رسالة جامعية
The effects of foliation orientation and foliation intensity on viscous anisotropy of granitic rocks with low mica content
| العنوان: | The effects of foliation orientation and foliation intensity on viscous anisotropy of granitic rocks with low mica content |
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| المؤلفون: | Waller, Jacob A. |
| بيانات النشر: | University of Akron / OhioLINK, 2022. |
| سنة النشر: | 2022 |
| المجموعة: | Ohiolink ETDs |
| Original Material: | http://rave.ohiolink.edu/etdc/view?acc_num=akron1658147040359233Test |
| مصطلحات موضوعية: | Geology, foliation orientation, foliation intensity, foliation, rock mechanics, geology, rock deformation, hard rock, viscous anisotropy, stress, crystal plastic deformation, high pressure and high temperature rock deformation |
| الوصف: | Stresses in the upper crust are redistributed to the lower crust after earthquakes. Stresses released by seismic slip induce crystal-plastic deformation in the mid to lower crust, which is composed of foliated, heterogeneous feldspathic rocks that deform and transfer stress back to the upper crust. Current models for the strength of the crust are primarily based on flow laws determined from experimentally deformed homogeneous quartzites or other monophase rocks. However, heterogeneities such as foliation orientations and foliation intensities, which are known to cause anisotropy of rock strength under brittle conditions, may cause viscous anisotropy at high temperatures and pressures where crystal-plastic mechanisms are dominant. To investigate if heterogeneities like foliation orientation and foliation intensity cause viscous anisotropy, I deformed weakly foliated Westerly Granite and strongly foliated Gneiss Minuti in different orientations that maximize (foliation at 45 degrees to the compression direction) and minimize (foliation parallel and foliation perpendicular to the compression direction) the shear stresses on the dispersed, elongate biotite grains in the quartz-feldspar framework, which should be the weakest and strongest orientations, respectively. These rocks were chosen because they both have similar low biotite contents (7%) and compositions: Westerly Granite is composed of 22 vol% quartz, 26 vol% K-feldspar, 45 vol% albite, and 7 vol% biotite and Gneiss Minuti is composed of 29 vol% quartz, 10 vol% K-feldspar, 53 vol% plagioclase and 7 vol% biotite. Experiments were performed using a Griggs apparatus at a temperature (T) of 800°C, confining pressure (Pc) of 1.5 GPa, and strain rate of 1.6 x 10-6/s. Westerly Granite and Gneiss Minuti reached peak stresses of 920 (+/- 50 MPa) and 670 (+/- 75 MPa), respectively, and viscous anisotropy was minor with anisotropy coefficients of 1.1x and 1.2x, respectively. Westerly Granite contained microstructures like deformation lamellae and undulatory extinction in quartz grains, consistent with dislocation creep, kinking and shearing of biotite grains, consistent with dislocation glide, and cracked grains that contain undulatory extinction in feldspars, consistent with semi-brittle flow. Every core of Westerly Granite contained biotite grains that deformed to be nearly perpendicular to the compression direction. Gneiss Minuti contained microstructures like deformation lamellae and undulatory extinction in quartz grains, consistent with dislocation creep, kinking and shearing of biotite grains, consistent with dislocation glide, and undulatory extinction in feldspars, consistent with dislocation creep. Biotite rotation was not consistent in the Gneiss Minuti, instead, polyphase four grain junctions were observed, indicating that grain boundary sliding is accommodating strain as a deformation mechanism. Comparing these experimental data with other studies performed on felsic crustal rocks at similar conditions indicates that overall rock strength is only mildly affected by foliation orientation and intensity, but considerably more affected by the feldspar content of the quartz-feldspar framework in the rock. |
| Original Identifier: | oai:etd.ohiolink.edu:akron1658147040359233 |
| نوع الوثيقة: | text |
| اللغة: | English |
| الإتاحة: | http://rave.ohiolink.edu/etdc/view?acc_num=akron1658147040359233Test |
| حقوق: | unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
| رقم الانضمام: | edsndl.OhioLink.oai.etd.ohiolink.edu.akron1658147040359233 |
| قاعدة البيانات: | Networked Digital Library of Theses & Dissertations |
| الوصف غير متاح. |