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Effect of Partial Melting on Lattice Preferred Orientations in Two Common Foliated Felsic Rocks.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Effect of Partial Melting on Lattice Preferred Orientations in Two Common Foliated Felsic Rocks./
Author:	Razo, Maria.
Description:	1 online resource (70 pages)
Notes:	Source: Masters Abstracts International, Volume: 84-11.
Contained By:	Masters Abstracts International84-11.
Subject:	Mineralogy. -
Online resource:	click for full text (PQDT)
ISBN:	9798379522797

Effect of Partial Melting on Lattice Preferred Orientations in Two Common Foliated Felsic Rocks.
Razo, Maria.

Effect of Partial Melting on Lattice Preferred Orientations in Two Common Foliated Felsic Rocks. - 1 online resource (70 pages)

Source: Masters Abstracts International, Volume: 84-11.

Thesis (M.S.)--The University of Akron, 2023.

Includes bibliographical references

Within the mid to lower continental crust distributed ductile thinning occurs, in orogens that form mountains like the Himalayas and Appalachia, due to a weak middle to lower crust that deforms laterally in response to loading of a thickened, cold upper crust. This thinning destabilizes large orogens and causes the exhumation of hot and weak rock from the mid to lower crust that begins to partially melt. This melting further weakens the rocks and may affect the deformation mechanisms operating in the crust. Melting has been seen to have impacts on the deformation mechanisms and resulting lattice preferred orientations (LPO) that form in olivine-basalt aggregates (Holtzman et al., 2003). To investigate the effects of partial melting on deformation mechanisms and LPO development in two common foliated felsic rocks, I performed general shear deformation experiments on a fine-grained quartzite and fine-grained gneiss at T = 800°C, 850°C, 900°C, 950°C, or 975°C, P = 1.5 GPa, and strain rate of 6*10-5/s. The quartzite (grain size ~30 microns) is composed of 90% quartz and 10% muscovite. The fine-grained gneiss (grain size ~50 microns) is composed of 43% quartz, 40% plagioclase, 16% biotite, and 1% accessory minerals. The foliation in the slices of each rock was oriented parallel to the shear plane between Al2O3 shear pistons with a cut made at 45° to the compression direction. Experiments were performed at a range of temperatures to change the melt fraction present in the rocks during deformation (Melt = ~0%, 0.25%, 0.5%, and 1%).The yield stress of Moine Thrust quartzite decreased as a function of increasing temperature from ~1000 to ~300 MPa. However, all the experiments with melt present (T equal to to greater than 850°C) significantly strain hardened after a shear strain (γ) of 1. This hardening may be due to the presence of melt along grain boundaries which is absorbing water from the recrystallizing quartz grains which slows diffusive recovery in quartz. The Gneiss Minuti strain weakened after reaching a peak equivalent stress of ~1000 MPa. Unlike the Moine Thrust quartzite slices with melt, the Gneiss Minuti had 1 vol% melt present which is located along grain boundaries parallel to the foliation. Microstructures in quartz grains in the quartzite include undulatory extinction, deformation lamellae, and fine recrystallized grains indicating deformation by dislocation creep. Microstructures in plagioclase grains include undulatory extinction. Microstructures in quartz grains in the quartzite include undulatory extinction, deformation lamellae, and fine recrystallized grains indicating deformation by dislocation creep. Microstructures in plagioclase grains include undulatory extinction. Microstructures in biotite include kinks in suitably oriented grains and shearing along (001) planes. These microstructures are consistent with deformation of quartz and plagioclase by dislocation creep and deformation of biotite grains by dislocation glide/kinking.The LPO of all the quartzite slices deformed with a melt fraction of <0.5% (T ≤ 900°C) is similar to the original LPO, consistent with deformation by dislocation creep on the basal c slip system (0001){112̅0}. However, the LPO in quartzite slices changes with the addition of melt to a LPO that is thought to be caused by dislocation creep on the prism slip system {101̅0}. This LPO is only observed in melt-free quartzites at lower differential stresses and greater strains than in this study (Heilbronner and Tullis, 2002; 2006). Heilbronner and Tullis (2006) speculate that the formation of this LPO was a function of increasing shear strain. However, this LPO is observed in naturally deformed quartzite rocks in the presence of melt. My results indicate the presence of melt likely facilitates a change in deformation mechanisms from dislocation creep to melt enhanced grain boundary sliding, causing the formation of this new LPO.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798379522797Subjects--Topical Terms:

670562
Mineralogy.
Subjects--Index Terms:

QuartzIndex Terms--Genre/Form:

554714
Electronic books.

Effect of Partial Melting on Lattice Preferred Orientations in Two Common Foliated Felsic Rocks.
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504 $a Includes bibliographical references
520 $a Within the mid to lower continental crust distributed ductile thinning occurs, in orogens that form mountains like the Himalayas and Appalachia, due to a weak middle to lower crust that deforms laterally in response to loading of a thickened, cold upper crust. This thinning destabilizes large orogens and causes the exhumation of hot and weak rock from the mid to lower crust that begins to partially melt. This melting further weakens the rocks and may affect the deformation mechanisms operating in the crust. Melting has been seen to have impacts on the deformation mechanisms and resulting lattice preferred orientations (LPO) that form in olivine-basalt aggregates (Holtzman et al., 2003). To investigate the effects of partial melting on deformation mechanisms and LPO development in two common foliated felsic rocks, I performed general shear deformation experiments on a fine-grained quartzite and fine-grained gneiss at T = 800°C, 850°C, 900°C, 950°C, or 975°C, P = 1.5 GPa, and strain rate of 6*10-5/s. The quartzite (grain size ~30 microns) is composed of 90% quartz and 10% muscovite. The fine-grained gneiss (grain size ~50 microns) is composed of 43% quartz, 40% plagioclase, 16% biotite, and 1% accessory minerals. The foliation in the slices of each rock was oriented parallel to the shear plane between Al2O3 shear pistons with a cut made at 45° to the compression direction. Experiments were performed at a range of temperatures to change the melt fraction present in the rocks during deformation (Melt = ~0%, 0.25%, 0.5%, and 1%).The yield stress of Moine Thrust quartzite decreased as a function of increasing temperature from ~1000 to ~300 MPa. However, all the experiments with melt present (T equal to to greater than 850°C) significantly strain hardened after a shear strain (γ) of 1. This hardening may be due to the presence of melt along grain boundaries which is absorbing water from the recrystallizing quartz grains which slows diffusive recovery in quartz. The Gneiss Minuti strain weakened after reaching a peak equivalent stress of ~1000 MPa. Unlike the Moine Thrust quartzite slices with melt, the Gneiss Minuti had 1 vol% melt present which is located along grain boundaries parallel to the foliation. Microstructures in quartz grains in the quartzite include undulatory extinction, deformation lamellae, and fine recrystallized grains indicating deformation by dislocation creep. Microstructures in plagioclase grains include undulatory extinction. Microstructures in quartz grains in the quartzite include undulatory extinction, deformation lamellae, and fine recrystallized grains indicating deformation by dislocation creep. Microstructures in plagioclase grains include undulatory extinction. Microstructures in biotite include kinks in suitably oriented grains and shearing along (001) planes. These microstructures are consistent with deformation of quartz and plagioclase by dislocation creep and deformation of biotite grains by dislocation glide/kinking.The LPO of all the quartzite slices deformed with a melt fraction of <0.5% (T ≤ 900°C) is similar to the original LPO, consistent with deformation by dislocation creep on the basal c slip system (0001){112̅0}. However, the LPO in quartzite slices changes with the addition of melt to a LPO that is thought to be caused by dislocation creep on the prism slip system {101̅0}. This LPO is only observed in melt-free quartzites at lower differential stresses and greater strains than in this study (Heilbronner and Tullis, 2002; 2006). Heilbronner and Tullis (2006) speculate that the formation of this LPO was a function of increasing shear strain. However, this LPO is observed in naturally deformed quartzite rocks in the presence of melt. My results indicate the presence of melt likely facilitates a change in deformation mechanisms from dislocation creep to melt enhanced grain boundary sliding, causing the formation of this new LPO.
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