Metamorphic Core Complexes vs. synkinematic plutons in continental extension setting: Insights from key structures (Shandong Province, eastern China)

摘要

Continental extension is an important geodynamical process mostly diagnostic of a peculiar behaviour of the crust accommodated by geological structures that highlight these specific conditions in the crust. Though a Metamorphic Core Complex (MCC) reveals a much stronger crustal extension than a synkinematic pluton, the nature of those two structures implies different implications in terms of crustal extension mechanisms and geodynamic significations. In eastern Asia, a major continental extensional event occurred during Mesozoic and early Cenozoic times. The resulting various extensional events described in previous studies consist in large intracontinental basins, important volcanism, emplacement of plutons in the upper crust and exhumation of MCCs. An efficient description of MCCs and plutons in eastern Asia is essential to discriminate important differences of those two structures in terms of strain amount undergone by continental crust and geodynamic significations. In that way, an integrated structural and geophysical study has been realized to precisely discriminate the structure in the Jiaodong Peninsula (Shandong Province, eastern China), previously regarded as simple sheared plutons. A succession of three main stages have been identified all pertaining to a NW-SE extensional setting: (1) the exhumation of the Late Jurassic-Early Cretaceous Linglong MCC below the SE-dipping Linglong detachment fault, (2) the emplacement of the Guojialing syntectonic pluton below the N-dipping extensional Guojialing intracru-stal shear zone (130-124 Ma) and (3) a penetrative brittle normal faulting associated with gold mineralizations (～120 Ma). As a result, the maximum amount of extension in Jiaodong Peninsula, characterized by partially-melted lower to middle crust upward into the Linglong MCC should be revised to Late Jurassic-Early Cretaceous period.