Petrogenesis of Variscan high-temperature Group A eclogites from the Moldanubian Zone of the Bohemian Massif, Czechoslovakia

Brian L. Beard*, L. Gordon Medaris, Clark M. Johnson, Hannes K. Brueckner, Zdenek Mísař

*Corresponding author for this work

Research output: Contribution to journalArticle

99 Citations (Scopus)

Abstract

High-temperature (HT), Group A eclogites from three localities in the Moldanubian Zone of the Bohemian Massif are interpreted to have formed in the mantle and to have been transported into the crust by their enclosing garnet peridotites during Variscan orogenesis. Garnet and omphacite are compositionally zoned and contain homogeneous cores and retrograde rims. Cores of minerals yield minimum temperatures and pressures of 850 to 985°C and 16.0 to 22.5 kb, based on Fe-Mg exchange between garnet and clinopyroxene and the jadeite content of clinopyroxene. Sugh high temperatures indicate equilibration in, and derivation from, the upper mantle. Trace element compositions, including the REEs, high MgO contents, and high Mg numbers suggest that the rocks formed by high pressure accumulation of garnet and clinopyroxene and variable amounts of trapped melt. Sm-Nd ages determined on four garnet-clinopyroxene pairs from the three localities are 377±20, 342±9, 336±16, and 323±7 Ma. e{open}Nd and initial 87Sr/86Sr are negatively correlated, varying from +6.7 to -0.1 and 0.7027 to 0.7057, respectively. Field, compositional, and isotopic data indicate that the eclogites were derived from heterogeneous mantle that included depleted and enriched compositions; this heterogeneity may have resulted from subduction processes that occurred prior to the late Variscan collision of Gondwana and Baltica.

Original languageEnglish
Pages (from-to)468-483
Number of pages16
JournalContributions to Mineralogy and Petrology
Volume111
Issue number4
DOIs
Publication statusPublished - Sep 1992
Externally publishedYes

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