青海玉龙滩地区托赖岩群中—早二叠世基性岩墙的发现及地质意义

在玉龙滩地区古元古代托赖岩群变质岩中发现了一套基性岩脉侵入体,岩石类型主要为辉长岩、辉绿岩,侵入于托赖岩群片麻岩、片岩,岩脉长轴走向大多以北西向为主,个别近南北向或北东向,露头规模一般长10~35m,宽5~10m。通过同位素测年分析辉绿岩脉地质时代为早二叠世,结合对地质特征、岩石学特征、岩石化学、地球化学特征的研究,认为其属于拉斑玄武系列,形成于伸展性构造环境。结合本区区域地质分析,该岩脉可能为祁连山造山带加里东期造山运动结束之后,由于陆壳加厚而发生伸展崩塌,造成幔源基性岩浆底侵,形成了该类相当于基性岩墙的产物。反映北祁连地区在早二叠世有一期陆壳加厚伸展背景下的基性岩浆底侵事件。

Discovery and Geological Significance of Early Permian Mafic Dike Rock of Yulongtan Region Which Intrusive into Tuolai Paleo-Proterozic Rock

A set of basic dyke intrusion has been found in metamorphic rocks of Tuolai Paleoproterozoic rock group in Yulongtan Region. Gabbro vein and diabasic dyke are found to be the main intrusive rocks and they intruded into the gneiss and schist of Tuolai rock group. The axes of the dykes are mostly NW, with a few close to SN or NE, the outcrop scale is within 10- 35m in length and 5-10m in width. Isotope dating analysis on diabasic dyke shows its geological age as early Permian. Combined with its geological features, petrology, petrochemistry and geochemistry characteristics, it is suggested that the dyke belongs to thoteiitic series and forms in extensional tectonic setting. Considering the regional geological analysis, it is concluded that after Caledonian orogeny, Qilianshan orogenic belt had experienced a stretch and collapse due to the thickening of continental crust, and the process led to the underplating of basic mantlederived magma, thus formed the basic dyke. It is reflected that in early Permian a basic magma underplating event occurred with continental crust thickening and extension in north Qilian area.