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pure and applied geophysics

, Volume 143, Issue 1–3, pp 229–254 | Cite as

Microstructural analysis of faulting in quartzite, Assynt, NW Scotland: Implications for fault zone evolution

  • Robert J. Knipe
  • Geoffrey E. Lloyd
Faulting and Fault Zones: Field Observations

Abstract

Macroscopic fracture arrays, microstructures and interpreted deformation mechanisms are used to assess the development of a minor reverse fault (backthrust) in quartzite from the Moine Thrust Zone, Assynt, NW Scotland. Fracturing dominates the faulting via the progression: intragranular extension microcracks; transgranular, cataclasite absent extension fractures; through-going, cataclasite filled shear microfaults, within which fracturing and particulate flow operate. However, both diffusive mass transfer (DMT) and intracrystalline plasticity (low temperature plasticity, LTP) processes also contribute to the fault zone deformation and lead to distinct associations of deformation mechanisms (e.g., DMT-fracture and LTP-fracture or low-temperature ductile fracture, LTDF). Over a large range of scales the fault zone consists of blocks of relatively intact rock separated by narrow zones of intense deformation where fracture processes dominate. The populations of fragments/blocks of different sizes in the fault zone have a power-law relationship which is related to the dimension of the fault zone. These observations are used to develop a general model for fault zone evolution based on the distribution of deformation features as a function of either time or space. A systematic variation in the deformation rate: time histories is recognised, associated with different positions within the fault zone. Thus, the fault zone preserves elements of the “birth, life and death” sequences associated with the displacement history and strain accommodation.

Key words

Structural geology faults deformation mechanisms NW Scotland SEM 

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Copyright information

© Birkhäuser Verlag 1994

Authors and Affiliations

  • Robert J. Knipe
    • 1
  • Geoffrey E. Lloyd
    • 1
  1. 1.Department of Earth Sciences, The UniversityLeedsEngland

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