Geochemistry and petrogenesis of volcanic rocks from the northern part of the Lahrud region (Ardabil): An example of shoshonitic occurrence in northwestern Iran

Basalts, andesites, trachyandesites and latites with shoshonitic affinity are the main volcanic rocks of Eocene age in the Lahrud region (Ardabil). Plagioclase, K-feldspar, biotite and amphibole associated with clinopyroxene are the main constituents of trachyandesites (shoshonites) while clinopyroxene, plagioclase and biotite are the rock-forming minerals of basalts (absarokites). The Lahrud volcanic rocks show enrichment in LREE and are characterized by enrichment in LILE and depletion in HFSE. Petrographical observations along with geochemistry of rare earth and trace elements of these lavas suggest shoshonitic affinity and derivation from a subduction zone. The geochemical behavior of the Lahrud lavas reveals the role of the trench sediments in the source region and genesis of these volcanic rocks. These lavas exhibit low degree of partial melting from a garnet-spinel lherzolite source. The comparison between the Lahrud volcanic rocks with Plio-Quaternary lavas of Sabalan and Eocene lavas of Hashtjin region highlights the different mantle source and degree of partial melting for the genesis of these volcanic rocks. The formation of these lavas is linked to slab steepening and breakoff in a post subduction collision zone.