Low-temperature Thermochronology Study On Ore-forming Intrusions In The Jiulianshan Anticlinorium And Its Adjancent Areas,the Middle And Lower Reacher Of The Yangtze River

The preservation and evolution of the ore deposits are an important part of the study of the metallogenic system.After the deposits were formed,it could also be affected by various geological factors to change their initial composition,and thus affect the final occurrence of the deposits.The Middle and Lower reaches of the Yangtze River is one of the important metallogenic belts in the eastern China,and is also a heavily studied area in eastern China.However,there are few studies on precise low-temperature chronology based on the ore-forming intrusions in this area so far.In this work,in order to obtain the history of uplift and denudation of the ore-forming intrusions and regional evolution history,zircon(U-Th)/He(ZHe)and apatite fission track(AFT)dating of 12 late Mesozoic intrusions in the Tongling-Xuancheng area,the Jiulianshan anticlinorium and its adjacent area were dated.Zircon U-Pb dating experiments have been carried out on Yaocun pluton and the veins in it.The zircon U-Pb dating results of the quartz monzodiorite in the Yaocun pluton show that the emplacement time is about 140.2±1.4 Ma,and the emplacement time of the porphyry granite veins is about 125.7±1.3 Ma.ZHe and AFT dating results show that the dating results of the intrusions in the Tongling-Xuancheng area are positively correlated with their emplacement time.According to the difference of emplacement time of the 12 intrusions,the results of ZHe and AFT ages can be divided into two parts: the ZHe and AFT ages of early intrusions are 111.0-153.7 Ma and 89.4-123.1 Ma,and the ages of late intrusions are 71.3-119.9 Ma and 66.9-96.7 Ma.Combining the ZHe and AFT ages,the low-temperature thermal history of these intrusions are simulated.It is revealed that the Tongling-Xuancheng area experienced three rapid cooling stages in the late Mesozoic: the earlier Early Cretaceous(about 140-132 Ma),the middle Early Cretaceous(about 120 Ma)and the end of the Early Cretaceous(about 100 Ma).In the the earlier Early Cretaceous,the Middle and Lower reaches of the Yangtze River experienced a tectonic transformation from pression to extension.The cooling in the middle Early Cretaceous occurred in the regional extensional mechanism characterized by the development of large-scale rifited basins and intrusions.The rapid cooling at the end of the Early Cretaceous is related to the Pacific plate low-angle subduction towards NNW,which resulted in large-scale regional unconformity between the Lower and Upper Cretaceous and basin reversal in eastern China.