In this manuscript, we present the results of a physical properties investigation carried out on basaltic cores recovered from the four Leg 192 basement sites, focusing on the relationship between physical properties and alteration in basalts. Variations in physical properties in the Leg 192 basement sites closely resemble each other and reflect the amount of alteration and vein formation in the basement basalts. P-wave velocities, magnetic susceptibilities, and densities for the dense massive basalts are higher than those of more altered and heavily veined basalts. Porosity-dependent alteration is observed at Leg 192 basement sites: P-wave velocity displays a general decrease with increasing loss on ignition and potassium content. These trends are consistent with trends documented for typical alteration of oceanic crust and suggest that basalt alteration is largely responsible for the variation of the physical properties exhibited by rocks at Leg 192 basement sites. Our physical property data support the conclusion that only low-temperature seawater-mediated alteration occurred in the lava flows of the Ontong Java Plateau (OJP). This lack of higher-temperature hydrothermal alteration is consistent with the idea that the OJP basement sites are far from their eruptive vents.
1Zhao, X., Antretter, M., Kroenke, L., Riisager, P., and Hall, S., 2004. Relationships between physical properties and alteration in basement rocks from the Ontong Java Plateau. In Fitton, J.G., Mahoney, J.J., Wallace, P.J., and Saunders, A.D. (Eds.), Proc. ODP, Sci. Results, 192 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/192_SR/109/109.htm>. [Cited YYYY-MM-DD]
2Center for Study of Imaging and Dynamics of the Earth, Institute of Geophysics and Planetary Physics, University of California, Santa Cruz CA 95064, USA. Correspondence author: xzhao@es.ucsc.edu
3Institut für Geophysik, University of München, Theresienstrasse 41, D-80333 München, Germany.
4Institute of Geophysics, University of Hawaii, Honolulu HI 96822, USA.
5Danish Lithosphere Centre, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
6Department of Geosciences, University of Houston, Houston TX 77204-5007, USA.
Initial receipt: 30 December 2003
Acceptance: 6 July 2004
Web publication:
14 September 2004
Ms 192SR-109