Abstract
The Miocene sequence of felsic extrusive rocks of about 1000 m total thickness on Gran Canaria is divided into three units: a) A lower unit of trachytic rhyolites (lavas, composite flows, ignimbrites) characterized by a phenocryst assemblage of anorthoclase (Or15–20, wt%), clinopyroxene, hypersthene (amphibole substituted for both in ignimbrites), and Fe/Ti-oxides. The commonest groundmass minerals are anorthoclase and alkali-amphibole, with minor quartz and aegirine. b) A middle unit of comenditic and pantelleritic ignimbrites characterized by anorthoclase (Or20–32) and amphibole. Phenocryst minerals restricted to individual flows are Fe/Ti-oxides (several comendites), clinopyroxene, biotite, and sphene. The commonest groundmass minerals are anorthoclase and Tiaegirine, with lesser katophorite, arfvedsonite and quartz. c) An upper unit of trachvtic and phonolitic ignimbites and lava flows (normative ne rarety exceeding 10%) with nepheline phonolite lava flows becoming increasingly abundant upwards. The ignimbrites have mostly anorthoclase (Or30-04), and biotite, with rarer Fe/Ti-oxides, hornblende, and clinopyroxene. The commonest groundmass minerals are anorthoclase, aegirine, and alkali-amphiboles, and in some flows nepheline.
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