Olivine crystallographic control and anisotropic melt distribution in ultramafic partial melts

Jung, Haemyeong; Waff, Harve S.

doi:10.1029/98gl02177

Cited by 22 publications

(13 citation statements)

References 48 publications

(23 reference statements)

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“…9D). The existence of partial melt (Jin et al, 1994;Jung and Waff, 1998;Zimmerman et al, 1999;J. Zhang et al, 2004) may also cause a similar effect.…”

Section: Discussion and Geophysical Implicationsmentioning

confidence: 98%

Experimental Faulting of Serpentinite during Dehydration: Implications for Earthquakes, Seismic Low-Velocity Zones, and Anomalous Hypocenter Distributions in Subduction Zones

Jung

Green

2004

International Geology Review

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Dehydration embrittlement of serpentine was investigated by employing triaxial deformation experiments at high pressure and temperature (P = 1-6 GPa; T = 550-820ºC). A modified Griggs apparatus was used up to 3.4 GPa and a Walker-type multi-anvil apparatus was used at 3.5-6 GPa). The investigated specimen is a serpentinized peridotite from Val Malenco, Italy. Dehydration of the sample under differential stress resulted in faults associated with ultrafine-grained solid reaction products, formed as byproducts of antigorite dehydration. This phenomenon was observed under all conditions tested (1-6 GPa, 630-820ºC), independent of pressure, even though the sign of total volume change (∆V) of the dehydration reaction changes from positive to negative at 2.2 GPa. This observation confirms that dehydration embrittlement is a viable mechanism for triggering earthquakes independent of depth, so long as there is a hydrous mineral breaking down under differential stress. Aligned Mode-I cracks and fluid inclusion trails are common in relict olivines in the deformed serpentinite. We suggest that some of the puzzling observations, including a seismic lowvelocity zone (LVZ) at the top of subducting slabs, can be attributable to aligned fluid-filled Mode-I cracks and enhanced defect mobility in olivine in the presence of water. The anomalous hypocenter distributions of earthquakes can be attributed to the degree of dehydration of hydrous minerals in combination with a certain level of stress. In addition, low-seismicity regions in subduction zones may be explained by "superplastic" flow under low stress along the ultrafine-grained solid reaction products that are produced during dehydration reactions.

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“…9D). The existence of partial melt (Jin et al, 1994;Jung and Waff, 1998;Zimmerman et al, 1999;J. Zhang et al, 2004) may also cause a similar effect.…”

Section: Discussion and Geophysical Implicationsmentioning

confidence: 98%

Experimental Faulting of Serpentinite during Dehydration: Implications for Earthquakes, Seismic Low-Velocity Zones, and Anomalous Hypocenter Distributions in Subduction Zones

Jung

Green

2004

International Geology Review

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“…High surface energy anisotropies are expected to play a major role in fully wetted grain boundaries. Observations in olivine–ultramafic melt systems showed that completely wetted grain boundaries are often found parallel to low‐index facets [(010), (110) and (021)] (Jung & Waff 1998). These are similar to our observations of growing primary recrystallizing and exaggerated grains normal to the {100} faces.…”

Section: Discussionmentioning

confidence: 99%

Structure of grain boundaries in wet, synthetic polycrystalline, statically recrystallizing halite – evidence from cryo‐SEM observations

Schenk¹,

Urai²,

Piazolo³

2006

Geofluids

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It is well known from nature and experiments that the presence of brine strongly affects the microstructural evolution and the mechanical and transport properties of halite. Existing interpretations of the grain boundary structure in deformed, wet, salt samples annealed statically at room temperature are based on indirect evidence from reflected light microscopy and conventional scanning electron microscopy. This paper presents direct observations of fluid-filled grain boundaries using the cryogenic-scanning electron microscope (cryo-SEM) in which the grain boundary fluids were frozen before breaking the samples. The rapid cooling transforms the brine into two phases, i.e. ice and hydrohalite, which are easily recognized from characteristic segregation patterns. We studied samples of wet, synthetic, polycrystalline halite annealed under static conditions at room temperature. In coarse-grained samples, fine-scale segregation patterns were observed at the boundaries of the primary recrystallizing grains. These points indicate the existence of fluid films with a thickness in the range of 30 nm, but the finer scale structure of the fluid remains unknown. In fine-grained samples, the distribution and reorganization of fluids with annealing time is recorded by the combination of contact healing and successive accumulation of fluids in triple junction tubes. The contact healing is attributed to the small initial grain size, such that the fluid film necks down by accumulating the fluids into previously existing triple junctions via neck growth. Electron backscatter diffraction measurements of both primary and secondary recrystallized grains indicate that they are euhedral, i.e. the grain growth morphology is controlled by the anisotropy of the grain boundary energy of the growing grain, which results in planar growth faces.

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“…Bussod and Christie, 1991, Daines and Kohlstedt, 1997, Takei, 2010. The alignment may be attributed to the instantaneous state of deviatoric stress [Daines and Kohlstedt, 1997, Takei andHoltzman, 2009a], or to the combined effects of finite strain, lattice-preferred orientation, and anisotropic surface energy of olivine grains [Bussod and Christie, 1991, Daines and Kohlstedt, 1997, Jung and Waff, 1998; it is likely some combination of the two. Since the Darcian permeability of partially molten rocks arises from the shape and interconnectedness of melt pockets at the grain scale [e.g.…”

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confidence: 99%

Melt-preferred orientation, anisotropic permeability and melt-band formation in a deforming, partially molten aggregate

Taylor-West

Katz

2015

Geophys. J. Int.

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Shear deformation of partially molten rock in laboratory experiments causes the emergence of melt-enriched sheets (bands in cross-section) that are aligned at about 15-20 • to the shear plane. Deformation and deviatoric stress also cause the coherent alignment of pores at the grain scale. This leads to a melt-preferred orientation that may, in turn, give rise to an anisotropic permeability. Here we develop a simple, general model of anisotropic permeability in partially molten rocks. We use linearised analysis and nonlinear numerical solutions to investigate its behaviour under simple-shear deformation. In particular, we consider implications of the model for the emergence and angle of melt-rich bands. Anisotropic permeability affects the angle of bands and, in a certain parameter regime, it can give rise to low angles consistent with experiments. However, the conditions required for this regime have a narrow range and seem unlikely to be entirely met by experiments. Anisotropic permeability may nonetheless affect melt transport and the behaviour of partially molten rocks in Earth's mantle. arXiv:1505.00559v2 [physics.geo-ph] 5 Sep 2015 whether the low angles could arise as a consequence of a permeability that is directionally dependent (i.e. anisotropic).Anisotropic permeability could be a consequence of another empirically known feature of partially molten rocks subjected to deviatoric stress: the microstructural alignment of interconnected pockets of melt between solid grains. This is called melt-preferred orientation (MPO) and has been observed in many laboratory studies [e.g. Bussod and Christie, 1991, Daines and Kohlstedt, 1997, Takei, 2010. The alignment may be attributed to the instantaneous state of deviatoric stress [Daines and Kohlstedt, 1997, Takei andHoltzman, 2009a], or to the combined effects of finite strain, lattice-preferred orientation, and anisotropic surface energy of olivine grains [Bussod and Christie, 1991, Daines and Kohlstedt, 1997, Jung and Waff, 1998; it is likely some combination of the two. Since the Darcian permeability of partially molten rocks arises from the shape and interconnectedness of melt pockets at the grain scale [e.g. Bear, 1972, Scheidegger, 1974, it is reasonable to assume that the anisotropic alignment of pores between grains leads to anisotropy in permeability. Daines and Kohlstedt [1997] estimated this anisotropy as a function of differential stress and found that permeability in the direction parallel to the maximum compressive stress σ 1 was enhanced by a factor of up to 15 over that parallel to the direction of maximum tensile stress. This is consistent with a theoretical model for anisotropy of permeability due to MPO by Hier-Majumder [2011].Since both melt-banding at the macroscopic scale and melt-preferred orientation at the microscopic scale emerge under the same physical conditions, it is logical to ask whether their dynamics are linked. In particular, the question we address here is whether the low angle of high-porosity bands observed in experiments [see s...

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Olivine crystallographic control and anisotropic melt distribution in ultramafic partial melts

Cited by 22 publications

References 48 publications

Experimental Faulting of Serpentinite during Dehydration: Implications for Earthquakes, Seismic Low-Velocity Zones, and Anomalous Hypocenter Distributions in Subduction Zones

Experimental Faulting of Serpentinite during Dehydration: Implications for Earthquakes, Seismic Low-Velocity Zones, and Anomalous Hypocenter Distributions in Subduction Zones

Structure of grain boundaries in wet, synthetic polycrystalline, statically recrystallizing halite – evidence from cryo‐SEM observations

Melt-preferred orientation, anisotropic permeability and melt-band formation in a deforming, partially molten aggregate

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