Fluid relationships in the Northern Gulf of Mexico using dissolved ion concentrations and strontium isotopes
Hubbard, L. Ashley
Dugan, Brandon; Dickens, Gerald R.
Master of Science
Pore fluids from the slope in the Gulf of Mexico demonstrate specific ion enrichment and a range in concentration. Dissolved metal and halogen fluid concentrations and strontium isotope ratios from ten sites on the Gulf of Mexico (GoM) continental slope were compared to identify the variations in chemistry. Geochemical discrepancies are interpreted as coming from chloride sources, fluid mixing and fluid diagenesis at depth. We have adapted a grouping scheme developed by Fu and Aharon (1998) in order to highlight seep fluid relationships, including seep fluid from six additional locations. Chloride sources were assessed based on bromide to chloride and sodium to chloride trends and strontium isotope ratios. Chloride source end members include connate seawater, dissolved salt, and ancient evaporated seawater. Out of the sites examined, three sites are classified as having a chloride signal dominated by salt dissolution. Bromide to chloride ratios fall between 0.23 x 10 -3 and seawater (1.5 x 10 -3 ). Sodium to chloride ratios fall between 1.16 and seawater (0.85) and strontium ratios have a large distribution (0.707911-0.709220). Evidence of subaerially evaporated seawater is preserved in fluids from at least two or three sites. Bromide to chloride ratios fall between 2.47 x 10 -3 and seawater. Sodium to chloride ratios fall between 0.75 and seawater and strontium ratios demonstrate a narrow range of values in the least altered fluids (0.708662-0.709172). The majority of saline vent fluids demonstrate mixing between chloride source end members and a wide range of dissolved ion concentrations. Diverse ion enrichment behavior clearly indicates that the processes controlling GoM seep fluid chemistries are complicated and often site dependent resulting from differences in flux, early brine generation and fluid/sediment interactions.
Geochemistry; Earth sciences