Geochemical Characteristics and Emplacement Mechanism of the Late Carboniferous Intrusive Rocks in Alatubai of Qinghe County, Xinjiang

The late Carboniferous adamellite spread to the southwest of Mayin'ebo fracture on a NW-SE long strip in Alatubai area of Xinjiang Qinghe County. They have obvious mylonitized deformation characteristics and are strictly controlled by faults. The grade of the rock K₂O + Na₂O is 7.55%-9.09%,the ratio of K₂O/Na₂O is 1-1.88, the Rittman combination index σ is 2.35-2.86. The data suggest that the late Carboniferous adamellite is high-K calc-alkaline rocks; the CIPW standard mineral Q content of 23.14%-31.41% and C content of 0.54%-1.69% indicate that the intrusive body is supersaturated SiO₂ metaluminous-peraluminous rock, known as type I granite. The ∑REE value of late Carboniferous adamellite is (227.04-326.42)×10^-6, with most L/H values less than 10. The enrichment of light REE is middle, with medium δEu anomaly of 0.42-0.58. The trace elements took on positive anomaly of K, Rb, Th, Ce and negative anomaly of Sr, Ba, Nb, P, Ti, and experienced some degree of plagioclase, apatite, ilmenite and other minerals fractional crystallization. The whole-rock δ18O value is 4.4‰-4.6‰, a strong oxygen isotopic exchange occurred between the rock and low 18O meteoric water along fissures infiltration under subsolidus conditions. Together with ⁸⁷Sr/⁸⁶Sr ratio of 0.70434, it is speculated that the adamellite would be variants of mantle-derived magma. The Rb-Sr isochron age of whole rock minerals is (300±4) Ma. In the middle-late period of Neo-Carboniferons epoch, after the extension stage colliding and connecting between Kazakstan-Junggar and Siberia Plate, the deep mantle-derived basaltic magma raised along faults with partial melting of crustal material, and eventually emplaced by dike spreading with moderate erosion in the latter stage.