Are feldspar-to-mica reactions necessarily reaction-softening processes in fault zones?

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doi: 10.1016/S0191-8141(99)00019-X
Authors:Wibberley, Christopher
Author Affiliations:Primary:
Université Montpellier II, Laboratorie de Géophysique et Tectonique, Montpellier, France
Other:
University of Manchester, United Kingdom
Volume Title:Questions in structural geology; 20th anniversary special issue
Volume Authors:Evans, James P., editor; Treagus, Susan H.
Source:Questions in structural geology; 20th anniversary special issue, edited by James P. Evans and Susan H. Treagus. Journal of Structural Geology, 21(8-9), p.1219-1227. Publisher: Pergamon, Oxford-New York, International. ISSN: 0191-8141
Publication Date:1999
Note:In English. 38 refs.; illus., incl. geol. sketch maps
Summary:Reaction-softening by mineralogical changes from feldspar to sericite has been recorded in many fault zones. During external crystalline basement deformation in the Alpine orogeny, the Ser Barbier thrust and splay faults in the Pelvoux massif experienced ultracataclasis and sericitization. Microstructural and geochemical data suggest different muscovitization reactions occurred at different times during evolution of the fault zone, and that each reaction has its own effect on fault rheology. Early cataclasis aided breakdown of orthoclase feldspars to muscovite, yet accompanying quartz release caused local cementation and hardening of the ultracataclasite. Continued deformation was accompanied by muscovitization of albite feldspar, and formation of mica-rich fault rocks which with increasing deformation were progressively depleted in silica. At this stage, reaction-enhanced ductility dominated. Much of the early cemented ultracataclasite escaped later deformation, and its low permeability allowed preservation of early geochemical characteristics by preventing later fluid access. These data show how the complex interaction of deformation processes and geochemical reactions produce rheological changes during fault zone evolution. [J.F.]
Sections:Petrology
Subsections:Igneous petrology
Subjects:Albite; Alpine Orogeny; Basement; Cataclasis; Cementation; Deformation; Diagenesis; Ductile deformation; Fault zones; Faults; Feldspar group; Framework silicates; Granites; Igneous rocks; Metasomatism; Mica group; Muscovitization; Orogeny; Permeability; Plagioclase; Plutonic rocks; Rheology; Sericite; Sheet silicates; Silicates; Thrust sheets; Alps; Dauphine Alps; Europe; France; Pelvoux Massif; Western Alps; Western Europe; Ser Barbier Faults
Coordinates:N451100 N451100 E0054300 E0054300
Abstract Numbers:00M/928
Record ID:1999059229
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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