Emplacement Mechanism of the Akebasitao Pluton: Implications for Regional Tectonic Evolution of West Junggar, NW China

Late Carboniferous to Early Permian A-type granites are extensively distributed throughout the West Junggar region, NW China, and the Akebasitao pluton is extremely distinguished among these plutons. In this paper, we reported new anisotropy of magnetic susceptible (AMS) data combine with detailed field study and audio magnetotelluric (AMT) sounding to assess the three-dimensional shape and magmatic emplacement mechanism of the Akebasitao pluton. The geological features and the AMT sounding indicate that the pluton had a slightly oblique movement of magma from northwest to southeast, which was most likely to correspond to an asymmetrical torch with a laccolith-shaped upper part, and a lower part formed by sub-vertical root that was located within its northwestern part, probably controlled by the NE-trending Anqi fault. The AMS fabrics of all the specimens reveal a low P-j value (mean of 1.02) and a low T value (mean of -0.024), suggesting that the deformation of the AMS ellipsoid is relatively weak. The specimens exhibit both oblate and prolate shapes of the AMS ellipsoid. Magnetic lineations and foliations are randomly distributed throughout the pluton without any preferred orientation. These AMS patterns indicate that the pluton formed in a relatively stable structural environment with no regional extrusion. Therefore, we propose a complex emplacement process in which the magmas reached the shallower crust levels via deep-faults and subsequently occupied the room created by doming, accompanied by stoping near the pluton roof. Additionally, the regional tectonic setting was relatively stable during the emplacement of the Akebasitao pluton, indicating the termination of compressional orogeny during the late Late Carboniferous in the West Junggar region. This conclusion perfectly coincides with the regional tectonic paleogeography, magmatic system, and paleostress field.