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Quantifying the Effects of Non-Hydrostatic Stress on Mineral Thermodynamics and Kinetics /

Record Type:	Electronic resources : Monograph/item
Title/Author:	Quantifying the Effects of Non-Hydrostatic Stress on Mineral Thermodynamics and Kinetics // Benjamin Levi Hess.
Author:	Hess, Benjamin Levi,
Description:	1 electronic resource (414 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 86-08, Section: B.
Contained By:	Dissertations Abstracts International86-08B.
Subject:	Petrology. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31562874
ISBN:	9798302884640

Quantifying the Effects of Non-Hydrostatic Stress on Mineral Thermodynamics and Kinetics /
Hess, Benjamin Levi,

Quantifying the Effects of Non-Hydrostatic Stress on Mineral Thermodynamics and Kinetics /Benjamin Levi Hess. - 1 electronic resource (414 pages)

Source: Dissertations Abstracts International, Volume: 86-08, Section: B.

Metamorphic rocks in active tectonic environments are subjected to non-hydrostatic stresses whose magnitudes differ with direction. Non-hydrostatic stresses are particularly large in subduction zone settings where up to GPa-level differential stresses are inferred from geodynamic and field studies. Nonetheless, standard petrological techniques implicitly assume a constant pressure, and the implications of non-hydrostatic stress for mineral thermodynamics are actively debated. The landmark work of F. Larche and J. Cahn provides a quantitative basis for treating the thermodynamics of non-hydrostatically stressed crystals that is consistent with and extends Gibbs' work. This dissertation develops and applies Larche-Cahn theory to common rock-forming minerals, quantifying how stress affects mineral thermodynamics and developing new methods that use mineral chemistry to determine stress states and timescales of tectonic processes.After the introductory Chapter 1, Chapter 2 quantifies how stress affects the stability between single-component polymorphs. At a constant temperature, the stability of each mineral interface is primarily a function of its normal stress. Mineral reactions in a prograde metamorphic system are expected to begin when the maximum stress of a system crosses a reaction boundary. Reactions will preferentially occur along interfaces oriented normal to the maximum stress. This may affect where devolatilization reactions occur in Earth, influence crystallographic- or shape-preferred mineral orientations, and trigger reaction-induced earthquakes.Chapter 3 quantifies the effects of stress on the compositions of multicomponent minerals. Stresses on the order of several hundred MPa will shift the compositions of minerals such as garnet, plagioclase, and omphacite by up to a tenth of a mole fraction. Moreover, structurally anisotropic minerals will have different compositions depending on their crystallographic orientations relative to the stress. These results provide the foundation for assessing how non-hydrostatic stress impacts geothermobarometers and for using mineral chemistry to infer stress states in the lithosphere.Chapter 4 develops novel orientation barometry methods that estimate stress from mineral compositions and orientations. Two types of orientation barometers utilizing maximum likelihood estimation inverse modeling are presented. The coupled orientation barometer estimates stress using both mineral orientations and compositions. The decoupled orientation barometer estimates stress using only the observed spread of mineral compositions. Whereas the former method has greater precision, the latter is more general in its applicability. Both allow for stress states to be determined from mineral compositions, offering potential insights into lithosphere dynamics.Chapter 5 presents a method for modeling intracrystalline diffusion in multicomponent minerals with arbitrary stress states. The model is applied to garnet and shows that internal stress gradients will cause smaller species to preferentially diffuse toward higher stresses and larger species, toward lower stresses. Hundreds of MPa of stress are required to shift garnet compositions by several hundredths of a mole fraction. Stress-driven diffusion around inclusions in garnet may provide estimates for magnitudes of intracrystalline stresses and the timescales of exhumation.Chapter 6 examines the case where diffusion itself generates stress in crystals. Interdiffusion of different-sized species will create intracrystalline compositional stress, limiting the relaxation of sharp chemical contacts and oscillatory zonation. A case study of garnet from Scotland reveals the preservation of micrometer-scale Ca variations superimposed on diffuse contacts between chemical zones. The diffuse contacts provide a timescale >105 years, consistent with previous studies, whereas the sharp oscillations indicate a much shorter 103-year timescale. Model results that incorporate compositional stress preserve the oscillatory zonation at the longer timescale, showing that stress may preserve sharp features for longer than standard diffusion models predict. Not accounting for compositional stress may cause timescales of lithospheric processes to be underestimated.Chapter 7 explores how compositional stress affects both the chemical and structural evolution of subducted rocks from Holsnoy, Norway. Metamorphic garnet has younger eclogite facies rims and relict granulite facies cores. Chemical profiles reveal smooth, diffuse core-rim contacts in garnets with minimal variation in the mole fraction of the grossular endmember, XGrs, and extremely sharp contacts in garnets with large, 0.08-0.10 XGrs variation. Standard diffusion models suggest a much shorter timescale for the garnets with sharp contacts compared to the smooth contacts. When compositional stress is incorporated, both types of contacts indicate a consistent 300 kyr timescale for peak eclogite facies metamorphism. The garnet rims also record smaller changes in XGrs that imply pulsed fluid infiltration events with a ~104 year recurrence time that may be tied to cycles of dehydration and seismicity. Finally, up to GPa-level variations in stress are predicted across the core-rim contacts, and consistently, healed microfractures are observed propagating from core-rim boundaries. Thus, compositional stresses may affect the structural evolution of minerals.

English

ISBN: 9798302884640Subjects--Topical Terms:

535210
Petrology.
Subjects--Index Terms:

Kinetics

Quantifying the Effects of Non-Hydrostatic Stress on Mineral Thermodynamics and Kinetics /
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520 $a Metamorphic rocks in active tectonic environments are subjected to non-hydrostatic stresses whose magnitudes differ with direction. Non-hydrostatic stresses are particularly large in subduction zone settings where up to GPa-level differential stresses are inferred from geodynamic and field studies. Nonetheless, standard petrological techniques implicitly assume a constant pressure, and the implications of non-hydrostatic stress for mineral thermodynamics are actively debated. The landmark work of F. Larche and J. Cahn provides a quantitative basis for treating the thermodynamics of non-hydrostatically stressed crystals that is consistent with and extends Gibbs' work. This dissertation develops and applies Larche-Cahn theory to common rock-forming minerals, quantifying how stress affects mineral thermodynamics and developing new methods that use mineral chemistry to determine stress states and timescales of tectonic processes.After the introductory Chapter 1, Chapter 2 quantifies how stress affects the stability between single-component polymorphs. At a constant temperature, the stability of each mineral interface is primarily a function of its normal stress. Mineral reactions in a prograde metamorphic system are expected to begin when the maximum stress of a system crosses a reaction boundary. Reactions will preferentially occur along interfaces oriented normal to the maximum stress. This may affect where devolatilization reactions occur in Earth, influence crystallographic- or shape-preferred mineral orientations, and trigger reaction-induced earthquakes.Chapter 3 quantifies the effects of stress on the compositions of multicomponent minerals. Stresses on the order of several hundred MPa will shift the compositions of minerals such as garnet, plagioclase, and omphacite by up to a tenth of a mole fraction. Moreover, structurally anisotropic minerals will have different compositions depending on their crystallographic orientations relative to the stress. These results provide the foundation for assessing how non-hydrostatic stress impacts geothermobarometers and for using mineral chemistry to infer stress states in the lithosphere.Chapter 4 develops novel orientation barometry methods that estimate stress from mineral compositions and orientations. Two types of orientation barometers utilizing maximum likelihood estimation inverse modeling are presented. The coupled orientation barometer estimates stress using both mineral orientations and compositions. The decoupled orientation barometer estimates stress using only the observed spread of mineral compositions. Whereas the former method has greater precision, the latter is more general in its applicability. Both allow for stress states to be determined from mineral compositions, offering potential insights into lithosphere dynamics.Chapter 5 presents a method for modeling intracrystalline diffusion in multicomponent minerals with arbitrary stress states. The model is applied to garnet and shows that internal stress gradients will cause smaller species to preferentially diffuse toward higher stresses and larger species, toward lower stresses. Hundreds of MPa of stress are required to shift garnet compositions by several hundredths of a mole fraction. Stress-driven diffusion around inclusions in garnet may provide estimates for magnitudes of intracrystalline stresses and the timescales of exhumation.Chapter 6 examines the case where diffusion itself generates stress in crystals. Interdiffusion of different-sized species will create intracrystalline compositional stress, limiting the relaxation of sharp chemical contacts and oscillatory zonation. A case study of garnet from Scotland reveals the preservation of micrometer-scale Ca variations superimposed on diffuse contacts between chemical zones. The diffuse contacts provide a timescale >105 years, consistent with previous studies, whereas the sharp oscillations indicate a much shorter 103-year timescale. Model results that incorporate compositional stress preserve the oscillatory zonation at the longer timescale, showing that stress may preserve sharp features for longer than standard diffusion models predict. Not accounting for compositional stress may cause timescales of lithospheric processes to be underestimated.Chapter 7 explores how compositional stress affects both the chemical and structural evolution of subducted rocks from Holsnoy, Norway. Metamorphic garnet has younger eclogite facies rims and relict granulite facies cores. Chemical profiles reveal smooth, diffuse core-rim contacts in garnets with minimal variation in the mole fraction of the grossular endmember, XGrs, and extremely sharp contacts in garnets with large, 0.08-0.10 XGrs variation. Standard diffusion models suggest a much shorter timescale for the garnets with sharp contacts compared to the smooth contacts. When compositional stress is incorporated, both types of contacts indicate a consistent 300 kyr timescale for peak eclogite facies metamorphism. The garnet rims also record smaller changes in XGrs that imply pulsed fluid infiltration events with a ~104 year recurrence time that may be tied to cycles of dehydration and seismicity. Finally, up to GPa-level variations in stress are predicted across the core-rim contacts, and consistently, healed microfractures are observed propagating from core-rim boundaries. Thus, compositional stresses may affect the structural evolution of minerals.
546 $a English
590 $a School code: 0265
650 4 $a Petrology. $3 535210
650 4 $a Mineralogy. $3 516743
650 4 $a Thermodynamics. $3 517304
653 $a Kinetics
653 $a Metamorphism
653 $a Non-hydrostatic stress
653 $a Subduction
653 $a Mineral thermodynamics
690 $a 0584
690 $a 0411
690 $a 0348
710 2 $a Yale University. $b Geology and Geophysics. $e degree granting institution. $3 3823488
720 1 $a Ague, Jay James $e degree supervisor.
773 0 $t Dissertations Abstracts International $g 86-08B.
790 $a 0265
791 $a Ph.D.
792 $a 2024
856 4 0 $u https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31562874