HR: 0800h
AN: V31B-1435    [Abstracts]
TI: Gabbro fracturing and elemental analysis in the Costa Rica margin (ODP Leg 205): Core-log integrated high-resolution study
AU: * Thu, M K
EM: moe@jamstec.go.jp
AF: IFREE, JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Saito, S
EM: saito@jamstec.go.jp
AF: IFREE, JAMSTEC, 3173-25 Showa-machi, Kanazawa-ku, Yokohama, 236-0001 Japan
AU: Chavagnac, V
EM: vmcc@soc.soton.ac.uk
AF: Southampton Oceanography Centre, University of Southampton, Southampton, SO14 3ZH United Kingdom
AU: Schramm, B
EM: bschramm@uni-bremen.de
AF: Department of Earth Sciences, University of Bremen, Bremen, 28334 Germany
AU: Morris, J D
EM: jmorris@wustl.edu
AF: Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130 United States
AB: Costa Rica margin is an important area for studies of the seismogenic zone and subduction factory. Building on Ocean Drilling Program (ODP) Leg 170 coring and logging while drilling (LWD) at the same sites, Leg 205 drilled three sites to determine the igneous and alteration history of the upper most part of the down going plate, to characterize the hydrological regime above and within the decollement, and successfully installed long-term borehole observatories to monitor downhole pressure and temperature and sample fluids and gases. Among the several highlights from the results, coring and logging of thick gabbro zone at Site 1253 was significant to detail the fracture distribution, structure and nature of oceanic crust through core-log data integration. Even thought logging runs in the sediment section was failed due to the hole conditions, triple combination and FMS-sonic tool strings made successful measurements. Post-cruise research work included quality control on several wireline logs and processing of Formation MicroScanner (FMS), and interpreting these logging data and core sample analysis results in integrated manner. Among several downhole logging results, FMS images are used to characterize structure and fabric in the igneous units. As the hole conditions were good in most of the igneous intervals, the textural and structural variation is clear between the sections and also shows differences within the section itself. Moreover, mineralogic results from the recovered cores are combined with logging data through level-by-level multi-mineral evaluation with an optimized simultaneous equation solver and model combining method. Due to the good logging results and simple mineral composition of the single rock type, the results from the process filled mineral percentage of the no core recovery depths as well. High-resolution core-log integration in this study enhanced the understanding of structural process and nature of the oceanic crust of this particular region.
DE: 7220 Oceanic crust
DE: 8010 Fractures and faults
DE: 3640 Igneous petrology
DE: 3035 Midocean ridge processes
DE: 0915 Downhole methods
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting