The maficdykes in Wadhrai show considerable variation in texture and modal composition from distinctly porphyritic to aphyric
, medium to (mostly) fine-grained, and fairly fresh to completely altered (Fig.
The microstructure of this facies is aphyric
to porphyritic (Fig.
Trachyphonolites and trachytes are porphyritic to aphyric
. The phenocrysts are alkali feldspar (Or60-65) [+ or -] clinopyroxene (Wo46-49Fs14-20) [+ or -] plagioclase (An14-16), pseudomorphosed leucite, amphibole, and biotite in a hypocrystalline to glassy groundmass containing microlites of alkali feldspar, biotite, and clinopyroxene [+ or -] biotite [+ or -] amphibole [+ or -] magnetite [+ or -] Ti-andradite [+ or -] haematite.
The Endeavour Seamount lava is highly plagioclasephyric, but all others are aphyric
to sparsely phyric (plagioclase +/- olivine, rare clinopyroxene).
The settling and flotation of cumulus crystals is also restricted to low viscosity aphyric
magmas, which would allow rapid and unimpeded vertical movements of cumulus crystals.
They present quartz and K-feldspar phenocrysts in an aphyric
matrix composed by quartz, K-feldspar(orthoclase?) and clinopyroxene.
Unit F is composed of essentially aphyric
basalt of varied petrography and chemistry, which suggests that it consists of at least two flows, although they were not distinguished in the field.
The mafic rocks are porphyritic to aphyric
and consist of calcic plagioclase, clinopyroxene +- olivine or hornblendic amphibole, ilmenite, titanite, and a range of secondary minerals.
Dacites are minor in the Sabalan region and occur mostly as aphyric
lavas associated with trachyandesites.
This is close to the composition of aphyric
komatiites and chilled margins of komatiitic flows.