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?
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.
This host unit is underlain by a sequence of aphyric
andesite or latite volcanic flows which to date have not been found to host mineralization.
The marginal zones of the dyke are aphyric
and free of xenoliths and megacrysts, both of which were concentrated in the dyke interior by flow differentiation and show varying degrees of flow alignment (Fig.
This is close to the composition of aphyric
komatiites and chilled margins of komatiitic flows.
Thus, the porphyritic rock types are the result of mineral accumulation, and the aphyric
rock types are the result of mineral separation.
All three holes intersected interbedded units of massive grey aphyric
ryholite and intermediate to felsic tuffaceous rocks and bottomed in K-feldspar-quartz augen schist.
The fragmentation depth for the aphyric
magma occurs near the base of the conduit for water contents of 10% or more.
The rarer type of tuff is a foliated, green-grey aphyric
felsite with a porcelain-like texture.
At least a few aphyric
basalts on most oceanic islands have Mg# values around 0.