Two A—type Syenite—Granite Belts in Anhui

Two A-type syenite-granite belts in Anhui

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. Financially supported by the National Eighth-Five-Year Science and Technology Breakthrough Project No. 85-901-03-04.