Browsing by Author "Vargas, Jaime Araya"

Now showing 1 - 3 of 3
  • No Thumbnail Available
    Item
    Magnetotelluric image of the Patagonian slab window: Constraints on upper mantle physical properties and sources of intraplate magmatism
    (2024) Vargas, Jaime Araya; Sanhueza, Jorge; Diaz, Daniel; Segovia, Maria Jose; Pasten-Araya, Francisco; Slezak, Katarzyna
    The Patagonian slab window (PSW) is a region of the Southamerican subduction zone where the absence of subducted slabs is interpreted, due to the subduction of the Chile Mid-Ocean Ridge at the Chile Triple Junction. Here we report the results of a long-period magnetotelluric (MT) study conducted in two 300 km-long trenchparallel transects crossing the northern boundary of the PSW in the proximal backarc. We modeled the MT data using 3-D inversion, obtaining an electrical resistivity model of the continental crust and upper mantle up to a depth of similar to 150 km. Our model shows a heterogeneous resistivity structure in the uppermost mantle, dominated by resistivities >300 Omega m below the array of sites even within the PSW, and some low-resistivity zones (LRZs, <10 Omega m) mainly at the edge of the array. Using petrophysical models, we estimated the mantle temperature, water content, melt fraction, and viscosity based on obtained resistivity values and a preexistent model of P-wave velocity (Vp) at 50 km and 100 km depth. These estimates suggest that the uppermost mantle within the PSW region is heterogeneous and dominated by high-viscosity blocks, compatible with the continental mantle lithosphere or even subducted slabs. Based on relatively hot and low-viscosity zones estimated in the periphery of LRZs, we interpret the presence of asthenospheric mantle in areas where LRZs coincide with relatively low Vp. According to this interpretation, asthenospheric upwelling in the study area at depths <= 150 km would be localized rather than ubiquitous over the interpreted extent for the PSW. Such localized asthenosphere upwelling processes in the past could explain the scattered distribution of Neogene basaltic lavas in the southern Patagonia backarc. The continental crust exhibits LRZs in the upper and lower crust. Remarkably, ensembles of LRZs at different crustal depths within the presumable area of the PSW were found below the General Carrera Lake, and towards the North Patagonian Icefield, likely indicating the presence of hidden intraplate magmatic and/or hydrothermal systems.
  • No Thumbnail Available
    Item
    Ridge Subduction: Unraveling the Consequences Linked to a Slab Window Development Beneath South America at the Chile Triple Junction
    (2023) Sanhueza, Jorge; Yanez, Gonzalo; Buck, W. Roger; Vargas, Jaime Araya; Veloso, Eugenio
    The subduction of an active spreading center generates a clear signature in the temporal evolution of subduction zones. It disrupts the typical arc-type magmatism and intraplate seismicity, enhances the emplacement of backarc plateau lava and profoundly change the tectonics and topographic relief. These distinct observations are commonly linked to a slab window opening and mantle upwelling. The Chile Triple Junction provides the ideal setup to study the mid-ocean ridge subduction process where both sides of the spreading center continue to subduct. Here, we use 2-D numerical petrological-thermomechanical modeling to focus on transient geodynamic processes caused by mid-ocean ridge subduction. Model results show slab separation along the ridge axis with the opening of a slab window. During the opening, partial melts from the spreading center migrate toward the subcontinental mantle and high temperatures in the forearc are predicted. The temporal evolution of the modeled temperature is consistent with observed heat flow data, and with magmatism and high-temperature metamorphism recorded in Chilean forearc rocks. Such migrated partial melts might explain the low viscosity inferred and low seismic velocity anomalies imaged in the slab window beneath South America, and the common geochemical signature of the Chile Ridge, the Taitao Ophiolite and the backarc magmatism. Following slab separation, our models suggest forearc uplift and changes in the stress regime, processes which are consistent with deformation records. Summarizing, our model of the geodynamic evolution of the Chile Ridge subduction provides a consistent framework that explains diverse records of magmatism, metamorphism, deformation and mantle physical properties.
  • No Thumbnail Available
    Item
    Towards linking slab window geodynamics with the geophysical and geochemical signature of the upper mantle
    (2023) Sanhueza, Jorge; Yanez, Gonzalo; Buck, W. Roger; Sawant, Amol Dayanand; Vargas, Jaime Araya; Lloyd, Andrew J.
    Slab windows have clear consequences for surface observations that are the manifestations of asthenospheric upwelling and uppermost mantle temperature anomalies. In this contribution we link geophysical and geochemical observations from modern slab windows to the asthenospheric flow, temperature field and extent of melting using different geometries. We use an analytical solution for the slab window geometry and implement this solution in 3D steady-state thermomechanical models to calculate the temperature and velocity field. Our results show that upwelling (>1 cm/yr) and temperature anomalies (>1400 C-degrees) are controlled by the ratio between the half-spreading rate and velocity of the overriding plate. The extent of melting depends on both the ratio of these velocities and ridge obliquity while flow patterns are controlled only by ridge obliquity. Finally, we construct ternary diagrams to estimate the efficiency of matrix/melt upwelling and maximum mean mantle temperatures based on plate kinematics and ridge obliquity. This novel approach was used to investigate the slab windows in Antarctica, South America and western North America.