HR: 0800h
AN: OS51A-0178    [Abstracts]
TI: Determination of Volcanostratigraphy of ODP/IODP Hole 1256D: Qualitative and Quantitative Core-Log Integration
AU: * Tominaga, M
EM: masako@ocean.tamu.edu
AF: Department of Oceanography, Texas A&M University, 3146 TAMU, College Station, TX 77840, United States
AU: Teagle, D A
EM: dat@noc.soton.ac.uk
AF: School of Ocean & Earth Science, University of Southampton, National Ocenaographic Centre, European Way, Southampton, SO14 3ZH, United Kingdom
AU: Alt, J C
EM: jalt@umich.edu
AF: Department of Geological Science, 2534 CC Little Bldg 1100 North University Ave, Ann Arbor, MI 48109-1005, United States
AU: Umino, S
EM: sesumin@ipc.shizuoka.ac.jp
AF: Institute of Geoscience, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka-shi, 422- 8529, Japan
AB: The objective of this study is to use electrofacies analysis to construct a less biased volcanostratigraphy of Ocean Drilling Program (ODP)/Integrated Ocean Drilling Project (IODP) Hole 1256D, the first complete penetration of upper oceanic crust. An accurate knowledge of the volcanostratigraphy is vital to understand processes of crustal construction, submarine magmatism, and to estimate chemical exchange with seawater. However, this is often not achieved due to very low core recovery rate in most basement holes. Detailed electrofacies analyses of Formation MicroScanner (FMS) images together with other wire line logs made it possible to investigate lithology types in volcanic and plutonic sections in ODP/IODP Hole 1256D where core recovery rates averaged 36 % and 16%, respectively. The electrofacies analyses in this study overcome previous issues, such as distinction of pillows and different degrees of brreciation, with more detailed lithologic classifications. Relocating recovered core pieces to in situ intervals provides verification of the classifications. We propose ten lithologic types for the new, qualitative volcanostraitgraphy model of Hole 1256D. Three major lithology types in the volcanic section are Massive Flows (22%), Physically Altered Flows (23 %), and Fragmented Intervals (13 %). These flows characterize fast-spreading oceanic crust formation. Subordinate intervals are classified as Possible Pillows (1.36 %), which are localized within a 100 m interval. Electrofacies analyses indicate that the boundary between the extrusive and intrusive (the lower boundary of the Transition Zone) is located at 1064 mbsf. Subvertical contacts in dikes are typically observed every 1 ~ 2 m with breciated regions around the contacts. This volcanostratigraphy model represents that the first, intact vertical section through fast-spreading oceanic crusts. Together with the observation about surface lava morphology at the other East Pacific Rise site, the volcanostratigraphy in this study documents on- and off-axis lava deposition. Additionally, we carried out artificial neural network analyses of the lithologic types using multiple parameters from the logging data to evaluate a less subjective, quantitatively determined volcanostratigraphy. This quantitative volcanostratigraphy agrees well with the qualitative lithologic subdivisions below the lower part of Sheet and Massive flows (~ 950 mbsf), whereas it primarily depicts gradual changes in porosity from one formation to the other in the upper part of the hole instead of differentiating lithologic types as in the qualitative model.
DE: 0915 Downhole methods
DE: 3035 Midocean ridge processes
DE: 3036 Ocean drilling
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting