ORIGIN OF FLUIDS AND RELATED BARITE DEPOSITS AT VENT SITES ALONG THE PERU CONVERGENT MARGIN

The venting at the northern Peru convergent margin, unlike at other ma rgins, has produced large barite deposits, which have not been observe d outside the vents. The Sr-87/Sr-86 isotopic ratios of the fluids are more radiogenic than seawater. To explain these elevated values, we p ropose either the influence of a fluid characterized by a more radioge nic signature originating from the continent, or a reaction between se awater and the underlying continental metamorphic basement. The presen ce of this nonlocal radiogenic component is marked more strongly on th e Sr-87/Sr-86 ratios measured in the barite deposits. We assume that t he fluid sampled at the venting site and the fluid responsible for the barite deposit sampled at the same site originated from the same sour ce, i.e., the Paleozoic metamorphic basement of the Andean continental margin.