Three types of quartz single crystals with different fluid inclusions compositions were used in this study, originating from Victoria (Australia), Naxos (Greece, Schuiling and Kreulen, 1979), and Scandinavia (Table 1).
The fluid inclusions that occur in these samples can roughly be divided into three categories: large, medium, and small inclusions. Detailed descriptions of the quartz and the inclusions are given below. The fluid composition in our starting materials was determined using a heating stage in optical microscopy. We did not characterise the water related point-defect structure of the samples by FTIR (Keppler and Rauch, 2000). The large quantity of bulk water in fluid inclusions makes FTIR characterisation of point defects very difficult. Therefore we cannot determine a possible interaction between properties of the samples and their point defect structure, but only with the bulk fluid composition.
The Victoria samples are milky vein quartz with straight extinction, with approximately 4 vol.% fluid inclusions. The larger fluid inclusions occurring in clusters are 20-40 μm in size and irregular in shape. These inclusions contain 0-20 vol.% gas and 80-100 vol.% liquid. The medium size inclusions (5-10 μm) are homogeneously distributed throughout the grains and have a smooth shape. They contain 0-20 vol.% gas and 50-100 vol.% liquid, and 0-30 vol.% solid (in the form of cubic crystals). The small inclusions are found in trails and have a spherical shape. These inclusions are 1-5 μm in size and contain 0-70 vol.% gas and 30-100 vol.% liquid (Table 2).
Table 1. Experimental conditions and details.
|Fluid inclusions (main phase)||aqueous||aqueous||aqueous||gaseous||aqueous||gaseous|
|strain rate (x10-6/s-1)||0.9||10||11||9||11||3.8|
|P confining (GPa)||1.16||1.17||1.16||1.17||1.16||1.16|
|T (annealing under stress)||800||800||900||820||820||820|
|t (annealing under stress) h:m||2:20||107:30||32:30||97:30||279:05||78:20|
|Recrystallized area (%)||1||30||15||10||30||10|
|*Cylindrical samples (length ∼12 mm, diameter 5.9 mm) were cored at an angle of 56 – 86° with respect to the c-axis.|
The material from Naxos has faint undulose extinction and contains ∼1-2 vol.% fluid inclusions which are inhomogeneously distributed in clusters and along healed cracks. The large, 5-20 μm fluid inclusions contain 20-100 vol.% gas and 0-80 vol.% liquid. These inclusions are irregular and prolate in shape. Small inclusions (<5 μm) contain only gas (Table 2).
The quartz from Scandinavia is clear to milky, contains 4-5 vol.% fluid inclusions, and has blocky undulose extinction. Large inclusions (10-35 μm) are irregular in shape and cluster along healed cracks. These inclusions contain 0-60 vol.% gas, but mostly in the range of 10 vol.%. Medium-size inclusions are 1-5 μm in size and spherical to round in shape. They contain 10 vol.% gas and 90 vol.% liquid, and infrequently they also contain cubic crystals, inferred to be NaCl. The small, spherical inclusions of 0.5-3 μm contain liquid.
Cylindrical samples (length ∼12 mm, diameter 5.9 mm) were cored at an angle of 56° - 86° with respect to the c-axis (see Table 1). Samples were bench-dried and then weld-sealed in thick-walled gold or platinum capsules (Table 1). The samples were deformed in a Tullis-modified Griggs-rig (Tullis and Tullis, 1986) at the Utrecht University, The Netherlands, using an all-salt assembly (for details see den Brok, 1992). For this type of assembly no pressure correction is required (Johannes, 1978).
Stresses were applied at temperatures between 710 and 820°C, 1200 MPa confining pressure and strain rates ranging from 0.9 to 11 x 10-6 s-1 (see Table 1). In order to avoid decrepitation of the fluid inclusions as much as possible during heating and pressurisation of the samples, the pressure and temperature were raised along the isochore of water density (1 gcm-3, Fisher, 1976). Samples were then axially shortened to bulk strains ranging from 6.5 - 38.4 %. After the deformation the samples were held at high temperature and pressure for various time periods (2 – 280 h) allowing annealing and static recrystallization of the samples. Annealing temperatures were similar to or higher than temperatures during deformation (Table 1). At the conclusion of deformation, the σ1–piston was not reversed, so that the samples annealed under stress. At the conclusion of each experiment the sample was cooled rapidly in order to avoid changes in microstructure. We prepared standard thin-sections (30 μm) parallel to the shortening direction. Stress-strain curves were calculated from the force-displacement record assuming homogeneous shortening of the sample and assuming the same linear increase in friction before and after the top piston reaches the sample (den Brok, 1992).
Slabs of material 1 mm thick were cut parallel to the shortening direction and prepared for Scanning Electron microscopy (SEM, glued to SEM stubs and carbon and gold coated). The slabs were carefully broken along planes either parallel to σ1 or perpendicular to σ1. The polycrystals break along the grain boundaries of recrystallized grains and this method thus allows observation of the grain boundary morphology (see also Urai 1983, Olgaard and Fitz Gerald, 1993; Mancktelow et al. , 1998).
Table 2. Fluid inclusion types and distribution.
|Fluid inclusion characteristics in starting material|
|Victoria||Grains with straight extinction and 4 vol.% fluid inclusions.||20-40 μm in diameter, with 0-20% gaseous and 80-100% aqueous inclusions, irregular in shape and arranged in clusters.||5-10 μm in diameter, with 0-20% gaseous, 50-100% aqueous and 0-30% solid, cubic inclusions. All are smooth in shape. The distribution is homogeneous.||1-5 μm in diameter, with 0-70% gaseous, 30-100% aqueous inclusions occurring in trails infrequently containing salt. The shape is spherical.||25|
|Scandinavia||Blocky grains with undulose extinction and 4-5 vol.% fluid inclusions.||10-35 μm in diameter, with 0-60 % (mostly 10%) gaseous inclusions. They are irregular in shape and cluster along cracks.||1-5 μm in diameter, with 10% gaseous, 90% aqueous inclusions, infrequently containing salt. The shape is spherical.||Aqueous inclusions with 0.5-3 μm in diameter. The shape is spherical.||33|
|Naxos||Grains with faint undulose extinction and 1-2 vol.% fluid inclusions, in-homogeneously distributed.||5-20 μm in diameter, with 20-100% gaseous and 0-80% aqueous inclusions. They are irregular and prolate in shape and some appear along healed cracks.||-||Only gaseous inclusions smaller than 5 μm in diameter.||32 + 34|
|Fluid inclusion characteristics after deformation|
|Victoria||Small and large inclusions are found along grain boundaries. In non-recrystallized areas the fluid inclusion distribution has not changed.||5-20 μm in diameter with irregular shape, some snaffle-shapes, often elongated parallel to σ1.||0.3-3 μm in diameter, split up into larger number, often with round shapes.||Usually arranged in trails.||25|
|Victoria||Fluid inclusions in bands, 50-150 μm long and sub-parallel to σ1 arranged in clusters. Recrystallized grains are free of fluid inclusions. Many elongated inclusions along grain boundaries with extra large ones on triple junctions, sometimes connected by fluid films.||2-15 μm in diameter with 20-30% gaseous inclusions.||Smaller than 2μm.||Appear in trail at 70° relative to σ1.||27|
|Victoria||Fluid inclusions are homogeneously distributed outside recrystallized areas and cluster on grain boundaries. Recrystallized grains contain no inclusions, except some large gaseous ones, also along grain boundaries.||5-40 μm in diameter with very irregular shape.||Smaller than 3 μm in diameter, with no changes in shape.||No planar arrays.||30|
|Scandinavia||Recrystallized grains contain only few fluid inclusions (< 0.5 μm), also along grain boundaries. Large inclusions are found in "pressure shadows" of recrystallized grains. In non-recrystallized areas fluid inclusions are homogeneously distributed. In recrystallized areas inclusions cluster on triple junctions (SEM). Some large inclusions on triple junctions are connected by fluid films.||Around 20 μm in diameter.||Elongated perpendicular to σ1, around 3-8 μm long and 1-2 μm wide.||33|
|Naxos||Fluid inclusions are small (<4 μm) and arranged in bands. Large, elongated inclusions on grain boundaries, less inside recrystallized grains. Small inclusions appear also in recrystallized grains, but less than in non-recrystallized.||32 + 34|