Uplift Time Of The Jingtingshan-liqiao Anticlinorium In The Lower Yangtze Region

The Jingtingshan-Liqiao anticlinorium belongs to the southern section of the Mount.Maoshan-Jiulianshan and is the southern extension of the Maoshan nappe.The Maoshan nappe is mainly characterized by the Paleozoic strata overlying the Cretaceous strata,so its age is often limited since the Cretaceous.Late Mesozoic thrusting developed obviously in the Jingtingshan-Liqiao anticlinorium,but the research on its uplift history is relatively less.Now,the uplift time and mechanism of the Jingtingshan-Liqiao anticlinorium are ambiguous.Based on detailed field investigation,conglomerate deposits were observed at the bottom of the Upper Cretaceous on both sides of Jingtingshan-Liqiao anticlinorium and in the Muzhen area,southwest margin of the Nanling Basin.The gravel is mainly limestone,with poor sorting and roundness,indicating a close deposition.In order to obtain more detailed provenance information of sedimentary strata,14 samples were collected from the Upper Cretaceous Chishan Formation,the Paleogene Shuangtasi Formation,the Silurian Maoshan Formation,and detrital zircon LA-ICP MS U-Pb dating was carried out.The dating results show that the age peaks of Maoshan Formation are 438 Ma,783 Ma and 964 Ma,and the zircon age composition of Chishan Formation is simple,most of which are between 139 and 128 Ma.The age characteristics of the Paleogene Shuangtasi Formation are complex,with major clusters of Early Cretaceous,Early Paleozoic and Neoproterozoic.It is obvious that the sediments of Silurian strata have been added,and the provenance composition has changed.The age cluster of Cretaceous strata in the Muzhen area is obviously complex,similar to that of Paleogene,and is speculated that the Silurian and Devonian strata were exposed in Muzhen in Cretaceous.According to the detrital zircon results,it is speculated that the Jingtingshan-Liqiao anticlinorium was still mostly exposed the Carboniferous-Triassic limestone before the Late Cretaceous.Volumes of limestone was eroded in the intense uplift event and then transported to form the conglomerates at the bottom of Upper Cretaceous Chishan Formation.In the Late Cretaceous,the uplift weakened and the Silurian strata began to emerge in Jingtingshan-Liqiao anticlinorium area.