International Journal of Earth Sciences

, Volume 89, Issue 2, pp 295–306

Metamorphic discontinuities in orogenic belts: example of the garnet–biotite–albite zone in the Otago Schist, New Zealand

  • N. Mortimer
ORIGINAL PAPER

DOI: 10.1007/s005310000086

Cite this article as:
Mortimer, N. Int Journ Earth Sciences (2000) 89: 295. doi:10.1007/s005310000086

Abstract

A regional petrographic reconnaissance of psammitic and pelitic rocks in the Otago Schist, New Zealand, has revealed the presence of garnet (“grossalspite” with typical rim composition almandine41, spessartine25, grossular33, pyrope1) and biotite in 37 new samples, more than doubling the previously known number. A new garnet–biotite–albite zone can now be defined in the greenschist facies Otago Schist that is distinct from the better-known biotite, garnet and oligoclase zones in the along-strike Alpine Schist. The garnet–biotite–albite zone is in part metamorphically discontinuous with adjacent schists and does not support models of simple, continuous, progressive Jurassic regional metamorphism in Otago. The structurally higher (lower grade) boundary of the zone coincides in at least three places with previously mapped regional shear zones. The structurally lower (expected higher grade) boundary of the zone appears to be obliterated by a chlorite zone overprint which can be spatially related to Alpine Schist recrystallisation of ?Cretaceous age. The Otago situation serves as an example of the subtle metamorphic discontinuities that probably pervade many orogenic belts.

Key words New ZealandHaast SchistOtago SchistMetamorphic rocksGarnet zoneGreenschist faciesStructural discontinuityOverprinting

Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • N. Mortimer
    • 1
  1. 1.Institute of Geological and Nuclear Sciences, Private Bag 1930, Dunedin 9020, New Zealand e-mail : n.mortimer@gns.cri.nz, Tel.:+64-3-4774050, Fax:+64-3-4775232NZ