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Heavitree quartzite (HQ) starting material. Non-porous quartzite, with ~1% impurities, and equant grains with average diameter ~200 mm. Diagenetic overgrowths visible. x 10.
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HQ shortened 65% at 850°C, 10-5/sec and 1200 MPa, in the lowest temperature dislocation creep regime
(regime 1 of Hirth & Tullis, 1992). Temperature is too low for dislocation climb to operate as a recovery process.
Strain is very inhomogeneous on the grain scale; parts of original grains remain as augen, whereas other parts
appear as thin irregular ribbons. The undulatory extinction is strong and patchy. Dynamically recrystallized grains
form by grain boundary migration but are extremely small (d~1 mm) and thus are not resolvable optically. W374 x
10.
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| 3 |
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HQ shortened 42% at 800°C, 10-6/sec and 1200 MPa, in the intermediate temperature dislocation creep
regime (regime 2 of H & T). Temperature is high enough for dislocation climb to serve as the recovery process.
Original grains have been fairly homogeneously flattened, and exhibit smooth and continuous undulatory
extinction; sub-basal deformation lamellae are quite common. Recrystallized grains form at original grain
boundaries as a result of progressive subgrain misorientation. In this regime the subgrains and the recrystallized
grains have about the same size, but both are too fine to resolve optically in this section. W339 x 10.
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HQ shortened 64% at 800°C, 10-6/sec and 1200 MPa (regime 2 dislocation creep). This higher strain sample
also shows moderately homogeneous flattening of original grains. There is a greater volume % of recrystallized
grains, again mostly located on original grain boundaries. The `puckered' appearance within many original grains
is due to subgrains, although those that are optically visible are larger than those that would be observed in
transmission electron microscopy (TEM). W370 x 10.
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Black Hills quartzite (BHQ) starting material. Quartzite with up to 1% porosity and very few impurities. Equant
grains have an average diameter of ~100 mm. x10.
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BHQ shortened 50% at 800°C, 10-6/sec and 1200 MPa, with ~0.2 wt % water added. (The added water has the
same effect as increasing the deformation temperature by ~100°C). Deformation occurred by regime 2 dislocation
creep; note the homogeneously flattened original grains. The recrystallized grains are larger than those in slide #4
because of the added water. BA20 x 10.
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BHQ deformed by a combination of simple shear (g = 2.1) and axial compression (shortening ~50%) at 800°C,
10-6/sec and 1200 MPa (regime 2). The shear zone boundaries are parallel to the horizontal edges of the photo;
shearing was sinistral. Note that the recrystallized grains, which result from progressive subgrain misorientation,
define a foliation which is oblique to the shear plane (and which does not change in angle with progressive strain).
W432 x 25.
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| 8 |
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BHQ shortened 37% at 900°C, 10-6/sec and 1200 MPa, with ~0.2 wt % water added. Deformation occurred in
the transition region between regime 2 and regime 3 dislocation creep. Recovery occurs by dislocation climb,
thus subgrains form within original grains. All grain boundaries are very mobile at this tempera ture,despite the low
driving force (e.g., low dislocation density contrast), thus there is much more dynamic recrystallization at a low
sample strain than is the case for regime 2 dislocation creep. In addition, in regime 3 the recrystallized grains tend
to be substantially larger than the subgrains within original grains, again due to high grain boundary mobility.
CQ78 x 10.
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BHQ shortened 37% at 900°C, 10-6/sec and 1200 MPa, with ~0.2 wt % water added. This slide shows a higher
strain portion of the same sample illustrated in #8. The original grains are not visibly flattened but have been about
half consumed by relatively large dynamically recrystallized grains. Deformation lamellae are rare, but evidence
of subgrains can be seen within original grains. CQ78 x 10.
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| 10 |
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BHQ shortened 57% at 900°C, 10-6/sec and 1200 MPa, with ~0.2 wt % water added. This sample is
~80-90% recrystallized, with only a slight indication of flattening of original grains. For conditions of steady state
flow (constant flow stress), which this sample exhibited, the recrystallized grain size should depend only on the
stress magnitude. CQ82 x 10.
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Arkansas novaculite with an original grain size of 5 mm which has been shortened 54% at 900°C, 10-6/sec
and 1200 MPa, with ~0.2 wt % water added. In this sample, dynamic recrystallization has involved an increase in
grain size, to essentially the same size developed in a quartzite (slide #10). CQ84 x 10.
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| 12 |
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BHQ shortened 50% at 1200°C, 10-6/sec and 1200 MPa, in regime 3 dislocation creep. This sample has
been completely dynamically recrystallized, to form relatively large polygonal grains which might at first appear
`annealed' (compare with slide #14). The higher the temperature of deformation, the more closely the rate of
recovery can match the rate of deformation. W857 x 10.
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BHQ shortened 60% at 800°C, 10-6/sec and 1200 MPa (regime 2). Same features as described for slide #6.
Compare this slide with slide #14 which shows a sample that was deformed at identical conditions but then
statically annealed. AN8 x 10.
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| 14 |
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BHQ shortened 60% at 800°C, 10-6/sec and 1200 MPa (regime 2) and then statically annealed at 900°C for
120 hours. The deformation microstructure has been completely replaced by strain-free polygonal recrystallized
grains, but the pattern and the strength of the c-axis crystallographic preferred orientation has not changed.
Compare this slide with #12, which shows a sample dynamically recrystallized at high temperature; in the
annealed sample the grain boundaries are straighter, but both samples were quenched. Would differences be
preserved and noticeable in naturally deformed (and possibly annealed) samples? AN9 x10.
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