Boron, Sr, O, and H isotope geochemistry of groundwaters from Mt. Etna (Sicily) - hydrologic implications

Combined B, O, H, and Sr isotopic studies of groundwaters from Mt. Etna pro vide new constraints on their origin and the consequences of fluid-rock int eraction within this hydrologic system. Variations in delta(18)O (-9.7 to - 7.2 parts per thousand) and delta D (-62 to -23 parts per thousand) mainly lie along the regional meteoric waterline and suggest that most waters orig inated as local precipitation. However, small shifts in delta(18)O, and var iable Sr-87/Sr-86 (0.70355 to 0.70879) and delta(11)B (-5.2 to +25.8 parts per thousand) indicate that subsequent interactions occurred between the fl uids and local rocks. High B/Cl ratios in all samples seemingly preclude di rect involvement of seawater in the hydrologic system despite the proximity to the coast and, in some samples, elevated Sr-87/Sr-86 and delta(11)B Two general 'end-member' water types are recognized on the basis of their chem istry. These apparently are produced by interactions of local meteoric wate rs with the dominant reservoir rocks-either basaltic lavas of Etna or the u nderlying sediments, respectively; high delta(11)B in the sediment-hosted e nd-member points to a significant marine carbonate contribution. Subsequent mixing between these or similar end-members produced a range of intermedia te composition groundwaters. Certain anomalous water compositions require t he presence locally of a distinct component with high B and moderate delta( 11)B (ca. +10 parts per thousand) but relatively low Sr-87/Sr-86; an anthro pogenic source for this component is plausible. One unusual sample has B an d Sr isotopic compositions similar to the other volcanic rock-hosted waters , but anomalously high Cl content that likely reflects local magmatic outga ssing near this sampling locality. In general, this study indicates that,gr oundwater B and Sr isotopic compositions are rock-dominated; these data pro vide useful constraints on the origin and evolution of groundwaters. Copyri ght (C) 2000 Elsevier Science Ltd.