Petrology of the ultramafic and basic rocks of betancuria massif,fuerteventura Island (Canarian Archipelago) |
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| Authors: | P Gastesi |
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| Abstract: | The petrological and geochemical aspects of the ultramafic and basic plutonic rocks of Betancuria Massif are examined. The rocks consist of gradational varieties of wehrlite, pyroxenite, olivine-gabbro and gabbro formed mainly by magnesium-rich olivine, clinopyroxene and plagioclase. The Complex exhibits structures and textures characteristic of layered igneous rocks;i.e., banding, layering, lamination, etc...; rocks are therefore considered as cumulates or magmatic sediments. The Complex has undergone a deep process of alkalinisation produced by the syenite and trachyte ring-dykes intrusion and by the existence of carbonatite veins. Rocks close to the syenite-trachyte intrusions show an increase in alkali feldspars. The presence of amphibole (kaersutite) is the first steep in the alkalinisation process and it is related to the disappearence of pyroxene. Extreme transformations of the gabbroidic rocks are found when they come in contact with the carbonatites. The age of the Complex is unknown but field evidence lead us to conclude that it is older than any other visible formation of the Island. |
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