| The petrogenesis of granites and related crustal evolution history are always a hot topic among the geologist.As the main component of the upper continental crust,granites bear key information about crustal growth and reworking processes.Based on reading the detailed field geological survey and related documents,in this paper,Donggu granite body in Jiangxi Province is selected as the research object.The earliest chronological studies of Donggu granite bodies were carried out in the previous 1: 5 million permanent trenches in 1988,the K-Ar dating method used at that time showed that the three rock units of the Donggu rock mass were formed 146±3Ma,125 Ma,172.2Ma.For the cause of the Donggu rock mass,the magma source area and the detailed geochemical characteristics of the rock mass are not mentioned.In this paper,U-Pb chronological studies of zircon and detailed geochemical work are carried out in view of the above problems,to accurately determine the formation of rock age,genesis and tectonic background.In this study,the LA-ICP-MS chronology and the LA-MC-ICPMS zircon Hf isotope study of the granite samples in the Donggu area,get a lot of accurate chronology and isotope data,the results show that the age of different rock mass units in Donggu area is 152±2Ma,belong to Yanshan period,rather than the predecessor of the report mentioned in the different rock mass units formed in different times.In this study,seven representative samples of the Donggu granite body were studied by geochemistry,Donggu solid rock at higher SiO2,and lower MnO?MgO?TiO2?P2O5 is characterized,in the Tas intrusive rock diagram are falling into the typical granite range.Donggu rock mass has the characteristics of light rare earth enrichment,the ?Eu is between 0.18 and 0.33,specific obvious negative Eu anomalies.La / Yb larger value range,is between 3 and 32.It is shown that the evolution of magma in the diagenesis of Donggu rock mass leads to the decrease of light rare earth.Inheritance Zircon is the most direct geological evidence magma source materials,a total of six Inheritance zircons were found in the Donggu rock mass,its formation age were 428±4Ma,820±10Ma,196±6Ma,612±14Ma,737±7Ma and 222±4Ma,indicating that the components of these times were involved in the formation of granite,regardless of whether these zircons are in the source area or in the process of magma intrusion,it is also shown that the composition of the Donggu rock mass is not a single component.Indicating that it may be partially fused in the Paleoproterozoic metamorphic base.This work shows that Donggu rock formation is around 152 Ma,belong to Yanshan period.Yanshan tectonic movement is mainly based on fault block activity,formed a series of north-east,north-west fracture.At the same time,accompanied by large-scale magmatic activity,the magma intrudes mainly along the north-east fracture and the turning end of the base twist,Formed Donggu granite body.Therefore,in this paper,the Donggu rock mass is formed under the tectonic background,closely related to the ancient subduction of the Pacific Plate. |
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