Mantle earthquakes frozen in mylonitized ultramafic pseudotachylytes of spinel-lherzolite facies
T. Ueda and Masaaki Obata et al., Dept. of Geology and Mineralogy, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan. Pages 607-610.
Ueda et al. present a new type of ultramafic pseudotachylyte from Balmuccia peridotite, a "fossil" of mantle earthquakes. They report a case in which a ductile shear localization led to a seismic rapture and frictional melting of spinel peridotite, and the thus-produced pseudotachylyte was subsequently mylonitized and recrystallized in spinel lherzolite facies. Ueda et al. hypothesize that the chemical evolution of fluid phases, from H2O-rich to CO2-rich, played a critical role for such a rheological transition.
Hydrothermal venting at pressure-temperature conditions above the critical point of seawater, 5S on the Mid-Atlantic Ridge
Andrea Koschinsky et al., Jacobs University Bremen, P.O. Box 750561, D-28725 Bremen, Germany. Pages 615-618.
Volcanic activity on mid-ocean ridges produces very hot fluids circulating in the oceanic crust and emanating as black smokers at the seafloor. Koschinsky et al. document results from recent research cruises at the Mid-Atlantic Ridge, revealing the hottest fluids ever found, with a stable maximum temperature of 407 degrees Celsius and maximum temperatures that spike u
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