Experimental deformation of flint in axial compression

Abstract

The experimental deformation of flint, a water-rich (1-2 wt%) fine-grained (1 Ixm) microcrystalline quartz, has been studied using a gas-confining medium apparatus at 300 MPa confining pressure in the temperature range 500-1000 ~ In constant strainrate axial compression tests a mechanically unstable behaviour with peaked and undulating stress-strain curves, especially at the faster strain rates, is manifest. The rheology of these tests can be approximately described by the traditional power-law equation with a stress exponent (n) of between 3 and 5, and an apparent activation energy (Q) of 108 kJ mo1-1. However, the strain-independent ('steady-state') equation is only a partial description of the data. The mechanical properties were studied at lower stresses using stress relaxation testing, this method has the advantage of recording specimen response over a very small strain interval (c. 1%), i.e. nearly constant structure. These tests revealed that in a high stress regime above 100 MPa the rheology was only weakly dependent on strain and very similar to the constant strain-rate behaviour. Below 100 MPa the rheology can be described by a power law with Q = 64 kJ mol-l and n = 1. The low-stress behaviour is extremely sensitive to specimen strain, the strain rate decreasing with increasing strain for a given stress.The optical microstructure reveals that the mechanical instabilities are related to localized displacement zones, sometimes en echelon, consisting of relatively large grains (10 ~m). The important reduction of the integral infrared absorption of deformed specimens, a 98% reduction of the initial water content, suggests that a pore fluid was developed by specimen dehydration in the sealed (undrained) assembly. The presence of pores or bubbles decorating grain boundaries and microfractures normal to the piston-specimen interface both testify to the presence of the pore fluid during deformation. The pore fluid pressure may have approached the confining pressure resulting in a near-zero effective pressure. Transmission electron microscopy revealed the presence of many Brazil micro-twins parallel to grain boundaries. The twins are thought to be growth defects indicating rapid grain growth during deformation. Dislocations in the basal plane were observed with a 1/3 (a)-type Burgers vector. Dislocations were also observed in the grain boundaries, possibly caused by grain-boundary sliding in the low stress regime.The complete lattice preferred orientation (LPO) of homogeneously deformed specimens has been determined by X-ray texture goniometry. The inverse pole figures have a strong concentration of compression axes parallel, and a weaker concentration normal, to the c-axis. The local c-axis pole figures in heterogeneously deformed specimens were characterized by the photometric technique. The c-axis pole figures in the bulk are identical to that determined by X-rays in homogeneously deformed specimens. In the displacement zones the fabrics are asymmetric with respect to the zone boundaries. The asymmetry is not...

Strain localization during high temperature creep of marble: The effect of inclusions

“…At a shear stress of about 20 MPa (vertical dotted line in Fig. 2c), which corresponds to the average bulk shear stress measured in inclusion-bearing hollow samples (Table 1), the creep rate of CM is about 1.8% of SH and ≈ 10 4 times higher than of Novaculite, estimated from the flow law for wet flint (Mainprice and Paterson, 2005). For the applied bulk shear strain rate of about 1.9x10 -4 s -1 , CM is ≈9 times stronger than SH and ≈10 times weaker than NC (horizontal dotted line in Fig.…”

Rheological profile across the NE Japan interplate megathrust in the source region of the 2011 Mw9.0 Tohoku-oki earthquake

“…The strength of flint determined by Mainprice and Paterson (2005) is considerably lower than the strength http://www.earth-planets-space.com/content/66/1/73 of fine-grained synthetic quartz aggregates (Paterson and Luan 1990;Luan and Paterson 1992;Rutter and Brodie 2004). The weakness of the flint samples may be related to the formation of localized shear bands that were observed in the deformed samples.…”

“…Extrapolation of experimentally determined dislocation flow laws of wet quartz and gabbro to a natural strain rate (ε = 10 −12 s −1 ) are shown. LP, fine quartz aggregate synthesized from silicic acid (Paterson and Luan 1990;Luan and Paterson 1992); MP, Mainprice and Paterson (2005); RB, fine quartz aggregate synthesized from Brazilian quartz (Rutter and Brodie 2004); GT, Black Hills quartzite (Gleason and Tullis 1995); DD, synthetic gabbro (An50Di50, 'wet') of Dimanov and Dresen (2005).…”

“…rate (ε = 10 −12 s −1 ), which was estimated from flow laws determined by gas-medium apparatuses at a 300 MPa confining pressure (Paterson and Luan 1990;Luan and Paterson 1992;Rutter and Brodie 2004;Mainprice and Paterson 2005) and by a Griggs apparatus with moltensalt cells at higher P c (approximately 1.5 GPa) (Gleason and Tullis 1995). Large variations in flow stress arise from differences in P c , the starting materials used, and the chemical environments.…”

Dauphiné twinning and texture memory in polycrystalline quartz. Part 3: texture memory during phase transformation

“…It has been suggested that trace amounts of aluminum may influence the phase transformation in volcanic quartz (Ghiorso et al 1979). Water may be enriched along grain boundaries and upon heating significant water is lost (Jaoul et al 1984), particularly in fine-grained flint (Mainprice and Paterson 2005) and novaculite . From the healing of the neutron-induced point defects we know that some mobility of defects occurs during heating that does not seem to affect variant selection.…”