北秦岭松树沟榴闪岩中锆石包裹体、U-Pb定年和Lu-Hf同位素特征及其地质意义

We extract zircons and heavy minerals ilmenite、rutile from garnet amphibolite，which located to the north of the Songshugou ultramafic pluton in Northern Qinling.Through the way of laser Raman microprobe,we recognize plagioclase，augite，garnet，quartz，sphene and apatite in metamorphogenic zircons. we also recognize some mineral inclusions in the ilmenite,such as plagioclase，zircon，rutile and apatite.In the rutile,we recognize titanite and calcite.This result indicates that these metamorphogenic zircons crystallized with garnets or crystallized a little later.Zircons from the garnet amphibolite are dated by LA-ICP-Ms,and yielded a zircon U /Pb metamorphic age of 496.2±9.1Ma with 13 regions’ data, corresponding Tu/U ration is 0.02~0.11.Three relict cores of zircons yielded a zircon U /Pb age of 729±24Ma, corresponding Tu/Pb ration is 0.70~1.01.Use MC-ICP-MS to measure the Lu-Hf isotopic features of Songshugou garnet amphibolite.21 metamorphogenic zircons yielded Hf(500Ma)= 0.282560~0.282728,and εＨf=3.49~7.14.The Hf model age is815to957, the largest age is corresponded to the age of Songshugou mafic rock(973 ±35Ma)which was researched by Liu et al，2004. These data suggest that the granulite facies peak metamorphic period is ~496Ma，and the age of virgin rock of Songshugou garnet amphibolite should greater than 729Ma.In addition,the information of Hf isotopic data indicate that there existed the growth of new crust or crust-mantle differentiation in Northern Qinling area in the Neoproterozoic.