庐山岩浆核杂岩隆起-快速伸展变形特征和时代

华南板块中东部晚中生代广泛发育伸展构造变形事件, 不仅发育沉积红盆、伸展穹窿、变质核杂岩、韧性拆离断层带等, 也发育大规模的同构造岩浆和成矿作用, 但是快速伸展时限仍然存在争议。选取庐山岩浆核杂岩, 针对岩浆核杂岩两侧的晚中生代韧性剪切带及周缘开展野外地质调查及同构造变形分析。构造变形的运动学解析结果表明, 庐山岩浆核杂岩拆离正断层的伸展方向为NW—SE向, 同构造40Ar-39Ar测年获得白云母主坪视年龄为105.20±0.23 Ma和黑云母主坪视年龄95.84±0.09 Ma, 限定了庐山岩浆核杂岩隆升-快速伸展时限集中于95~105 Ma。庐山岩浆核杂岩本期伸展构造变形特征及形成时代与华南板块区域性的隆升-伸展变形特征一致, 代表了华南板块晚中生代以来快速的伸展构造变形事件, 形成机制可能与古太平洋板块向华南板块俯冲后的板块弯转后撤有关。

Characteristics and ages of uplift-rapid extension deformation of Lushan magmatic core complex

The extensional tectonic events during the Late Mesozoic were widely distinguished in the east central part of the South China Plate.These events are characterized by red sedimentary basins, dome extensional structure, metamorphic core complex, ductile detachment fault zone, and simultaneous large-scale of syntectonic magma and metallogenic processes.But the late Mesozoic extensional deformation sequence of the region is still controversial, especially the formation ages of rapid extension.In this paper, the authors focus on the time of intensive extension of the Lushan magmatic core complex(LMCC)in middle-east part of the South China Plate.Field investigation was carried out to analyze the syntectonic deformation of the ductile shear zone on both sides of the LMCC and its periphery.The new results show that the detachment normal fault of shear zone has NW-SE extensional direction, and 40Ar-39Ar dated the apparent main plateau ages of muscovite and biotite at 105.20±0.23 Ma and 95.84±0.09 Ma, respectively.The uplift-rapid extension formation age of LMCC is thus concentrated at 95~105 Ma.It is noticeable that the extensional deformation of the characteristics and formation age of the LMCC is consistent with the regional extensional deformation of the Southern China Plate.The uplift-rapid extension formation of LMCC represents a rapid extensional tectonic deformation event in the South China Plate since the Late Mesozoic.The formation mechanism of the uplift-rapid extension formation of LMCC may be associated with rollback after the Paleo-Pacific Plate had subducted into the Southern China Plate.