The Age, Petrological-Geochemical Characteristics, and Origin of Igneous Rocks of the Middle Jurassic Khulam Volcano-Plutonic Complex, North Caucasus.

This paper is concerned with new petrological-geochemical, and isotope-geochronological data for the igneous rocks that compose the Khulam volcano-plutonic complex in the central part of the North Caucasus (Kabardino-Balkaria). It is shown that the moderately-alkaline rocks of the Khulam complex are represented by a bimodal association of gabbro + basaltic trachyandesites and trachytes and rhyolites. The fractional crystallization had a leading role in the formation of this bimodal association. Assimilation of the material of host crustal rocks by magmatic melts did not exert any appreciable influence. According to the results of U‒Pb and K‒Ar dating, the Khulam rocks were formed in the Middle Jurassic (Bajocian–Callovian, 167 ± 4 Ma ago). It was found that the Khulam rocks possess geochemical characteristics that are similar to those for intraplate continental rocks, and were erupted in a postcollisional geotectonic setting (when the subduction in the region came to an end) in a local extensional zone that arose in the rear of a former active continental margin. The magma melts that were generated by the mantle source of the Khulam complex had overall geochemical characteristics proper to enriched mid-oceanic ridge basalts (E-MORB). [ABSTRACT FROM AUTHOR]