Search: onr:"swepub:oai:gup.ub.gu.se/104381" >
Eclogite-hosting me...
Eclogite-hosting metapelites from the Pohorje Mountains (Eastern Alps): P-T evolution, zircon geochronology and tectonic implications
-
Janak, M. (author)
-
- Cornell, David H., 1948 (author)
- Gothenburg University,Göteborgs universitet,Institutionen för geovetenskaper,Department of Earth Sciences
-
Froitzheim, N. (author)
-
show more...
-
de Hoog, Cees-Jan, 1969 (author)
-
Broska, I (author)
-
Vrabek, m (author)
-
Hurai, V (author)
-
show less...
-
(creator_code:org_t)
- Schweizerbart, 2009
- 2009
- English.
-
In: European Journal of Mineralogy. - : Schweizerbart. - 0935-1221.
- Related links:
-
https://gup.ub.gu.se...
-
show more...
-
https://doi.org/10.1...
-
show less...
Abstract
Subject headings
Close
- Abstract: Phase-equilibrium modelling, geothermobarometry, ion-microprobe dating and mineral chemistry of zircon have been used to constrain the P–T–t evolution of metapelitic kyanite-bearing gneisses from the ultrahigh-pressure (UHP) metamorphic terrane of the Pohorje Mountains in the Eastern Alps. These eclogite-hosting rocks are part of the continental basement of the Austroalpine nappes. Based on calculated phase diagrams in the system Na2O-CaO-K2O-FeO-MgO-MnO-Al2O3-SiO2-H2O (NCKFMMnASH) and conventional geothermobarometry, the garnet-phengite-kyanite-quartz assemblages of gneisses record metamorphic conditions of 2.2–2.7 GPa at 700–800 C. These are considered as minima because of the potential for a diffusion-related modification and reequilibration of the garnet and phengite during early stages of decompression. It is therefore most likely that the gneisses experienced the same peak UHP metamorphism at 3 GPa as associated kyanite eclogites. Decompression and cooling to 0.5 GPa and 550 C led to the consumption of garnet and phengite, and the development of matrix consisting of biotite, plagioclase, K-feldspar sillimanite and staurolite. Textures and phase diagrams suggest a low extent of partial melting during decompression. Cathodoluminescence images as well as zircon chemistry reveal cores encompassed by two types of metamorphic zircon rims. Ion probe U-Pb dating of three zircon cores yielded Permian (286 10, 258 7 Ma) and Triassic (238 7 Ma) concordia ages. The zircon rims are Cretaceous with a mean concordia age of 92.0 0.5 Ma and some cores gave a similar age. The Cretaceous zircons all exhibit very low Th/U ratio (,0.02) typical of metamorphic origin. In these zircons, nearly flat HREE patterns, (Lu/Gd)N ¼ 1–4, and only small negative Eu anomalies indicate formation in the presence of garnet and absence of plagioclase, which is corroborated by occurrence of Mg- and Ca-rich garnet inclusions. Therefore, these zircons are interpreted to record the Cretaceous HP/UHP metamorphism. The 92.0 0.5 Ma age obtained in this study agrees with that (93–91 Ma) determined earlier in the Pohorje eclogites from U/Pb zircon, Sm-Nd and Lu-Hf garnet-whole-rock dating. This implies that the eclogites and their country rocks were subducted and exhumed together as a coherent piece of continental crust. There is no evidence for a me´lange-like assemblage of rocks, which followed different P–T–t paths, or several subduction and exhumation cycles as proposed for some other UHP metamorphic terranes.
Subject headings
- NATURVETENSKAP -- Geovetenskap och miljövetenskap (hsv//swe)
- NATURAL SCIENCES -- Earth and Related Environmental Sciences (hsv//eng)
Keyword
- UHP metamorphism
- continental crust subduction
- Eastern Alps
- ion probe zircon dating
- phase equilibrium
Publication and Content Type
- ref (subject category)
- art (subject category)
Find in a library
To the university's database