Page 90 - Volcanic Textures A Guide To The Interpretation of Textures In Volcanic Rocks

5. Basalt-mudstone peperite in pillow basalt
This photograph shows a cross-section through a
basaltic pillow from which the outer, dark grey,
chilled margin has partly spalled (arrow). The matrix
between the spalled pillow fragments is grey,
massive, siliceous mudstone that was probably
unconsolidated when the basalt was emplaced.

Mount Read Volcanics, Cambrian; Hellyer mine,
western Tasmania.

6. Basalt-siliceous mudstone peperite
Textural zones at the margin of a basaltic pillow
consist of: the pale grey interior (I), a zone of ovoid
carbonate alteration spots (O) and the chloritic rim
(R). The spots may be altered varioles (radial
pyroxene and feldspar microlites).
Mount Read Volcanics, Cambrian; DDH HL52
(148.2 m), Hellyer mine, western Tasmania.
7. Basalt-siliceous mudstone peperite
Vesicular, pale green ro dark grey, chloritized basalt
clasts (C) are separated by grey massive, siliceous
mudstone (Mx). The basalt clasts have quenched
rims and curviplanar outlines.
Mount Read Volcanics, Cambrian; DDH HL53
(116.95 m), Hellyer mine, western Tasmania.
8. Altered basalt(?)-siliceous siltstone peperite
Blocky clasts of amygdaloidal, porphyritic, altered
basalt(?) display jigsaw-fit texture (J). The clasts are
separated by grey siltstone and some also contain
ovoid siltstone inclusions (S).
Mount Read Volcanics, Cambrian; DDH HL629
(570.9 m) Hellyer mine, western Tasmania.
9. Altered basalt(?)-siliceous siltstone peperite
The distribution of dark grey basalt(?) clasts varies
from jigsaw-fit clusters, to clasts dispersed in pale
grey, siliceous siltstone matrix. Adjacent to the clasts,
the colour of the siltstone becomes paler, possibly
reflecting induration.
Mount Read Volcanics, Cambrian; DDH MCH1 (380
m), Mount Charter, western Tasmania.
Plate 15 — Pillowed lava flows and pillows

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