SHAO Xiao-yue1, 2，TANG Hong-feng1*
(1. Key Laboratory of High Temperature & High Pressure Study of the Earth's Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China)
Abstract: Numerous post-collisional granites developed in the eastern Junggar of Xinjiang can be classified into I-type and A-type ones based on their geochemical characteristics. In order to explore the genesis of these granites. In this paper, we have carried out partial melting experiments, under high temperature and high pressure conditions, of an starting material which was composed of the basic rocks (altered basalt, gabbro) collected from the Kalamaili ophiolite and the argillaceous rock (representing sediments) collected from the eastern Junggar, with the mass ratio of 9:1 for the mixing of basic rock and argillaceous rock. The results show that the partial melting of the mixture of 90% altered basalt plus 10% sediment with 0%－4% added water under 925 ℃ and 1.0 GPa had produced the metaluminous granodioritic melt, which was coexisted with main mineral of amphibole, and was characterized with low SiO2 content and low A/CNK value, but high contents of Al2O3, FeO*, and CaO. The melt has similar chemical compositions to those of the post-collisional I-type granites in the eastern Junggar. However, the melt generated by the partial melting of the mixture of 90% gabbro plus 10% sediment with 2%－4% added water under the same high temperature and high pressure conditions belongs to the slight peraluminous tonalitic melt, which was coexisted with mineral phase of amphibole and was characterized with low contents of SiO2, but high contents of Al2O3, FeO*, and CaO and high A/CNK value. The melt has obvious different chemical compositions from those of the post-collisional I-type granites in the area. Therefore, the post-collisional I-type granites in the eastern Junggar could be formed by the partial melting of the mixture of altered basalt plus sediments under the above experimental conditions, while the A-type granites with high SiO2 contents cannot be formed by the partial melting of the above starting material under these experimental conditions.
Keywords: Post-collisional granite; mixed starting material; partial melting; the eastern Junggar; Xinjiang
ACTA MINERALOGICA SINICA Vol.41, No.6, 2021, page 713
