title: Talc-dominated seafloor deposits reveal a new class of hydrothermal system.
abstract: The Von Damm Vent Field (VDVF) is located on the flanks of the Mid-Cayman Spreading Centre, 13 km west of the axial rift, within a gabbro and peridotite basement. Unlike any other active vent field, hydrothermal precipitates at the VDVF comprise 85-90% by volume of the magnesium silicate mineral, talc. Hydrothermal fluids vent from a 3-m high, 1-m diameter chimney and other orifices at up to 215 °C with low metal concentrations, intermediate pH (5.8) and high concentrations (667 mmol kg(-1)) of chloride relative to seawater. Here we show that the VDVF vent fluid is generated by interaction of seawater with a mafic and ultramafic basement which precipitates talc on mixing with seawater. The heat flux at the VDVF is measured at 487±101 MW, comparable to the most powerful magma-driven hydrothermal systems known, and may represent a significant mode of off-axis oceanic crustal cooling not previously recognized or accounted for in global models.
authors.affiliation: National Oceanography Centre, Waterfront Campus, Southampton SO14 3ZH, UK.|Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton SO14 3ZH, UK.
authors.forename: Matthew R S
authors.initials: MR
authors.lastname: Hodgkinson
authors.affiliation: National Oceanography Centre, Waterfront Campus, Southampton SO14 3ZH, UK.
authors.forename: Alexander P
authors.initials: AP
authors.lastname: Webber
authors.affiliation: Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton SO14 3ZH, UK.
authors.forename: Stephen
authors.initials: S
authors.lastname: Roberts
authors.affiliation: Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton SO14 3ZH, UK.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Mills
authors.affiliation: National Oceanography Centre, Waterfront Campus, Southampton SO14 3ZH, UK.
authors.forename: Douglas P
authors.initials: DP
authors.lastname: Connelly
authors.affiliation: National Oceanography Centre, Waterfront Campus, Southampton SO14 3ZH, UK.
authors.forename: Bramley J
authors.initials: BJ
authors.lastname: Murton