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| Titel |
P-T conditions of Stor Jougdan garnet pyroxenite and phengite-bearing eclogite: further evidence of UHP metamorphism in the Seve Nappe Complex of northern Jämtland (Swedish Caledonides) |
| VerfasserIn |
Iwona Klonowska, Marian Janak, Jarosław Majka, Karolina Kośmińska |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092114
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| Publikation (Nr.) |
 EGU/EGU2014-6440.pdf |
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| Zusammenfassung |
| The most recent comprehensive petrological studies of high grade rocks within the Seve
Nappe Complex (SNC) in the Scandinavian Caledonides have resulted in new discoveries
of ultrahigh pressure metamorphism (UHPM) probably of Late Ordovician age.
The first evidence was documented in the kyanite-bearing eclogite dyke within
the garnet peridotite at the lake Friningen locality (Janák et al. 2013) in northern
Jämtland, Sweden (Gee et al. 2013). A peak pressure assemblage yielded metamorphic
conditions within the coesite stability field (~30 kbar and 800°C). About 25 km
to the southeast, the Tjeliken eclogite records P-T conditions of 25-26 kbar and
650-700°C (Majka et al. 2013). The study presented here, concerns P-T conditions of
garnet pyroxenite and newly discovered, phengite-bearing eclogite located in the
SNC about 4 km SE of Tjeliken Mt. on the northern side of lake Stor Jougdan. The
investigated garnet pyroxenite, found as small veins within the garnet peridotite
body, is composed essentially of Mg-garnet, -orthopyroxene, -clinopyroxene and
-olivine, minor constituents include Cr-spinel, amphibole and phlogopite. The main
mineral assemblage of phengite eclogite consists of garnet, omphacite, amphibole and
minor phengite, plagioclase-diopside symplectites, rutile, titanite, zoisite and quartz
(possibly former coesite). Garnet peridotite occurring by the Stor Jougdan lake was
studied by Van Roermund (1989) who estimated the temperatures of c. 720-800°C
using Fe-Mg geothermometer (Harley 1984a) and the pressures of 14-18 kbar using
Al2O3 contents of the orthopyroxene (Harley 1984b) to constrain the P-T conditions
of Caledonian metamorphism (M2 garnet with prograde growth zoning and M2
orthopyroxene according to Van Roermund 1989). In the present work, we have used
garnet-orthopyroxene (Harley 1984b) and Ca in orthopyroxene (Brey & Koehler 1990)
geothermometry in combination with Al in orthopyroxene geothermobarometry (Brey
& Koehler 1990) and obtained the peak metamorphic conditions of 30-32 kbar
and 800-825°C for garnet pyroxenite. For the phengite-bearing eclogite, results
from Ravna & Terry (2004) geothermobarometric method applied for the garnet +
clinopyroxene + phengite + quartz/coesite assemblage yield pressure conditions in the
stability field of coesite (≥30 kbar at 800-900°C). Our calculated P-T conditions thus
provide further evidence for the Late Ordovician UHPM within the SNC in northern
Jämtland.
Brey, G.P. & Koehler, T. (1990) Journal of Petrology, 31, 1353-1378.
Gee, D. G., Janák, M., Majka, J., Robinson, P. & Van Roermund, H. 2013. Lithosphere, 5,
169-178.
Harley, S.L. (1984a). Contributions to Mineralogy and Petrology 86, 353–373.
Harley, S.L. (1984b). Journal of Petrology 25, 665-696.
Janák, M., Van Roermund, H., Majka, J. & Gee, D. G. 2013. Gondwana Research, 23,
865–879.
Majka, J., Janák, M., Andersson, B., Klonowska, I., Gee, D. G., Rosén, Å. & , Kośmińska K.
2013. Geological Society, London, Special Publications, 390.
Ravna, E. J. K. & Terry, M. P. (2004). Journal of Metamorphic Geology, 22, 579–592.
Van Roermund, H.L.M. (1989). The Caledonide geology of Scandinavia: London, Graham &
Trotman, 205-219. |
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