Inefficient high-temperature metamorphism in orthogneiss

Timothy Chapman, Geoffrey L. Clarke, Sandra Piazolo, Nathan R. Daczko

Research output: Contribution to journalArticleResearchpeer-review

Abstract

A novel method utilizing crystallographic orientation and mineral chemistry data, based on large-scale electron backscatter diffraction (EBSD) and microbeam analysis, quantifies the proportion of relict igneous and neoblastic minerals forming variably deformed high-grade orthogneiss. The Cretaceous orthogneiss from Fiordland, New Zealand, comprises intermediate omphacite granulite interlayered with basic eclogite, which was metamorphosed and deformed at T ≈ 850 °C and P ≈ 1.8 GPa after protolith cooling. Detailed mapping of microstructural and physiochemical relations in two strain profiles through subtly distinct intermediate protoliths indicates that up to 32% of the orthogneiss mineralogy is igneous, with the remainder being metamorphic. Domains dominated by igneous minerals occur preferentially in strain shadows to eclogite pods. Distinct metamorphic stages can be identified by texture and chemistry and were at least partially controlled by strain magnitude. At the grain-scale, the coupling of metamorphism and crystal plastic deformation appears to have permitted efficient transformation of an originally igneous assemblage. The effective distinction between igneous and metamorphic paragenesis and their links to deformation history enables greater clarity in interpretations of the makeup of the crust and their causal influence on lithospheric scale processes.

LanguageEnglish
Pages17-30
Number of pages14
JournalAmerican Mineralogist
Volume104
Issue number1
DOIs
Publication statusPublished - Jan 2019

Fingerprint

orthogneiss
Minerals
eclogite
metamorphism
minerals
protolith
mineral
chemistry
clarity
omphacite
microbeams
Mineralogy
New Zealand
plastic deformation
mineralogy
paragenesis
granulite
Electron diffraction
backscatter
Temperature

Keywords

  • Neoblasts
  • EBSD
  • recrystallization
  • strain
  • tectonometamorphism
  • microstructure
  • Understanding of Reaction and Deformation Microstructures

Cite this

Chapman, Timothy ; Clarke, Geoffrey L. ; Piazolo, Sandra ; Daczko, Nathan R. / Inefficient high-temperature metamorphism in orthogneiss. In: American Mineralogist. 2019 ; Vol. 104, No. 1. pp. 17-30.
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Inefficient high-temperature metamorphism in orthogneiss. / Chapman, Timothy; Clarke, Geoffrey L.; Piazolo, Sandra; Daczko, Nathan R.

In: American Mineralogist, Vol. 104, No. 1, 01.2019, p. 17-30.

Research output: Contribution to journalArticleResearchpeer-review

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