西藏泽当地区晚白垩世埃达克岩的发现及其成矿意义

DISCOVERY AND METALLOGENIC SIGNIFICANCE OF THE LATE CRETACOUS ADAKITES FROM ZETANG,TIBET

埃达克岩对造山带深部构造和热体制具有指示意义,与Cu、Au等成矿关系密切。冈底斯成矿带东段南缘泽当地区桑布加拉矽卡岩型铜矿成矿母岩花岗闪长岩的主量元素测量结果显示高SiO2(>56%)、高Al2O3(>15%)、低MgO(<3%),Na2O含量≥3.5%,K2O含量>2%,Na2O/K2O为1.03～1.43,平均1.22;稀土元素和微量元素测量结果显示高Sr(>400×10-6),低Yb(<1.9×10-6)、低Y(<15×10-6),高Sr/Y(86.88～132.22,>20)、高La/Yb(>10),LREE富集,HREE亏损,无负Eu异常,为埃达克岩地球化学特征。结合地质特征分析认为其是由俯冲洋壳板片部分熔融后与地幔橄榄岩发生相互作用形成的O型埃达克岩,说明冈底斯南缘存在O型埃达克岩成矿。

Adakites have an indicative significance to deep-seated structures of orogenic belt and thermal regime, and a closely relationship with the minralization of Cu and Au. The metallogenic mother rock of Sangbujiala skarn copper deposit, in Zetang, southern belt is Late Cretaceous granodiorite. The major elements are AlE03 （〉15%）, Na20 （≥3.5%） and K20 （〉2%）, low 1.43, with an average of 1.22. The analyzing results of race margin of the East Gangdise metallogenic characterized by higher SiO2 （ 〉 56% ）, er MgO （〈3%）. Na2O/K2O is 1.03 - earth and trace elements show higher Sr （〉400×10^-6）, lower Yb （ 〈1. 9 ×10^-6） and Y （ 〈15 ×10^-6）, higher Sr/Y （86.88-132.22, 〉 20） and La/Yb （ 〉 10）, enriched in LREE and depleted in HREE, and no negative anomalies of Eu, similar to those of adakite. By geochemical and geological characteristics, it was may be formed in partial melting of subduction oceanic plate of the O-type adakites, which interacted with mantle peridotite, showing that the southern margin of Gangdise has O-type adakites mineralization.