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Brittle Fracture in Oceanic Basalts
Koons, Mary-Linda
Koons, Mary-Linda
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1972
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Earth and Environmental Science
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http://dx.doi.org/10.34944/dspace/8389
Abstract
Basalt samples dredged from the ocean floor were experimentally fractured in tension while being observed microscopically. Five basaltic textural types were chosen: (1) cotectic crystallization of olivine, plagioclase, and pyroxene Juan de Fuca, (2) dark glass matrix with phenocrysts of plagioclase and clinopyroxene Gorda Ridge, (3) vesicular black glass matrix with trachytic micro-phenocrysts Mid Atlantic Ridge Rift Valley, (4) black glass pillow with an hollow-centered phenocrysts Mid Atlantic Ridge Rift Valley, (5) black glass matrix with micro-phenocrysts of olivine, pyroxene, plagioclase Mid Atlantic Ridge Rift Valley. Fracturing was done in the ¼ inch direction of precisely machined chips 1 x ¾ x ¾ inches. Test conditions were dry at 20°C, wet at 20°c, and 300°c. Modal integration of the crack path length and general modal analyses indicate that regardless of texture or test parameter: (1) the fracture path seeks out voids, glass, and grain boundaries to the exclusion of mineral grain cleavage, (2) a propagating fracture is offset by pre-existing fractures perpendicular to the propagation direction, (3) within the locus of the propagation direction, a propagating fracture coalesces with a pre-existing parallel or sub-parallel fracture. The off-setting behavior of pre-existing fractures for newer fractures bears a striking geometric resemblance to the Mid Atlantic Ridge and its transform faults.
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