HR: 1340h
AN: T33A-0520    [Abstracts]
TI: Insights of ridge-flank hydrothermal processes through minor and trace element geochemistry of sediment pore fluids from IODP Site 1301
AU: * Hulme, S M
EM: hulme@hawaii.edu
AF: Hawai'i Inst. of Geophysics & Planetology, University of Hawai'i 1680 East-West Road POST Bldg. Rm # 502, Honolulu, HI 96822 United States
AB: The volumetric flux of seawater that flows through the oceanic crust rivals that which flows from rivers into the oceans. As seawater or formation fluid circulates through oceanic basement it is warmed and reacts with basalt and secondary minerals. In addition, diffusive exchange with overlying pore fluids may also impact the composition of the circulating fluid in basement. This interplay among seawater (formation fluid) reaction with basalt, diffusive exchange, and warming continues to the point of egress. How this seawater circulates through the crust and the chemical, mass, and thermal fluxes that it generates was the focus for drilling IODP Leg 301 on the eastern flank of the Juan de Fuca Ridge on 3.5-m.y.-old crust. We have conducted a comprehensive series of chemical analyses on pore waters from IODP Expedition 301 to constrain the composition of the formation fluid within the upper-most basaltic basement and compared it to the composition from nearby springs and borehole data. Sediments were recovered from IODP Holes 1301C (29 samples) and 1301D (9 samples) using the advanced piston coring (APC) technique. Sediments for pore fluid extraction were collected throughout the sediment column with a greater vertical resolution at the sediment-basement contact. Pore fluids were extracted in a nitrogen atmosphere to minimize potential oxidation reactions. Shipboard analyses included Ca, Mg, Alkalinity, pH, chlorinity, ammonium, phosphate, sulfate, K, Si, Li, B, Mn, Fe, Sr, DIC, total C, and Ba. Subsequent sample analysis with a Finnagin Element 2 high-resolution ICP-MS included: the trace elements Rb, Cs, Ba, Y, Cd and U; transition metals Mo, V, Cr, Co, Cu, Ni and Zn; and the complete suite of rare earth elements (REE). These data provide additional constraints to determine diffusive fluxes between the sediment and basement reservoirs, allowing us to refine models that constrain the rate of fluid flow within the crust and re-affirm the directionality of flow along the buried ridge. Coupling the compositions of the formation fluids with recent advances in thermodynamic databases for low temperature mineral formation-dissolution provides an avenue not only for understanding present crustal conditions, but also for being able to envision conditions at which particular reactions occur.
DE: 1021 Composition of the oceanic crust
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1050 Marine geochemistry (4835, 4845, 4850)
DE: 1065 Major and trace element geochemistry
DE: 8135 Hydrothermal systems (0450, 1034, 3017, 3616, 4832, 8424)
SC: Tectonophysics [T]
MN: Fall Meeting 2005