Mechanical mixing of garnet peridotite and pyroxenite in the orogenic peridotite lenses of the Tvaerdal Complex, Liverpool Land, Greenland Caledonides

Hannes K. Brueckner*, L. Gordon Medaris, Scott M. Johnston, Ebbe H. Hartz, Norman Pearson, Yue Cai, Arild Andresen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

The Tvaerdal Complex is an eclogite-bearing metamorphic terrane in Liverpool Land at the southern tip of the Greenland Caledonides. It is a Baltic terrane that was transferred to Laurentia during the Scandian orogeny. It exposes a few small garnet dunite and harzburgite lenses, some containing parallel layers of garnet pyroxenite and peridotite (including lherzolite). Sm-Nd mineral ages from the pyroxenites indicate recrystallization occurred at the same time (≈405Ma) as eclogite recrystallization in the enclosing gneiss. Geothermobarometry indicates these eclogites and pyroxenites shared a similar pressure-temperature history. This congruent evolution suggests pyroxenite-bearing peridotite lenses were introduced from a mantle wedge into subducted Baltic continental crust and subsequently shared a common history with this crust and its eclogites during the Scandian orogeny. Some garnet peridotite samples contain two garnet populations: one Cr-rich (3·5-6·2wt % Cr2O3 ) and the other Cr-poor (0·2-1·4wt %). Sm-Nd analyses of two such garnet peridotites define two sets of apparent ages: one older (>800Ma) for Cr-rich garnets and the other younger (<650Ma) for Cr-poor garnets. We propose that the younger Cr-poor garnets were derived from fractured and disaggregated garnet pyroxenite layers (i.e. are M2 ) and were mixed mechanically with older (i.e. M1 ) garnets of the host peridotite during intense Scandian shearing.Mechanical mixing may be an important mantle process.

Original languageEnglish
Pages (from-to)2191-2220
Number of pages30
JournalJournal of Petrology
Volume59
Issue number11
DOIs
Publication statusPublished - Nov 2018

Keywords

  • orogenic peridotite
  • mechanical mixing
  • pyroxenite
  • peridotite, Greenland Caledonides

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