductile shear zone formed by the translation of the Tanlu fault. Based on the geometry and kinematics analysis of gently dipping ductile shear zone, combined with the characteristics of the Early Cretaceous basins and the isotopic dating of extensional detachment faults and syntectonic magmatic rocks of the metamorphic core complexes in eastern China, the Early Cretaceous metamorphic core complex of Zhangbaling uplift is defined. Its upper plate is composed of the Nanhua-Ordovician sedimentary strata and the Early Cretaceous sediments, the lower plate is composed of Neoproterozoic metamorphic clastic sedimentary rocks, metamarine volcanic rocks (basement) and early Cretaceous intrusive rocks. The upper and lower plates are separated by a main extensional detachment fault. The long axis of the metamorphic core complex is NE-SW, with indicative structure reflecting shear slipping to SE of the upper plate, which is completely consistent with the extension direction of the metamorphic core complex in eastern China. Through the determination of the metamorphic core complex, combined with field geological facts, it is believed that the Guandian-Machang fault is a secondary fault of Tanlu fault, which is a response to the third left-lateral translation of Tanlu fault zone at the end of Early Cretaceous. On the basis of comprehensive research, a regional tectonic-magmatic-metallogenic relationship model is established, which revealing that the Zhangbaling uplift has undergone three tectonic stages during early Cretaceous: Early extension(metamorphic core complex stage)-compression strike-slip (Guandian-Machang fault formation stage)-late extension (dioritic dike emplacement stage). The superimposition of multi-stage structuring and magmatism results in the formation of gold polymetallic minerals deposits in this area.

       

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