COMPOSITIONS AND SOURCES OF FLUIDS IN SEDIMENTS OF THE PERU SUBDUCTION ZONE

Sediments of the middle-to-lower slope regions of the Peru continental margin drilled during Ocean Drilling Program (ODP) leg 112 contain interstitial waters with chloride concentrations as low as 454 mM Cl-, equivalent to ~20% dilution of seawater with fresh water. Strontium isotope data suggest that two separate fluid regimes are present: a northerly one in which fluids contain more radiogenic Sr than seawater (87Sr/86Sr up to 0.70996), possibly originating from continental crust, and a southerly regime where fluids contain Sr less radiogenic than seawater (87Sr/86Sr down to 0.70722), and which are also enriched in Ca2+ and depleted in Mg2+ and δ18O, that appear to have interacted with oceanic basement. O, C, and He isotopic data support these interpretations. -Authors