Mineralogy and Geochemistry of Alteration Products in Leg 81 Basalts

Abstract

Alteration products of basalts from the four holes drilled during Leg 81 were studied and found to be characterized by the widespread occurrence of trioctahedral clay minerals (Mg smectite to chlorite). In some cases zeolites (analcite, chabazite) are associated with the saponite. A more oxidizing stage is marked by a saponite-celadonite association, presenting the geochemical characteristics of hydrothermal processes. Later stages of alteration are represented by palagonitization and subaerial weathering at two sites. These different alteration processes of basalts from Leg 81 record the paleoenvironment during the first opening stages of the Northeast Atlantic Ocean in the Paleocene-Eocene periods.

Morphological, Chemical, and Isotopic Evidence for an Early Diagenetic Evolution of Detrital Smectite in Marine Sediments

“…Since the work of Biscaye (1965) and earlier studies, clay minerals in Recent sediments in the Atlantic Ocean have been considered to be mainly of detrital origin (Chamley, 1979;Grousset, 1983), except for those in volcano-sedimentary sequences (Chamley and Bonnot-Courtois, 1981) and in material near hydrothermal effusive structures (Desprairies et al, 1984). Strontium (Dasch, 1969) and oxygen Epstein, 1970a, 1970b) isotope data support such interpretation.…”

Lithium and its isotopes as tracers of subduction zone fluids and metasomatic processes: Evidence from the Catalina Schist, California, USA

“…Previous workers have suggested that uptake of Li in basalt during seafloor alteration is tied to the stabilization of secondary minerals such as smectite (saponite), celadonite, and phillipsite, with Li residing in octahedral sites in suitable phases (Chan et al, 2002;Vigier et al, 2008). Major and trace element analyses of these minerals in various modern sedimentary and altered basalt settings indicate that the LILE tend to be incorporated into interlayer sites in illite/celadonite (perhaps also K-rich phillipsite), whereas Li is more concentrated in Mg-rich phases such as saponite and other K-poor smectite phases (see Desprairies et al, 1984;Berndt and Seyfried, 1986;Heling et al, 1992;Porter et al, 2000). Varying relative modal abundances of these phases, among a suite of samples from the same site, would result in a general lack of correlation between concentrations of Li and LILE in the same rocks, whereas the LILE would tend to show co-enrichments because of their general similarity in geochemical behavior (see Fig.…”

Palaeoenvironmental significance of clay minerals in Upper Cenomanian–Turonian sediments of the Western High Atlas Basin (Morocco)

“…A global increase in explosive volcanism coinciding with the flooding of land areas, the low tectonic activity and subsidence in the margin basins as well as a hot and seasonally humid climate are contributing factors to the sedimentation of smectite in marine environments. Thus, four main genetic hypotheses were frequently invoked to explain smectite occurrences in these sediments: (1) inheritance from continental input and soils and enrichment by differential settling (Chamley & Debrabant, 1982;Robert, 1982;Chamley, 1989); (2) alteration of oceanic volcanic rocks (Desprairies & Bonnot-Courtois, 1980;Desprairies et al, 1981;Claparols et al, 1990);…”