Page 93 - Volcanic Textures A Guide To The Interpretation of Textures In Volcanic Rocks

Plate 16 — Rinds and crusts on pillow lobes
1. Multiple-rind structure in basaltic pillow lava
Some pillows in this outcrop show multiple-rind
structure, considered to indicate emplacement in
relatively shallow water (Kawachi and Pringle,
1988). The rinds of the pillows comprise an outer,
black sideromelane layer that is partly altered to
palagonite and which passes gradationally into dark
grey tachylite and tachylitic basalt. The multiple-rind
structure consists of: (A1, A2) one side of a broken
rind thrust over its counterpart; (B) overlapping
detached rinds; or (C) the inward buckling of a rind.
Overlapping rinds are in direct contact (A1), or else
separated by interpillow sediment (A2). The much
larger area of overlapping rinds at (D) may have been
formed by pulses in growth of the pillow lobe.

The interpillow sediment (S) is a mixture of shell
fragments, calcareous ooze and sideromelane
particles. A concentric zone of calcite filled vesicles
(v) occurs near the inner rind boundary of the pillow
rinds. Radial pipe vesicles (p), some filled with
calcite, are distributed in a narrow zone inside the
concentric vesicle zone. Subrounded vesicles are
scattered in the pillow core; many are filled with
calcite. Radial columnar joints dissect the pillow
surface (j) and extend inward to the pillow

Waiareka Volcanics, Eocene; Boatmans Harbour,
Oamaru, New Zealand

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