在华南内陆的赣南地区,发育早白垩世早期武夷群火山岩系,其不整合覆盖于南华纪?寒武纪变质岩系之上,且被早白垩世晚期罗塘群红色沉积岩系不整合覆盖.火山岩系内发育直立甚至倒转褶皱、逆掩断层等挤压变形和构造变质现象,并被南华纪变质岩系推覆逆掩;罗塘群红色沉积岩系变形微弱,底部发育近源快速堆积的砾岩层,其中所夹粗面岩具有埃达克岩和高压型粗面岩的地球化学特征.上述地质事实表明,赣南地区在武夷群火山岩系形成之后、罗塘群红色沉积岩系形成之前发生过强烈的挤压构造事件.定年资料显示,武夷群火山岩系顶部流纹岩和罗塘群红色沉积岩系底部的粗面岩SHRIMP锆石U-Pb年龄分别为131.4±1.3 Ma和110.7±1 Ma,不仅说明江西南部地区缺失131~110 Ma的地层,而且指示挤压构造事件发生在131~110 Ma之间.逆冲断层中新生矿物绢云母K-Ar稀释法年龄为118.2±3.2 Ma和112.9±3.7 Ma,指示挤压构造发生时间在118~113 Ma之间.运动学特征显示挤压应力方向为NW-SE向,与华南陆缘早白垩世中期挤压构造事件的挤压应力方向一致,指示早白垩世中期华南内陆和陆缘的挤压构造事件存在内在联系.%The Wuyi Group volcanic sequences outcropped in the southern Jiangxi province were formed in the early stage of Early Cretaceous Epoch. The volcanic series unconformably overlain the Sinian?Cambrian metamorphic rocks. Detailed field observations and structural measurements revealed that abundant compressive structures were developed in the Wuyi Group volcanic rocks. The structures include up-right to overturned folds, and overthrusting faults. The Nanhua metamorphic series napped upon the Wuyi Group volcanic rocks. Besides, rocks from the Luotang Group exhibited weak deformation and included a layer of basal conglomerate, indicative of rapid erosion and proximal deposition. Additionally, the intercalated trachyte within the Luotang redbed shows geochemical affinities with adakitic rocks and high-pressure trachyte, which was interpreted to derived from over thickened crust. The occurrence of the trachyte in the redbed implies that the crustal thickening took place before the formation of Luotang Group. Zircon SHRIMP U-Pb dating showed that the rhyolite at the top of Wuyi Group and trachyte at the bottom of the Luotang Group were formed at 131.4±1.3 Ma and 110.7±1 Ma, respectively. These data unraveled that this region lacks 131–110 Ma rock records. Sericite separates from overthrust fault, yielded K-Ar ages of 118.2±3.2 Ma and 112.9±3.7 Ma, which suggests compression and/or extrusion tectonic event occurred at 118–113 Ma in the middle stage of Early Cretaceous. A series of kinematic and stress analyses demonstrated that the direction of extrusion stress was NW-SE in consistence with the NE strike-slip fault zone. We tentatively propose that this deformation was remote response of the pacific plate subduction.
展开▼
