Sedimentology, Provenance and Radiometric Dating of the Silante Formation: Implications for the Cenozoic Evolution of the Western Andes of Ecuador

Abstract

The Silante Formation is a thick series of continental deposits, exposed along a trench-parallel distance of approximately 300 km within the Western Cordillera of Ecuador. The origin, tectonic setting, age and stratigraphic relationships are poorly known, although these are key to understand the Cenozoic evolution of the Ecuadorian Andes. We present new sedimentological, stratigraphic, petrographic, radiometric and provenance data from the Silante Formation and underlying rocks. The detailed stratigraphic analysis shows that the Silante Formation unconformably overlies Paleocene submarine fan deposits of the Pilalo Formation, which was coeval with submarine tholeiitic volcanism. The lithofacies of the Silante Formation suggest that the sediments were deposited in a debris flow dominated alluvial fan. Provenance analysis including heavy mineral assemblages and detrital zircon U-Pb ages indicate that sediments of the Silante Formation were derived from the erosion of a continental, calc-alkaline volcanic arc, pointing to the Oligocene to Miocene San Juan de Lachas volcanic arc. Thermochronological data and regional correlations suggest that deposition of the Silante Formation was coeval with regional rock and surface uplift of the Andean margin that deposited alluvial fans in intermontane and back-arc domains.

Timing of Quaternary volcanism and its relationship with tectonics in the central segment of the Ecuadorian Andes

“…However, we do not exclude the occurrence of sporadic magmatic pulses and short periods of quiescence that could affect this rate over at shorter timescales. Litherland et al, 1994;Hughes and Bermúdez, 1997;Egüez et al, 2017;Vallejo et al, 2020). Dashed lines show tectonic structures inherited from the basement.…”

“…The Quaternary volcanic arc overlies the Miocene-Pliocene volcanoclastic deposits found in both Cordilleras and in the Inter-Andean Valley. In particular, the volcanoes of the central segment were built on the sedimentary Silante (Late Oligocene-Middle Miocene) and volcanoclastic Zumbahua (Middle Miocene) formations in the Western Cordillera (Vallejo et al, 2019(Vallejo et al, , 2020, and the Pisayambo volcanics (Miocene) in the Eastern Cordillera (Barberi et al, 1988;Lavenu et al, 1995;Egüez et al, 2017).…”

Blossoming of the Pleistocene volcanism in the Ecuadorian Andes: a review based on new and recent geochronological data

“…The basement of the Oriente basin corresponds to the PreCambrian Guyanese craton, overlain by a thick Mesozoic to Cenozoic sedimentary sequence (Ibanez-Mejia et al, 2011; Baby et al, 2013;Gutiérrez et al, 2019;Vallejo et al, 2021). The Miocene-Pliocene volcanic activity formed thick volcanic sequences (Lavenu et al, 1995;Vallejo et al, 2019Vallejo et al, , 2020Chiaradia et al, 2021), presently exposed over both cordilleras, on which part of the Pleistocene-Holocene volcanic edi ces developed. The thickness of the continental crust is estimated to be ~ 55-60 km for both Western and Eastern Cordilleras (e.g., Koch et al, 2021).…”

Geochronological evolution of the potentially active Iliniza Volcano (Ecuador) based on new K-Ar ages

“…These units are in turn overlain by the Silante Formation, which is exposed to the northwest of Iliniza volcano. It is composed of volcanoclastic sandstones, conglomerates and red mudstones derived from the erosion of the San Juan de Lachas volcanic island arc, of Early Miocene age (Boland et al, 2000;Vallejo, 2007;Vallejo et al, 2020).…”