Extension induced by volcanic loading in regional strike-slip zones

Open University, Department of Earth Sciences, Milton Keynes, United Kingdom
Universite Blaise Pascal, France

Volcanoes and strike-slip pull-apart structures are commonly found together. We use theoretical predictions and analogue modeling to evaluate the effect of volcanic loading in strike-slip zones, and the converse effect of regional strike-slip faults on volcano structure. Theoretical predictions indicate that regional stress is reoriented by volcano loading to cause extension. Analogue models indicate that volcanoes in strike-slip zones develop extensional pull-apart structures. A graben typically forms normal to the minimum regional stress axis (sigma 3) at a cone. Cones emplaced onto preexisting faults increase that fault's tensional component. If the substratum is weak enough to permit volcano spreading, thrusts form normal to the maximum stress axis (sigma 1). A feedback situation can arise, i.e., loading-related extension allows more magma influx, more eruption, and thus increased loading. This process can create large volcano-tectonic depressions. Volcano structures may also be used as indicators of regional strike-slip movements.

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