北淮阳变质单元岩石学、年代学分析及对大别造山带构造缝合线位置的探究

直至现今，大别造山带构造缝合线确切位置一直不是十分明朗，争议颇多。为此，本研究以该造山带最北缘防虎山-舒城地区为研究靶区，对该地区出露的片岩、片麻岩进行了细致的变质岩石学和年代学分析。研究显示，防虎山地区出露的为含石墨片岩，其变质级别为绿片岩相：T=300 ℃～450 ℃和P=0.2～0.7 GPa，并具有4组碎屑锆石U-Pb年龄：2 465～1 522 Ma（5颗），1 140～938 Ma（14颗），804～646 Ma（4颗），460～422 Ma（14颗）。舒城地区的2个花岗片麻岩的锆石U-Pb年龄显示，它们的原岩年龄为767.9±7.8 Ma和770±16 Ma，其变质PT条件则为600 ℃～700 ℃和0.2～0.8 GPa。因此，可以确定这两类岩石应属于北淮阳变质单元中佛子岭群和卢镇关群物质，具明显的亲扬子性。结合前人断裂构造分析和相关的年龄资料，可以判定扬子板块和华北板块的构造缝合线位置应位于肥中断裂附近。

Analysis of petrology,geochronology for Beihuaiyang metamorphic unit,and discussion about the suture of Dabie Orogen

Up to now,the concreted location of the suture of Dabie Orogen is still ambiguous and more controversial. In this study,the bearing-graphite quartz schists and granitic gneisses have been inspected carefully across Fang Hushan(FHS)-Shu Cheng(SC) area in the most-north of Dabie Orogen. According to the analysis from petrology and geochronology,the P-T conditions for the schists in the FHS are T=300 ℃～450 ℃ and P=0.2～0.7 GPa,and in the range of green-schist facies,while four groups of detrital zircons U-Pb ages for these schists have been distinguished: 1)2 465～1 522 Ma(5 grains); 2)1 140～938 Ma(14 grains); 3)804～646 Ma(4 grains); 4)460～422 Ma(14 grains). Other,zircon U-Pb ages from two granitic gneisses in the SC are 767.9±7.8 Ma and 770±16 Ma,respectively,and these gneisses have been formed in the range of 600 ℃～700 ℃ and 0.2～0.8 GPa. Hence,these two types of rocks should be attributed into Foziling Group and Lu Zhenguan Group in Beihuaiyang metamorphic unit,respectively,and belong to Yangzi Craton. Combined with the previous analysis of faulted structure and the related ages investigation,the suture of Dabie Orogen between Yangzi and Huabei Cratons can be defined at Feizhong fault.