Geochemical types of subvolcanic dacite – rhyolite complexes from the сentral part of the Vedlozero-Segozero greenstone belt (Karelian Craton)

Abstract

The paper presents the results of detailed geological, petrographic and geochemical studies of Archean acidic subvolcanic rocks from the Koikary domain located in the central part of the Vedlozero-Segozero greenstone belt. Three petrologically contrasting groups are clearly distinguished in the investigated dacite-rhyolite association: 1) dacite with high content of Cr, Ni, Ti, Nb, and heavy REE, which are characterized by εNd (2935 Ma) from +0.72 to +2.93 and contain porphyritic phenocrysts of several generations; 2) rhyolite with a strongly fractionated REE distribution, negative anomalies in Nb, Sr and Ti, and with εNd (2935 Ma) from +1.15 to +3.37; 3) dacite and rhyolite with a moderately fractionated REE distribution, negative anomalies in Nb, Sr and Ti, and with εNd (2935 Ma) = –6.47. The above mentioned features of the rocks reflect the contrasting conditions of generation of acidic subvolcanic rocks in the Koikary domain and mark different time stages of the greenstone belt development.

Keywords

• архей
• дациты
• риолиты
• геохимия
• зеленокаменный пояс