Trace element systematics in granulite facies rutile: Implications for Zr geothermometry and provenance studies

  • Kooijman E
  • Smit M
  • Mezger K
 et al. 
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Abstract

Metamorphic rutile from granulite facies metapelitic rocks of the Archean Pikwitonei Granulite Domain (PGD; Manitoba, Canada) provides constraints on the systematics of trace elements in rutile during high-temperature conditions and subsequent slow cooling. Compositional profiles and maps of the Zr concentrations in rutile grains (120–600 μm) from three metapelitic gneisses were acquired by electron probe micro-analysis, using a spatial resolution of down to 2 μm. Simultaneously, profiles were analysed for Nb, Cr and V, which have significantly different diffusion characteristics in rutile. The profiles of all elements show relatively homogeneous concentrations within most grains, but significant inter-grain differences even within a single thin section. Some rutile grains display a slight concentration decrease from a neighbouring garnet towards the matrix for all measured elements. The lack of diffusion profiles for all analysed elements shows that these are highly immobile in rutile and that distributions of these elements are primary and preserve prograde information. The Nb and Cr concentrations overlap with ranges that are ascribed to different provenances indicating that source discrimination based on these elements is not possible in all cases. High retentiveness for Zr implies that the Zr-in-rutile geothermometer is highly robust to diffusive re-equilibration, even during very slow cooling (

Author-supplied keywords

  • Diffusion
  • Granulite
  • Metamorphism
  • Rutile
  • Thermometry

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