Chronology,Geochemistry And Genesis Of Intrusive Rocks In Jiaochong Deposit,Tongling,Anhui Province

Jiaochong deposit is one of the seven largest deposits in Tongling area,Anhui province.The age of magma emplacement and genesis of the intrusions are not clear yet.Therefore,this paper is mainly consisted of five research methods and aimed to solve the previous problems,which are the field and microscopy observation,whole rock geochemical features,LA-ICPMS zircon U-Pb dating,zircon Lu-Hf isotopic analysis and electron probe analysis.According to the field and microscopy observation and geochemical features of the intrusive rocks,it is obvious that the intrusions can be divided into two type of rocks in Jiaochong area,which are high-K calc-alkaline rocks and shoshonitic intrusive rocks.The shoshonitic intrusive rocks is mainly contained of the gabbro monzodiorite,and the high-K calc-alkaline rocks is mainly contained of the quartz monzodiorite and granodiorite.At meanwhile,the Jiaochong intrusion rocks belong to I-type granite with the similar genesis of the arc igneous rock.Beyond the LA-ICPMS zircon U-Pb dating,the age of the gabbro monzodiorite is 136Ma,the age of quartz monzodiorite is 142Ma,and the age of granodiorite is 143Ma.Compared to the other intrusions in Tongling area,the gabbro monzodirite is formed by the latest magma activity of the shoshonitic intrusive magma,and the quartz monzodiorite and granodiorite has the similar age with the other same type intrusions in Tonling area.Considering the results of the electron probe analysis of hornblende and pyroxene and the Zr contents in whole rocks,with different temperature-pressure calculation formulas,the temperature of the high-K calc-alkaline magma is 888?955?,and that of the shoshonitic intrusive magma is 885?1127?.The pressure is in three intervals which are corresponding to three depth zone of magma emplacement,38-25km,2210.5km and 6.5-1.5km.Thus,these depth zone can be regarded as the deep magma chamber,shallow magma chamber and intrusions emplacement,respectively.The research shows that the high-K calc-alkaline rocks have more old inheritance zircon nucleus compared to the shoshonitic intrusions.This indicates the origin of this type rocks have some materials of the old crust.At meanwhile,the intrusions contained large quantities of dark dioritic microgranular enclaves that can reveal the genesis of magma mixing.In contrast,there is no evidence of having inheritance zircon nucleus in the shoshonitic intrusions but contain a large quantities of pyroxene cumulates of xenoliths that shows the origin of enriched mantle,and a strong magmatic fractional crystallization.In conclusion,the origin of the shoshonitic intrusions are formed from the magma derived from enriched mantle with small amount of crustal materials;the origin of the high-K calc-alkaline rocks are produced from the mixing of mantle derived magma and partial melting of the old crusts.