皖东滁州、上腰铺埃达克质侵入岩年代学及地球化学特征:岩石成因与成矿意义  

Geochronology and geochemistry of Chuzhou and Shangyaopu adakitic intrusive rocks in the eastern area of Anhui province:Implications for petrogenesis and mineralization

作　　者：资锋[1] 王强[1] 戴圣潜[2] 许卫[2] 许继峰[1] 邱华宁[1] 梁细荣[1] 涂湘林[1] 刘颖[1] 

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]安徽省地质调查院,合肥230001

出　　处：《岩石学报》2007年第6期1485-1500,共16页Acta Petrologica Sinica

基　　金：中科院创新项目(KZCX2-YW-128);国家自然科学基金项目(40572042;40421303;40673037)的资助

摘　　要：皖东的滁州、上腰铺岩体位于扬子地块东缘、毗邻郯庐断裂带东侧,与之伴生有一些铜(金或铁)矿化。它们的黑云母的^(40)Ar-^(39)Ar 定年结果分别为127.17±0.40Ma,129.90±0.23 Ma。滁州、上腰铺侵入岩在地球化学特征上与埃达克岩基本一致:如 SiO_2>56%,高 Al_2O_3(14.84%～16.38%)、Sr(369×10^(-6)～1335×10^(-6))、Sr/Y(43～185)与 La/Yb(22～44),但低 Y(5.51×10^(-6)～11.0×10^(-6)),Yb(0.51×10^(-6)～1.09×10^(-6)),无明显 Eu 异常-正的 Eu 异常(δEu=0.75～1.28)。另外,岩体中部分样品具有较高的 MgO(2.23%～5.25%)、Mg~#(53～68)和 Cr(89.6×10^(-6)～206×10^(-6))、Ni(43.0×10^(-6)～72.0×10^(-6)),类似于高镁安山岩。这两个岩体的 Nd-Sr 同位素特征为:(^(87)Sr/^(86)Sr)_i=0.7060～0.7067,ε_(Nd)(t)=-11.53～-14.07,说明其由俯冲洋壳熔融形成的可能性较小。我们认为,滁州、上腰铺埃达克质侵入岩可能由拆沉下地壳熔融形成,熔融产生的岩浆在穿过上覆地幔的过程中,与地幔橄榄岩发生强烈相互作用,一方面,由于地幔橄榄岩的混染而使得埃达克质岩浆的MgO、Cr 和 Ni 含量显著增高;另一方面,岩浆中的 Fe_2O_3可能加入到地幔中,导致地幔的氧逸度(f_(o_2))增高,地幔中金属硫化物被氧化,地幔中亲铜元素则以硫酸盐的形式进入熔体中。富含 Cu、Au 等成矿物质的熔体在快速上升到地壳浅处时,可能由于温度、压力或氧逸度(f(o_2))的降低,释放出 Cu、Au 等成矿物质,导致矿化。The Chuzhou and Shangyaopu plutons are located in the eastern area of the Yangtze Craton and to the east of the Tan-Lu Fault Belt, and associated with Cu （Au or Fe） mineralization. They have ^40 Ar-^39Ar ages （biotite） of 127.17 ±0.40Ma, 129.90 ± 0.23Ma, respectively. The Chuzhou and Shangyaopu intrusive rocks are geochemically similar to adakites, e. g. , SiO2 〉 56% , high Al2 O3 （ 14.84% - 16.38% ） , Sr （369× 10^ -6- 1335 × 10^ -6 ） , Sr/Y （43 - 185 ） and La/Yb （22 - 44） , but low Y （5.51 ×10^ -6 -11.0 × 10^-6） and Yb （0.51 ×10^-6 - 1.09 × 10^-6） , with negligible to positive Eu anomalies （δEu = （0.75 - 1.28）. Moreover, most samples have relatively high MgO （2.23% -5.25% ） , Mg#（53 -68） , Cr（89.6× 10^-6 -206 × 10^-6） and Ni （43.0 ×10^-6 - 72.0 × 10^ -6 ） values, similar to high-Mg andesites. The Chuzhou and Shangyaopu adakitic rocks exhibit high （^87 Sr/^86 Sr） .（0. 706-0 0.7067 ） and low εNd （t） （ - 11.53 - - 14.07 ）, indicating that they were impossibly derived by partial melting of subducting oceanic crust. We suggest that the Chuzhou and Shangyaopu adakitic rocks were most probably generated by partial melting of delaminated lower crust. The interaction between these adakitic magmas and surrounding mantle peridotites possibly took place during the ascent of magmas., on the one side, MgO, Cr and Ni contents of the adakitic magmas were remarkably elevated due to the contamination of mantle peridotites; on the other side, the Fe203 from the adakitic magmas was likely added into the mantle and the oxygen fugacites （fo2） of the mantle were obviously elevated, which made metallic sulfide in the mantle oxidized and the chalcophile elements were incorporated into the adakitic magmas in the form of sulphate. En route to the shallow part of crust, the adakitic magmas enriched in metallogenetic materials possibly released Cu or Au owing to the rapid depressing of temperature, pressure and fugacites（fo2 ）, which led to Cu or A

关 键 词：埃达克岩 拆沉作用 下地壳 铜矿床 滁州 中国东部 

分 类 号：P588.122[天文地球—岩石学] P618.41[天文地球—地质学]