Strontium isotopes in Chilean rivers: The flux of unradiogenic continental Sr to seawater
Résumé
Analyses of Chilean river waters indicate that the average yield of unradiogenic Sr (~ 517 mol Sr km− 2 yr− 1, 87Sr/86Sr ~ 0.7057) from western South America (1,220,853 km2) into the southeastern Pacific Ocean is ~ 2-4 times higher than that from Iceland (~ 110 mol Sr km − 2 yr− 1, 87Sr/86Sr ~ 0.7025) and the Deccan traps, but lower than fluxes of unradiogenic Sr from ocean islands in the Lesser Antilles and Réunion. The Sr flux from western South America accounts for about 1.8% of the annual dissolved Sr delivered to the ocean via rivers. If Chilean rivers analyzed in this study accurately characterize runoff from western South America, active convergent continental margins release about as much unradiogenic Sr to seawater as a 0-1 Myr old mid-ocean ridge segment of equivalent length. Modulations of the flux of unradiogenic Sr from active margins over geologic time scales have to be considered as an additional driving force of change in the marine Sr isotope record, supplementing temporal variations in the submarine hydrothermal flux as a source of unradiogenic Sr to seawater. Such modulations can be driven by changes in the surface exposure of volcanic arc terrains, changes in climate, ocean currents and geographic latitude due to plate tectonics, as well as topographic changes that can affect local rainfall, runoff and erosion.