Integrated Ocean Drilling Program, United States

The data presented in this report demonstrate significant improvements in the ability to constrain trace element and Sr isotopic concentrations in sediments overlying ridge-flank hydrothermal systems. Improved sampling methods orchestrated by the Integrated Ocean Drilling Program (i.e., advanced piston coring and anoxic sample processing) enabled the collection of reactive pore water species with minimal alteration and sampling artifacts. Improved methods of high-resolution inductively coupled plasma-mass spectrometry trace element analysis, including the use of the 8-hydroxyquinoline functional group to extract and preconcentrate rare earth elements and other trace metals, were used to compile a data set of 28 trace element concentrations and (super 87) Sr/ (super 86) Sr ratios. From this extensive data set, we were able to increase the current understanding of how redox-reactive species respond to diagenic processes. Near-basement trends were used in combination with the known composition of hydrothermal fluids that exit Baby Bare Springs to asses our ability to predict basement fluid compositions using sediment pore water profiles collected by deep-sea drilling. The results show that prediction of basement fluid composition is possible for many trace elements, provided the near-basement concentration gradients are minimal. In order to place the Ge/Si systematics in a broader context, pore water and borehole fluid Ge and Si data are presented from additional sites across the Juan de Fuca Ridge flank and from two additional ridge-flank settings. These data show that Ge concentrations and Ge/Si ratios are much higher in the basement fluids than in the basal sediments because of increased mobilization of Ge relative to Si within the basement hydrothermal reservoir. Solid-phase sediment data are presented, highlighted by the occurrence of Mn- and carbonate-rich layers.