Explosive ocean-island volcanism: the 1.8–0.7 Ma explosive eruption history of Cañadas volcano recorded by the pyroclastic successions around Adeje and Abona, southern Tenerife, Canary Islands

2011-11-25T14:33:47Z (GMT) by Pablo Dávila Harris
The 1.8 to 0.7 Ma explosive eruption history of Las Cañadas volcano is recorded by the pyroclastic stratigraphy of southern Tenerife. A large pyroclastic apron is well exposed in the Bandas del Sur. It is divided into two regions, Adeje (southwest) and Abona (southeast). The lower stratigraphy of both successions is described here for the first time, and is divided into soil-bound eruption-units. The lithofacies record repeated phonolite explosive eruptions involving Plinian eruption columns and ignimbrite emplacement, with sedimentary reworking and soilification during repose intervals. The southwestern pyroclastic apron of Cañadas, around Adeje, includes eleven eruption-units, with one explosive eruption every 24,300–31,200 years. Two major unconformities are identified in this region, each representing ~0.6 myr hiatuses. The southeastern pyroclastic apron, around Abona, reveals nine newly discovered phonolitic eruption-units, eight of which are dated by 40Ar/39Ar. The eruptions span 1.6 Ma, and occurred with frequencies averaging one per 21,000 years to one per 79,556 years. The deposits include welded and non-welded ignimbrites and numerous fallout layers. Documentation of the ‘lower’ Bandas del Sur Group allows the entire pyroclastic record of southeast Tenerife to be constrained for the first time: over 18 explosive eruptions occurred during the past 1.6 myr, of which 7 may have been caldera-forming. Eruption frequencies cluster and are separated by unconformities that span from 184,000–563,000 years. A debris-avalanche deposit was discovered on the southeast flank of Cañadas. It records a catastrophic landslide, the Abona landslide, triggered by a phonolite explosive eruption 735 ± 5 ka ago. The Abona debris-avalanche deposit is enclosed between pyroclastic units of the Helecho Formation, and represents a single eruptionunit. Debris avalanche block and mixed facies, and a hummocky topography that dammed small ephemeral perched lakes, are exceptionally well-preserved. Limited disruption and mixing, and a general absence of clast segregation within the deposit, indicate that the landslide did not move as a rapid granular flow. The debris-block characteristics indicate that pervasive shattering and microbrecciation occurred progressively during transport, and were accompanied by limited shear, mixing and substrate erosion during predominantly laminar emplacement of a dilated, but essentially solid, shearing mass. The deposit is the only precisely dated giant landslide on Tenerife and provides the first unequivocal evidence of an eruption trigger on an ocean-island volcano.




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