A low-temperature ductile shear zone: The gypsum-dominated western extension of the brittle Fella-Sava Fault, Southern Alps

Based on structural and fabric analyses at variable scales we investigate the evaporitic gypsum-dominated Comeglians-Paularo shear zone in the Southern Alps (Friuli). It represents the lateral western termination of the brittle Fella-Sava Fault. Missing dehydration products of gypsum and the lack of...

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Bibliographic Details
Published in:Journal of structural geology Vol. 69; pp. 18 - 31
Main Authors: Bartel, Esther Maria, Neubauer, Franz, Heberer, Bianca, Genser, Johann
Format: Journal Article
Language:English
Published: England Elsevier Ltd 01.12.2014
Elsevier Limited
Subjects:
Ductile shear zone
Fault termination
Gypsum
Porphyroclast system
Stretching fault
Transpression
Gypsum
Stretching fault
Porphyroclast system
Transpression
Ductile shear zone
Fault termination
ISSN:0191-8141, 1873-1201
Online Access:Get full text
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Summary:Based on structural and fabric analyses at variable scales we investigate the evaporitic gypsum-dominated Comeglians-Paularo shear zone in the Southern Alps (Friuli). It represents the lateral western termination of the brittle Fella-Sava Fault. Missing dehydration products of gypsum and the lack of annealing indicate temperatures below 100 °C during development of the shear zone. Despite of such low temperatures the shear zone clearly exhibits mylonitic flow, thus evidencing laterally coeval activity of brittle and viscous deformation. The dominant structures within the gypsum rocks of the Lower Bellerophon Formation are a steeply to gently S-dipping foliation, a subhorizontal stretching lineation and pure shear-dominated porphyroclast systems. A subordinate simple shear component with dextral displacement is indicated by scattered σ-clasts. Both meso- and microscale structures are characteristic of a subsimple shear type of deformation with components of both coaxial and non-coaxial strain. Shortening in a transpressive regime was accommodated by right-lateral displacement and internal pure shear deformation within the Comeglians-Paularo shear zone. The shear zone shows evidence for a combination of two stretching faults, where stretching occurred in the rheologically weaker gypsum member and brittle behavior in enveloping lithologies. [Display omitted] •The Comeglians-Paularo shear zone is the western extension of the Fella-Sava Fault.•Steeply dipping gypsum determines propagation and termination of the shear zone.•Mylonitic deformation of gypsum in the shear zone occurred at temperatures <100 °C.•The shear zone impedes fluid flow and possibly earthquake propagation.
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ISSN:0191-8141
1873-1201
DOI:10.1016/j.jsg.2014.09.016