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© 2024. This work is published under https://creativecommons.org/licenses/by/4.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.

Abstract

We investigated rare earth element (REE) minerals in low- to medium-grade metapelites sampled in two nappes of the Austroalpine Unit (Eastern Alps, Austria). Combining microstructural and chemical characterization of the main and REE minerals with thermodynamic forward modeling, Raman spectroscopy on carbonaceous material (RSCM) thermometry and in situ U–Th–Pb dating reveal a polymetamorphic evolution of all samples. In the hanging wall nappe, allanite and REE epidote formed during Permian metamorphism (275–261 Ma, 475–520 °C, 0.3–0.4 GPa). In one sample, Cretaceous (ca. 109 Ma) REE epidote formed at 440 °C and 0.4–0.8 GPa at the expense of Permian monazite clusters. In the footwall nappe, large, chemically zoned monazite porphyroblasts record both Permian (283–256 Ma, 560 °C, 0.4 GPa) and Cretaceous (ca. 87 Ma, 550 °C, 1.0–1.1 GPa) metamorphism. Polymetamorphism produced a wide range of complex REE-mineral-phase relationships and microstructures. Despite the complexity, we found that bulk rock Ca, Al and Na contents are the main factor controlling REE mineral stability; variations thereof explain differences in the REE mineral assemblages of samples with identical pressure and temperature (PT) paths. Therefore, REE minerals are also excellent geochronometers to resolve the metamorphic evolution of low- to medium-grade rocks in complex tectonic settings. The recognition that the main metamorphic signature in the hanging wall is Permian implies a marked PT difference of 250 °C and at least 0.5 GPa, requiring a major normal fault between the two nappes which accommodated the exhumation of the footwall in the Cretaceous. Due to striking similarities in setting and timing, we put this low-angle detachment in context with other Late Cretaceous low-angle detachments from the Austroalpine domain. Together, they form an extensive crustal structure that we tentatively term the “Austroalpine Detachment System”.

Details

Title
Pressure–temperature–time and REE mineral evolution in low- to medium-grade polymetamorphic units (Austroalpine Unit, Eastern Alps)
Author
Hollinetz, Marianne Sophie 1   VIAFID ORCID Logo  ; Huet, Benjamin 2 ; Schneider, David A 3   VIAFID ORCID Logo  ; McFarlane, Christopher R M 4 ; Schuster, Ralf 5   VIAFID ORCID Logo  ; Rantitsch, Gerd 6 ; Schantl, Philip 7 ; Iglseder, Christoph 2 ; Reiser, Martin 2   VIAFID ORCID Logo  ; Grasemann, Bernhard 1   VIAFID ORCID Logo 

 Department of Geology, University of Vienna, Josef-Holaubek-Platz 2, 1090 Vienna, Austria 
 Division of Basic Geological Services, GeoSphere Austria, Hohe Warte 38, 1190 Vienna, Austria 
 Department of Earth and Environmental Sciences, University of Ottawa, 150 Louis-Pasteur Private, Ottawa, K1N 6N5, Canada 
 Department of Earth Sciences, University of New Brunswick, 3 Bailey Drive, Fredericton, E3B 5A3, Canada 
 Division of Geophysical and Applied Geological Services, GeoSphere Austria, Hohe Warte 38, 1030 Vienna, Austria 
 Department Applied Geosciences and Geophysics, University of Leoben, Peter-Tunner-Straße 5, 8700 Leoben, Austria 
 Institute of Earth Sciences, University of Graz, Universitätsplatz 2, 8010 Graz, Austria; Department of Petrology and Geochemistry, NAWI Graz Geocenter, University of Graz, Universitätsplatz 2, 8010 Graz, Austria 
Pages
943-983
Publication year
2024
Publication date
2024
Publisher
Copernicus GmbH
ISSN
0935-1221
e-ISSN
1617-4011
Source type
Scholarly Journal
Language of publication
English; French
ProQuest document ID
3133140325
Copyright
© 2024. This work is published under https://creativecommons.org/licenses/by/4.0/ (the “License”). Notwithstanding the ProQuest Terms and Conditions, you may use this content in accordance with the terms of the License.