Fission track ages of Mahanshan Metamorphic Rock Group in Gansu Province, Northwest China

Fission track dating was used to determine the ultimate rock-forming epoch of Mahanshan Group of metamorphic rocks and involved granitite in NW China. The quartz and hornblende fission tracks revealed that Mahanshan metamorphic rocks were formed during 3.66 ∼ 3.56 x 108 years before. Xiaoshima granitite rock body was dated 3.30 ∼ 3.41 x 108 years which present the migmatization time in Mahan Shan Mountains area. Geological and geographical features indicate that the latter regional geological process should be dominated with physical tectonic activities including uplifting and fracturing. (author)