Mantle Flow and Deep Electrical Anisotropy ? an MT investigation in Tierra del Fuego, South America

GONZÁLEZ-CASTILLO, LOURDES; GALINDO-ZALDÍVAR, JESÚS; BOHOYO, FERNANDO; RUIZ-CONSTÁN, ANA; CEMBROWSKI, MARCEL; PEDRERA, ANTONIO; IBARRA, P.; RUANO, PATRICIA; JUNGE, ANDREAS; TORRES CARBONELL, PABLO J.; MAESTRO, ADOLFO

Chiang Mai

Workshop; 23rd Electromagnetic Induction Workshop; 2016

Department of Physics, Faculty of Science, Mahidol University y otros

The mantle cell features most likely are reflected by the spatial pattern of the directional properties ofmaterial parameters such as seismic velocity and electrical conductivity. The understanding of mantleflow is substantially supported by the investigation of the spatial distribution of the deep electricalconductivity and its possible preferential direction. The Drake Passage constitutes a key area as it isone of the main gateways in the global pattern of mantle flows. It was formed since the Oligoceneby the fragmentation of the former continental connection between South America and AntarcticPeninsula and the subsequent development of the Scotia Arc. In this area, the Scotia and Sandwichplates are surrounded by the South America and Antarctic plates. Petrological and geophysical data,including gravity and magnetic researches provide evidences that support the inception of the Pacificmantle in the Atlantic during the development of this tectonic arc. However, seismic anisotropystudies are scarce due to the lack of seismic stations in this region. Tierra del Fuego (Argentina),located in a continental lithospheric area at the northern branch of the Scotia Arc, is crossed by theSouth America-Scotia sinistral transcurrent plate boundary. This area has special interest to analyzethe effect of the mantle flow in the northern margin of the mantle gateway.Thus a Long Period MT study conducted by the Spanish Geological Survey (IGME) and the Universityof Granada was performed along 2 profiles in Tierra del Fuego to investigate the deep crustal andupper mantle conductivity in 2012. The profiles were approximately 105 and 73 km long and 40 kmapart. They consisted of 18 sites recording the 3 magnetic and 2 telluric field components with asampling rate of 4 Hz using LEMI-417 system. Standard robust processing was performed yieldinghigh quality transfer functions. The interpretation of phase tensor invariants and tipper vectorswas undertaken by 3D anisotropic modeling using the Frankfurt group software based on ComsolMultiphysics 5.2TM. Special care was taken to allow for the influence of the surrounding seawaterby including a detailed model of the bathymetry based in GEBCO database. The implementationof an azimuthally anisotropic upper mantle significantly improved the data fit. The high conductingprinciple axis describes the assumed direction of mantle flow confirming the importance of electricalmantle signatures found by MT investigations. The main results of MT research reveal the existenceof a main NW-SE oriented anisotropy in the upper mantle. Although alternative models may beproposed including former mantle anisotropies parallel to the Andes Cordillera, rotated during thedevelopment of the northern branch of the Scotia Arc, the most suitable interpretation suggests thatthe anisotropy may be related to the active eastwards mantle flow across the Drake Passage.