New KAr age dates of Neogene and Quaternary volcanic rocks from the Ecuadorian Andes: Implications for the relationship between sedimentation, volcanism, and tectonics

Abstract New KAr ages of Tertiary and Quaternary volcanic and sedimentary sections in the Interandean Depression and the southern Ecuadorian basins give an indication of the duration of sedimentary events and the timing of magmatic and tectonic events in the Ecuadorian Andes. In southern Ecuador, the syn-tectonic infilling of the Cuenca basin began in the early Miocene and ceased by the late Miocene. An andesitic stock in this region shows evidence of late Miocene magmatism. Sporadic development of the Pleistocene volcanic-rich Tarqui Formation suggests, contrary to previously held views, that Plio-Pleistocene volcanism is not as well developed in southern Ecuador. In the Alausi region, an Oligocene age for calc-alkaline volcanism, subsequent to the Macuchi Arc accretion, is confirmed. The existence of younger volcanic events is also proved. In central Ecuador, the Western Cordillera is covered in part by volcanic rocks of the mainly Miocene Pisayambo Formation. The age of the Latacunga Formation of the Latacunga-Riobamba basin (Interandean Depression) is established as late Pliocene to Pleistocene.