Coupled extrusion of sub-arc lithospheric mantle and lower crust during orogen collapse: a case study from Fiordland, New Zealand

T. A. Czertowicz*, J. M. Scott, S. Piazolo

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)

Abstract

The Anita Peridotite is a ~20 km long by 1 km wide exhumed fragment of spinel facies sub-arc lithospheric mantle that is enclosed entirely within the ≤4 km wide ductile Anita Shear Zone, and bounded by quartzofeldspathic lower crustal gneisses in Fiordland, south-western New Zealand. Deformation textures, grain growth calculations and thermodynamic modelling results indicate the mylonitic peridotite fabric formed during rapid cooling, and therefore likely during extrusion. However, insights into the exhumation process are gained through examination of aluminous garnet-bearing meta-sedimentary gneisses also enclosed within the shear zone. P-T calculations indicate that prior to mylonitization the gneisses enclosing the peridotite equilibrated at 675-746 °C in the sillimanite stability field (stage I), before being buried to near the base of thickened arc crust (stage II; ~686 ± 26 °C and 10.7 ± 0.8 kbar). From this point on, the peridotite unit and the quartzofeldspathic rocks share a deformation history involving extensive recrystallization (stage III) within the Anita Shear Zone. Coupled exhumation of these portions of lower crust and upper mantle occurred during regional thinning of over-thickened lithosphere at c. 104 Ma (U-Pb zircon). Our favoured model for the exhumation process involves heterogeneous transpressive deformation within the translithospheric Anita Shear Zone, which provided a conduit for ductile extrusion through the crust.

Original languageEnglish
Pages (from-to)501-524
Number of pages24
JournalJournal of Metamorphic Geology
Volume34
Issue number5
Early online date12 Mar 2016
DOIs
Publication statusPublished - Jun 2016

Keywords

  • Fiordland
  • garnet zoning
  • mantle exhumation
  • P-T-t path
  • zircon U-Pb

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