Page 89 - Volcanic Textures A Guide To The Interpretation of Textures In Volcanic Rocks

2. Dacite-siltstone peperite
The contact between feldspar-phyric dacite (P) and
siltstone (S) comprises of zone of intricate mixing
between the two. There is a clear transition from
dacite that contains thin lenses and seams of siltstone
(arrow) below the contact, to siltstone that contains
rags and elongate blobs of dacite above the contact.

Berserker Beds, Early Permian; Mount Chalmers,
Queensland.

3. Rhyolite-pumice breccia peperite
Recognition of peperite is sometimes especially
challenging. The magmatic component in this
example is represented by the flow-banded, blocky,
feldspar-phyric rhyolite clasts (C). The rhyolite
intruded and mixed with pumiceous breccia and
sandstone (Pb) that now forms a matrix between the
rhyolite clasts. The rhyolite-pumice breccia peperite
has gradational contacts with in situ rhyolitic breccia
and coherent rhyolite.

Mount Read Volcanics, Cambrian; DDH 102R (22-
32 m), Rosebery mine, western Tasmania.
4. Porphyritic rhyolite-fine sandstone peperite
Pillow-like masses of quartz- and feldspar-phyric
rhyolite (P) occur within massive fine sandstone (S),
along the top contact of an extensive, thick sill. The
sandstone is indurated and has a subconchoidal
fracture. The bulbous shapes of the porphyritic
rhyolite clasts are typical of globular peperite
described by Busby-Spera and White (1987).

Tennant Creek porphyry, Early Proterozoic; Tennant
Creek, Northern Territory.

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