Data report: minor element concentrations in pore fluids from the CRISP-A transect drilled during Expedition 334

Abstract

We report on the minor element composition of pore fluids recovered during Integrated Ocean Drilling Program (IODP) Costa Rica Seismogenesis Project (CRISP) Expedition 334 from two sites (U1378 and U1379) drilled in the slope sediments of the overriding Caribbean plate and one site (U1381) that sampled sediments in the incoming Cocos plate. Sr, Ba, Li, B, and Mn were measured using a Leeman Labs Prodigy inductively coupled plasma–optical emission spectrometry, on acidified dilutions of pore water samples at Oregon State University. H4SiO4 concentrations were determined colorimetrically in unacidified samples using a Thermo Scientific Genesys 10s Vis spectrophotometer at the University of Washington. In the slope sediment, alteration of reactive ash layers exerts a control on H4SiO4 concentrations and leads to increases in Ba and to some degree Mn. Sr is also released from this reaction, but the pore water profiles also reflect carbonate diagenesis, which is also known to occur in these sediments. Li increases with depth and has a discrete maximum at a shear zone that marks the unconformity between the slope apron sediments and the underlying margin wedge. B shows an increase over seawater values in the shallowmost sediments, possibly due to release of this element from organic matter alteration. A decrease below the near-surface maxima suggests incorporation of this element on clay minerals. At the incoming site, the concentration-depth profile of H4SiO4 reflects lithology with lower concentrations in Unit I and elevated concentrations in Unit II resulting from biogenic silica dissolution. Sr reflects ash alteration within the sediments, and a reversal close to the sediment basement contact indicates diffusional communication with altered seawater in the oceanic basement. Li and Mn profiles are also indicative of diffusional communication with the basement aquifer.