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Detecting a master thrust system by magnetotelluric sounding along the western Andean Piedmont of Quito, Ecuador

Abstract:

The Quito Basin, a narrow NE-trending tectonic depression, contains a perched Quaternary volcaniclastic sequence juxtaposed against the Interandean Depression through the Quito fault system (QFS). Syntectonic infilling, which occurs during a piggy-back phase, consists of alluvial fan sets grading eastward into lacustrine facies. The western piedmont margin overlies the foothills of Quaternary volcanoes. Classic thrust tectonic models pbkp_redict basinward propagation of low-angle thrusts ahead of master faults. A magnetotelluric survey was used to investigate the western Quito piedmont. Three resistivity sections show similar geoelectrical assemblages. From west to east, a wedge-shaped high-resistivity structural high abuts a low-resistivity domain, representing a fold-thrust belt overriding a foreland basin. This set continues to the east with a new high-resistivity structural high sliced by low-angle imbricated thrusts that culminate in local thrust-top troughs before grading into a deeper low-resistivity trough against the younger QFS anticlines. Thus, the Quito master thrust system results in a prominent basin-facing monocline affecting the foothills of Quaternary volcanoes.