西秦岭东段构造演化及成矿作用的讨论

在对西秦岭重点地区地质建造、结构构造等研究基础上 ,结合前人工作成果 ,对西秦岭造山带地质结构、构造演化及成矿作用等提出了新的认识 ,包括 :1,首次对前人在西秦岭北带厘定的晚泥盆世磨拉石地层 -大草滩群 (D3dc)进行分解 ,认为它是晚泥盆世滨浅海相砂岩、粉砂岩及碳酸盐岩在不同地段分别逆冲到二叠系、侏罗系及白垩系之上所形成的岩片叠置体系。并根据构造解析的原则 ,结合区域地层结构 ,将西秦岭北带构造 -地层体划分为三个单元 ,即上古生界 -中生界表构造层次准原地系统、古生界浅构造层次推覆岩片及元古界中深构造层次推覆岩片 ,它们相互叠置而成的西秦岭北带的岩片堆垛体系 ;2 ,对西秦岭西成矿田的研究表明 ,西成矿田的容矿地层不仅包括泥盆系 ,而且还包括元古宇 ,其中最大的矿床 -厂坝 -李家沟超大型铅锌矿床产于元古宇而不是泥盆系 ,西成矿田是后生热液矿床而不是海底喷流沉积矿床 ,它的形成完全受元古宇构造岩片由西向东的逆冲 -推覆及其所造成一系列构造效应所控制 ;3 ,西秦岭南带勉略构造带为一构造走滑体系 ,产于勉略带的蛇绿岩与产于勉略宁地块内部的蛇绿岩是同一时期、同一构造背景的产物 ,为中新元古代板快构造演化的记录 ,在南秦岭 ,不存在可靠的晚古生代蛇绿岩

On several problems concerning the tectonic evolution and metallogenesis of Western Qinling, China

Several new points of tectonic evolution and metallogenesis are put forward on the base of our and previous studies on the geological formation, structure and texture of western Qinling orogen, China, which include: (1) Late Devonian molass stratum-Dacaotan Group (D3dc) was regarded as a pile of sheets formed by late Devonian neritic sandstone, fine sandstone and limestone thrusting onto Permian, Jurassic and Cretaeous molass. According to tectonic analysis and stragraphic structures, the western Qinling can be divided into three different tectonic-level sheets, the up-Paleozoic-Mesozoic surface tectonic-level parautochthonous sheet, Paleozoic shallow tectonic-level sheet and Precambrian middle to deep tectonic sheet. The three sheets were piled to each other by thrusting tectonic interface, (2) studies on the Xicheng orefield show that the orebodies occurred not only in Devonian but in Proterozoic in which the largest deposit-Changba-Lijiagou Pb-Zn deposits occurred. The Xicheng orefield was epigensis type rather than homogensis SEDEX deposit. The metallogensis was completely controlled by the Proterozoic thrusting from west to east and its concerning tectonic effect, (3) the Mianlue zone in southern Qinling is a strike-slip tectonic belt. The ophiolites in Mianlue zone and in Mian-Lue-Ning block were formed in same time and same tectonic background, which were Meso-Neoproterozoic oceanic crust slice and recorded plate tectonic evolution at that time. The study shows that there didn't exit reliable late Paleozoic ophiolite in the suthern Qinling.