Zircon U-Pb Age And Nd Isotopic Composition Of The Susong Group In The Dabie Orogenic Belt:Evidence For Provenance And Crustal Evolution

The Susong Group is located in the northern margin of the Yangtze block and the southern part of the Dabie orogenic belt. It is close to the South Dabie low-temperature ultra-high pressure eclogites zone, separated by the Taihu-Mamiao fault. The Susong Group formed in Neoproterozoic era approximately at750Ma, it is caused by the intracontinental rift happened in the Yangtze block which is initated by the decomposition of Rodinia supercontinental at825-740Ma and it is also the formation of back-arc basin with the sedimentation meanwhile. There are various types of rocks in the Susong Group and can be divided into metamorphosed sedimentary rocks and meta-igneous rocks. The samples of this study are schist, metagranite, gneiss and metabasite. The LA-ICPMS U-Pb dating of detrital zircon yields ages of2836Ma to1532Ma and the weighted mean age of2500Ma for schist JH-13-02and2424Ma to1069Ma and weighted mean age of2000Ma for schist JH-13-03. The metagranite sample JH-13-05gives a weighted mean age of754±15Ma and the gneiss sample JH-13-06yields767±18Ma for. Clear magmatic oscillation appears in CL images for the majority of zircons and Th/U ratios of all detrital zircons are larger than0.1, they are typical characteristics for magmatic zircons. Zircons of all the samples have similar chondrite-normalized REE patterns, showing significant enrichment of heavy REE relative to light REE and the negative Eu anomalies but positive Ce anomalies. The schists show enrichment in contents of K, Na, Al2O3. Contents of SiO2are57.2-77.1wt.%for the schists and45.6-50.8wt.%for metabasites. All the samples have similar chondrite-normalized REE patterns, showing significant enrichment of LREE relative to heavy REE, but the schists have significant negative Eu anomaly. All the samples show similar patterns of trace elements with enrichments in large iron lithophile elements, such as Ba, Rh, Th, and depletion of high field-strength elements. Initial ENd values vary from-12.0to-2.8and for schists and gneisses, corresponding to TDM values of1.6-3.1Ga, while the metabasites have initial εNd values of-9.3to1.9, corresponding to TDM values of1.6-2.1Ga. When compared with gneisses of the Haizhou Group in the Sulu belt, which have relatively homogeneous initialεNd values of-8.8to-2.8, corresponding to TDM values of2.1-2.4Ga, The Susong Group has more complex crustal material or multiple sedimentary sources.