东北地区的印支运动

东北地区的印支运动,一直受到地学界的关注(赵宗溥,1959;潘广,1963;黄振辉,1966),但由于缺乏三叠纪地层资料而未能作深入论述。近年来,本区三叠纪的调查研究有了重大进展,相继在东北南部发现或对比确定了早、中、晚三叠世的陆相地层(张武、董国义,1983);在东北北部,除早已报道的海相三叠系外,又发现早、晚三叠世的陆相堆积层和火山岩建造(长春地质学院等,1977;吴水波等,1980;陈巫基等,1981)¹⁾。

INDOSINIAN MOVEMENT IN NORTHEASTERN CHINA

Recently, the study on the Triassic system in the northeastern China has had a significant advance. The terrestrial Triassic beds have been found or recognized with correlation in the south part of the northeastern Chute and the Lower and Upper Triassic terrestrial aceumurated deposits and volcanic formation in the north in addition to the reported marine Upper Triassic, with sufficient fossils for establishing various series of the Triassic in this region. There are two significant unconfomities: one is represented by the unconformable contact of Middle Triassic Houfulongshan Formation (T2h) with Upper Triassic Laohugou Formation (T31) at Nanpiao in Liaoning and this tectonic level should be also found in the southern Jilin, and the other one is the unconformity between the Upper Triassic and Lower Jurassic, which has been met at Caoy-ang in western Liaoning, Suanyang and LingJiang in Jilin. And, there are evident overlaps of the Upper Triassic and Lower Jurassic in this region. In addition, the Lower-Middle Triassic and the Upper Triassic have their individual features in sedi-mental environment, rock facies and formation, and structural deformation, respectively. Magmaticly, both Triassic magma eruption and intrusion were greatly intensive. There are two stages of magma eruption: in Early-Middle Triassic and in Late Triassic with the latter predominant, and relevant intrusives, which are mainly composed of granitoid and some alkaline and intermediate-basic rocks, to be intruted into Lower (Middle) Triassic or Permian strata and covered by the Upper Triassic or Lower-Middle Jurassic in the first stage, and into the Upper Triassic and/or the older strata and covered by the Middle-Upper Jurassic in the late stage. These intrusives have been dated as 250-210 and 220-185 my., with K-Ar, U-Pb and Rb-Sr methods. Those indicate that the Indosinian movement is obviously evident in the northeastern China and may be divided into two phases. The early tectonic cycle at the end of Middle Triassic has characteristics inheriting that of Varisciaii movement and the late cycle at the end of Upper Triassic was a large scale one involving almost the wholl area of the northeastern China and bringing the south platform part and the north geosyncline part together to begin a new tectonic stage in Cireuni-Pacific region.