Two A—type Syenite—Granite Belts in Anhui
摘要
There exist two parallel A-type syenite-granite belts on both banks of the Yangtze River in Anhui Province:one is the Dalongshan-Chengshan-Huangmeijian belt on the north bank and the other is the Huayuangong Maotan-Banshiling belt on the south bank.Both of them consist of syenite,quartz-syenite and alkali feldspar granite,which were formed at about 125 Ma ago and are enriched in alkalies and high-field-strength elements but depleted in water,with the total alkali accounting for 9-12%,and H2O^+only for 0.50%.The Ga×10^-4/Al ratio is as high as 2.7 to 3.8 for granite.They were formed in the extension stage of ancient rifting.So they are considered to be the A-type syenite-granite belts.Granites in the two belts resulted from a syenite magma by an AFC mechanism while the magma was derived from alkali basalt magma through the fractional-crystallization-dominated AFC mechanism.