滇西保山地块三叠纪裂谷盆地的演化

The Evolution of the Triassic Rift Basin in the Baoshan Block of Western Yunnan

裂谷是地质时期伸展构造的典型地质构造现象。保山地块三叠纪裂谷是在二叠纪浅海环境基础上拉伸发展形成的裂谷,经历了拉伸变薄(斜坡–盆地)形成阶段–地幔岩浆喷发(裂谷形成)阶段–(斜坡–盆地)裂谷夭折阶段,在这三个阶段的演化过程中,裂谷中心(永德–黑山)堆积物厚约6000 m。裂谷在三叠纪晚期拉张达到了顶峰,形成了三叠系上统牛喝塘组基性–酸性–基性火山岩浆的喷发。在裂谷的后期,以深海浊积平原沉积为主,反映出沉积基准面位于碳酸盐补偿面之下。在裂谷的形成–消亡过程中,始终伴随着强烈的地震,并形成了大规模的震积岩和滑塌堆积。尽管这是一个夭折的裂谷,但裂谷中发育的钙质浊积岩普遍含有浓烈的(煤)油气味和双峰式火山岩、碱性花岗岩,具大陆板内裂谷环境的特征。因此,研究(永德–黑山)裂谷不仅具有沉积学、地层学、大地构造学的意义,更具有研究地史时期的古地震分布、裂谷与油气的联系、及其与昌宁–孟连带的联系等多方面的意义。

The rifts are typical geologic structural phenomena of the extensional tectonics during the geolog-ical period. The Triassic Rift Basin in the Baoshan Block had formed on the Permian neritic envi-ronment foundation because of tension that it had experienced the formation stage of extension and thinning (slope-basin)-the stage of mantle magma eruption (formation of the rift)-the stage of the rift aborting (slope-basin). During the evolution process of these three stages, the thickness of accumulations was about 6000 m in the rift center. The pull-apart of the rift valley had reached its peak in the late Triassic that it had formed the magma eruption of basic-acid-basic volcanic rocks of the Niuhetang Formation in the Upper Triassic series. The deposition of deep-sea turbidite plain is the main in the late period of the rift. It reflected the sedimentary base level was located below the carbonate compensation surface. In the process of formation-extinction of the rift valley, it was always accompanied by strong earthquake and it had formed large-scale seismites and slump ac-cumulations. Although this was a die young rift valley, the auxetic calcareous turbidites in the rift generally contained a very strong smell of oil, bimodal volcanism and alkaline granite. These showed that they had the characteristics of continental intraplate rifting settings. Therefore, the study on the Yongde-Montenegro rift has significances for Sedimentology, Stratigraphy and Tec-tonics, and also has many aspects of significances for researching on the paleo-seism distribution, the relation between rift and Hydrocarbon, and the relationship with Changning-Menglian belt in the geological period.