@article {Seyfried2015,
	title = {{The Lost City hydrothermal system: Constraints imposed by vent fluid chemistry and reaction path models on subseafloor heat and mass transfer processes}},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {163},
	year = {2015},
	pages = {59{\textendash}79},
	abstract = {Since the first reported discovery of the Lost City hydrothermal system in 2001, it was recognized that seawater alteration of ultramafic rocks plays a key role in the composition of the coexisting vent fluids. The unusually high pH and high concentrations of H2 and CH4 provide compelling evidence for this. Here we report the chemistry of hydrothermal fluids sampled from two vent structures (Beehive: \~{}90{\textendash}116 {\textdegree}C, and M6: \~{}75 {\textdegree}C) at Lost City in 2008 during cruise KNOX18RR using ROV Jason 2 and R/V Revelle assets. The vent fluid chemistry at both sites reveals considerable overlap in concentrations of dissolved gases (H2, CH4), trace elements (Cs, Rb, Li, B and Sr), and major elements (SO4, Ca, K, Na, Cl), including a surprising decrease in dissolved Cl, suggesting a common source fluid is feeding both sites. The absence of Mg and relatively high concentrations of Ca and sulfate suggest solubility control by serpentine{\textendash}diopside{\textendash}anhydrite, while trace alkali concentrations, especially Rb and Cs, are high, assuming a depleted mantle protolith. In both cases, but especially for Beehive vent fluid, the silica concentrations are well in excess of those expected for peridotite alteration and the coexistence of serpentine{\textendash}brucite at all reasonable temperatures. However, both the measured pH and silica values are in better agreement with serpentine{\textendash}diopside{\textendash}tremolite-equilibria. Geochemical modeling demonstrates that reaction of plagioclase with serpentinized peridotite can shift the chemical system away from brucite and into the tremolite stability field. This is consistent with the complex intermingling of peridotite and gabbroic bodies commonly observed within the Atlantis Massif. We speculate the existence of such plagioclase bearing peridotite may also account for the highly enriched trace alkali (Cs, Rb) concentrations in the Lost City vent fluids. Additionally, reactive transport modeling taking explicit account of temperature dependent rates of mineral dissolution and precipitation clarifies the feedback between permeability, heat loss, and changes in the dissolved Si of the vent fluids. Assuming both the Beehive and M6 vent fluids were sourced at similar subseafloor conditions (tremolite buffered at 200 {\textdegree}C), model results indicate loss of approximately 30{\%} Si upon cooling to \~{}150 {\textdegree}C during upflow. However, Si concentrations remained largely conservative with continued cooling to lower temperatures owing to unfavorable reaction kinetics. While consistent with the Beehive endmember composition, these results fail to explain the relative Si depletion in the lower temperature M6 fluids. Thus, it may be that more robust kinetic models for silicates are needed to accurately account for the mechanism and rate of silica removal in the unusually high pH of the Lost City vent fluids.},
	keywords = {HOV Alvin (Human Occupied Vehicle)},
	doi = {10.1016/j.gca.2015.04.040},
	author = {Seyfried, W E and Pester, N J and Tutolo, B M and Ding, K}
}
@article {Pester2011,
	title = {{A new Fe/Mn geothermometer for hydrothermal systems: Implications for high-salinity fluids at 13{\textdegree}N on the East Pacific Rise}},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {75},
	number = {24},
	year = {2011},
	pages = {7881{\textendash}7892},
	abstract = {Field and experimental investigations demonstrate the chemistry of mid-ocean ridge hydrothermal vent fluids reflects fluid{\textendash}mineral reaction at higher temperatures than those typically measured at the seafloor. To account for this and, in turn, be able to better constrain sub-seafloor hydrothermal processes, we have developed an empirical geothermometer based on the dissolved Fe/Mn ratio in high-temperature fluids. Using data from basalt alteration experiments, the relationship; T ({\textdegree}C)~=~331.24~+~112.41*log[Fe/Mn] has been calibrated between 350 and 450~{\textdegree}C. The apparent Fe{\textendash}Mn equilibrium demonstrated by the experimental data is in good agreement with natural vent fluids, suggesting broad applicability. When used in conjunction with constraints imposed by quartz solubility, associated sub-seafloor pressures can be estimated for basalt-hosted systems. As an example, this methodology is used to interpret new data from 13{\textdegree}N on the East Pacific Rise, where high-temperature fluids both enriched and depleted in chloride (339{\textendash}646~mmol/kg), relative to seawater, are actively venting within a close proximity. Accounting for these variable salinities, active phase separation is clearly taking place at 13{\textdegree}N, yet the fluid Fe/Mn ratios and the silica concentrations suggest equilibration at temperatures less than those coinciding with the two-phase region. These data show the chloride-enriched fluid reflects the highest temperature and pressure (\~{}432~{\textdegree}C, 400~bars) of equilibration, consistent with circulation near the top of the inferred magma chamber. This is in agreement with the elevated CO2 concentration relative to the chloride-depleted fluids. The noted temperature derived from the Fe/Mn geothermometer is higher than the critical temperature for a fluid of equivalent salinity. This carries the important implication that, despite being chloride-enriched relative to seawater, these fluids evolved as the vapor component of even higher salinity brine.},
	keywords = {HOV Alvin (Human Occupied Vehicle)},
	issn = {0016-7037},
	doi = {10.1016/j.gca.2011.08.043},
	url = {http://dx.doi.org/10.1016/j.gca.2011.08.043},
	author = {Pester, N J and Rough, M and Ding, K and Seyfried, W E}
}
@inbook {Pester2008,
	title = {{The chemistry of diffuse-flow vent fluids on the Galapagos Roft (86 degrees W) : temporal vaiability and subseafloor phase equilibria controls}},
	booktitle = {Magma to microbe : modeling hydrothermal processes at ocean spreading centers},
	series = {Geophysical Monograph},
	number = {178},
	year = {2008},
	pages = {123{\textendash}144},
	publisher = {American Geophysical Union},
	organization = {American Geophysical Union},
	address = {Washington, DC},
	keywords = {HOV Alvin (Human Occupied Vehicle)},
	isbn = {0875904432},
	doi = {10.1029/178GM07},
	url = {http://dx.doi.org/10.1029/178GM07},
	author = {Pester, N J and Butterfield, D A and Foustoukos, D I and Roe, K K and Ding, K and Shank, T M and Seyfried, W E},
	editor = {Lowell, R P}
}
