Study On Apatite And Zircon Fission-track Of Early Cretaceous Granite Of Sanfoshan In Jiaodong

The Sanfoshan granite at the eastern Jiaodong Peninsula is the research target of this paper,through collect and analyze the existing data of the granite and gold ore,focus on apatite fission track to discuss the thermal evolution history of Sanfoshan granite, combining zircon fission track to calculate the rock uplift and erosion rate quantitatively. Through the comparative study of gold ore-forming depth and denudation quantity to analyze the alteration and preservation conditions after gold deposit formed in the region, which could supply theoretical evidence for potential capacity evaluation and deep mineral prospecting of regional ore deposit.The samples were collected from Early Cretaceous graniteat the eastern Jiaodong Peninsula, conducting fission track analysis and date on 10 apatite and 11 zircon samples.According to the test results obtained zircon fission track ages range is 86~118Ma, single particle zircon ages were divided into 115~100Ma、100~75Ma and 54~70Ma,which represent Early Cretaceous to Paleocene ‘s three tructure thermal events in Sanfoshan rock, the peak age of about 96 Ma might represent Sanfoshan rock ‘s once complete uplift-cooling event in late Early Cretaceous.Apatite fission track ages range is 16~68Ma,and far less than the age of rock and zircon fission track ages, single particle age appeared unimodal distribution,the peak age is 33 Ma which represent Sanfoshan ‘s another uplift-cooling event in Early Tertiary. The average length of the apatite tracks is 12.4~13.2um, suffered serious annealing, most of the standard error of the samples were more than 2um, appeared wide unimodal distribution,which proof Sanfoshan rock was cooling monotonically,and did not experience the complex thermal history. Thermal evolution of time-temperature curve show that rock experiencing fast-slow-fast cooling process. Using the agetemperature method and zircon、apatite "minerals" method, selecting 250℃ and 120℃ as zircon and apatite fission-track closure temperature, taking Sanfoshan average surface temperature of 15℃, Cretaceous ‘s ancient geothermal gradient of 44℃∕km and Cenozoic ‘s geothermal gradient of 35℃/ Km, calculated result: Early Cretaceous to Paleocene,the cooling rate of the rock was 2.6~5.0℃/Ma,uplifting rate was 59 ~ 110m/Ma,uplifting size was 2900~2970m;since the Paleocene, the cooling rate of the rock was 1.35~6.7℃/Ma, uplifting rate was 30~200m/Ma,uplifting size was about 3000 m.So,the uplifting size of the Sanfoshan rock was about 6000 m,which proof Sanfoshan rock suffered intensive uplift and erosion since late Early Cretaceous,and the amount of uplift was decreasing from the southwest to the northeast.