HR: 1340h
AN: T33A-0509    [Abstracts]
TI: Volcanic Architecture and Hydrogeology at the Juan de Fuca Ridge - First results from Downhole Logging in Hole U1301B (IODP Expedition 301)
AU: * Bartetzko, A C
EM: bartetzko@uni-bremen.de
AF: Research Center Ocean Margins, University of Bremen, P.O. Box 330440, Bremen, 28359 Germany
AU: Iturrino, G J
EM: iturrino@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, P.O. Box 1000, 61 Route 9W, Palisades, NY 10964 United States
AU: Tsuji, T
EM: tsuji@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, University of Tokyo, 1-15-1 Minamidai, Nakano-ku, Tokyo, 164-8639 Japan
AU: Fisher, A T
EM: afisher@ucsc.edu
AF: Earth Sciences Department, University of California Santa Cruz, 1156 High Steet, Santa Cruz, CA 95064 United States
AB: Hole U1301B was drilled during Integrated Ocean Drilling Program (IODP) expedition 301 to investigate the hydrogeologic situation in the oceanic basement at the eastern flank of the Juan de Fuca Ridge. The hole transects 265 m of sediments and 318 m of volcanic basement. Average core recovery in the basement is 30 %. Downhole wireline measurements were carried out in the basement section and included measurements of electrical resistivity, natural radioactivity, density, neutron porosity and sonic velocity. Integrating core lithostratigraphy and logging data, three major lithostratigraphic sequences may be distinguished: (a) an upper pillow basalt sequence from the bottom of the casing down to 420 mbsf, (b) a middle sequence with massive lava flows and pillow basalts between 420 and 465 mbsf, and (c) a low pillow basalt sequence down to the bottom of the hole. Strong borehole enlargements within the pillow basalts of the upper and middle sequence indicate strong fracturing and/or brecciation of the rocks and affect the quality of most downhole measurements, particularly of the density, neutron porosity, and p-wave velocity logs. Massive lava flows of the middle sequence have slightly higher density and lower neutron porosity values than the surrounding pillow basalts but these differences in physical properties are not significant. In the lower pillow basalt sequence the borehole is mostly on gauge and discrete peaks of low density and high neutron porosity indicate the position of local fracture zones. The differences in fracturing between the pillow basalt sequences probably reflect differences in porosity and permeability and thus suggest that permeability is higher in the upper part of the basement than in the lower sequence. The more massive lava flows may represent hydraulic barriers between the upper and lower sequence.
DE: 3017 Hydrothermal systems (0450, 1034, 3616, 4832, 8135, 8424)
DE: 3021 Marine hydrogeology
DE: 3035 Midocean ridge processes
DE: 3036 Ocean drilling
DE: 5104 Fracture and flow
SC: Tectonophysics [T]
MN: Fall Meeting 2005