华北地区的燕山运动

燕山运动为1926年翁文灏所创立,半个多世纪以来,随着地质工作的开展,对中生代地层、岩浆活动和构造形迹特征的深入研究,许多学者曾撰文进行讨论(表1)。燕山运动系指发生于侏罗、白垩纪时期的构造运动。燕山运动形成了华北盖层主要的构造形迹,伴随强烈的岩浆活动,形成丰富的矿产资源,是华北地块显生宙最重要的构造运动。尽管对燕山运动已进行了大量的研究工作,但目前对燕山运动的分期,各期构造活动方式、构造应力场特征,构造演化,构造活动机制等,仍众说纷云,本文将对这些问题进行讨论。

THE YANSHANIAN MOVEMENT IN THE NORTH CHINA

The Yanshanian movement is the most impotent tectonic movement of the North China Massif in phanerozoic. It may be divided into three stages: the early, middle and late stage, of which there were five episodes. In the early stage of the Yanshanian movement the North China Massif gradually fragmented and East-West trending fracture zones formed, accompanied by the intrusion and eruption of intermediate-basic magmas. The middle stage was an abrupt turn in the development of the North China Massif. During this stage, the Massif further dismembered and the NNE trending fracture zones, of which the intensive activities controlled intrusion and eruption of a great volume of intermediate-acidic magmas, formed. During the late stage the characteristics of the tectonic activities inherited those in the middle stage. The Yanshanian movement shows following characteristics, i.e. pulsation and migration of the tectonic activity and variation of the main compressive (or tensile) stress in the tectonic stress field with time. The mechanism of the tectonic activity of the Yanshanian movement was mainly controlled by the rotation, the general expansion trend of the Earth and gravitation isostasy.