The sub-aerial basement shield of Tenerife is comprised largely of basanites, ankaramites, and rarer oceanites. Near the centre of the island, in the area now termed Las Canadas, extensive intermediate and salic volcanism followed the shield building stage,producing the Vilaflor volcanic complex. Detailed mapping indicates that the Vilaflor volcanics were erupted from a series of poorly defined centres lying along an east-west fissure, one of two or possibly three fissures that have dominated the major sub-aerial volcanic history of Tenerife. In the major growth period of the Vilaflor complex, traehybasanite, plagioclase phonolite, and phnnolite flows were erupted, along with phonolitic pumice lapilli,s coria, and an ash flow. Following this the final growth period represents a restriction of volcanism to local centres, phonolites were the dominant rock type and viscous flows, thick pumice lapilli and abundant volcanoclastic deposits were formed. A major collapse along the length of the complex completely removed the northern part and some of the southern part of the complex,leaving two depressions,bounded southward by two curved escarpments, the Portillo escarpmen in the east,and the Tauce escarpment in the west. Comparison of the escarpments with the Orotave and Guimar valleys on Tenerife, El Golfo on Hierro, and La Taburiente caldera on La Palma, indicates that landsliding, in conjunction with magmatic processes has produced all these features. Post-collapse activity north of the escarpments has built up the twin volcanoes of Viejo and Teide, both displaying central and flank vent activity. Viejo is surmounted by a dormant caldera, whilst Teide displays weak fumerole activity from the top cone, El Piton, and from an arcuate region on the southern flanks.The Viejo flows are trachybasanites, rarer plagioclase phonolites and late, viscous phonolites. The Teide volcanics are entirely phonolitic. Chemically the rocks are divided into basanites, trachybasanites, plagioclase phonolites, and phonolites, they are all strongly alkaline, and most are strongly undersaturated. High-alumina trachybasanites are very common whilst the phonolites are very variable in degree of undersaturation,and minor element geochemistry. The suite is thought to be formed by crystal fractionation from a basanite parent.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:623119 |
| Date | January 1968 |
| Creators | Ridley, William Ian |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/16059 |
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