16 research outputs found
A geothermobarometric investigation of garnet peridotites in the Western Gneiss Region of Norway
Petrogenesis of Variscan high-temperature Group A eclogites from the Moldanubian Zone of the Bohemian Massif, Czechoslovakia
Geochemistry and petrology of pyroxenite xenoliths from Cenozoic alkaline basalts, Bohemian Massif
The mantle and crustal evolution of two garnet peridotite suites from the Western Gneiss Region, Norwegian Caledonides:An isotopic investigation
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An Orphaned baltic terrane in the Greenland caledonides : a Sm-Nd and detrital zircon study of a high-pressure/ ultrahigh-pressure complex in Liverpool Land
Liverpool Land, at the southern tip of the Greenland Caledonides, exposes a composite metamorphic terrane: the midcrustal granulite-facies Jaettedal Complex tectonically juxtaposed against the eclogite-facies, peridotite-bearing Tvaerdal Complex. The Jaettedal Complex is a Laurentian terrane, whereas the Tvaerdal Complex was proposed by earlier investigators to be a Baltic terrane. PT estimates (880°–920°C at 35–40 kbar) and Sm-Nd mineral isochrons from Tvaerdal eclogites indicate that recrystallization occurred under ultrahigh-pressure (UHP) metamorphic conditions ≈400 m.yr. ago, the same time and under similar conditions as the Western Gneiss Complex of the Norwegian Caledonides. Detrital zircons from the Tvaerdal Complex, analyzed for U-Pb, Lu-Hf, and trace elements by laser ablation inductively coupled plasma mass spectrometry, give concordantMesoproterozoic ages but not the Archean and ≈1.8 Ga Proterozoic ages characteristic of Laurentian terranes. Most remaining concordant U-Pb ages are 411–375Ma (i.e., Scandian), which contrast with older (≈460–410 Ma) zircon ages from the Jaettedal Complex as well as other Laurentian terranes. Both the Precambrian and the Scandian age sets confirm the Tvaerdal Complex as an orphaned Baltic terrane. The Jaettedal Complex underwent a lengthy Caledonian history as part of a continental arc systemduring the closure of Iapetus, whereas the Tvaerdal Complex was a fragment of the approaching Baltic passive margin. UHP metamorphism occurred when this margin subducted into the mantle beneath Laurentia. We propose that the Tvaerdal Complex separated fromBaltica and rose through the hot mantle wedge to the base of the overriding Laurentian crust by diapirism, a process that may explain its abundant anatectic granitoid intrusions.27 page(s