Abstract:

The Indosinian granitoid belt in South Qinling, Central China, is lithologically composed of diorite, monzodiorite, tonalite, granodiorite and granite, as well as widely distributed mafic microgranular enclaves and dykes within the intrusions. Majority (>50％) of samples have high Mg＃(<076), high Cr(>100×10-6,max=1 600×10-6), high Sr(>500×10-6) and high Ba(>1 000×10-6) content, i. e. having the “mantle signature”. The partial melting of garnet bearing metabasic rocks can explain high LREE, low HREE and high Sr, low Y characteristics of some samples, but cannot explain the “mantle signature”. Although simple mantle upwelling and adiabatic melting model is reasonable for producing mantlederived magma and mixing between basic and acidic magma, the enriched Sr, Nd isotope (ISr=0705 40708 5;εNd(t)=-152-917)of samples with mantle signature and the regional geological settings do not favor this model. Similarities to high Mg adakite and sanukitoid imply that the samples having mantle signature could be derived from direct partial melting of hydrous enriched mantle.

Key words: high Mg adakite; sanukitoid; partial melting; mantle signature; South Qinling