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Title: Geological link between fluid inclusions, dilatant microcracks, and paleostress field

Abstract

Seismic investigations using three-component instruments have demonstrated shear wave splitting in widely different geological and tectonic environments. Shear wave analysis suggests that the inferred anisotropy can best be explained if the rocks contain distributions of subparallel, subvertical, fluid-filled microfractures which are aligned according to the current stress field (the Crampin extensive dilatancy anisotropy (EDA) model). Geological evidence for widespread fluid activity in the Earth's crust supports this hypothesis and suggest that the myriads of planes of microscopic secondary fluid inclusions which characterize most geological materials represent fossil EDA cracks. Field studies confirm a strong spatial relationship between the orientation of fluid inclusion arrays and the paleodirections of maximum compressive stress. At elevated temperatures and pressures, the healing of fluid-filled cracks in the crust, of whatever origin, is considered to be a fairly rapid process. Moreover, the inclusions which form as a result of crack healing respond to changes in temperature, pressure, and stress by changing shape and/or volume. This indicates a high degree of fracture compliance; sufficient perhaps to react to rapid changes in the current stress field and associated shear wave splitting. Though individual inclusions (typically <20 {mu}m) will have no effect on the propagation of seismic waves withmore » wavelengths of tens to hundreds of meters, the rock volume sampled by the waves will be rendered anisotropic if the overall average of the inclusions shows a preferred orientation. Thus fluid inclusions may constitute one of the principal types of fluid-filled microcrack described by the EDA hypothesis.« less

Authors:
 [1]
  1. British Geological Survey, Keyworth (England)
Publication Date:
OSTI Identifier:
5456128
Report Number(s):
CONF-880531-
Journal ID: ISSN 0148-0227; CODEN: JGREA
Resource Type:
Conference
Journal Name:
Journal of Geophysical Research; (United States)
Additional Journal Information:
Journal Volume: 95:B7; Conference: 3. international workshop on seismic anisotropy, Berkeley, CA (United States), 31 May - 4 Jun 1988; Journal ID: ISSN 0148-0227
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CONTINENTAL CRUST; STRESS ANALYSIS; GEOLOGIC FRACTURES; ORIENTATION; INCLUSIONS; COMPRESSION; CORRELATIONS; CRACKS; FRACTURE MECHANICS; GEOLOGIC HISTORY; GEOLOGIC MODELS; PRESSURE DEPENDENCE; RESERVOIR FLUIDS; RESERVOIR PRESSURE; RESERVOIR TEMPERATURE; ROCK MECHANICS; SEISMIC S WAVES; SEISMIC SURVEYS; TECTONICS; TEMPERATURE DEPENDENCE; WAVE PROPAGATION; EARTH CRUST; FLUIDS; GEOLOGIC STRUCTURES; GEOPHYSICAL SURVEYS; MECHANICS; SEISMIC WAVES; SURVEYS; 580000* - Geosciences

Citation Formats

Shepherd, T J. Geological link between fluid inclusions, dilatant microcracks, and paleostress field. United States: N. p., 1990. Web.
Shepherd, T J. Geological link between fluid inclusions, dilatant microcracks, and paleostress field. United States.
Shepherd, T J. 1990. "Geological link between fluid inclusions, dilatant microcracks, and paleostress field". United States.
@article{osti_5456128,
title = {Geological link between fluid inclusions, dilatant microcracks, and paleostress field},
author = {Shepherd, T J},
abstractNote = {Seismic investigations using three-component instruments have demonstrated shear wave splitting in widely different geological and tectonic environments. Shear wave analysis suggests that the inferred anisotropy can best be explained if the rocks contain distributions of subparallel, subvertical, fluid-filled microfractures which are aligned according to the current stress field (the Crampin extensive dilatancy anisotropy (EDA) model). Geological evidence for widespread fluid activity in the Earth's crust supports this hypothesis and suggest that the myriads of planes of microscopic secondary fluid inclusions which characterize most geological materials represent fossil EDA cracks. Field studies confirm a strong spatial relationship between the orientation of fluid inclusion arrays and the paleodirections of maximum compressive stress. At elevated temperatures and pressures, the healing of fluid-filled cracks in the crust, of whatever origin, is considered to be a fairly rapid process. Moreover, the inclusions which form as a result of crack healing respond to changes in temperature, pressure, and stress by changing shape and/or volume. This indicates a high degree of fracture compliance; sufficient perhaps to react to rapid changes in the current stress field and associated shear wave splitting. Though individual inclusions (typically <20 {mu}m) will have no effect on the propagation of seismic waves with wavelengths of tens to hundreds of meters, the rock volume sampled by the waves will be rendered anisotropic if the overall average of the inclusions shows a preferred orientation. Thus fluid inclusions may constitute one of the principal types of fluid-filled microcrack described by the EDA hypothesis.},
doi = {},
url = {https://www.osti.gov/biblio/5456128}, journal = {Journal of Geophysical Research; (United States)},
issn = {0148-0227},
number = ,
volume = 95:B7,
place = {United States},
year = {Tue Jul 10 00:00:00 EDT 1990},
month = {Tue Jul 10 00:00:00 EDT 1990}
}

Conference:
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