安徽铜陵早白垩世埃达克质岩地球化学:成岩成矿制约  

Geochemistry of Early Cretaceous adakitic rocks in Tongling region of Anhui Province:Constraints for rock-and ore-forming

作　　者：谢建成[1,2] 陈思[1] 孙卫东[2] 杨晓勇[3] 

机构地区：[1]合肥工业大学资源与环境工程学院,合肥230009 [2]中国科学院广州地球化学研究所,广州510640 [3]中国科学技术大学地球和空间科学学院,合肥230026

出　　处：《岩石学报》2012年第10期3181-3196,共16页Acta Petrologica Sinica

基　　金：高等学校博士学科点专项科研新教师类基金(20100111120012);国家自然科学基金项目(40830426);合肥工业大学博士专项基金(GDBJ2008-041)联合资助

摘　　要：安徽铜陵地区是我国最著名的铜金产地之一,成矿与岩浆作用关系密切。近十年来,铜陵及长江中下游地区早白垩世埃达克岩的成因仍然存在分歧。本次我们报道了铜陵地区埃达克质岩新的元素和Sr-Nd-Pb同位素数据。铜陵埃达克质岩(SiO2=57.6%～64.2%)具有高Al2O3(>15.3%)、相对高MgO含量、高Ba(Ba>640×10-6)和Sr含量(>483×10-6,平均900×10-6)、高Sr/Y(>41.3)和(La/Yb)N(>12.1)比值、低Yb和Y含量、低K2O/Na2O(0.54～0.83)和Th/U(2.62～5.75)比值,表明其来源于俯冲洋壳部分熔融,在上升过程中与富集地幔发生相互作用。相对低εNd(t)值(-11.3～-13.7)和较高的(87Sr/86Sr)i比值(0.7068～0.7092)反映本区埃达克质岩可能遭受富集地幔物质或陆壳的混染作用。铜陵埃达克质岩具有高放射性Pb同位素组成((206Pb/204Pb)i=17.93～18.64、(207Pb/204Pb)i=15.46～15.59、(208Pb/204Pb)i=37.88～38.51),主要落在MORB区域,靠近EM1和EM2交集,明显不同于那些上、下陆壳和大别埃达克岩,排除了陆壳的混染作用。中国东部具有EM1和EM2富集地幔特征,而铜陵地区近于EM1和EM2过渡,铜陵埃达克质岩的上述同位素特征最好的解释是板块熔体同化富集地幔。这些埃达克质岩形成于高温和低压环境,与板块俯冲相关。这些明显的地球化学特征表明铜陵和长江中下游地区埃达克质岩和大规模Cu、Au成矿作用是俯冲洋壳部分熔融结果。Tongling region is one of the most important non-ferrous metal producers where the formation of Cu-Au deposits has closely genetic relations with Early Cretaceous adakitic intrusions. However, petrogenesis of adakitic intrusions has been hotly debatec in the past decade. Here we report new elemental and Sr-Nd-Pb isotopic data in Tongling region. The Tongling adakitic rock （SiO2 = 57. 6% ～ 64. 2% ） have high Al2O3 （ 〉 15. 3% ） and relatively high MgO concentrations, high Ba （ 〉 640 x 10-6 ） and Sr concentrations （ 〉 483 ×10-6, average 900 × 10 -6 ）, high Sr/Y （ 〉 41.3 ） and （La/Yb） N （ 〉 12. 1 ） ratios, low Y and Yb contents, low KEO/Na20 （0. 54 ～0. 83） and Th/U ratios （2. 62 ～5.75 ）, indicating that they are genetically related to slab melting ant subsequent interaction with the enriched mantle. The relatively low CNa（t） values （-11. 3 to -13. 7） and high （87Sr/86Sr）i ratios, （0. 7068 to 0. 7092） of the Tongling adakitic rocks may be plausibly explained by contamination of enriched mantle materials and/or continental crust. The Tongling adakitic rocks are characterized by high radiogenic Pb isotopic compositions with （206pb/204pb）; = 17.93 ～ 18.64, （207Pb/204Pb）; = 15.46 ～15.59, and （208pb/204Pb）;= 37.88～38.51, which are mainly plotted in the field oJ MORB, near the intersection of EM1 and EM2, and are obviously different from those of the upper and lower continental crust anc Dabie adakites. These exclude major contamination from the continental crust. Given that eastern China has both EM1 and EM2 types of enriched mantle, whereas the Tongling region is located near the transition from EM1 to EM2, these isotopic characteristics of Tongling adakitic rocks are best explained by slab melts with assimilation of enriched mantle components. The Tongling adakitic rocks have a high temperature, low pressure regime, possibly resulted from slab subduction. These distinctly geochemistry characteristics indicate the adakitic rocks and th

关 键 词：埃达克质岩 洋壳部分熔融 铜金成矿 早白垩世 铜陵地区 

分 类 号：P588.122[天文地球—岩石学]