Detrital zircon typology and U/Pb geochronology for the Miocene Ladrilleros-Juanchaco sedimentary sequence, Equatorial Pacific (Colombia) : new constraints on provenance and paleogeography in northwestern South America

Typology and internal texture analyses were performed on detrital zircons obtained from the Miocene sandstones of the Ladrilleros-Juanchaco sedimentary sequence (Colombia, Equatorial Pacific). This analysis was complemented with zircon U/Pb dating to identify typology-age associations as indicators of provenance of these sediments. Our results show that zircons with S and P dominant typology have internal structures/zoning that indicate mostly igneous and possibly some metamorphic origins. Morphometric results suggest little transport from source areas. Both typology and U/Pb data point to the Western Cordillera as the main source of the detrital materials of this sedimentary sequence. A paleogeographic reconstruction shows that during Late Miocene times there were significant portions of the Western Cordillera uplifted, eroding away and acting as a fluvio-topographic barrier blocking sediments from the Central Cordillera to reach the Pacific basins. Miocene plutons at the axis of the Western Cordillera were also probably exhumed and played a role as geomorphologically active massifs. This study demonstrates that typologic analysis on detrital zircon grains is a powerful tool as indicator of provenance and paleogeography in complex litho-tectonic areas where overlapping U/Pb signatures can lead to contradictory results

Comentario a “Emplazamiento del magmatismo Paleoceno-Eoceno bajo un régimen transtensional y su evolución a un equilibrio dinámico en el borde occidental de Colombia” por Grajales et al., Rev. Mex. Cienc. Geol. (2020), 37(3), 250-268

Grajales et al. (2020) hacen una revisión de la información geocronológica y geoquímica de rocas plutónicas y volcánicas aflorantes en el Bloque Panamá-Chocó (norte de la Cordillera Occidental), sur de la Cordillera Occidental, así como la Cordillera Central de Colombia. Estos datos fueron usados para plantear un modelo de un arco continental del Paleógeno continuo a lo largo del margen continental colombiano y para proponer un modelo paleogeográfico y de emplazamiento para las rocas ígneas del arco propuesto. Sin embargo, los autores no discutieron los datos geoquímicos, geocronológicos, termocronológicos y de proveniencia publicados para rocas cretácicas-miocénicas del noroccidente colombiano, Panamá y Ecuador, los cuales sugieren un modelo más probable de doble subducción controlado por la convergencia de las placas Caribe y Farallón bajo el Bloque Norandino durante el Paleógeno. En este comentario, se discuten algunos problemas relacionados con la compilación e interpretación de los datos y el modelo presentados por Grajales et al. (2020). Después de esta discusión llegamos a la conclusión que la presencia de un sistema de subducción doble es la explicación más razonable para el magmatismo de arco paleógeno, actualmente presente en los sectores sur y norte de los Andes del Nort

Detrital zircon typology and U/Pb geochronology for the Miocene Ladrilleros-Juanchaco sedimentary sequence, Equatorial Pacific (Colombia) : new constraints on provenance and paleogeography in northwestern South America

Typology and internal texture analyses were performed on detrital zircons obtained from the Miocene sandstones of the Ladrilleros-Juanchaco sedimentary sequence (Colombia, Equatorial Pacific). This analysis was complemented with zircon U/Pb dating to identify typology-age associations as indicators of provenance of these sediments. Our results show that zircons with S and P dominant typology have internal structures/zoning that indicate mostly igneous and possibly some metamorphic origins. Morphometric results suggest little transport from source areas. Both typology and U/Pb data point to the Western Cordillera as the main source of the detrital materials of this sedimentary sequence. A paleogeographic reconstruction shows that during Late Miocene times there were significant portions of the Western Cordillera uplifted, eroding away and acting as a fluvio-topographic barrier blocking sediments from the Central Cordillera to reach the Pacific basins. Miocene plutons at the axis of the Western Cordillera were also probably exhumed and played a role as geomorphologically active massifs. This study demonstrates that typologic analysis on detrital zircon grains is a powerful tool as indicator of provenance and paleogeography in complex litho-tectonic areas where overlapping U/Pb signatures can lead to contradictory results