granophyric

Liquid (l) is seen at the bottom right, the rest being vapor (v). (g) Primary vapor-rich inclusion at the tip of a quartz stringer (outlined for clarity) in the granophyric groundmass.

granophyre_photos.html 1998

Photomicrographs of areas within granophyric block found as a lithic in the "pf unit" at Alid volcanic center.

granophyre_photos.html 1998

Extreme U-Th disequilibrium in rift-related basalts, rhyolites and granophyric granite and the timescale of rhyolite generation, intrusion and crystallization at the Alid volcanic center, Eritrea: Journal of Petrology, v. 47, p. 2105-2122.

references 1998

Similar quartz grains in the granophyric blocks contain primary, 2-phase, vapor-rich fluid inclusions, consistent with vapor saturation during growth of these igneous phenocrysts.

Granophyre.html 1998

The presence of such inclusions requires that growth of the granophyric texture from the silicate melt was accompanied by degassing (2nd boiling).

Granophyre.html 1998

K/Na of the groundmass feldspar equals K/Na in pumiceous glass of the host pumice, hinting that the granophyric minerals grew by closed-system crystallization of the rhyolitic melt.

Granophyre.html 1998

Micrographic and granophyric textures are consistent with such undercooling, and will be most common in shallow intrusive settings where pressure remains high enough to retain ~1-1. 5 wt. % H2O.

Granophyre.html 1998

We have begun a study of porphyritic pyroxene rhyolite, erupted as pyroclastic flow, and its intrusive equivalent, ejected during the same eruption as blocks of miarolitic granite with spectacular granophyric groundmass.

Granophyre.html 1998

The granite's granophyric groundmass consists of intergrown quartz and potassium feldspar (~Or45), the latter consisting of plumose splays that nucleated directly from pre-existing phenocrysts.

Granophyre.html 1998

Rapid growth of the granophyric texture may have been initiated during quench/degassing episodes.

Granophyre.html 1998