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Title: Ferromagnesian minerals from the volcanic suite of Tenerife
Author: Scott, Peter Wright
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1971
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The Tenerife rocks have been classified as ankaramites, alkali basalts, trachybasalts, trachyandesites, trachytes and phonolites on the basis of their chemical and petrographic characteristics. Wet chemical and microprobe analyses and some optical data for olivines, pyroxenes, micas, garnets and sphene are presented; and, cell parameters for olivines, pyroxenes, garnet and sphene are also given. Olivine is restricted in its occurrence to the more basic rocks and is always forsterite rich (approx. Fo 80), although it may become more fayalitic in the groundmasses. A salitic clinopyroxene is present throughout the suite but aegirine is developed in the groundmass of some phonolites and in a nepheline-syenite boulder. The salites show only limited enrichment in hedenbergite with magmatic differentiation whilst the aegirines are enriched in diopside relative to hedenbergite. This is thought to be due to the limited amounts of Fe2+ present in the "parental" magmas after the removal of varying proportions of olivine and kaersutite. Seven types of zoning have been recognised in the salites: normal, reversed, irregular, large scale oscillatory, minute scale oscillatory, hourglass, and a special "zoning" caused by the presence of green cores. The origin of most types of zoning can be explained by changes in conditions during crystallisation, but it appears unlikely that hourglass crystals have formed as suggested by Strong (1969). A kaersutite of uniform composition occurs in most rock types although it becomes barkevikitic in the salic differentiates. It is thought to have formed as a stable cumulus phase at depth in magmas of intermediate composition but to have become unstable on being brought to the surface. The presence of magnesioarfedsonite and aenigmatite in the groundmass of some phonolites indicates crystallisation under low oxygen fugacities. A titaniferous, relatively magnesium-rich, biotite, and melanite and sphene are found in the phonolites as minor phenocrystal phases.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available