On the compressibility of minerals and rocks at high pressures

Adams, L. H.; Williamson, Erskine D.

doi:10.1016/s0016-0032(23)90314-5

Cited by 169 publications

(43 citation statements)

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“…This set of microcracks may have developed later, either because of unloading during the uplift of the transverse ridge to the present depth of Hole 735B (Gallo et al, 1987;Robinson, Von Herzen, et al, 1989) or to drilling. As we pointed out previously, open fractures can lower seismic velocities significantly (Adams and Williamson, 1923;Birch andBancroft, 1938, 1940;Birch, 1961;Hyndman and Drury, 1976). The application of confining pressure closes fractures caused by conventional drilling techniques and also diminishes anisotropy created by the presence of oriented cracks.…”

Section: Crack Porositymentioning

confidence: 71%

Seismic Velocities and Elastic Properties of Oceanic Gabbroic Rocks from Hole 735B

Iturrino¹,

Christensen²,

Kirby³

et al. 1991

Proceedings of the Ocean Drilling Program

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The nearly continuous recovery of 0.5 km of generally fresh, layer 3 gabbroic rocks at Hole 735B, especially near the bottom of the section, presents scientists an unusual opportunity to study the detailed elastic properties of the lower oceanic crust. Extending compressional-wave and density shipboard measurements at room pressure, V p and V s were measured at pressures from 20 to 200 MPa using the pulse transmission method. All of the rocks exhibit significant increases in velocity with increasing pressure up to about 150 MPa, a feature attributed to the closing of microcrack porosity. , reflecting the higher densities and lower velocities of oxide minerals compared to olivine. About 30% of the core is plastically deformed, and the densities and directionally averaged velocities of these shear-zone tectonites are generally consistent with those of the gabbros, their protoliths. Three sets of observations indicate that the shear-zone metagabbros are elastically anisotropic: (1) directional variations in V p , both vertical and horizontal and with respect to foliation and lineation; (2) discrepancies among V p values for the horizontal cores and the VRH averages of the component minerals and their mineral proportions, suggesting preferred crystallographic orientations of anisotropic minerals; and (3) variations of V s of up to 7%, with polarization directions parallel and perpendicular to foliation. Optical inspection of thin sections of the same samples indicates that plagioclase feldspar, clinopyroxene, and amphibole typically display crystallographic-preferred orientations, and this, plus the elastic anisotropy of these minerals, suggests that preferred orientations are responsible for much of the observed anisotropy, particularly at high pressure. Alteration tends to be localized to brittle faults and brecciated zones, and typical alteration minerals are amphibole and secondary plagioclase, which do not significantly change the velocity-density relationships.

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Section: Crack Porositymentioning

confidence: 71%

Seismic Velocities and Elastic Properties of Oceanic Gabbroic Rocks from Hole 735B

Iturrino¹,

Christensen²,

Kirby³

et al. 1991

Proceedings of the Ocean Drilling Program

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“…The Moho corresponds to a compressional wave velocity increase from ~6.7 km/s to between 7.6 and 8.6 km/s, typically at ~7 km beneath the oceans. Since the work of Adams and Coker (1906), Adams and Williamson (1923), and Wrinch and Jeffreys (1923), the Moho has generally been regarded as the boundary between crust and mantle; however, an al-…”

Section: Discussionmentioning

confidence: 99%

Untitled

2017

Proceedings of the International Ocean Discovery Program

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“…Changes in seismic velocity, velocity anisotropy, and bulk density, and a strong pressure-dependence of the elastic moduli, have been partly attributed to the crack distribution within the rocks. Although first reported for laboratory samples (Adams and Williamson, 1923;Birch, 1960a, b), the effects ought to be observed also in the field. Fractures in a geologic formation greatly affect its bulk permeability, thus controlling the amount of fluid and any fluid flow patterns within the rock complex.…”

Section: Introductionmentioning

confidence: 83%

Crack Distribution in the Upper Oceanic Crust and Its Effects Upon Seismic Velocity, Seismic Structure, Formation Permeability, and Fluid Circulation

Johnson¹

1980

Initial Reports of the Deep Sea Drilling Project

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The open cracks and filled veins visible in the basalts drilled at DSDP Hole 418A in the North Atlantic have been analyzed and counted for the entire cored section of 546 meters. A discrimination of crack types was developed by counting separately the carbonate-filled, clay-filled, and open (unfilled) cracks, and recounting for crack orientation (horizontal, oblique, and vertical). The crack-depth profiles show several regions of intense fracture, some peaks correlating with lithology change and tectonic activity. The total volume of free interstitial water has been calculated from the primary porosity and open cracks, demonstrating that more water is available from Layer 2 than from the overlying sediments, thus eliminating the need to subduct sediments at the trench to provide fluid for serpentinization and the formation of andesites. From the crack data, bulk fluid permeability of the rock was computed, with an average permeability of 3.9 × 1O 4 cm 2 . The permeability profiles reveal a pattern of thick, highly permeable sequences bounded above and below by less fractured, thin, low-permeable zones, suggesting a model for fluid convection cells in the upper oceanic crust. Cross-correlation of the permeability functions with the downhole geochemistry analyses of the fresh basalts resulted in zero correlation; but, future cross-correlation of the permeability profiles with the geochemical variations in altered materials in the hole may yield important details of the alteration phenomena. The crack data were utilized in conjunction with shipboard physical property measurements to calculate the true bulk density, compressional wave velocity, and total porosity for the entire hole. This revealed a series of layers of high and low velocities, and demonstrated that the laboratory physical property measurements, in concert with the crack-distribution information, can accurately simulate the seismic structure of the oceanic crust. Using the combined physical property data, synthetic seismograms have been computed for Hole 418A, showing that the zones of high crack density are at least one of the causes of sub-basement reflectors in the upper crust.

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On the compressibility of minerals and rocks at high pressures

Cited by 169 publications

References 1 publication

Seismic Velocities and Elastic Properties of Oceanic Gabbroic Rocks from Hole 735B

Seismic Velocities and Elastic Properties of Oceanic Gabbroic Rocks from Hole 735B

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Crack Distribution in the Upper Oceanic Crust and Its Effects Upon Seismic Velocity, Seismic Structure, Formation Permeability, and Fluid Circulation

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