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Constraining Stress and Structural Development Within Subduction Zones Using Rock Deformation Experiments /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Constraining Stress and Structural Development Within Subduction Zones Using Rock Deformation Experiments // Stewart A Williams.
Author:	Williams, Stewart A.,
Description:	1 electronic resource (102 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 87-02, Section: B.
Contained By:	Dissertations Abstracts International87-02B.
Subject:	Geology. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=32260699
ISBN:	9798290947037

Constraining Stress and Structural Development Within Subduction Zones Using Rock Deformation Experiments /
Williams, Stewart A.,

Constraining Stress and Structural Development Within Subduction Zones Using Rock Deformation Experiments /Stewart A Williams. - 1 electronic resource (102 pages)

Source: Dissertations Abstracts International, Volume: 87-02, Section: B.

Some of the deadliest and most destructive natural hazards occur as a result of active subduction zones. The stresses at and around the subduction interface can directly control the natural hazard potential, controlling the magnitude of ground motion translated up to the surface. Stress calculations of in-situ conditions often only provide rough estimates and are limited in their applications and fidelity. Alternatively, we can study the exhumed rock record as analog systems; however, this results in generalizations across subduction zones. Many important factors that can vary between system to system can get lost in these generalizations, such as the presence of frictionally weak materials, elevated pore fluid pressures, or thermal structures, many of which can drastically alter the expected strength and slip behaviors. We conduct rock deformation experiments to bridge our remote observations and structural evidence between active and exhumed subduction zones, correlating the microstructures and attributed mechanisms of deformations to the stress states that caused them to develop.In the first chapter, we study the process of dilatant hardening, one proposed mechanism that causes slow earthquakes along faults. Previous experiments and models show that dilatant hardening can stabilize fault rupture and slip in several lithologies. However, few studies have systematically measured the mechanical behavior across the transition from dynamic to slow rupture or considered how the associated damage varies. To constrain the processes and scales of dilatant hardening, we conducted triaxial compression experiments on cores of Crab Orchard sandstone and structural analyses using micro-computed tomography imaging and petrographic analysis. Experiments were conducted at an effective confining pressure of ~10 MPa, while varying confining pressure (10-130 MPa) and pore fluid pressure (1-120 MPa). Above 15 MPa pore fluid pressure, dilatant hardening slows the rate of fault rupture and slip and deformation becomes more distributed amongst multiple faults as microfracturing increases. The resulting increase in fracture energy has the potential to control fault slip behavior.In the second chapter, we turn to the natural rock record of the The Sestola-Vidiciatico Unit (SVU) in the Northern Apennines, an exhumed subduction zone. This unit experienced a relatively limited deformation history and serves as a rare analog to the shallowest portions of active subduction megathrusts. We use calcite twinning from shear veins along mineralized faults surrounding the exhumed subduction interface to reconstruct paleostress orientations through calcite twin stress inversion. Combining orientation data with calcite twin paleopiezometry and geothermometry, we are able to reconstruct the stress state of the SVU during peak subduction and subsequent exhumation. We note similarities in the orientation of principal stresses to those estimated for active subduction zones, and gauge the applicability and accuracy of calcite twin analytical methods.In the third chapter, we conduct deformation experiments on calcite to better understand the role of different deformational parameters on the behaviors and morphology of calcite twinning. Many calcite twin-based analytical methods are developed over a broad range of deformation conditions, such as confining pressures, temperatures, strains, strain rates, etc.; however, there is a critical transition between different deformation mechanisms that is largely disregarded. As a result, there are large discrepancies between different analytical methods, not only with each other, but with observations in natural samples. For this study, we document differences in how calcite twinning accommodates strain at three different temperatures - 150, 175, and 200°C - spanning the semi-brittle range where different deformation mechanisms become more or less prevalent. In addition to the deformation experiments, we compile and compare our results with previous calcite twin studies to conduct statistical modeling to determine the contributing deformation parameters on calcite twin densities between brittle to semi-brittle to ductile deformation.

English

ISBN: 9798290947037Subjects--Topical Terms:

516570
Geology.
Subjects--Index Terms:

Earth science

Constraining Stress and Structural Development Within Subduction Zones Using Rock Deformation Experiments /
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520 $a Some of the deadliest and most destructive natural hazards occur as a result of active subduction zones. The stresses at and around the subduction interface can directly control the natural hazard potential, controlling the magnitude of ground motion translated up to the surface. Stress calculations of in-situ conditions often only provide rough estimates and are limited in their applications and fidelity. Alternatively, we can study the exhumed rock record as analog systems; however, this results in generalizations across subduction zones. Many important factors that can vary between system to system can get lost in these generalizations, such as the presence of frictionally weak materials, elevated pore fluid pressures, or thermal structures, many of which can drastically alter the expected strength and slip behaviors. We conduct rock deformation experiments to bridge our remote observations and structural evidence between active and exhumed subduction zones, correlating the microstructures and attributed mechanisms of deformations to the stress states that caused them to develop.In the first chapter, we study the process of dilatant hardening, one proposed mechanism that causes slow earthquakes along faults. Previous experiments and models show that dilatant hardening can stabilize fault rupture and slip in several lithologies. However, few studies have systematically measured the mechanical behavior across the transition from dynamic to slow rupture or considered how the associated damage varies. To constrain the processes and scales of dilatant hardening, we conducted triaxial compression experiments on cores of Crab Orchard sandstone and structural analyses using micro-computed tomography imaging and petrographic analysis. Experiments were conducted at an effective confining pressure of ~10 MPa, while varying confining pressure (10-130 MPa) and pore fluid pressure (1-120 MPa). Above 15 MPa pore fluid pressure, dilatant hardening slows the rate of fault rupture and slip and deformation becomes more distributed amongst multiple faults as microfracturing increases. The resulting increase in fracture energy has the potential to control fault slip behavior.In the second chapter, we turn to the natural rock record of the The Sestola-Vidiciatico Unit (SVU) in the Northern Apennines, an exhumed subduction zone. This unit experienced a relatively limited deformation history and serves as a rare analog to the shallowest portions of active subduction megathrusts. We use calcite twinning from shear veins along mineralized faults surrounding the exhumed subduction interface to reconstruct paleostress orientations through calcite twin stress inversion. Combining orientation data with calcite twin paleopiezometry and geothermometry, we are able to reconstruct the stress state of the SVU during peak subduction and subsequent exhumation. We note similarities in the orientation of principal stresses to those estimated for active subduction zones, and gauge the applicability and accuracy of calcite twin analytical methods.In the third chapter, we conduct deformation experiments on calcite to better understand the role of different deformational parameters on the behaviors and morphology of calcite twinning. Many calcite twin-based analytical methods are developed over a broad range of deformation conditions, such as confining pressures, temperatures, strains, strain rates, etc.; however, there is a critical transition between different deformation mechanisms that is largely disregarded. As a result, there are large discrepancies between different analytical methods, not only with each other, but with observations in natural samples. For this study, we document differences in how calcite twinning accommodates strain at three different temperatures - 150, 175, and 200°C - spanning the semi-brittle range where different deformation mechanisms become more or less prevalent. In addition to the deformation experiments, we compile and compare our results with previous calcite twin studies to conduct statistical modeling to determine the contributing deformation parameters on calcite twin densities between brittle to semi-brittle to ductile deformation.
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650 4 $a Sedimentary geology. $3 3173828
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650 4 $a Plate tectonics. $3 542702
653 $a Earth science
653 $a Structural geology
653 $a Rock deformation
653 $a Subduction zones
653 $a Rheology
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690 $a 0592
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710 2 $a Rice University. $b Earth Science. $e degree granting institution. $3 3814516
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