Triaxial extension experiments on Carrara Marble demonstrate that there is a
continuous transition from extension to shear fracture on the basis of mechanical
behavior, macroscopic fracture orientation and fracture morphology where hybrid
fractures with extension and shear fracture characteristics are formed at the intermediate
stress conditions. Extension fracture surfaces display discrete, highly reflective cleavage
planes and shear fracture surfaces are covered with calcite gouge and display grooves
and striations that are aligned parallel to slip. This study uses the fractured samples that
were formed under triaxial extension experiments to characterize 1) microscopic surface
features using scanning electron microscopy, 2) fracture surface morphology using laser
profilometry, and 3) off-fracture damage using optical microscopy. These data are used
to test the step-crack model of fracture development for the formation of hybrid fractures.
Spectral analysis of the profiles demonstrates that microscopic roughness
decreases gradually across the extension-to-shear fracture transition in both the
orientations parallel and perpendicular to slip. However, macroscopic roughness
gradually increases then decreases across the transition in the direction parallel to slip.
The greatest macroscopic roughness occurs at the transition from extension fractures to tensile-hybrid fractures and is attributed to the presence of macroscopic steps in hybrid
fractures surfaces. The treads of the steps in the hybrid fracture surfaces have
characteristics of extension fracture surfaces and the risers have characteristics of shear
fracture surfaces. The treads have a right-stepping left lateral geometry that is
consistent with the step-crack model. Thin sections of hybrid fractures display
systematically spaced, pinnate, microfractures that emanate from both sides of the
macroscopic fracture surface. The pinnate fractures on both sides correlate across the
macroscopic fracture, suggesting that they are precursory to the formation of the
macroscopic fracture surface. The spacing to length ratio of the pinnate fractures and the
macroscopic orientation of the fracture surface are also consistent the relationship
dictated by the step-crack model of fault formation.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/2587 |
| Date | 01 November 2005 |
| Creators | Rodriguez, Erika |
| Contributors | Chester, Judith S. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | 3463424 bytes, electronic, application/pdf, born digital |
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