Rebecca Pearce
Solid Earth Dynamics
Exploratory field geophysics Gravity anomaly, seismic & magnetotelluric surveying Andean crustal scale fault dynamics and magma conduit evolution
PhD Research

Nature of the link between tectonics and volcanism in the Centra and Southern Andes

In a tectonic regime dominated by North-South oriented convergent stresses, margin oblique lineaments in the main cordillera of the Chilean Andes are theorized to significantly contribute to the dynamic evolution of this mountain belt as hydrothermal and geothermal fluid migrational pathways. In order to deduce the role of these transverse structures in magma and hydrothermal fluid transport within the volcanic arc, the depth extent, lithological composition and architectural properties of the faults must be assessed. High density mineral constituents associated with hydrothermally metasomatized fault zones generate a positive, short-wavelength gravity and magentotelluric signature and are characterized by high velocity seismic wave signals; planar interfaces between fault fracture zones and surrounding intact host rocks are also detectable through seismic readings. This study is a combined geophysical seismic and gravity survey assessment of the misoriented fault systems that occur within the Rio Teno & Rio Tinguiririca region of the Transitional Southern Volcanic zone. The concluding analysis of the structural and compositional properties of these structures will contribute to the four year FONDECYT 1141139 research project that aims to comprehensively determine the role of these fault zones in the orogenic evolution of this latitudinal section of the Andean mountain range.
Surficial evidence of geothermal fluid propagation along the WNW-ENE striking faults will be observable in the hydrothermal alteration halo surrounding the fault plane. These high density mineral constituents will generate a positive gravity anomaly and megnetotelluric signal along a lateral gravity gradient that traverses the dipping plane of the fault. These prominent structural features will also be detectable in seismic reflection and refraction surveys due to both the juxtaposing fault plane interfaces, and the relatively high seismic velocities associated with the metasomatized mineral halo. Constraints provided by the sample analysis will be used to conduct highly accurate geophysical data reduction, the results of which will be extrapolated to the extensive margin-oblique fault systems that occur throughout the transitional southern volcanic zone. It is hypothesized that these large scale margin oblique structures are reactivated pre-Andean reverse faults that have acted as geothermal and hydrothermal fluid conduits due to the ambient NS-oriented compressional tectonic stresses that characterize this orogenic setting.
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Tom Mitchell
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