The Role of Temperature in the Along‐Margin Distribution of Volcanism and Seismicity in Subduction Zones: Insights From 3‐D Thermomechanical Modeling of the Central Andean Margin

Abstract

AbstractThe 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°–26°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°–23°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°C at 80–100 km depth below the arc, with comparatively higher temperatures at ∼22°–25°S. The obtained along‐margin variations in temperature and in estimated melt velocity suggest that the subarc mantle south of 22°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°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.