Pleistocene - Holocene volcanism at the Karkar geothermal prospect, Armenia

Pleistocene to Holocene volcanic centres north of the Bitlis-Zagros suture in Turkey, Iran, Armenia and Georgia represent both volcanic hazards and potential or actual geothermal energy resources. Such challenges and opportunities cannot be fully quantified without understanding these volcanoes’ petrogenesis, geochronology and magmatic, tectonic or other eruption triggers. We discuss the age and igneous geology of the Karkar monogenetic volcanic field in Syunik, SE Armenia. The ~30 km2 field is beside the location of Armenia’s only geothermal energy test drilling site. Eruptions of fissure-fed trachybasaltic andesite to trachyandesite occurred on a trans-tensional pull-apart segment of the Pambak-Sevan-Syunik Fault and have previously been interpreted to be of Holocene age. We conducted high-resolution duplicate 40Ar/39Ar dating of 7 groundmass separates, providing composite plateau or inverse isochron ages ranging from 6 ± 3 ka to 332 ± 9 ka (2). Each lava flow displays petrographic and geochemical patterns consistent with melting of subduction-modified lithospheric mantle and crystal fractionation involving ol, sp, opx and cpx, amp and plg. Some crystal-scale zoning was observed, implying recharge prior to eruption, and a preliminary estimate of cpx crystallisation pressures indicates storage in the mid- to upper crust, which may be of relevance for geothermal developments. These data indicate that volcanic activity in Syunik and elsewhere in Armenia overlapped with human occupation and that the presence of a substantive heat source for geothermal energy and a lava inundation hazard for local infrastructure should be further considered. Additional geophysical monitoring of the Pambak-Sevan-Syunik Fault is merited, along with detailed determination of the depths of magma storage both here and also at Porak volcano 40 km north of Karkar