Lithologic sequence and geochemical characteristics of Second phase of Paleogene volcanic rocks in Deylaman area, Western Alborz

Deylaman area lies on Paleogene volcanic rocks in Western Alborz near the border between Central and Western Alborz structural zones. The succession of Paleogene rocks in the area is comprised of three separate phases each of which representing one stage of volcanic events. The main purpose of this paper is to study the lithologic sequence and geochemical characteristics of phase two volcanic rocks with Oligocene age (?). Rocks from the second phase are made of three separate parts (subunits) which by the order of age from the oldest to the youngest are; subunit one: basalts and basaltic andesite lavas, subunit two: coarse and fine grained tuffs and volcanic breccia, subunit three: andesitic tuffs with andesitic lenses. Geochemical studies on major and trace elements of lavas show that these rocks have calc-alkaline characteristic of volcanic arcs. Meanwhile, there are some similarities between REE patterns, for example LREE are more enriched, HREE have flat patterns as well as Eu negative anomalies. Therefore, the magmas of these rocks formed from a garnet-free but feldspar-bearing source. Immobile trace element data such as Cr and Th confirm their volcanic arc origin.