燕山构造带北部喀喇沁地区晚古生代-中生代岩浆活动的构造背景分析

燕山构造带北缘喀喇沁地区发育了晚古生代一中生代多期岩浆活动,记录了多期构造变形事件,是认识该构造带大地构造演化的理想地区。本文通过对该地区岩浆岩的系统定年及各期构造变形事件的研究,结合区域地质资料,综合分析了晚古生代一中生代的大地构造演化历史。分析结果表明,燕山构造带在早石炭世晚期一早二叠世处于古亚洲洋俯冲背景下的活动陆缘环境,出现了弧岩浆活动。中二叠世古亚洲洋沿索伦克缝合线关闭,使得燕山构造带成为周缘前陆挤压变形带,并对应着岩浆活动的平静期。之后燕山构造带分别出现了晚二叠世一三叠纪、中侏罗世、晚侏罗世与早白垩世4期伸展背景下的岩浆活动。在这些岩浆活动之间的平静期,先后发生了早侏罗世、晚侏罗世初、早白垩世初3期挤压事件。这些现象还表明,岩浆活动与构造演化具有明显的耦合关系,板内环境下岩浆活动发生在伸展背景中,而岩浆活动平静期多对应区域挤压活动。

Tectonic setting of Late Paleozoic-Mesozoic magmatic activities in the Kalaqin area of the northern Yanshan tectonic belt

The Kalaqin area, located in the northern Yanshan tectonic belt, is considered to be an ideal area for understanding tectonic evolution of the Yanshan tectonic belt due to the presence of several phases of Late Paleozoic-Mesozoic magmatic activities and deformation events. Based on dating of the igneous rocks and studying of the deformation events, combining with the regional geological data, tectonic evolution history in the Yanshan tectonic belt during Late Paleozoic and Mesozoic was deduced comprehensively in this study. It shows that the Yanshan tectonic belt was in an active continental margin setting with arc-related magmatism during the latest Early Carboniferous and Early Permian due to the subduction of the Paleo-Asian ocean. The closure of Paleo-Asian ocean along the Solonker suture in Middle Permian resulted in foreland shortening deformation zone and appearance of magmatic quiescent period correspondently in the Yanshan tectonic belt. The belt was followed by four periods of extension-related magmatic activities in Late Permian-Triassic, Middle Jurassic, Late Jurassic and Early Cretaceous respectively. Each of the magmatic events was interrupted by a quiescent period of magmatism related to a compressive event happening in Early Jurassic, Early Late Jurassic and Early Cretaceous respectively. These phenomena suggest that there exists coupling relation between the magmatic activities and tectonic evolution. Each of the intraplate magmatic events happened under the extensional setting whereas every compressive event corresponds to the magmatic quiescent period in the Yanshan tectonic belt.