陕西北秦岭地区多旋迥发展特征及其构造演化史

位于陕西中部的北秦岭地区在中国大地构造部位中占有十分重要的位置。该区构造作用、岩浆活动和变质作用十分复杂而强烈,矿产资源亦颇为丰富,对该区的研究工作一直被广大地质工作者所重视,陆续发表了不少有关研究成果和论文。。近几年来,我们对该区做了一些野外地质观察和综合分析,对其多旋回发展特征及其演化历史获得了一点粗浅的认识。在此提出,供同志们参考。一、基本地质构造概况

CHARACTERISTICS OF THE STRUCTURES IN THE NORTHERN QINLING MOUNTAINS AREA IN SHAANXI PROVINCE AND THEIR EVOLUTIONAL HISTORY

The Northern Qinling Mountains area in central Shaanxi is located in a relatively peculiar tectonic position. Its northern part belongs to the SinoKorean platform,while its southern part the Qilian-Qinling geosyncline. It has undergone the effects of almost all previous tectonic movements. As a result,in the area the tectonism,magmatism and metamorphism are very strong,the tectonic movements are especially complex,and mineral resources of various kinds are quite rich. In view of such complex geological processes,the authors used the theory and method of polycyclic tectonics founded by Prof. Huang Jiqing,drew on the theory of plate tectonics and based themselves on such geological records as the stratigraphy,contact relationships,lithofacies and formations,biotic fossils,metamorphism,magmatism,tectonism,isotopic ages and mineralization to divide the histeory of tectonic evolution in the area into 12 tectonic cycles and 4 development stages. Such division is relatively objective. In elucidating the history of tectonic evolution,this paper deals with the evolution of uranium in more detail. In the Precambrian,uranium deposits were not formed and the uranium content was not high in the terranes,but the folding and uplift of the Qilian-Qinling geosyncline gave rise to the Caledonian Northern Qinling tectono-magmatic belt and uranium mineralization of pegmatite type. Since the Mesozoic,the area had been strongly affected by the tectonism of the Tethyan and circum-Pacific tectonic domains,thus forming the early Yanshanian E-W-trending tectono-magmatic belt and the late Yanshanian NNE-trending tectono-magmatic belt. Under the effects of such tectonism,uranium was continuously mobilized and migrated,and was precipitated in favourable structural positions,thus forming a number of uranium occurrences or mineralizations in the E-W-trending tectono-magmatic belt and the major 401 uranium deposits and some minor uranium deposits and occurrences in places where the two belts are superimposed. So the Yanshanian cycle is an important metallogenic epoch of uranium in the area. In summary,the use of the polycyclic tectonic theory may better reveal the history of the crustal evolution and uranium mineralization in the area and yields better results in the prediction of uranium deposits.