Fission Track Thermochronology Of The Yangshan Gold Belt,Western Qinling Orogen,Central China

The study of the tectonic evolution of the orogenic belt is a global hotspot,and low-temperature thermochronology is an effective way to understand the evolution of ore deposits in the orogenic belt.The Yangshan gold belt is located within the archaic tectonic belt of the Wenxian in the West Qinling's Mian-Lue suture zone and is the largest independent gold deposit in the Qinling orogenic belt.It is an ideal constituency for the study of geochronology in the mineral deposits.Based on the previous research,this paper carried out research on zircon and apatite fission track for the thermochronology of the Yangshan gold ore belt and obtained the following results:The zircon fission track age distribution range is 287.0±21 Ma?1??¹00.5±3.4Ma?1??,and some age values are larger than the metallogenic age of the Yangshan gold ore belt.Different lithologies and age values have their own characteristics:?1?Sandstone and Slate zircon fission track age values span the largest,ranging from 287Ma to 107 Ma;?2?The phyllite zircon fission track values range from 184 Ma to 100Ma,and the minimum median age of zircon fission tracks is 100.5±3.4 Ma.;?3?Plagiogranite porphyry,zircon fission track age range,193 Ma¹85 Ma.The apatite fission track age?69±7 Ma?1??⁴6±14 Ma?1???and fission track length and its distribution characteristics show that the Yangshan gold ore zone was monotonous between Late Cretaceous and Paleocene.And the cooling temperature of the apatite fission track was slowly cooled.The thermal history evolution process of gold ore belts can be divided into five stages based on the thermal history simulation comprehensive constraints of the sericite/muskite ⁴⁰Ar-³⁹Ar age,zircon fission track age,and apatite fission track thermal history closely related to gold mineralization.?1?210 Ma to 195 Ma,in the interval of 295°C to 260°C,the stratum was rapidly cooled.?2?195 Ma to 125 Ma,in the interval of 260°C to 220°C,the stratum was slowly cooled.?3?125 Ma to 90Ma,in the interval of 220°C to 90°C,the stratum was rapidly cooled.?4?90 Ma to9.6 Ma.In the interval of 90°C to 65°C,the stratum was slowly cooled.?5?From 9.6Ma to today,the stratum is rapidly cooled again in the interval of 65°C to 20°C.The slow cooling of the strata indicates that the regional stratum is in a relatively stable tectonic environment,and the strata are rapidly cooled,indicating that the strata in the study area undergoes strong uplift and erosion,and the tectonic environment has changed.Based on the study of the thermal history of the Yangshan gold deposit,the cause of the differences in the thermal history of the post-mineralization of the Nishan ore section and the Getiaowan ore section may be the Nishan section which is closer to the side of the Wenxian arc-shaped tectonic center was lifted and denuded first,while the Getiaowan and Anba sections that were slightly farther away were subsequently uplifted and eroded.Based on the thermal history analysis of the apatite fission track lengths and ages's inversion,combined with the ancient geothermal gradient and the ore body metallogenic depth in the study area,the Yangshan gold ore belt has been obtained from the Cretaceous to the present,and the total eroded amount in the study area has been calculated about 12.24km,the upper limit of ore body erosion is about 880m.