Mineral Chemistry of Primary and Secondary Phases in Basaltic Rocks, Leg 129

Rowbotham, G.; Floyd, P. A.

doi:10.2973/odp.proc.sr.129.127.1992

Cited by 16 publications

(3 citation statements)

References 24 publications

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“…Plagioclase phenocrysts exhibit a systematic chemical variation between labradorite/bytownite cores (An 60 –An 75 ) and andesine/labradorite rims (An 37 –An 63 ). Such features of plagioclase composition are concordant with those reported for tholeiitic basalts from Hole 801C [ Rowbotham and Floyd , 1992; Bourasseau , 1996]. The plagioclases are K‐poor (Or 0–1 ) but a true K‐feldspar (Or 99 ) was observed associated with secondary phyllosilicates replacing plagioclase.…”

Section: Resultssupporting

confidence: 86%

“…, the formation mechanism, in the study samples, of phyllosilicates with intermediate compositions between celadonite and Mg-smectite if demonstrated to be mixed layered could be the progressive transformation of a phyllosilicate precursor as already suggested byRowbotham and Floyd [1992].…”

supporting

confidence: 60%

“…Phyllosilicates with intermediate chemical composition between Mg‐smectite and celadonite, may be defined as transitional phases that could either be mixed‐layered phases or mixtures between two distinct minerals. Since direct precipitation from solution is not an adequate mechanism for the formation of mixed‐layer clays [ Srodon , 1999], the formation mechanism, in the study samples, of phyllosilicates with intermediate compositions between celadonite and Mg‐smectite if demonstrated to be mixed layered could be the progressive transformation of a phyllosilicate precursor as already suggested by Rowbotham and Floyd [1992].…”

Section: Discussionmentioning

confidence: 93%

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Low‐temperature alteration of mesozoic oceanic crust, Ocean Drilling Program Leg 185

Talbi

Honnorez

2003

Geochem Geophys Geosyst

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[1] Basalts drilled from the Mesozoic crust at Ocean Drilling Program (ODP) Sites 801 and 1149 during Leg 185 have been affected by a succession of submarine, variably oxidative alteration processes by cold seawater. The low-temperature alteration resulted in various combinations of secondary minerals both as replacements of igneous phases, and as void and crack fillings. Mg-smectite, calcite, celadonite and Feoxyhydroxide are the dominant secondary minerals. Quartz, chalcedony and phillipsite are always very minor phases that fill open spaces. The rocks generally exhibit concentric haloes, 0.5 to 1 cm in thickness, around gray inner cores and usually adjacent to exposed surfaces. Color zonations result from the abundance of various secondary mineral assemblages present in each zone. The green rocks are dominated by celadonitic phyllosilicates, whereas the dusky red haloes are characterized by abundant iddingsite and Fe-oxyhydroxides replacing the fine clinopyroxene. Finally Mg-smectite ± calcite, are the most common secondary phases in the inner gray cores. The most unusual effects of the low-temperature alteration of the study rocks are the pervasive, pale green to gray green color and the relatively abundant dusky red haloes surrounding inner reddish gray cores. Alteration of Mesozoic crust cored during Leg 185 is comparable with low-temperature alteration of 310 m thick uppermost volcanic section of the 5.9 My old crust of Hole 504B. Except the renewed precipitation of calcite in veins, the aging of oceanic crust does not depend on time probably because it occurs during the first few millions of years after the accretion, and ceases when the crust is sealed off.Components: 13,976 words, 12 figures, 9 tables.