Low temperature alteration of the ocean crust: a study of hydrothermal alteration of basalts from near the Australia Antarctic Discordance of the Southeast Indian Spreading Ridge

Abstract

The nature of long term, low temperamre hydrothermal alteration of the ocean crust has remained elusive, due mainly to the limited scope of previous studies, which used single or a very few 011 holes and samples representing only a few million years age range. As a result of the sampling strategy of Ocean Drilling Program Leg 187 near the Australian Antarctic Discordance region of the Southeast lndian Spreading Ridge, fresh and altered basalt, and glass, spanning 14 to 28 Ma, were recovered. These rocks, when combined with 0-7 Ma altered dredge basalts from the same region, provide an opportunity to study long-term alteration and to determine the most important intluencing factorts). Mgo content, loss on ignition, and amount of secondary minerals, were used to measure relative extent of alteration. Consideration of the relative penneability o ̋the basalts along with these indicators reveal that permeability seems to have a greater influence on degree of alteration than does the age of the rock.