Abstract
In North Xinjiang there is an alkali granite belt extending in the NW-SE direction along the southern bank of the Ulungur River and running parallel to the suture zone, i.e., Aermantai-Zhaheba Ophiolitic Melange Zone, between the Junggar Plate and the Altay Orogenic Belt. Whole-rock Rb-Sr isochron ages of the Ulungur alkali granites are within the range of 292–309Ma, showing that they were genetically connected with the latest episode of Hercynian magmatism subsequent to the syncollision S-type and post-collision uplifting I-type granitoids in the Altay region. The alkali granites are mineralogically characterized by the occurrence of aegirine and arfvedsonite and chemically by high silicon and alkali, low calcium and magnesium and abundant high-field elements, being typical A-type granites. The alkali granites were formed in the final stage of the Hercynian calc-alkaline magmatic cycle in a very short period of time. They are in line with the post-orogenic A-type (PA-type) granites, implying that the tectonic regime was changed from compression to extension.
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