Geochemical Characteristics,Chronology and Geological Significance of Hercynian Granitic Pegmatites in the Altai Orogenic Belt,Xinjiang
Altai is the most important pegmatite distribution area in my country and the world.As an independent de-posit type,pegmatite is of great significance in the study of mineral deposits.In this study,the Burjin donggelei pegma-tite and Qinghebei pegmatite in the western part of the Altai orogenic belt were selected as the research objects,and the LA-ICP-MS zircon U-Pb age was obtained as(343.7±1.7)Ma,which is the Early Carboniferous Pegmatites are the prod-ucts of the Hercynian movement.Geochemical characteristics show that pegmatites are characterized by rich silicon,per-aluminum,medium alkali and medium calcium.It has the characteristics of transition from low-potassium series to high-potassium calcium-alkaline series.The trace elements have relatively negative anomalies of Ba,Ta,Nb,Sr,Zr,and Ti,and relatively positive anomalies of Rb,K,Nb,P,Hf,and Y,which are close to the original mantle.The distribution curve is in the form of a"seagull"distribution,showing the characteristics of a"quadruple effect".The content of rare earth is low,the fractionation of light and heavy rare earth is medium,the fractionation of light rare earth is obvious,and the fractionation of heavy rare earth is not obvious.The distribution pattern is right-leaning.Showing a"V"shaped val-ley.Its genetic type is differential metamorphic pegmatite,which is NYF type.Formed in the subduction and accretion stage,it is in an extrusion environment,and the tectonic activity is strong,which is not conducive to the stabilization of the melt-fluid with strong fluidity,and it is not easy to form rare metal pegmatite deposits.
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