Porphyritic rhyolite

The intrusion of the Admiralty plutons was accompanied by the eruption of porphyritic rhyolites at Gallipoli Heights (72°26 S, 163°48 E) in the southern Freyberg Mountains located in the eastern province of the Wilson Terrane in Fig. 4.19 (Gair et al. 1969). 

The early Earth was probably much more geothermaUy active than the Earth is today. [122] The continents of early Earth were most likely small with vertical profiles at, or near, sea-level. [125,181] Subaerial (in addition to submarine) tectonic rift zones and hydrothermal vent fields were probably ubiquitous and vigorous. [182] Extensive continental hydrothermal zones enriched in reducing inorganic and organic vent products and subject to wet/dry cycles were probably common. The low-profile shield continents of the early Earth must have been extensively surfaced with basalt and rhyolite, [183] some of which could have been porphyritic. 

Lake to just south of where the Victoria River empties into Red Indian Lake (Fig. 1). Light grey-green to white, dacitic to rhyolitic quartz-feldspar-porphyritic... 

W21d. 12.27.63) Rhyolite, grayish red with prominent red-brown flow banding. Porphyritic texture, highly embayed quartz, and pseudomorphs of seridte after feldspar with inclusions of altered pumice. Red-Brown Member, Bragg Valley, southern... 

Acidic rocks occurring in dykes or sills are often porphyritic, quartz porphyry being the commonest example. Quartz porphyry is similar in composition to rhyolite. 

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