Comparison of the Flow Properties of Rocks at Crustal Conditions
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
It is inferred that, although both primary and tertiary creep may be im portant in certain regions, large-scale ductile deformation in the E arth's crust must be governed by secondary creep (steady state). This flow involves plastic deformation resulting from dislocation motion and diffusion. Geological, geophysical and geochemi cal observations constrain the temperature (T ), strain rate (e), and stress difference for rocks undergoing secondary creep to: -30-800 °C, 10~7-10~15 s-1, and up to
... 15 s-1, and up to 300 M Pa (3 kbar). The actual conditions of secondary creep are strongly dependent on rock type and depth of deformation. Useful laboratory data on rocks obtained over wide ranges of T, e and are limited to ice, halite, marble, dolomite, quartzite and dunite. Steady-state flow results are available for both wet and dry rocks; H 20 strongly affects the behaviour of both quartzite and dunite, but has a negligible effect on halite and marble. Secondary creep data for each rock are well fitted by exp ( ) where is an activation energy for creep (diffusion) and R, n are constants. Comparison between those rocks expected in the deep crust indicates that at the highest T and at e of 1(U12-1 0 _15 s-1, cr is largest for dry dunite and dolomite, followed by dry quartzite, marble and wet quartzite. Equivalent viscosities range from 1018-1022 Pa s (1019-1023 P). At intermediate depths (at T -300-500 °C), cr in dolomite is slightly greater than dry quartzite; both are much stronger than marble. In the shallow crust, secondary creep is expected only in marble ( T > 250 °C) and in halite ( T > 25 °C). The y of halite at 25-250 °C, range from 10 the surface and at e of 10~7-10-10 s-1 (glacier flow), y of ice would be 1015 to 1012 Pa s between -30 and 0 °G. Values of yf or all rocks examined appear inse except wet quartzite and all dunite.