Metapelite from the high- to ultrahigh-pressure terrane of the Eastern Alps (Pohorje Mountains, Slovenia)—New pressure, temperature and time constraints on a polymetamorphic rock
- Author(s)
- Botao Li, Hans Joachim Massonne, Friedrich Koller, Junfeng Zhang
- Abstract
The Austroalpine nappe stack of the Pohorje Mountains (Mts.) in northeastern Slovenia comprises a suite of eclogite facies metamorphic rocks that were partially assigned to Eo-Alpine ultrahigh-pressure metamorphism (UHPM). We selected a micaschist, which was previously related to this metamorphism, for a detailed study including the chemical zonation of garnet and potassic white mica, the identification of mineral inclusion assemblages, pseudosection modelling with PERPLE_X, and monazite in-situ dating with the electron microprobe. Polymetamorphism was revealed by (at least) two generations of garnet and phengite and four populations of monazite yielding ages of 283.6 ± 6.1 (2σ), 94.1 ± 3.7, 47.9 ± 10.8 and 26.2 ± 2.8 Ma. The Permian monazite population is characterized by relatively high Y contents (~1.15 wt% Y) and low La/Gd mass ratios (8.7) indicating its formation before the growth of porphyroblastic garnet. The Eo-Alpine population, however, grew synchronously with garnet based on low Y contents (~0.05 wt%) and high La/Gd ratios (21.4). The older Tertiary population (48 Ma) shows also high Y contents (1.1 wt%) and low La/Gd ratios (10.6) whereas the younger Tertiary population is characterized by low Y contents. The Permian P–T conditions of 7.5–10 kbar at 600–650°C were obtained using the inclusion assemblage of staurolite+rutile+biotite in porphyroblastic garnet. High pressure (HP) but no UHPM was reconstructed for both Eo-Alpine coarse phengite (Si = 3.22 per formula unit = pfu) and small Tertiary garnet+fine-grained phengite (Si = 3.27 pfu) at peak pressures ~16 kbar and 18.5–23 kbar respectively. Maximum temperatures close to 650°C were likely reached during the Eo-Alpine HP event, whereas those of the Tertiary HP event were probably ~580°C. These HP metamorphic events suggest that the Pohorje Mts. experienced both an Eo-Alpine and a Tertiary subduction–exhumation history, the latter of which was mainly reported for underlying Penninic nappes so far.
- Organisation(s)
- Department of Lithospheric Research
- External organisation(s)
- China University of Geosciences, Universität Stuttgart
- Journal
- Journal of Metamorphic Geology
- Volume
- 39
- Pages
- 695-726
- No. of pages
- 32
- ISSN
- 0263-4929
- DOI
- https://doi.org/10.1111/jmg.12581
- Publication date
- 08-2021
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105120 Petrology
- Keywords
- ASJC Scopus subject areas
- Geology, Geochemistry and Petrology
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/24b2f12e-37f6-434a-bf5b-a41da54a6aed