大别山东南麓宿松群铷—锶年龄及其构造意义的探讨

THE Rb-Sr AGES OF METAMORPHIC SERIES OF THE SUSONG GROUP AT THE SOUTHEASTERN FOOT OF THE DABIE MOUNTAINS, ANHUI PROVINCE, AND THEIR TECTONIC SIGNIFICANCE

摘要: 本文根据对宿松群变质岩的宏观地质调查,结合室内岩石与矿物的镜下鉴定,测定全岩及单矿物Rb-Sr等时线年龄数据,认为该变质岩系曾经过二次变质与变形作用。第一次是加里东期褶皱及变质作用,形成绿帘角闪岩相,其时限为470～448Ma;第二次是印支期,表现为岩石片理化、塑性变形、推复构造及退变质作用,形成低绿片岩相,其时限为231～211Ma。

Abstract: Isotopic age determination on the Susong Group metamorphic rocks yields Rb-Sr whole-rock isochron ages of 448 Ma and 470 Ma, a Rb-Sr whole rock- mineral isochron age of 231 Ma and a phengite K-Ar age of 210 Ma. The results show that for the Susong Group folding and metamorphism occurred in the Caledonian movement and that compresso-shear took place in the Indosinian Cycle. The rocks exhibit well-developed schistosity and gravels in fractures are plastically deformed to assume a "S" shape, so the rocks appear to be both ductile and brittle. Petrological and isotope chronological studies show that the nappe structure of the Susong Group were formed during the Indosinian period.