Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (9) Citing Articles via Google Scholar Google Scholar Articles by McCaig, A. M. Articles by MacLeod, C. J. Search for Related Content GeoRef GeoRef Citation

Oceanic detachment faults focus very large volumes of black smoker fluids

¹ School of Earth and Environment, Leeds University, Leeds, LS2 9JT, UK
² Centre National de la Recherche Scientifique—Groupe de Géosciences Marines (CNRS UMR7097), Institute de Physique du Globe de Paris, France
³ Scottish Universities Environmental Research Centre Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride, G75 0QF, Scotland, UK
⁴ School of Earth, Ocean and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE, UK

It is generally assumed that the seawater-derived fluids that feed black smoker vent fields on the seafloor are discharged vertically from depths of 1–3 km. We present new oxygen and strontium isotope data that show that fluids at black smoker temperatures of 300–400 °C were focused along a low-angle detachment fault at 15°45'N near the Mid-Atlantic Ridge. Isotopic alteration is the most extreme ever reported from oceanic rocks altered at similar temperatures, indicating intensely focused fluid flow both in recharge and discharge parts of the hydrothermal system. Rare earth element mobility in the fault rocks demonstrates isotopic alteration by evolved hydrothermal fluids, not conductively heated seawater. The fault zone protolith was predominantly ultramafic, but also included mafic rocks, with metasomatic alteration to talc-tremolite-chlorite schists resulting mainly from chemical exchange between these lithologies during fluid flow. Fluids in equilibrium with this assemblage would be similar to ultramafic-hosted black smoker fluids. We present a new model in which hydrothermal circulation around detachment faults evolves from basalt hosted (TAG type), to footwall ultramafic hosted (Rainbow type), to low-temperature ultramafic hosted (Lost City type). Key features of our model are the intrusion of gabbro bodies immediately below the detachment to provide a heat source for circulation, and focusing of fluid flow into the detachment fault to allow venting away from the neovolcanic axis.

Key Words: ocean crust • hydrothermal circulation • oxygen isotopes • strontium isotopes • detachment faults • talc-tremolite schist

This article has been cited by other articles:

				F. J. Fontaine, M. Cannat, and J. Escartin Hydrothermal circulation at slow-spreading mid-ocean ridges: The role of along-axis variations in axial lithospheric thickness Geology, October 1, 2008; 36(10): 759 - 762. [Abstract] [Full Text] [PDF]