Monogenetic Volcanism in Compressional Tectonics: Insights from the Lesser Caucasus (Georgia, Armenia, Azerbaijan)

We present a detailed study of the volcanotectonics in the Lesser Caucasus compressive belt, analysing 744 Quaternary monogenetic volcanoes using structural and geophysical field data. The study focuses on the interplay between tectonics and volcanism within this compressional setting. We analysed only volcanoes formed on horizontal or subhorizontal substrates, excluding those on the flanks of polygenetic volcanoes. For 394 volcanoes, we identified the underlying magma-feeding fractures based on volcanotectonic morphometric parameters. We also examined the spatial relationships between volcanoes and Quaternary faults, calculating the distance of each cone from the nearest main fault and considering fault kinematics. Furthermore, we correlated the azimuths of magma-feeding fractures with fault geometry, kinematics, GPS motion data, and focal mechanism solutions for shallow earthquakes.

The study reveals that most volcanoes are located more than 1 km away from regional Quaternary faults, suggesting these faults are not the primary conduits for shallow magma migration. Volcanoes near normal and strike-slip faults sometimes align with fault traces, confirming these faults can guide magma to the surface. The highest cone densities are linked to strike-slip faults, with magma pathways generally aligning WNW-ESE and NNE-SSW. Within tectonic blocks near strike-slip faults, magma-feeding fractures often deviate obliquely.

Magma can reach the surface also in contractional settings characterised by reverse faulting. In this case, no cones are within 200 m from reverse faults, indicating that magma can follow reverse faults at depth but migrates upward via secondary splays near the surface. Local structures formed by tectonic or magmatic stresses and self-generated hydrofractures from dyke overpressure also contribute to magma ascent, with hydrofractures aligned perpendicular to σHmin, depending on the stress regime.

Our findings emphasize that regional Quaternary faults are not the dominant pathways for shallow magma ascent in the Lesser Caucasus. Instead, magma utilizes local fractures within major tectonic blocks and self-generated hydrofractures. We also conclude that shallow magma paths are not necessarily always perpendicular to the least principal stress σ3, especially in the case of pre-existing mechanical discontinuities, suggesting caution in the use of volcano alignment or cone elongation (and similar morphometric parameters) to extrapolate stress orientations.