Semi-brittle deformation of granitoid gouges in shear experiments at elevated pressures and temperatures

Matej Pec; Holger Stünitz; Renée Heilbronner

doi:10.1016/j.jsg.2011.09.001

Semi-brittle deformation of granitoid gouges in shear experiments at elevated pressures and temperatures

Matej Pec, Holger Stünitz, Renée Heilbronner

Earth and Environmental Sciences-Twin Cities

Research output: Contribution to journal › Article › peer-review

55 Scopus citations

Abstract

The physical and chemical processes acting in the 'brittle-to-plastic' transition are of great interest for a better understanding of fault rheology. We performed a series of experiments on granitoid gouge material under high confining pressures (Pc = 500-1500 MPa), temperatures (T = 300 °C and 500 °C) and fast shear strain rates (∼1.8 × 10 ^-4 s ^-1) where the material deforms by semi-brittle flow. Samples deformed at 500 °C are systematically weaker than samples deformed at 300 °C over the whole examined confining pressure range indicating a non-frictional component of the deformation. All samples develop an S-C' fabrics and deformation localizes in slip zones containing 'amorphous' feldspar material with an intermediate composition (Na, Ca and K-rich). Further, we observe changes in composition of feldspars (enrichment in the albite component) in the highly fragmented - but crystalline - regions with increasing finite shear strain. Our results indicate that mass-transfer processes keep pace with frictional deformation even at high strain rates and together with viscous flow of the 'amorphous' material are responsible for the observed strength difference.

Original language	English (US)
Pages (from-to)	200-221
Number of pages	22
Journal	Journal of Structural Geology
Volume	38
DOIs	https://doi.org/10.1016/j.jsg.2011.09.001
State	Published - May 2012

Bibliographical note

Funding Information:
We would like to thank Rüdiger Kilian, Caleb Holyoke and Kathi Faak for stimulating discussion and comments on the early version of the manuscript. We also wish to thank Christian De Capitani for assistance with the microprobe measurements and discussion of the results, Daniel Mathys and Marcel Düggelin for support with SEM imagining, Willy Tschuldin for preparation of excellent thin sections and the technicians Hans-Rudolf Rüegg, Steinar Iversen, Silvio Mini and Asle Lilletun for technical assistance – without their support this study would not have been possible. Very constructive reviews from Greg Hirth and Elisabetta Mariani improved the manuscript and are gratefully appreciated. Funding by the Swiss National Foundation grant No. 200020-129976 is gratefully acknowledged.

Copyright:
Copyright 2012 Elsevier B.V., All rights reserved.

Keywords

Brittle-plastic transition
Fault rocks
Microstructures
Rock deformation
Semi-brittle flow

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10.1016/j.jsg.2011.09.001

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title = "Semi-brittle deformation of granitoid gouges in shear experiments at elevated pressures and temperatures",

abstract = "The physical and chemical processes acting in the 'brittle-to-plastic' transition are of great interest for a better understanding of fault rheology. We performed a series of experiments on granitoid gouge material under high confining pressures (Pc = 500-1500 MPa), temperatures (T = 300 °C and 500 °C) and fast shear strain rates (∼1.8 × 10 -4 s -1) where the material deforms by semi-brittle flow. Samples deformed at 500 °C are systematically weaker than samples deformed at 300 °C over the whole examined confining pressure range indicating a non-frictional component of the deformation. All samples develop an S-C' fabrics and deformation localizes in slip zones containing 'amorphous' feldspar material with an intermediate composition (Na, Ca and K-rich). Further, we observe changes in composition of feldspars (enrichment in the albite component) in the highly fragmented - but crystalline - regions with increasing finite shear strain. Our results indicate that mass-transfer processes keep pace with frictional deformation even at high strain rates and together with viscous flow of the 'amorphous' material are responsible for the observed strength difference.",

keywords = "Brittle-plastic transition, Fault rocks, Microstructures, Rock deformation, Semi-brittle flow",

author = "Matej Pec and Holger St{\"u}nitz and Ren{\'e}e Heilbronner",

note = "Funding Information: We would like to thank R{\"u}diger Kilian, Caleb Holyoke and Kathi Faak for stimulating discussion and comments on the early version of the manuscript. We also wish to thank Christian De Capitani for assistance with the microprobe measurements and discussion of the results, Daniel Mathys and Marcel D{\"u}ggelin for support with SEM imagining, Willy Tschuldin for preparation of excellent thin sections and the technicians Hans-Rudolf R{\"u}egg, Steinar Iversen, Silvio Mini and Asle Lilletun for technical assistance – without their support this study would not have been possible. Very constructive reviews from Greg Hirth and Elisabetta Mariani improved the manuscript and are gratefully appreciated. Funding by the Swiss National Foundation grant No. 200020-129976 is gratefully acknowledged. Copyright: Copyright 2012 Elsevier B.V., All rights reserved.",

year = "2012",

month = may,

doi = "10.1016/j.jsg.2011.09.001",

language = "English (US)",

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pages = "200--221",

journal = "Journal of Structural Geology",

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AU - Pec, Matej

AU - Stünitz, Holger

AU - Heilbronner, Renée

N1 - Funding Information: We would like to thank Rüdiger Kilian, Caleb Holyoke and Kathi Faak for stimulating discussion and comments on the early version of the manuscript. We also wish to thank Christian De Capitani for assistance with the microprobe measurements and discussion of the results, Daniel Mathys and Marcel Düggelin for support with SEM imagining, Willy Tschuldin for preparation of excellent thin sections and the technicians Hans-Rudolf Rüegg, Steinar Iversen, Silvio Mini and Asle Lilletun for technical assistance – without their support this study would not have been possible. Very constructive reviews from Greg Hirth and Elisabetta Mariani improved the manuscript and are gratefully appreciated. Funding by the Swiss National Foundation grant No. 200020-129976 is gratefully acknowledged. Copyright: Copyright 2012 Elsevier B.V., All rights reserved.

PY - 2012/5

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N2 - The physical and chemical processes acting in the 'brittle-to-plastic' transition are of great interest for a better understanding of fault rheology. We performed a series of experiments on granitoid gouge material under high confining pressures (Pc = 500-1500 MPa), temperatures (T = 300 °C and 500 °C) and fast shear strain rates (∼1.8 × 10 -4 s -1) where the material deforms by semi-brittle flow. Samples deformed at 500 °C are systematically weaker than samples deformed at 300 °C over the whole examined confining pressure range indicating a non-frictional component of the deformation. All samples develop an S-C' fabrics and deformation localizes in slip zones containing 'amorphous' feldspar material with an intermediate composition (Na, Ca and K-rich). Further, we observe changes in composition of feldspars (enrichment in the albite component) in the highly fragmented - but crystalline - regions with increasing finite shear strain. Our results indicate that mass-transfer processes keep pace with frictional deformation even at high strain rates and together with viscous flow of the 'amorphous' material are responsible for the observed strength difference.

AB - The physical and chemical processes acting in the 'brittle-to-plastic' transition are of great interest for a better understanding of fault rheology. We performed a series of experiments on granitoid gouge material under high confining pressures (Pc = 500-1500 MPa), temperatures (T = 300 °C and 500 °C) and fast shear strain rates (∼1.8 × 10 -4 s -1) where the material deforms by semi-brittle flow. Samples deformed at 500 °C are systematically weaker than samples deformed at 300 °C over the whole examined confining pressure range indicating a non-frictional component of the deformation. All samples develop an S-C' fabrics and deformation localizes in slip zones containing 'amorphous' feldspar material with an intermediate composition (Na, Ca and K-rich). Further, we observe changes in composition of feldspars (enrichment in the albite component) in the highly fragmented - but crystalline - regions with increasing finite shear strain. Our results indicate that mass-transfer processes keep pace with frictional deformation even at high strain rates and together with viscous flow of the 'amorphous' material are responsible for the observed strength difference.

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JO - Journal of Structural Geology

JF - Journal of Structural Geology

ER -

Semi-brittle deformation of granitoid gouges in shear experiments at elevated pressures and temperatures

Abstract

Bibliographical note

Keywords

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