Causes of complexity in a fallout dominated plinian eruption sequence: 312 ka Fasnia Member, Diego Hernandez Formation, Tenerife, Spain

摘要

The 312 ka Fasnia eruption from the Las Canadas Caldera on Tenerife, Canary Islands, Spain, produced a complex sequence of twenty-two intercalated units, including 7 pumice fall, 7 ignimbrite and 8 ash surge and fall deposits that define two distinct eruption sequences (Lower and Upper Fasnia sequences). The fallout units themselves are internally complex, reflecting waxing and waning of the eruption column, while many of the ignimbrites reflect multiple intra-plinian partial column collapse events associated with the injection of lithic clasts into the eruption column. The Lower and Upper Fasnia eruption phases were each terminated by caldera collapse and complete column collapse events. Probable blockage of the conduit and vent system during Lower Fasnia caldera collapse event briefly terminated the eruption, resulting in a short-lived period of erosion and sedimentation prior to the onset of the Upper Fasnia phase. The transition to the Upper Fasnia eruption phase coincided with the eruption of more geochemically homogeneous pyroclasts. In total, 62 km(3) of tephra were erupted, including 49 km(3) of juvenile clasts and > 12 km(3) of lithic clasts. The DRE volume of magma erupted was 13 km(3) (Lower Fasnia > 5 km(3), Upper Fasnia > 8 km(3)), two thirds of which (similar to 9-10 km(3)) was deposited purely by fallout. The Fasnia Member is one of the most complex plinian sequences known. (C) 2017 Elsevier B.V. All rights reserved.