安徽池州的铜山岩体是长江中下游地区沿江岩浆岩主带中的含矿岩体之一，其形成年龄及岩石成因尚存在争议。该岩体主要由石英闪长玢岩、石英二长斑岩和花岗闪长岩组成，与铜金矿化关系密切。对铜山矽卡岩型铜（金）矿床的花岗闪长岩开展了锆石 U-Pb定年和 Hf同位素地球化学研究。岩石地球化学及同位素年代学研究结果表明：花岗闪长岩侵入年龄为（146．3±3．2）Ma，形成于早白垩世；锆石εHf（t）值平均为-5．23，说明铜山侵入岩具有壳幔混合的岩浆岩源区性质；锆石的二阶段 Hf模式年龄分布在1184．51～1422．72 Ma之间，说明岩浆源区与皖南地区出露的中元古代基底有密切关系。构造判别图解显示，铜山岩体属火山弧花岗岩，与长江中下游铜金矿床含矿岩体形成于同一构造背景下，据此推测铜山地区大地构造背景形成于与古太平洋板块俯冲密切相关的大陆边缘岩浆弧环境。%Tongshan intrusion in Chizhou of Anhui is one of the ore-bearing intrusions in the main magmatic belt along the middle-lower Yangtze River,and the formation age and rock genesis are still controversial. The intrusion is mainly composed of quartz diorite, quartz monzonitic porphyry and granodiorite,and has close relationship with the Cu-Au mineralization.Zircon U-Pb geochronology and Hf isotopic geochemistry of granodiorite in Tongshan skarn Cu (Au) deposit were studied.Results of petrogeochemistry and isotope chronology show that the age of granodiorite intrusion,which forms in Early Cretaceous,is (146.3 ± 3.2)Ma;the average of zirconεHf (t)is -5.23,illustrating that Tongshan intrusion has the characteristics of magmatite provenance with crust mantle mixing;distributions of two-phase Hf model ages of zircon are 1 184.51-1 422.72 Ma,indicating that magma source has significant relationship with the outcropped Mesoproterozoic basement in southern Anhui.The discrimination diagrams show that Tongshan intrusions belong to the island-arc granite (VAG),and the tectonic background of the intrusions is same as the ore-bearing rocks of Cu-Au deposits along the middle-lower Yangtze River,so that it is inferred that the geotectonic backgrounds form in continental margin magmatic arc related to Paleo-Pacific Plate subduction.
展开▼
