Water input and water release from the subducting Nazca Plate along southern Central Chile (33°S–46°S)

Abstract

The age of the subducting Nazca Plate off Chile increases northward from 0 Ma at the Chile Triple Junction (468S) to 37 Ma at the latitude of Valparaıso (328S). Age-related variations in the thermal state of the subducting plate impact on (a) the water influx to the subduction zone, as well as on (b) the volumes of water that are released under the continental fore arc or, alternatively, carried beyond the arc. Southern Central Chile is an ideal setting to study this effect, because other factors for the subduction zone water budget appear constant. We determine the water influx by calculating the crustal water uptake and by modeling the upper mantle serpentinization at the outer rise of the Chile Trench. The water release under fore arc and arc is determined by coupling FEM thermal models of the subducting plate with stability fields of water-releasing mineral reactions for upper and lower crust and hydrated mantle. Results show that both the influx of water stored in, and the outflux of water released from upper crust, lower crust, and mantle vary drastically over segment boundaries. In particular, the oldest and coldest segments carry roughly twice as much water into the subduction zone as the youngest and hottest segments, but their release flux to the fore arc is only about one fourth of the latter. This high variability over a subduction zone of <1500 km length shows that it is insufficient to consider subduction zones as uniform entities in global estimates of subduction zone fluxes.

Fluid and Melt Pathways in the Central Chilean Subduction Zone Near the 2010 Maule Earthquake (35–36°S) as Inferred From Magnetotelluric Data

“…The Nazca plate in south Chile is younger and hotter, which may lead to basalt‐eclogite dehydration at shallower depths than central Chile. This is supported by numerical modeling by Völker and Stipp () who showed that a significant dehydration event occurs approximately 50 km west of the volcanic arc for the Maule region but occurs further west when the Nazca plate is younger (i.e., in south Chile). This is also supported by earlier numerical work showing that intermediate temperature slabs release more water earlier (i.e., shallower) than low‐temperature slabs (e.g., Kerrick & Connolly, ).…”

“…These fluids then lower the solidus temperature of the surrounding mantle rocks, generating hydrous mafic melts. Determining the amount of water, the depth at which it is released, and the zones of accumulation of aqueous fluids and partial melt are critical parameters in examining magma flux and magma genesis (Petrelli et al, ; Völker & Stipp, ). Furthermore, it has been widely suggested that fluids control the distribution of seismic and aseismic zones within a subduction zone and thus understanding seismicity and fluid relationships is important (Saffer, ).…”

Shear wave velocity and Poisson's ratio models across the southern Chile convergent margin at 38°15′S

“…This is, in turn, in agreement with the high-quality reflectivity images along the profile (Groß et al 2008;Micksch 2008). It is also in agreement, as will be discussed in more detail below, with a model for water being transported down and released from the subduction zone (Völker & Stipp 2015).…”

“…• W. A study from Völker & Stipp (2015) could explain this observation. They ran thermal models to estimate the amount of water carried into the south-central Chile subduction zone and released by the oceanic crust and mantle for Nazca plate segments of different age.…”

“…On the other hand, it supports the existence of a serpentinized continental mantle wedge, already proposed from seismological, gravity and resistivity studies (Krawczyk et al 2006;Haberland et al 2009;Kapinos 2011). According to Völker & Stipp (2015), the release of water to the overlying continental mantle would not be much. However, if it has been happening over a long period of time it could add up to a significant process.…”