Oceanic crustal velocities from laboratory and logging measurements of Integrated Ocean Drilling Program Hole 1256D

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doi: 10.1029/2011GC003750
Author(s): Gilbert, Lisa A.; Salisbury, Matthew H.
Author Affiliation(s): Primary:
Williams College and Mystic Seaport, Mystic, CT, United States
Other:
Geologic Survey of Canada, Canada
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 12(9). Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. 26 refs.; illus., incl. 3 tables
Summary: Drilling and logging of Integrated Ocean Drilling Program (IODP) Hole 1256D have provided a unique opportunity for systematically studying a fundamental problem in marine geophysics: What influences the seismic structure of oceanic crust, porosity or composition? Compressional wave velocities (Vp) logged in open hole or from regional refraction measurements integrate both the host rock and cracks in the crust. To determine the influence of cracks on Vp at several scales, we first need an accurate ground truth in the form of laboratory Vp on crack-free, or nearly crack-free samples. We measured Vp on 46 water-saturated samples at in situ pressures to determine the baseline velocities of the host rock. These new results match or exceed Vp logs throughout most of the hole, especially in the lower dikes and gabbros, where porosities are low. In contrast, samples measured at sea under ambient laboratory conditions, had consistently lower Vp than the Vp logs, even after correction to in situ pressures. Crack-free Vp calculated from simple models of logging and laboratory porosity data for different lithologies and facies suggest that crustal velocities in the lavas and upper dikes are controlled by porosity. In particular, the models demonstrate significant large-scale porosity in the lavas, especially in the sections identified as fractured flows and breccias. However, crustal velocities in the lower dikes and gabbros are increasingly controlled by petrology as the layer 2-3 boundary is approached.
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Acoustical waves; Body waves; Breccia; Cores; Crust; Dikes; East Pacific; Elastic waves; Equatorial Pacific; Expedition 309; Expeditions 309/312; Fractured materials; Gabbros; Guatemala Basin; Igneous rocks; Integrated Ocean Drilling Program; Intrusions; North Pacific; Northeast Pacific; ODP Site 1256; Ocean Drilling Program; Oceanic crust; P-waves; Pacific Ocean; Permeability; Physical properties; Plutonic rocks; Porosity; Seismic waves; Velocity; Well-logging
Coordinates: N064400 N064400 W0915600 W0915600
Record ID: 2012049125
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