Age and Provenance of the Metasedimentary Rocks of Hengxianhe Area in Mianlue Tectonic Belt of Southern Qinling: Evidence from Detrital Zircons LA-ICP-MS U-Pb Dating

The Zhujiashan Formation and Qiaozigou Slice are located in the north of Hengxianhe of Mianxian-Lueyang Tectonic Belt in the south of Qinling,which are the sedimentary rocks with intense ductile deformation in the Mianlue Tectonic belt. As the basement rock series of the Mianlue Tectonic belt,it is of great significance to research the yielded ages and sediment provenances for understanding the yielded ages and tectonic evolution of the Mianlue Tectonic belt. In this paper,the metamorphic sedimentary rocks (sericite phyllite) are studied by LA-ICP-MS detrial zircon U-Pb chronology in Zhujiashan Formation and Qiaozigou Slice in the north of Hengxianhe area to explore their yielded ages and sediment provenances. The obtained detrital zircon age can be divided into three groups:the Paleozoic age group, the Neoproterozoic age group and the Late Mesoproterozoic age group. the Paleozoic age group(375 to 542 Ma) can be divided into the early Late Paleozoic-late Early Paleozoic age group (from 375 to 424 Ma) and the Early Paleozoic Age group (from 530 to 542 Ma), with the prominent peaks age being 390 Ma and 394 Ma. the Neoproterozoic age group (from 552 to 977 Ma), with the prominent peaks age being 758 Ma and 787 Ma, can be divided into late Neoproterozoic age groups(from 552 to 797 Ma)and the Early-Middle Neoproterozoic age group (from 800 to 977 Ma) with the prominent peaks age being 855 Ma and 951 Ma. The Late Mesoproterozoic age is from 1008 to 1124 Ma. the minimum age group of detrital zircons of Zhujiashan Formation and Qiaozigou Slice is from 375 to 385 Ma (average age 380.3 Ma) and from 377 to 389 Ma (average age 383 Ma),indicating that the sedimentary age is not earlier than the Middle-Late Devonian. Comprehensive study shows that the provenances of the two samples are mainly derived from magmatic rock in Bikou block of Mianlue Tectonic Zone and the northern margin of Yangtze plate. The sedimentary environment is rift basin, and from extensional rifting to stable platform-platform deposition.