Microstructures, deformation mechanisms and seismic properties of a Palaeoproterozoic shear zone

the Mertz shear zone, East-Antarctica

Gaëlle Lamarque*, Jérôme Bascou, Claire Maurice, Jean Yves Cottin, Nicolas Riel, René Pierre Ménot

*Corresponding author for this work

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

The Mertz shear zone (MSZ) is a lithospheric scale structure that recorded mid-crustal deformation during the 1.7 Ga orogeny. We performed a microstructural and crystallographic preferred orientation (CPO) study of samples from both mylonites and tectonic boudins that constitute relics of the Terre Adélie Craton (TAC). The deformation is highly accommodated in the MSZ by anastomosed shear bands, which become more scattered elsewhere in the TAC. Most of the MSZ amphibolite-facies mylonites display similar CPO, thermal conditions, intensity of deformation and dominant shear strain. Preserved granulite-facies boudins show both coaxial and non-coaxial strains related to the previous 2.45 Ga event. This former deformation is more penetrative and less localized and shows a deformation gradient, later affected by a major phase of recrystallization during retrogression at 2.42 Ga. Both MSZ samples and granulite-facies tectonic boudins present microstructures that reflect a variety of deformation mechanisms associated with the rock creep that induce contrasted CPO of minerals (quartz, feldspar, biotite, amphibole and orthopyroxene). In particular, we highlight the development of an "uncommon" CPO in orthopyroxene from weakly deformed samples characterized by (010)-planes oriented parallel to the foliation plane, [001]-axes parallel to the stretching lineation and clustering of [100]-axes near the Y structural direction.Lastly, we computed the seismic properties of the amphibolite and granulite facies rocks in the MSZ area in order to evaluate the contribution of the deformed intermediate and lower continental crust to the seismic anisotropy recorded above the MSZ. Our results reveal that (i) the low content of amphibole and biotite in the rock formations of the TAC, and (ii) the interactions between the CPO of the different mineralogical phases, generate a seismically isotropic crust. Thus, the seismic anisotropy recorded by the seismic stations of the TAC, including the MSZ, must be due to mantle rather than crustal structures.

Original languageEnglish
Pages (from-to)174-191
Number of pages18
JournalTectonophysics
Volume680
DOIs
Publication statusPublished - 12 Jun 2016
Externally publishedYes

Keywords

  • crustal deformation
  • crystallographic preferred orientation (CPO)
  • East Antarctica
  • microstructures
  • shear zone
  • strain localization

Fingerprint Dive into the research topics of 'Microstructures, deformation mechanisms and seismic properties of a Palaeoproterozoic shear zone: the Mertz shear zone, East-Antarctica'. Together they form a unique fingerprint.

Cite this