METAVOLCANIC ROCKS OF THE XIAOXIHE GROUP IN ANHUI

A medium- and high- grade metamorphic rock series is exposed on the northern slope of the Dabie Mountains, Anhui; it is named the Xiaoxihe Group. Metavolcanic rocks are recognized in the middle and lower parts of this Group. According to the petrochemical characteristics and multiple diagrams, the nature of the protolith of the metamorphic rocks and the rock types have been identified. A comparison has been made between the chemical composition of the metavolcanic rocks and that of standard volcanic rocks both in China and abroad. Through the above-mentioned work, the protolith of basic metavolcanic lavas is determined to be alkali basalt, while those of intermediate and acid ones keratophyre and quartz keratophyre respectively. In terms of the chemical composition, the rocks belong to weakly alkaline rock series in M. A. Peacock’s classification. According to the rock association and rock series characteristics, the metavolcanic rocks of the Xiaoxihe Group whould belong to island arc-type volcanic rocks.