Chen, P., C. R. Bina, and E. A. Okal, Slab stress and volcanism in Nazca plate subduction: variations with dip angle and intermediate-depth seismicity, Eos, Transactions of the American Geophysical Union, 80, Fall Supplement, S12F-02, 1999.
S12F-02
We compile the intermediate-depth earthquakes of South America from the Harvard CMT catalogue to determine the along-strike dip variation of the subducted Nazca plate. We investigate the dip angles thus derived in terms of their correlations with both slab stress, as indicated by CMT solutions, and volcanism, as observed at the surface. Our primary results are three-fold. (1) The stress patterns of intermediate-depth earthquakes exhibit consistently down-dip extension for steeply dipping regions (20~30 degrees) but show significant scatter for shallowly dipping regions (<10 degrees). This is consistent with a significant contribution from buoyancy forces to the slab stress field. (2) In contrast to steeply dipping regions, there is little or no volcanism at the surface above shallowly dipping regions. The pressure-temperature path of the subducting slab, coupled with phase diagrams for dehydration reactions, may help to explain this observation. (3) The northern (5N~2S) and southern (31S~52S) zones of South American volcanism fall in regions which lack in seismicity below. This observation suggests that earthquake faulting by hydrofracture to interconnect water pores (Davies, 1999) is not a necessary condition for generating subduction-zone volcanism.
Davies, J. H. (1999) Nature, 398, 142-145.
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