燕山造山带燕山期构造叠加及其大地构造背景

STRUCTURE OVERLAP AND TECTONIC SETTING OF YANSHAN OROGENIC BELT IN YANSHAN ERA

广泛的岩浆活动和强烈的构造变形是中国东部燕山期造山作用的两个主要特征。火成岩的空间展布,特别是同构造侵入杂岩体和火山岩盆地的展布与同期变形带的走向(和构造指向)具有很强相关性。本文通过火成岩构造组合、构造形迹及岩浆-构造事件序列等的共同约束,讨论华北地区燕山板内造山带造山过程中的构造叠加、构造应力场转换及其形成的大地构造背景。研究认为,燕山地区发育的“花边状”的褶皱和被褶皱的逆冲推覆带等,是多幕挤压变形叠加的记录。早侏罗世晚期(J31 )、中侏罗世晚期(J32 )、晚侏罗世中期(J23 )、晚侏罗世晚期(J33 )和早白垩世早期(K11 )5期不同方向展布的火成岩对应方向不同的收缩构造,提出早白垩世早期(K11 )本区可能存在区域北西向挤压构造及该期华北地区总体仍处于收缩构造环境的认识。华北燕山造山带是在蒙古—鄂霍茨克构造带,上扬(斯克)—楚科奇(斯克) (Verkhoyano-Chukotsk)造山带,伊泽奈崎(Izanagi)洋俯冲带和特提斯洋俯冲带4个边界会聚大背景中形成和演化的。

Extensive magma activity and intensive tectonic deformation are two typical characteristics in Yanshanian orogenic belt, East China. The distribution of igneous, especially syn-tectonic intrusive core-complex and the spread of igneous basins, has a good correlation with the direction of syn-deformation belts. This paper discussed the structure overlap, the conversion of structure stress field, and the tectonic setting through the integrated study of igneous structure associations, structure deformation and magma-tectonic event sequence etc. We think that the “lacy” folds and the folded thrust-nappes etc. record multi-episode compressive deformation. The five different directions of igneous distribution (Late of Early Jurassic (J^3_1), late of mid-Jurassic (J^3_2), middle of Late Jurassic (J^2_3), late of Late Jurassic (J^3_3) and early of Early Cretaceous (K^1_1) are totally in accordance with the direction of compressive deformation. It is proposed in this paper that there is a regional northwest compression structure, and as a rule there is a compression situation in north China in the early stage of Early Cretaceous (K^1_1). And we think that Yanshanian orogenic belt of North China was formed and evolved in the assemblage setting defined by four tectonic boundaries, i.e., Mongolia-Okhotsk tectonic belt, Verkhoyano-Chukotsk orogenic belt, Izanagi ocean subduction, and Tethys ocean subduction.