Characteristics and geological significance of adakitic rocks in copper-bearing porphyry in Baogutu, western Junggar

Abstract：In the Darbute-Baogutu area, western Junggar, there outcrop two types of intermediate-acid intrusive rocks：late Hercynian (56%, Al2O3>15%, MgO400×10-6 and pronounced HREE depletion. Its Nd and Sr isotopic compositions are close to that of MORB. However, the composition of some samples, which is characterized by relatively high MgO contents (>3%) and a relatively low LREE abundance), is deviated from the compositional range of adakitic rocks. According to the geochemical composition of porphyries, combined with the regional geological characteristics, the authors think that the Baogutu copper-bearing porphyry originated in an island-arc environment related to intraoceanic subduction but that the initial melt of the oceanic crustal slab was subjected to inhomogeneous contamination with mantle peridotite during its rise.