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The effects of temperature, pressure, and alteration on seismic properties of diabase dike rocks from DSDP/ODP Hole 504B
Author(s) -
Carlson R. L.
Publication year - 2001
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2001gl013426
Subject(s) - geology , dike , pyroxene , hydrothermal circulation , amphibole , geochemistry , mineralogy , pressure gradient , olivine , seismology , paleontology , oceanography , quartz
A 0.4 to 0.5 s −1 in situ vertical velocity gradient in the diabase dike section of DSDP/ODP Hole 504B has been attributed to the effects of increasing pressure and downhole changes of mineralogy caused by hydrothermal alteration. An analysis of velocities measured in diabase samples as a function of pressure shows that increasing pressure accounts for a gradient of at most 0.1 s −1 . Neither laboratory data nor a Voigt‐Reuss‐Hill average velocity model in which V p pyx > V p amph shows a significant variation of velocity with depth; composition and pressure combined account for a gradient not greater than 0.2 s −1 . These results indicate that either the elastic moduli of the amphibole minerals in these rocks are higher than those of the pyroxene phase (V p amph > V p pyx,) or the seismic properties of the dikes are affected by a network of thin, large‐scale cracks.