徐州利国早白垩世高镁埃达克质侵入岩的成因及其动力学、成矿意义  

Liguo early Cretaceous high-Mg adakitic intrusive rocks in the Xuzhou region: petrogenesis and implications for geodynamics and mineralization.

作　　者：资锋[1] 何光玉[2] 戴圣潜[3] 许卫[3] 

机构地区：[1]中国科学院广州地球化学研究所同位素年代学与地球化学重点实验室 [2]浙江大学地球科学系,杭州310027 [3]安徽省地质调查院,合肥230001

出　　处：《岩石学报》2007年第11期2857-2868,共12页Acta Petrologica Sinica

基　　金：中科院创新项目(KZCX2-YW-128);国家"十五"科技攻关项目(2004BA616A-06-01)的资助。

摘　　要：位于华北克拉通东南缘、郯庐断裂带西侧的利国岩体形成于白垩纪,由闪长玢岩及少量花岗闪长斑岩组成,与之伴生有一些铜-铁矿化。利国岩体的元素地球化学特征与埃迭克岩的地球化学特征非常类似:如,SiO_2>56%,较高Al_2O_3 (13.69%～15.15%)、Sr(452×10^(-6)～617×10^(-6))、Sr/Y(30～93)与La/Yb(8～24),但低Y(4.84×10^(-6)～15.55×10^(-6)),Yb(0.48×10^(-6)～1.45×10^(-6)),无明显的Eu异常(δEu=0.87～0.98)。另外,根据其Mg^(4/5)、FeO^T/MgO值,又可以分为高镁、较高镁和低镁三类岩石。高镁的岩石类似于赞岐岩。利国埃达克质岩的(^(87)Sr/^(86)Sr)_i=0.7055～0.7071,ε_(Nd)(t)=-11.46～-4.64,不同于俯冲洋壳熔融形成的埃达克岩。我们认为,利国较高镁和低镁埃达克质岩的形成可能与拆沉榴辉质下地壳熔融产生的熔体受到地幔橄榄岩不同程度的混染有关,但是高镁埃达克质岩可能由被拆沉下地壳熔融产生的熔体交代的地幔橄榄岩熔融形成。利国岩体可能是中国东部中生代岩石圈减薄的产物,并可能与郯庐断裂带的活动有关。拆沉榴辉质下地壳熔融产生的熔体与地幔橄榄岩的强烈相互作用可能导致地幔中金属硫化物的分解,并最终导致区内铜矿化。The Liguo Cretaceous pluton,which is located in the southeastern margin of the North China Craton and to the west of the Tan-Lu fault belt, consists of dioritic porphyrise and minor granodioritic porphyries, and is associated with Cu-Fe mineralization. The Liguo intrusive rocks are geochemically similar to adakites, e. g., SiO(2) > 56%, relatively high Al(2)O(3)( 13. 69% - 15. 15%), Sr(452 -618 mu g/g), Sr/Y(30 - 93) and La/Yb(8 - 24) values, but low Y(4. 84 - 15. 55 mu g/g) and Yb(0.48 - 1.45 mu g/g) contents, and without obvious Eu anomalies (delta Eu = 0.87 - 0.98). In addition, the Liguo intrusive rocks may be classified as high-Mg, slightly high-Mg and low-Mg adakitic rocks according to Mg(4/5) and FeO(T)/MgO values. The high-Mg rocks are similar to sanukites. The Liguo adakitic rocks exhibit high ((87) Sr/(86) Sr)(i) (0.7055 - 0.7071) and low epsilon(Nd) (t) ( - 11.46 - - 4. 64) values, which are different from those of subducted oceanic crust-derived adakites. We suggest that the slightly high-Mg and low-Mg adakitic rocks likely originated from delaminated lower crust-derived adakitic magmas contaminated at different percentage by mantle peridotites. However, the high-Mg adakitic rocks were most probably derived by partial melting of mantle peridotites metasomatized by the adakitic magmas generated by partial melting of delaminated lower crust. The lithosphere thinning in eastern China and the activities of the Tan-Lu fault belt during Mesozoic possibly played an important role in the petrogenesis of the Liguo adakitic rocks. The intense interaction between mantle peridotite and the adakitic magmas derived from delaminated lower crust possibly caused the decomposition of sulfide in the mantle, and the Cu mineralization ultimately.

关 键 词：高镁埃达克质岩 拆沉作用 交代地幔 铜矿化 利国 华北 

分 类 号：P588[天文地球—岩石学] P618[天文地球—地质学]