| Yamansunan（YN）Indosinian granite pluton consists of YN numberⅠnumber of pluton and YN numberⅡof pluton.Zircon LA-MC-ICP-MS U-Pb dating results show that the crystallization age ofⅠandⅡare 243±6Ma and 217±12M a.Geochemically,YB numberⅠof pluton is characterized by high silicon（SiO2=75.83%75.83%）and alkali（Na2O+K2O=8.54%8.61%）,low titanium,calcium and magnesium,which attributes to peraluminous granite rock（A/CNK=1.031.05）and high K calc-alkaline granite;The pluton is also rich in Rb,K,Th,U,Zr,Ta and Hf,and depleted Sr,Ba,Eu,P,Ti and Nb;ΣREE is relatively low,and LREE and HREE fractions are not obvious,the Eu（δEu=0.080.10）is strongly negative anomalies.YB numberⅡof pluton is characterized by high silicon（SiO2=75.58%75.58%）and alkali（Na2O+K2O=8.36%8.68%）,low titanium,calcium and magnesium,which attributes to peraluminous granite rock（A/C NK=0.040.05）and high K calc-alkaline granite;The pluton is also rich in Rb,K,Th,U,Zr,Ta and Hf,and depleted Sr,Ba,Eu,P,Ti and Nb;ΣREE is relatively low,and LREE and HREE fractions are not obvious,the Eu（δEu=0.160.25）is strongly negative anomalies.TheⅡpluton of value is lower than theⅠpluton inΣHREE.The geochemistry characteristics of the two rocks are similar,and they show the characteristics of the Highly fractionated I-type granite.Zircon in-situ Hf isotopic composition analysis yields theεHf（t）and tDM2values of the YB numberⅠpluton varying-1.3+5.9 and 8911351Ma,and the εHf（t）and tDM2values of the YN numberⅡpluton varying+2.1+6.5 and 8351113Ma.Based on geochemical and Hf isotopic characteristics and the regional tectonic evolution,the study indicates that the YN pluton resulted from mantle magma underpalting induced partial melting of the Meso-neoproterozoic new-born crust.and it subjected to high degree of fractionation.Combining previous research this paper suggests the geodynamic background of the rock mass of YN may be a continuation of the post-collision phase of hercynian. |
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