Sedimentary Age And Provenance Analysis For The Clastic Rocks In Tangjiawu Formation,south Anhui:Constraints From Detrital Zircon Ages And Geochemistry Charateristics

Provenance and sedimentary age of Tangjiawu Formation from the South Anhui are still debated.The study focused on its petrography,geochemical features and detrital zircon ages of the sandstones.The Formation mainly consists of kelly,gray purple mudstone,siltstone and lithic quartz sandstones.The sandstones with medium round and high sorting essentially composed of metamorphic detritus and quartz with wave extinction.They exhibited relatively high compositional maturity.Their provenances were dominated by felsic materials that had undergone intensive chemical weathering or sedimentary recycling.Besides,the sedimentary structures such as bedding,ripple mark and fossil are completely preserved,which indicates littoral neritic facies—tidal-flat—lagoon facies.LA-ICP-MS zircon U-Pb dating yields a youngest age of 424 Ma,which represents the lower limit of deposition age of the Formation.In addition to the zircon ages,the Tangjiawu Formation is uncomfortably overlain by the Devonian Guanshan Formation,suggesting that it should be deposited in Late Silurian that approached to the termination timing of the Early Palaeozoic orogenic event.U-Pb dating informations of Seventy-nine detrital zircons with discordance <10% from the Tangjiawu Formation display a broadly age spectrum from 2912 to 424 Ma.Most of the detrital zircons have U-Pb age grouped between 731 and 1031 Ma,with two clusters peaking at 981 and 756 Ma.A few populations with peak ages of 2476,517 and 453 Ma are present as well.This suggested that the provenances of the Tangjiawu Formation were mainly derived from the early-to middle-Neoproterozoic igneous rocks,Late Neoproterozoic rift sequences and Sinian to Ordovician sedimentary rocks with subordinate syn-orogenic magmatic or sedimentary rocks.Partial quartzs in Tangjiawu Formation with secondary increase edge,and clastic components had been put in Q-F-L ternary diagram,which indicate recycling characteristic.What's more the main rock types by major elements are lithic quartz sandstones,this rocks is a typical product of recycling orogeny.Combine with detrital zircons infer The Early Palaeozoic intra-continental orogeny caused the uplifting of the sequences in the pre-middle-Ordovician basins,which mostly contributed to sources of the sediments in the intra-continental foreland basin.The deposition and evolution of the foreland basin in the South China were controlled by the Early Palaeozoic orogeny,reflecting the coupled material recycling between the orogen and the foreland basin.