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Chapter 4: Deformation of Rocks at 500° to 800° C.

By
D. T. Griggs
D. T. Griggs
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F. J. Turner
F. J. Turner
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H. C. Heard
H. C. Heard
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Published:
March 01, 1960

Extensive experiments on the deformation of rocks at temperatures from 25° to 800°C. have been performed in triaxial-test apparatus at 5 kb confining pressure, and in shearing apparatus at pressures to 20 kb. A variety of rocks, crystals, and mixtures have been tested, including peridotite, pyroxenite, basalt, granite, dolomite, marble, and quartz crystals and aggregates.

Strength is reported as a function of temperature. High quartz is found to be very strong. Peridotite, pyroxenite, and granite have nearly the same strength over the entire temperature range—20 kb at 25°C. and 7 kb at 800°C. Basalt has a similar strength to 600°C., but its strength decreases rapidly at higher temperatures. Dolomite is weaker than these rocks at low temperature but at 500°–800°C. has nearly the same strength as peridotite, pyroxenite, and granite. Marble is much weaker at low temperature and decreases in strength more rapidly than the other rocks as temperature increases.

The principal mechanism of deformation of diopside was found to be {100} translation. Grains of enstatite highly deformed at 500°C., 5 kb locally invert to clinoenstatite. The mechanism of deformation of olivine was not identified.

Stress-strain curves of calcite single crystals change character at 500°–600°C. At 600°C., f translation becomes important, and at 800°C. basal glide may occur. At 800°C., twinning is little easier than r translation, which is still the easiest translation. This large change in the relative ease of translation and twinning at high vs. low temperature has important consequences in the deformation of marble at 800°C.

Syntectonic recrystallization reaches a maximum at 600°C. in marble deformed at 3 per cent per minute. At a lower strain rate the maximum syntectonic recrystallization seems to occur at a lower temperature. The recrystallized grains show a pronounced orientation with the c-axes parallel to the maximum principal compressive stress. Water and CO2 do not affect this recrystallization in our experience to date. The recrystallization observed in these experiments is thought to be of the same type as that which occurs in metamorphic marmorization.

Only very limited plastic deformation of quartz has been observed at 500° and at 800°C., 5 kb. The mechanism could not be determined. High preferred orientations have been developed in quartz in shearing experiments, particularly when the quartz crystallized from an amorphous phase subject to large shear stress and strain.

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Contents

GSA Memoirs

Rock Deformation (A Symposium)

David Griggs
David Griggs
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John Handin
John Handin
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Geological Society of America
Volume
79
ISBN print:
9780813710792
Publication date:
March 01, 1960

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