The geochemical characteristics of Mesozoic intermediate-acid intrusives of the Tongling area and its metallogenesis-geodynamic implications
2004; Science Press; Linguagem: Inglês
ISSN
2095-8927
Autores Tópico(s)Geochemistry and Geologic Mapping
ResumoMesozoic intermediate-acid intrusive rocks from Tongling area have the characteristics of adakites in geochemistry, they show SiO2≥56% , high A12O, content ( 15%) , Na2O/K2O1, HREE depletion, (La/Yb)N12, 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.
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