PUMA
Istituto di Geoscienze e Georisorse     
Thoni M., Miller C., Blichert-Toft J., Whitehouse M., Kinzett J., Zanetti A. Timing of high-pressure metamorphism and exhumation of the eclogite type-locality (Kupplerbrunn-Prickler Halt, Saualpe, south-eastern, Austria): constrains from correlations of the Sm-Nd, Lu-Hf and Rb-Sr isotopic systems. In: Journal of Metamorphic Geology, vol. 26 pp. 561 - 581. Blackwell, 2008.
 
 
Abstract
(English)
Sm-Nd, Lu-Hf, Rb-Sr and SIMS U-Pb data are presented for meta-gabbroic eclogites from the eclogite type-locality (Hauš y, 1822) Kupplerbrunn-Prickler Halt and other areas of the Saualpe (SE Austria) and Pohorje Mountains (Slovenia). Mg-rich eclogites derived from early gabbroic cumulates are kyanite- and zoisite rich, whereas eclogites with lower Mg contents contain clinozoisite ± kyanite. Calculated P-T conditions at the final stages of high-pressure metamorphism are 2.2 ± 0.2 GPa at 630-740°C. Kyanite-rich eclogites did not yield geologically meaningful Sm-Nd ages due to incomplete Nd isotope equilibration, whereas Sm-Nd multifraction garnet-omphacite regression for a low-Mg eclogite from Kupplerbrunn yields an age of 91.1 ± 1.3 Ma. The Sm-Nd age of 94.1 ± 0.8 Ma obtained from the Fe-rich core fraction of this garnet dates the initial stages of garnet growth. Zircon that also crystallized at eclogite facies conditions gives a weighted mean U-Pb SIMS age of 88.4 ± 8.1 Ma. Lu- Hf isotope analysis of a kyanite-eclogite from Kupplerbrunn yields 88.4 ± 4.7 Ma for the garnet- omphacite pair. Two low-Mg eclogites from the Gertrusk locality of the Saualpe yield a multimineral Sm-Nd age of 90.6 ± 1.0 Ma. A low-Mg eclogite from the Pohorje Mountains (70 km to the SE) gives a garnet-whole-rock Lu-Hf age of 93.3 ± 2.8 Ma.These new age data and published Sm-Nd ages of metasedimentary host rocks constrain the final stages of the eo-Alpine high-pressure event in the Saualpe-Pohorje part of the south-easternmost Austroalpine nappe system suggesting that garnet growth in the high-pressure assemblages started at c. 95-94 Ma and ceased at c. 90-88 Ma, probably at the final pressure peak. Zircon and amphibole crystallization was still possible during incipient isothermal decompression. Rapid exhumation of the high-pressure rocks was induced by collision of the northern Apulian plate with parts of the Austroalpine microplate, following Jurassic closure of the Permo-Triassic Meliata back-arc basin.
URL: http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1525-1314
Subject eastern Alps
eclogite
eo-Alpine (Cretaceous) event
geochronology
high pressure metamorphism
Lu-Hf
SIMS U-Pb
Sm-Nd


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