@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}
}
