武当地块基性岩席群及其地质意义  

Basic Sill Swarms in Wudang Block of the Southern Qinling and Its Geological Significance

作　　者：胡健民[1] 孟庆任[2] 马国良[1] 张森琦[1] 高殿松[1] 

机构地区：[1]中国地质科学院地质力学研究所 [2]中国科学院地质与地球物理研究所,北京100101

出　　处：《地质论评》2002年第4期353-360,共8页Geological Review

基　　金：国家自然科学基金(编号49972066);博士后基金资助

摘　　要：侵位于武当地块内部的大量的板状变基性侵人体近年来一直被认为是800Ma左右发生的扬子古大陆裂解的重要依据。然而作者在武当地块北缘与西南部所做的1:5万地质填图以及相应的构造学和同位素年代学研究表明,它们与武当地块顺层伸展滑脱构造主滑脱面之顺层韧性—韧脆性变形带有密切的空间关系,是被褶皱了的岩席群。最新获得的岩体单颗粒锆石U-Pb年龄为401～407Ma,结合已有的地球化学研究成果,并考虑到邻区同时代碱性岩浆的侵位,作者认为,这套基性岩席群代表了泥盆纪时南秦岭地区曾发生过大规模的上地幔岩浆的底侵作用,并因此导致南秦岭上部地壳的伸展减薄。The tabular basic intrusives in Wudang block of Qinling orogen have been recognized as the result of the rifting of Yangtze ancient continent about 800 Ma. But recently, the geologic mapping finished by the authors in the north and southwest of Wudang block and the studying on the isotope geology and geochemistry of the swarms suggest that they are controlled by the major detachment plane of the Paleozoic extensional tectonics. The tabular basic intrusives mainly intruded at the core of the Wudang block, paralleling the boundary of the members of Wudang group, and along the major detachment plane and a series of low angular detachment zones in the basement rocks under the major detachment plane. These bodies, which usually occur on group, are thin in thickness, but extend up to 20km. They are conformity with the layers of the country rocks. It means that they are basic sill swarms and not dike swarms. We have got two sets of U-Pb isotopic ages, the zircons are selected from the basic sills in the southwestern of the block, which are 401 ± 14 Ma and 407 ± 12 Ma respectively. So the sills were intruded in the Devonian. It is in the Devonian that there occurred strongly alkali magmatism in the adjacent area and there were deposited conglomerates around the block. It is very possible that the intrusion of the basic magma suggests that there existed a strongly underplating of magma from the upper mantle in south Qinling during the Devonian. The underplating led the thinning of the upper lithosphere in south Qinling.

关 键 词：基性岩席群 底侵作用 伸展构造 武当地块 秦岭造山带 构造学 同位素年代学 

分 类 号：P588.124[天文地球—岩石学]