【摘要】 本文对铜陵地区晚侏罗世-早白垩世高钾钙碱性中酸性侵入岩进行了研究,发现该类岩体具有埃达克岩的地球化学特征,具体表现为:SiO2≥56％,Al2O3含量高(>15％),Na2O/K2O>1,亏损HREE,(La/Yb)N>12,负Eu异常不明显(Eu*/Eu=0.71-0.96),Sr含量高(>750μg/g),Sr/Y比值高(>38)。但是,由于岩石的K2O含量较高、εNd(t)较低和ISr值较高,又不同于典型的与板块俯冲有关的埃达克岩,而与中国东部中生代的C型埃达克岩比较类似,暗示铜陵地区的高钾钙碱性岩可能是加厚的下地壳底部基性岩部分熔融的产物。本文主要依据铜陵埃达克质岩的HREE特征,将其分为三类:第一类岩体为HREE平坦型,Yb含量较高(>1.8μg/g);第二类为HREE平坦型,Yb<1.8μg/g,(Ho/Yb)N≈1;第三类岩体HREE亏损,Yb<1.8μg/g,(Ho/Yb)N<1.2。上述三类岩石地球化学性质上的差异不太可能是分离结晶作用或地壳混染的 结果,而可能是由于幔源岩浆与下地壳物质混合的程度不同引起源区成分不同形成的。铜陵地区及中国东部埃达克质岩石可能代表了中国东部中生代时的地壳增生和加厚过程。铜陵埃达克岩主要是古老下地壳和底侵玄武岩不同比例混合部分熔融形成的,在岩浆演化过程中可能还不同程度地叠加了分离结晶作用和岩浆混合作用的影响。铜陵埃达克岩具岛弧特征,但并不表明其更多还原

【Abstract】 Mesozoic intermediate-acid intrusive rocks from Tongling area have the characteristics of adakites in geochemistry, they show SiO2≥56% , high A12O, content (> 15%) , Na2O/K2O>1, HREE depletion, (La/Yb)N>12, slightly negative Eu anomaly (Eu*/Eu= 0.71 (0.96) , high Sr concentration ( >750μg/g) and high Sr/Y ratios ( >38). The rocks are divided arbitrarily into three types according to their HREE patterns: (1) flat HREE pattern, with high Yb content ( > 1. 8μg/g) ; (2) flat HREE pattern, with Yb < 1. 8μg/g and (Ho/Yb)N≈1; (3) depleted HREE pattern, with Yb < 1. 8μg/g and ( Ho/Yb) N≈1.2. The high K2O content and the similarity to the composition of the lower crust of Yangtze basement in isotopic composition of the rocks exclude the possibility of direct derivation from slab partial melting, but suggest that the rocks are the products of partial melting of underplating basaltic rocks in the lower crust. The differences among the three types are not resulted from fractional crystallization or continental contamination. Differences in the source composition due to variable percentage of the mantle and the lower crust components are probably the main reasons for the differences of the three types. It is assumed that the adakitic rocks in Tongling and other areas in east China are related to crust accretion and thickening of east China in Mesozoic. The further discussion for the assumption will be helpful to understand the geodynamic process and evolution of east China in Mesozoic.更多还原