Browsing by Author "Araya Vargas, J."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Reactivation of Fault Systems by Compartmentalized Hydrothermal Fluids in the Southern Andes Revealed by Magnetotelluric and Seismic Data
    (2020) Pearce, R. K.; Sanchez de la Muela, A.; Moorkamp, M.; Hammond, J. O. S.; Mitchell, T. M.; Cembrano, J.; Araya Vargas, J.; Meredith, P. G.; Iturrieta, P.; Perez-Estay, N.; Marshall, N. R.; Smith, J.; Yanez, G.; Ashley Griffith, W.; Marquardt, C.; Stanton-Yonge, A.; Nunez, R.
    In active volcanic arcs such as the Andean volcanic mountain belt, magmatically sourced fluids are channeled through the brittle crust by faults and fracture networks. In the Andes, volcanoes, geothermal springs, and major mineral deposits have a spatial and genetic relationship with NNE trending, margin-parallel faults and margin-oblique, NW trending Andean Transverse Faults (ATF). The Tinguiririca and Planchon-Peteroa volcanoes in the Andean Southern Volcanic Zone (SVZ) demonstrate this relationship, as their spatially associated thermal springs show strike alignment to the NNE oriented El Fierro Thrust Fault System. We constrain the fault system architecture and its interaction with volcanically sourced hydrothermal fluids using a combined magnetotelluric (MT) and seismic survey that was deployed for 20 months. High-conductivity zones are located along the axis of the active volcanic chain, delineating fluids and/or melt. A distinct WNW trending cluster of seismicity correlates with resistivity contrasts, considered to be a reactivated ATF. Seismicity occurs below 4 km, suggesting activity is limited to basement rocks, and the cessation of seismicity at 9 km delineates the local brittle-ductile transition. As seismicity is not seen west of the El Fierro fault, we hypothesize that this structure plays a key role in compartmentalizing magmatically derived hydrothermal fluids to the east, where the fault zone acts as a barrier to cross-fault fluid migration and channels fault-parallel fluid flow to the surface from depth. Increases in fluid pressure above hydrostatic may facilitate reactivation. This site-specific case study provides the first three-dimensional seismic and MT observations of the mechanics behind the reactivation of an ATF.
  • Thumbnail Image
    Item
    Shallow Anatomy of the San Ramon Fault (Chile) Constrained by Geophysical Methods : Implications for its Role in the Andean Deformation
    (2020) Yáñez Carrizo, Gonzalo Alejandro; Pérez Estay, N.; Araya Vargas, J.; Sanhueza, J.; Figueroa, R.; Maringue, J.; Rojas, T.
  • No Thumbnail Available
    Item
    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
    (2021) Araya Vargas, J.; Sanhueza, J.; Yanez, G.
    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.