关于龙门山地区东吴运动的存在及其性质的认识

东吴运动是二叠纪的一次重要地壳运动,但对其位置、性质、发生时间历来都有不同的意见,而对于龙门山地区,更是很少有人专题涉及。近来,笔者等人对龙门山地区二叠系进行了实地考察,结合前人的研究成果,通过对该区地层缺失、不整合接触关系、沉积响应及火山岩分布等特征的分析,论述了龙门山地区东吴运动的存在及其性质。研究认为龙门山地区东吴运动主要表现为茅口组上部地层缺失;在茅口组和龙潭组之间普遍存在不整合面,并于不整合面的底界发现底砾岩;中、晚二叠世岩相古地理发生突变以及火山爆发等。其发生时间于晚二叠世早期至中期,即龙潭组沉积期,属于地壳的升降运动,并伴随龙门山南段玄武岩浆的爆发而结束。东吴运动结束了龙门山地区早二叠世以来的稳定地台沉积,使该区发生了强烈的岩相分异。

The Knowledge on the Existence and Nature of the Dongwu Movement in the Longmen Mountain Area

Dongwu movement is an important crustal movement activity happenning during the Permian, but arguments focus on its location, character and occurring time. Especially in Longmen mountain area, there are few people done any research. Recently some geological surveys were made in Longmen mountain area combined with the fruit of predecessors. Based on the analysis about absence of formation, unconformity relationship, sedimentation and distribution of the igneous rocks, this paper discussed the Dongwu movement in Longmen mountain area. Ample evidences include absence of top formation of Maokou Formation; the pervasive unconformity between Maokou Formation and Longtan Formation; the abrupt change of lithofacies and the eruption of volcanos. The occurring time is from early to middle Later Permian, which coincides with the sedimentary time of Longtan Formation. Dongwu movement is a vertical movement result of crust, and terminated with the outbreak of the igneous rocks in northern Longmen mountain. The movement is also signified the termination of sedimentation of sustained platform from early Permian, and made lithofacies differentiated in Longmen mountain area.