gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1981.044.334.03 Chemical and Mineralogical Changes During Basalt-Seawater Interaction: Site 223, Leg 23, D.S.D.P., North-West Indian Ocean Papavassiliou C. Th. * Cosgrove M. E. Department of Geology, The University, Southampton, SO9 5NH

Present address: Laboratory of Mineralogy and Petrology, University of Athens, Ano Ilissia (Panepistimioupolis), Athens, Greece.

 6 1981 44 334 141 146 25 3 1980 27 8 1980 Copyright © 1981, The Mineralogical Society 1981 Abstract

The development of low- and hightemperature alteration products in a 23 m section of ocean-floor basalts is described. Analcime, calcite and dioctahedral smectite are ubiquitous. Trioctahedral smectite, smectite-chlorite mixed layers, chabazite and scolecite occur in the deeper sections with Fe3+ oxides/hydroxides progressively becoming more abundant in the upper regions. The upper layers of the sequence show marked chemical reduction. High-temperature chemical changes include Na and Mg enrichment accompanied by Ca and Fe2+ losses. Superimposed low temperature changes include gains in Fe3+ K, Li, and Rb, and losses in Na, Ca, and Fe2+ Many trace elements also show consistent behaviour.