Volcano-plutonic relations in Lat-Bolukan district (North of Qazvin, Western Alborz): Petrogenetic analysis and geochemical modeling

The Lat-Blukan area situated on the western Alborz zone, 45 Km to the north of Qazvin. The area contains intrusive and extrusive bodies with intermediate to acidic composition belonging to Eocene or younger in age (Karaj Formation). This lithological sequence can be divided into three main facies: sedimentary-pyroclastic deposits resulted from explosive alternative eruptions in a shallow-depth sedimentary basin, andesitic lava flows from subaerial effusive fissure eruptions and subvolcanic bodies including dioritic bodies, dacitic domes and parallel dyke swarms. Dykes also are subdivided into andesitic feeder dykes and post-magmatic dioritic dyke. Several evidences including the Ba/La > 15, Ba/Ta > 450, enrichment of LREEs relative to HREEs, enrichment of LILEs and depletion of HSFEs (Ti and Ta) as well as different tectonic setting diagrams, the magmatic rocks appertain to the continental active margin. Geochemically and especially based on geochemical modeling of magmatic processes, the parent magma of these series is considered to be generated from the mantle that after the ascent and staying in lower continental crust, it contaminated by crustal components and created a variety of magmas in the area. Thus, it may be proposed that the andesitic lava flows formed as a result of the FCA process, diorites originated from the lower continental crust fragments assimilated in the evolved magma from initial magma and dacites are the products of the partial melts of the amphibolitic continental crust.