桐柏造山带中龟山杂岩的白云母^(40)Ar/^(39)Ar年龄及其地质意义

^(40)Ar/^(39)Ar Dating of Muscovite from the Guishan Complex in the Tongbai Orogen,Central China,and Its Geological Implications

出露于桐柏造山带松扒-龟梅断裂带南侧的龟山杂岩经历了两阶段变质及多期变形作用,但其变质变形时代及其与秦岭造山带中产于相同构造部位的武关杂岩的构造关系尚缺乏深入研究.为此,对取自于龟山杂岩中的4件变质沉积岩和2件变质火山岩样品中的白云母进行了^(40)Ar/^(39)Ar同位素定年.结果表明,白云母的^(40)Ar/^(39)Ar坪年龄从306.7±1.7Ma(保存最好的白云母斑晶)延续到279.2±2.6Ma(经历后期变形改造的白云母).结合前期锆石U-Pb定年结果推测龟山杂岩的两阶段变质及主期逆冲推覆变形均发生在石炭纪,并在二叠纪遭受到左行走滑剪切作用的改造.龟山杂岩与武关杂岩具有类似的岩石组成和变质变形演化历史,二者共同构成一条>500km的晚古生代中级变质带,是华北-华南陆块最终碰撞之前大洋俯冲-增生的产物.

The Guishan complex exposed to the south of the Songpa-Guimei fault in the Tongbai orogen underwent two-stage metamorphism and multiple deformation.However,the timing of metamorphism and deformation of the complex and its relation to the Wuguan complex occurring in the same tectonic position in the Qinling orogen remain poorly constrained.In this paper,4 metasedimentary rocks and 2 metavolcanic rocks from the Guishan complex were performed for muscovite ^40Ar/^39Ar dating.The results suggest that the plateau ages of muscovite range from 306.7±1.7 Ma（well-preserved muscovite porphyroblasts）to 279.2±2.6 Ma（muscovites overprinted by late deformation）.Coupled with published U-Pb zircon data,it is infered that two-stage metamorphism and main thrust deformation of the Guishan complex took place during the Carboniferous,and the reworking of sinistral slid-slip shearing occurred in the Permian.The Guishan and Wuguan complexes have similar rock associations and share the same metamorphic and deformational history.The two complexes constitute a〉 500 km-long Late Paleozoic medium-grade metamorphic belt,which was resulted from the oceanic subduction-accretion prior to the final collision between the North and South China blocks.