Page 57 - Volcanic Textures A Guide To The Interpretation of Textures In Volcanic Rocks

5. Planar flow banding in recrystallized dacitic lava
Planar, laterally continuous flow banding is
particularly well-developed in this evenly
porphyritic, feldspar-phyric dacite. The flow bands
accommodate the prominent siliceous boudin-like
structures which are probably the result of nodular
devitrification and overprinting siliceous alteration.

Mount Read Volcanics, Cambrian; Mount Huxley,
western Tasmania.

6. Flow folds in a rhyolite dyke
Highly contorted flow bands occur here in a fine-
grained, sparsely porphyritic rhyolite dyke. Flow
bands are defined by varying spherulite and
phyllosilicate content, and in the degree of
recrystallization.

Rhyolite dyke associated with the Lower Rhyolitic
Tuff Formation, Ordovician; Llanberis Pass,
northern Wales, UK.

7. Planar flow lamination in altered dacite
Flow lamination (arrow) comprises pink siliceous
domains that alternate with pale green domains. Dark
green, phyllosilicate stringers (S) transect the flow
foliation and overprint any pre-existing flow laminae.
Mount Read Volcanics, Cambrian; DDH SCS2

(102.2 m), Sock Creek South, western Tasmania.
8. Trachytic texture in basalt in thin-section
Clinopyroxene and plagioclase phenocrysts are set
within a finer grained groundmass of strongly flow-
aligned plagioclase laths, exemplifying trachytic
texture. Plane polarized light.
Mount Read Volcanics, Cambrian; DDH MC-1D
(256.9 m), Mount Charter, western Tasmania.
50