COLLISION-RELATED VOLCANISM AND FAULTING IN ARMENIA

We investigate the relationship between Quaternary volcanism and faulting in Armenia across several scales. Quaternary bimodal volcanism in Armenia is associated with collision between the Eurasian and Arabian lithospheric plates at 13 cm/yr, based on REVEL 2000. Volcanoes in Armenia can be spatially sub-divided into two regional volcano clusters: the Trans-Caucasian uplift zone (eastern Armenia) and the Ararat Depression (western Armenia). The Trans-Caucasian zone is dominated by small volume cinder cones, domes, and lava flow fields concentrated between the active Garni and Sevan-Pembak fault systems. Volcanism is concentrated between these continental scale right lateral strike-slip fault systems in pull-apart regions and along normal faults. Recurrence rate of volcanism in this region is relatively high, on the order of 100 volcanic events/million years and activity is predominantly monogenetic. Quaternary vent density in the Trans-Caucasian zone is up to 0.02 vents/km². On a local scale, ground magnetic surveys in the Lake Sevan region indicate that cinder cone volcanism is closely related to normal faults. In this region, cinder cones occur in the hanging-walls of normal faults oblique to the overall NW trend of strike-slip faults.

Volcanism in the Ararat Depression has a similar vent density (0.015 vents/km²) and recurrence rate (70 events/million years), but is less obviously associated with major fault zones. Nevertheless, ground magnetic mapping and geological studies in this area reveal that cinder cones and domes are often associated with local strike-slip faults, consistent with the idea that fault and dike injection are both working to accommodate crustal stress. Our working hypothesis is that differences in the rates of silicic and basaltic volcanism correlate with changes in the style and rate of crustal deformation. Along the Sevan-Pembak fault system, high strain rates (evinced by the 1988 Spitak earthquake) are not fully accommodated by comparatively high rates of volcanism. Further from the plate boundary, in the Sadarapat basin, lower rates of volcanism sufficiently accommodate tectonic stresses and rates of fault slip are apparently reduced. This model is supported by broad regional anti-correlation between historic seismicity and volcano distribution.