Geochemistry and Geochronology of Cretaceous Volcanism of the Chaun Area of Central Chukotka

Resumo

This paper reports new geochronological and geochemical data on the Cretaceous volcanic rocks of the Palyavaam River basin (Central Chukotka, Chaun area). The first of the considered complexes is mainly represented by rhyolites, ignimbrites, and felsic tuffs of the Chaun Formation of the Okhotsk–Chukotka volcanogenic belt (OCVB). The second complex comprises volcanic rocks of the Early Cretaceous latite–shoshonite series, which are united into the Etchikun Formation. The geotectonic affinity of the Etchikun Formation is controversial. Some researchers consider the rocks of the formation as representing the magmatic stage preceding the OCVB formation. Other geologists include the Etchikun Formation in the Chaun Group of the OCVB. Obtained data indicate that the volcanic rocks of the Etchikun Formation have a heterogeneous nature and can be subdivided into two groups. Andesites of the first group (Etchikun Formation proper) are Early Cretaceous in age and predate the formation of the OCVB. Andesites of the second group in age and composition are correlated with volcanic rocks of the OCVB. They lie at the base of the Chaun Group and testify to the basic to acid volcanic evolution in the Central Chukotka sector of the OCVB.