燕山板内造山带中段中生代构造格局与构造演化

Mesozoic tectonic framework and evolution in the central segment of the intraplate Yanshan orogenic belt

燕山板内造山带中段中生代构造格局由近东西向丰宁-隆化断裂、古北口-平泉断裂和密云-喜峰口-青龙断裂及马兰峪背斜组成。丰宁-隆化断裂为由北向南的低角度逆冲断层经后期改造而形成。古北口-平泉断裂系由柳河-承德县断层、乌龙矶-小料北沟断层、寿王坟-大杖子-下杖子断层组成的断裂系统,在剖面上呈正花状构造,具右行斜压性质,活动时代为148～132Ma。密云-喜峰口-青龙断裂为一右行走滑断裂。马兰峪背斜不具有变质核杂岩的构造组合特征,深部岩浆活动主导的、基底薄弱带控制的断块差异隆升可能是其形成的重要机制。三叠系砾岩中的砾石绝大多数具再生砾石特征,主要来自石炭系—二叠系,其中火山岩砾石的年代(240～248Ma)表明其沉积时间应明显小于240Ma。下板城盆地北部及西部王家店-小梁后盆地原所谓的早侏罗世南大岭组火山岩的时代分别为161Ma和126～127Ma。因此,原标志印支期变形的角度不整合的时代已被否定,印支运动构造表现需重新认识。

The Mesozoic tectonic framework of the middle segment of the intraplate Yanshan orogenic belt is composed of the nearly E-W-extending Fengning-Longhua fault, Gubeikou-Pingquan fault and Miyun-Xifengkou-Qinglong fault and the Malanyu anticline. The Fengning-Longhua fault is interpreted in this paper as a reworked south-vergent low-angle thrust fault. The Gubeikou-Pingquan fault system is composed of the Liuhe-Chengde County fault, Wulongji- Xiaoliaobeigou fault and Shouwangfen-Dazhangzi-Xiazhangzi fault. They are characterized by a flower structure in cross-section. This fault system shows a dextral transpressive nature and was active between 148 and 132 Ma. The Miyun-Xifengkou-Qinglong fault is an important dextral strike-slip fault system. The Malanyu anticline has no tectonic composite features of a metamorphic core complex. The formation of this anticline is interpreted to be the result of differential uplift of the blocks controlled by the weakness zones of the basement. Plutonism might contribute to some extent to the formation of this anticline. Most of the gravels in Triassic conglomerate have the features of reworked gravels. They were mainly derived from Carboniferous and Permian conglomerates and sandstones. The age rang of 240-248 Ma of volcanic gravels of the Triassic conglomerates indicates that the Triassic in this area should be much younger than 240 Ma. The so-called Early Jurassic Nandaling Formation volcanic rocks in the north of the Xiabancheng basin and the Wangjiadian-Xiaolianghou basin- west of Chengde County- yield ages of 161 Ma and 126-127 Ma respectively. Therefore, the age of angular unconformity marking the Indosinian deformation has been negated and the tectonic manifestations of the lndosinia movement should be re-evaluated.