rhyolitic lava

rhyolitic lava

[¦rī·ə¦lid·ik ′lä·və]
(geology)
A highly viscous, silica-rich lava.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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We studied 35 slabs of peralkaline rocks: 22 samples of vitrophyre facies of the ignimbritic deposits and 13 samples of glassy facies of porphyritic rhyolitic lava flows having the same chemical affinity.
In accord with previous analysis, results obtained by this approach on obsidians at the base of some peralkaline rhyolitic lava flows show also low Sr values that can be related to different percentages of alkali feldspar fractionation.
The peralkaline rhyolitic lavas and the metaluminous rhyolite were used as references for the geochemical discrimination.
2) Rocks of Early Permian ages (Pinero and Mata Oscura granites) were emplaced at swallow depth of the cortical block, in a relatively quiescent period at the end of the Appalachian orogeny, together with an Early Permian rhyolitic lava flow event of the Guacamayas volcanics, therefore they both could be part of the same mayor igneous event, emplaced in deep to shallow environments.
The Guacamayas Volcanic rocks have been grouped from old to young in: a) Teresen Rhyolitic Suite composed by flows of rhyolitic lavas interlayered with ash tuffs, agglomerate and sandstone, whose stratigraphic relations allow to separate three volcanic episodes with its pyroclastics equivalent, that from bottom up are: Corcovado Rhyolite, Tirado Rhyolite and La Bandola Rhyolite; b) El Penon Latitic Suite is composed by a sequence of porphyritic latitic lavas and flows of glassy tuffs that culminate in a thick accumulation of tuffs and agglomerates; it is divided in two subunits (El Oso Quartz Latite, Segoviera Rhyolite) with transitional contact between them.
The granophyres are progressively covered by rhyolitic lava flows.
a) Rhyolitic lavas, occasionally with porphyritic textures (approximately 10 to 15% of alkali feldspar and/or quartz phenocrysts), with vesicular levels filled by calcite, zeolite and quartz.
In southern Jordan, this structure has been subdivided into the lower Aqaba complex, comprised of a sequence of schistose and gneissic metamorphic remnants and plutonic rocks, and the overlying Araba complex, made up principally of alkaline, rhyolitic lavas and sub-volcanic intrusions.