Experimentally determined steady state flow properties and processes of important rock-forming materials are reviewed in reference to those of metals and ceramics and to physical conditions in the earth's crust and upper mantle. Dislocation motion controls the creep rate over a wide range of steady state conditions in the experiments, and the observation that the same processes have operated during natural deformations permits extrapolations of the mechanical data. Under these conditions, strain rate is related to stress raised to the power 2–9, depending on the material and conditions, and the resulting flow stresses and equivalent viscosities are compared at a representative geological strain rate of 10−14/s. The results are applied in brief discussions of diapirism, growth of folds, and flow in the upper mantle.

Steady state flow of rocks

The basal slip systems of biotite and their mechanical expressions have been investigated by shortening single crystals oriented to maximize and minimize shear stresses on (001). Samples loaded at 45° to (001) exhibit gentle external rotations associated with dislocation glide. High-angle kink bands in these samples, unlike those developed in micas loaded parallel to (001), are limited to sample corners. Samples shortened perpendicular to (001) show no evidence of nonbasal slip and fail by fracture over all conditions tested. The mechanical response of biotite shortened at 45° to (001) is nearly perfectly elastic-plastic; stress-strain curves are characterized by a steep elastic slope, a sharply defined yield point, and continued deformation at low (mostly 1%. Stresses measured beyond the yield point are insensitive to confining pressure over the range 200 to 500 MPa and exhibit weak dependencies upon strain rate and temperature. Assuming an exponential relationship between differential stress σd and strain rate e˙ of the form e˙=Cexp(ασd)exp(−Q/RT), the data collected over strain rates and temperatures of 10−7 to 10−4 s−1 and 20° to 400°C, respectively, are best fit by an exponential constant α of 0.41±0.08 MPa-1 and an activation energy Q of 82±13 kJ/mol. A power law fits the data equally well with n = 18±4 and Q = 51±9 kJ/mol. Samples oriented favorably for slip in directions [100] and [110] are measurably weaker than those shortened at 45° to [010] and [310], consistent with the reported Burgers vectors 〈100〉, 1/2 〈110〉, and 1/2 〈110〉. The anisotropy of biotite is further revealed by contrasting these plastic strengths with results of samples deformed parallel and perpendicular to (001). Previous studies have shown that biotite loaded in the (001) plane is strong prior to the nucleation of kink bands. The strength of biotite shortened perpendicular to (001) exceeds that measured parallel to (001) and is pressure dependent. Application of the results to deformation within the continental crust suggests that biotite oriented favorably for slip is much weaker than most other silicates over a wide range of geologic conditions. Its presence within foliated rocks and shear zones may limit locally the stresses that can be supported.

Basal slip and mechanical anisotropy of biotite

Faulting and Crustal Stress at Rangely, Colorado

Experimental Recrystallization of Ice Under Stress

Transmission Electron Microscopy of Experimentally Deformed Olivine Crystals

Grol3e Gl immer-Einkr i s t a l l e wurden bei D r u e k e n bis 5 kba r u n d Z i m m e r t e m p e r a t u r ve r fo rmt . D r u c k r i c h t u n g war die Normale an t (00t). Die Kris ta l le w u r d e n hierbei nach (111) u n d (032) (AuIs te l lung n a c h [t~) ge t rennt . (032) m i t e inem Winke l yon 59 ~ zu (001) is t in der N a t u r [2] u n d im E x p e r i m e n t [3] b isher n ich t beobach t e t worden. Die T r e n n u n g erfolgt in den Zonen I l l 0 ] und [~00]. I n diesen Zonen ve r laufen SiO~Te t raeder und M g O O k t a e d e r k a n t e n nahezu paral lel zu den Trennf lgchen . Fe rner l iegen den Trenn f lgchen die d ich tes t bese tz t en G i t t e r r i ch tungen (SiO~-Tetraederket ten) parallel. bal t ( I I)tel luri te : v iole t tes C%T%O s bei 300-310 ~ C und rub inro tes CoTeO aH~O bei 250-280 ~ C. RgSntgenographische U n t e r s n c h u n g e n (vgl. Tabelle) zeigten, dal3 Co2TeaO s m i t Zn2T%O s It ] bzw. Spiroffit (Mn, Zn, Ca)2T%O s [2] u n d CoTeO a. HeO mi t CoSeO a. H20 [3] i so typ ist.

P. Buck

Papers

Experimentelle Verformung von Glimmer- und Hornblende-Einkristallen