Pore water chemistry of the Mariana serpentinite mud volcanoes: A window to the seismogenic zone

摘要: [1] In 2003, we conducted a survey of 11 serpentinite mud volcanoes in the Mariana fore arc. Here report sediment pore water data from navigated gravity and piston cores push collected by ROV system Jason2-Medea. Systematic variations profiles chemical compositions these are consistent with models that include active upflow relative to surrounding matrix. The speed upwelling, based on fits an advection-diffusion model observed (K, Na, Rb, Cs), reaches maximum 36 cm/yr at Big Blue Seamount. Results simulations constrain composition depth degree additional alteration as ascends through sampled section. For example, transition metals (e.g., Mn, Fe, Co, Ni, Cu, Mo) mobilized under conditions low upwelling speeds microbial activity. Similarly, rare earth elements (REE) show evidence near-surface alteration. In addition surficial reactions, distinctive compositional patterns exist function distance trench axis, which is proxy for depths generation downgoing plate below each seamount. trends slab-sourced fluids increasing temperature pressure west trench. These increase K, sulfate, carbonate alkalinity, Na/Cl, B, Cs, Gd/Tb, Eu, light REE (LREE) decrease Ca, Sr, Y Mg U universally depleted water. We thermal along decollement using concentrations fluid mobile Rb) mobilization LREE heavy (HREE). 80°C isotherm estimated 15 km between Moon Seamount Cerulean Springs. At slab 17 24 km, waters lack significant Rb K enrichments seawater, suggesting upper bound near 150°C. There enrichment HREE (slab 25 km) indicating this site ∼200°C. Cs outpaced all seamounts survey. On basis laboratory experiments, observation sets limit ∼350°C 30 seafloor.