Teagle, D. A. H.; Alt, J. C.; Halliday, A. N. (1998): Tracing the evolution of hydrothermal fluids in the upper oceanic crust; Sr-isotopic constraints form DSDP/ODP Holes 504B and 896A. Geological Society of London, London, United Kingdom, In: Mills, R. A. (editor), Harrison, K. (editor), Modern ocean floor processes and the geological record, 148, 81-97, georefid:1999-034042
Abstract:
Whole rock and secondary mineral (super 87) Sr/ (super 86) Sr determinations from ODP Holes 504B and 896A have been compiled into a profile for the upper 2 km of in situ ocean crust to constrain the composition and evolution of recharge and discharge fluids. There is a gradual trend from elevated (super 87) Sr/ (super 86) Sr whole rock ratios at the top of the crust towards primary MORB compositions at the base of the sheeted dykes. Rocks from the mineralized lava-dyke transition zone have (super 87) Sr/ (super 86) Sr ratios clustering in the range of black smoker fluids. Igneous and alteration phases are not in Sr-isotopic equilibrium, therefore whole rock strontium isotopic ratios reflect the proportion of secondary minerals and the extent of plagioclase recrystallization. The (super 87) Sr/ (super 86) Sr of anhydrite directly records the chemical evolution of seawater during recharge. There is a slight decrease in anhydrite (super 87) Sr/ (super 86) Sr with depth in the volcanic rocks but anhydrite from the lowermost dykes yields diabasic (super 87) Sr/ (super 86) Sr ratios. Epidotes in cross-cutting veins have higher (super 87) Sr/ (super 86) Sr than the background alteration recorded by amphibole in the lower dykes. This elevated signature reflects the (super 87) Sr/ (super 86) Sr of 504B black smoker-type fluids and requires less fluid evolution than the background alteration, suggesting channelling of recharge fluids locally.
Coverage:
West: -85.0000 East: -83.0000 North: 2.0000 South: .0000
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