A first reconstruction of the evolution of Cubilche Volcanic Complex, Imbabura Province, Ecuador

摘要

Cubilche Volcanic Complex (Imbabura Province, Ecuador) includes three morphologically well-preserved erup-tive centers: in increasing size, Cunrru Dome Complex (3300 m above sea level, m asl), Panga Ladera (3420 m asl) and Cubilche (3836 m asl). As this complex is poorly known, we conducted a volcanological study of its evolution by combining geomorphological, lithostratigraphic, radiocarbon (14C), and petrological analyses, along with eruption size determinations. Cunrru Dome Complex shows an eastward-opening scarp formed during a dome collapse event that emplaced a small-volume debris avalanche deposit and a pumice-rich layer from an accompanying directed explosion. The higher Panga Ladera edifice is breached towards the north, and the emplacement of the resulting debris avalanche deposit was also accompanied by a blast-forming eruption of ash and pumice. The post-collapse vent subsequently produced dilute pyroclastic density currents (PDCs) that built a low cone. The Cubilche eruptive center comprises old and young edifices. The Old Cubilche edifice emitted lavas from a summit crater and flank vents before being partly destroyed during a flank failure event associated with an explosive eruption that produced a widespread pyroclastic density current deposit dated at ca 44 ka and an associated pyroclastic fall deposit. The Young Cubilche cone grew inside the Old Cubilche avalanche crater during similar to 14-19 ka over five eruptive episodes that included early effusive eruptions, a dome growth period that terminated with a PDC that emplaced scoria flow deposits at ca 29.6 ka, an explosive eruption at ca 26.3 ka, and final Strombolian activity emitting more mafic products. As the adjacent Imbabura Volcanic Complex erupted in early Holocene times and the two complexes seem to share common reservoirs and plumbing systems, we cannot fully discard a possible reactivation at Cubilche. Other more short-term hazards are debris flows and landslides potentially triggered by heavy rain fall and/or seismic events. (C) 2020 Elsevier B.V. All rights reserved.