EXTENSION INDUCED BY VOLCANIC LOADING IN REGIONAL STRIKE-SLIP ZONES

Volcanoes and strike-slip pull-apart structures are commonly found tog ether, We use theoretical predictions and analogue modeling to evaluat e the effect of volcanic loading in strike-slip zones, and the convers e effect of regional strike slip faults on volcano structure. Theoreti cal predictions indicate that regional stress is reoriented by volcano loading to cause extension. Analogue models indicate that volcanoes i n strike-slip zones develop extensional pull-apart structures. A grabe n 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 vol cano spreading, thrusts form normal to the maximum stress axis (sigma 1), A feedback situation can arise, i.e., loading-related extension al lows more magma influx, more eruption, and thus increased loading. Thi s process can create large volcano-tectonic depressions. Volcano struc tures may also be used as indicators of regional strike-slip movements .