鞍本地区晚太古宙高镁安山岩的成因解释

首次于鞍本地区发现晚太古宙晚期变质高镁安山岩，其主要矿物组合为角闪石+斜长石+云母+石英+少量辉石，并与~2.55~2.52Ga BIF和变质表壳岩互层产出.全岩主微量元素地球化学结果显示，鞍本地区高镁安山岩发育钙碱性，高MgO， Cr和Ni含量，以及低FeO_T/MgO比值等原始岩浆特征，并呈现强分异REE模式和明显Nb， Ta， Ti亏损等典型岛弧岩浆特征，与~2.7Ga Wawa绿岩带高镁安山岩和显生宙Setouchi地区赞岐质高镁安山岩具有相近的地球化学特征，将鞍本地区晚太古宙高镁安山岩解释为受到俯冲板片熔体交代的地幔橄榄岩部分熔融形成，为鞍本地区晚太古宙晚期存在俯冲机制提供了佐证.

Petrogenesis for Late Neoarchean Era High Magnesian Andesites in the Anshan-Benxi Area

The high magnesian andesites(HMAs)are first recognized from the Anshan-Benxi area， which comprise mineral assemblages of amphibole+plagioclase+mica+quartz+minor pyroxene. The Anshan-Benxi HMAs are interlayered with ~2.55~2.52Ga BIF and supracrustal rocks， therefore indicating that they are late Neoarchean products. Whole-rock major and trace geochemical results reveal that the Anshan-Benxi HMAs represent primary magmas with high MgO， Cr and Ni contents， low FeO_T/MgO ratios and calc-alkaline features， and are characterized by typical island arc compositions with strongly fractionated REE patterns and negative Nb-Ta-Ti anomalies. Besides， the Anshan-Benxi HMAs are geochemically analogous to ~2.7Ga HMA in the Wawa greenstone belt and Phanerozoic sanukoid HMA in the Setouchi. Taken together， the Anshan-Benxi HMAs are interpreted products of partial melting of mantle peridotites which are previously metasomatized by subducting slab released melts， consisting with a late Neoarchean subduction geodynamic setting in the Anshan-Benxi area.