Page 156 - Volcanic Textures A Guide To The Interpretation of Textures In Volcanic Rocks

C. Mudstone intraclasts (M) in the basal polymict
lithic breccia of the unit shown in 31.1A and 31.1B
have slabby shapes and are preserved in various
stages of disintegration. The pale matrix consists of
abundant quartz and feldspar crystals, with lesser
relict pumice clasts and shards (evident in thin-
section).

Mount Read Volcanics, Cambrian; G10 Pit, Hercules
mine, western Tasmania.

D. This photomicrograph shows the crystal-rich
character of the sandstone matrix of the polymict
lithic breccia in 31.1C. Dominant components are
sub-angular feldspar (Fl) and quartz (Q) crystal
fragments, accompanied by black mudstone clasts
(M) and fine, sericitic interstitial material (altered,
formerly glassy shards). Plane polarised light.

Mount Read Volcanics, Cambrian; specimen 91-146,
G10 Pit, Hercules mine, western Tasmania.
2. Lithic clast-rich base of a volcaniclastic
megaturbidite
A. This field sketch shows coarse, polymict lithic
breccia (31.2B, 31.2C) at the base of a ~25 m thick
graded unit. Above the lithic-rich base is finer
volcaniclastic sandstone rich in pumiceous
components. The unit overlies medium bedded,
volcaniclastic sandstone. Although partly sheared,
the contact truncates the gently dipping bedding in
the underlying unit. The breccia is interpreted to be
the basal part of a deposit from a high-density
volcaniclastic turbidity current that eroded the
substrate.
Mount Read Volcanics, Cambrian; Hall Rivulet
Canal, western Tasmania.

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