Abstract

Variolitic structures in the marginal zone of deep-water Ordovician pillow lava from the Solund area (western Norway) are thought to be primary and formed by liquid immiscibility in the basaltic magma at the time of eruption. The presence of these structures in connection with amygdale-free pillows, their association with hyaloclastite breccia almost free of shards in the matrix, and their apparent absence in subglacial and subaerial basaltic lava indicate formation in a deep-water environment under relatively high hydrostatic pressures.

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