Controls on hydrothermal alteration in a section of fast-spreading oceanic crust

Expedition 335 summary

“…Very low P 2 O 5 concentrations (<0.02 wt%) indicate low (<5%) proportions of trapped intercumulus liquids. Similar but less detailed observations are recorded from Hess Deep (Francheteau et al, 1992;Gillis, 1995).…”

“…Field mapping from the lower crust of the Oman ophiolite (e.g., Kelemen and Aharonov, 1998;MacLeod and Yaouancq, 2000;Nicolas and Boudier, 1991;Nicolas et al, 2000) and submersible studies and shallow drilling of EPR crust at Hess Deep (e.g., Francheteau et al, 1992;Gillis, 1995;Karson et al, 1992Karson et al, , 2002Natland and Dick, 1996) may be useful in this respect. However, because of the difficulties of detailed mapping and sampling using submersibles and remotely operated vehicles (ROVs) and the lack of deep drilling of the dike/gabbro boundary in Hess Deep, the well-exposed outcrops in Oman arguably provide the best available guide to the upper plutonic section of fast-spreading ocean crust (Fig.…”

“…Mineral geothermometers, crosscutting vein mineral sequences coupled with trace elements and strontium, and stable isotopic measurements of whole-rock samples and mineral separates can be used to establish the chemistry of fluids reacting with the lower crust (Gregory and Taylor, 1981;Bach et al, 2004;Coggon et al, 2004;Gillis, 1995;Manning et al, 1996;Teagle et al, 1998aTeagle et al, , 1998b. By looking at 87 Sr and 18 O profiles away from hydrothermal mineral veins, we can establish the scale of fluid channeling in the lower crust (e.g., Bickle, 1992;Teagle and Bickle, 1993).…”

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“…Field mapping from the lower crust of the Oman ophiolite (e.g., Kelemen and Aha-ronov, 1998;MacLeod and Yaouancq, 2000;Nicolas and Boudier, 1991;Nicolas et al, 2000) and submersible studies and shallow drilling of EPR crust at Hess Deep (e.g., Francheteau et al, 1992;Gillis, 1995;Karson et al, 1992Karson et al, , 2002Natland and Dick, 1996) may be useful in this respect. However, because of the difficulties of detailed mapping and sampling using submersibles and remotely operated vehicles (ROVs) and the lack of deep drilling of the dike/gabbro boundary in Hess Deep, the well-exposed outcrops in Oman arguably provide the best available guide to the upper plutonic section of fast-spreading ocean crust (Fig.…”

“…Mineral geothermometers, crosscutting vein mineral sequences coupled with trace elements and strontium, and stable isotopic measurements of whole-rock samples and mineral separates can be used to establish the chemistry of fluids reacting with the lower crust (Gregory and Taylor, 1981;Bach et al, 2004;Coggon et al, 2004;Gillis, 1995;Manning et al, 1996;Teagle et al, 1998aTeagle et al, , 1998b. By looking at 87 Sr and 18 O profiles away from hydrothermal mineral veins, we can establish the scale of fluid channeling in the lower crust (e.g., Bickle, 1992;Teagle and Bickle, 1993).…”