Do reduction spots predate finite strain? A magnetic diagnosis of Cambrian Slates in North Wales

Norihiro Nakamura, Graham Borradaile

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The purple Cambrian slates of North Wales contain green-colored, irregular patches drawn out along cleavage and the more familiar ellipsoidal reduction spots that are parallel to cleavage. Because parallelism of pre-strain ellipsoids could only be produced by extremely high strain, we reject the hypothesis that these are strain markers. Here, we use magnetic methods to resolve this argument. The magnetic analysis reveals that the magnetic fabric of purple slate differs from the green variety of the slate only in the oxidation state, and indicates that the reduction process postdates cleavage. This suggests that the shape of reduction spots reflects the anistropy of diffusion during reduction, not finite strain and alignment of an initially ellipsoidal object in the slates.

Original languageEnglish
Pages (from-to)133-139
Number of pages7
JournalTectonophysics
Volume340
Issue number3-4
DOIs
Publication statusPublished - 2001 Dec 8
Externally publishedYes

Keywords

  • AMS
  • Anisotropy of diffusion
  • Partial AARM
  • Reduction spots
  • Strain marker

ASJC Scopus subject areas

  • Geophysics
  • Earth-Surface Processes

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