THE TONGJIANG-MULENG DEEP BURRIED FRAUCTURE

The Tongjiang-Muleng deep burried fracture is an important boundary between two tectonic units——the Laoyeling uplift and the Taipingling fold belt. There occur mainly the lower Paleozoic Heilongjiang Group and the Mashan Group in the Laoyeling area and the Paleozoic strata in the Taipingling area. Basic and ultrabasic belts are developed respectively along both sides of the fracture.The rocks in the Taipingling area is obviously rich in Si,Ca,Na and K and poor in Mg as compared with the rocks in the Laoyeling area. Granitoids are well developed in the Laoyeling area,but their rock types are simple;whereas granitoids in the Taipingling area are far less developed than in the Laoyeling area but their rock types are more complex. Precambrian extrusive rocks are mainly distributed in the Laoyeling area,which have been already entirely metamorphosed;the Paleozoic rocks fare mainly developed in the Taipingling area,part of which have been meta- morphosed. From above it follows that the Laoyeling area and the Taipingling area had utterly different tectonic settings and rock-forming environments prior to the Jurassic. The structures are well developed in both areas,but show quite different features.In the Laoyeling area the fracture structure predominates and the fold structure is less important;while in the Taipingling area the fold stru- cture is predominant and the fracture structure is less important. Au,U,Th,Cu and Fe mineralizations are well developed in the Laoyeling area,forming many important metal deposits;while only sparse Au,Fe and Cu mineral occurrences（mineralizations）are observed in the Taipingling area.These phenomena reflect the difference in ore control of different tectonic units. There occur mountainous areas on the western side of the fracture and plains on the eastern side.Owing to the influence of the fracture several major rivers in the region turn or branch and extend along the strike of the fracture. The fracture in general strikes NNE,wtih its southern end swinging nearly N-S.Its northern end stretches into the Duji area of the U.S.S.R. accross the Heilingjiang River,whereas its southern end enters Jilin province and passes the Chunhua area of the province and then turns into the territory of the U.S.S.R.