鲁东地区古元古界形成的大地构造环境探讨

鲁东地区是我国古元古界典型发育地区之一,分布有荆山群和粉子山群,以产滑石矿、菱镁矿、石墨矿而举世瞩目。荆山群和粉子山群形成的大地构造环境多年来倍受争议,有裂谷盆地、活动大陆边缘和俯冲增生杂岩等认识。本文在分析研究这些争议原因的基础上,试图从荆山群和粉子山群层序特征、岩石建造构造组合、变质、变形和古构造环境等因素,并考虑其在后期的发展、演化和构造变形过程中所处的古构造部位和构造改造强度差异等去探讨古元古代荆山群和粉子山群形成的大地构造环境,认为荆山群、粉子山群形成的构造环境应是古弧盆相中陆缘裂谷盆地的组成部分,相当于弧后盆地靠近大陆边缘一侧的构造背景,在古元古代晚期的造山过程中,粉子山群和荆山群等岩石地层单位均卷入了造山作用,其中荆山群发生了深俯冲作用,导致了高压麻粒岩相变质。粉子山群形成的大地构造环境属弧后盆地相,早期具有古岛弧(火山弧)或是弧后伸展的属性,而荆山群形成的大地构造环境为弧后盆地俯冲杂岩亚相。

Palaeoproterozoic Tectonic Setting in the Eastern Shandong Province

The eastern Shandong area is a typical place where the Jingshan group and Fenzishan group (JFG for short) of Palaeoproterozoic formation outcrop, and it is famous for the gigantic reserves of talc, magnesite and graphite deposit. There has been a lot of controversy over the tectonic setting of JFG, with mainly three types of controversial academic view points: rift basin, active continental margin area and subduction-accretionary com-plex. After synthetical analysis of the above view points, this work discusses the tectonic setting of JFG through its stratigraphic sequence, rock assemblage,deformation,metamorphism, palaeotectonic environment and the changes of structure location and intensity during its evolutionary process. The article concludes that the JFG probably formed in the back-arc basins along continental margin. Both Jingshan group and Fenzishan group are all exposed to the paleoproterozoic collisional orogeny. The former probably formed in back-arc basins environ-ment, with the same characteristics as ancient island arc or back-arc extension. The latter probably formed in back-arc basins subduction-accretionary complex. The high-pressure metamorphic granulite facies rocks of Jing-shan group probably resulted from the plate subduction and collision.