Abstract

The distribution of volcanic and seismogenic zones is segmented along the trench-parallel direction in the Central Andes, and factors controlling their clustering are not fully understood. Here we present a 3-D thermomechanical model of the subduction zone at 18 degrees-26 degrees S to examine the role that temperature and mantle flow play in the distribution of active volcanoes and seismicity. We applied a steady state approach in which solid-state flow is driven by a kinematically prescribed slab with realistic geometry (including changes along the Bolivian Orocline) and using a 3-D model of the continental crust thickness. The obtained temperature distribution is consistent with proxies for isotherms derived from independent geophysical data, except below the Eastern Cordillera at 21 degrees-23 degrees S. The computed mantle flow pattern reveals the presence of along-margin dynamic pressure gradients. This 3-D preferential flow results in mantle temperatures of 1200-1400 degrees C at 80-100 km depth below the arc, with comparatively higher temperatures at similar to 22 degrees-25 degrees S. The obtained along-margin variations in temperature and in estimated melt velocity suggest that the subarc mantle south of 22 degrees S exhibits more favorable conditions for generation and upward migration of partial melts. This segment coincides with the higher concentration of active arc volcanoes and the presence of the Altiplano-Puna Volcanic Complex in the backarc. Intermediate-depth seismicity concentrates roughly below where the slab top is at 400-800 degrees C, suggesting that temperature exerts some control on the first-order distribution of intraslab seismicity. However, most intraslab seismicity occur at pressure-temperature conditions which are outside of the stability field expected for key dehydration reactions in slabs.