Thermobarometric constraints on pressure variations across the Plattengneiss shear zone of the Eastern Alps: implications for exhumation models during Eoalpine subduction |
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| Authors: | T Eberlei T E Johnson R W White C Roffeis K Stüwe |
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| Institution: | 1. Earth System Science Research Centre, Institute for Geosciences, University of Mainz, , D‐55099 Mainz, Germany;2. Department of Earth Science, University of Graz, , A‐8010 Graz, Austria |
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| Abstract: | Forward and inverse mineral equilibria modelling of metapelitic rocks in the hangingwall and footwall of the Plattengneiss, a major shear zone in the Eastern Alps, is used to constrain their tectonometamorphic evolution and assess models for their exhumation. Forward (pseudosection) modelling of two metapelitic rocks suggests a steep clockwise P–T path with a near‐isothermal decompression segment from a pressure peak at ~18–19 kbar and 670 °C to the metamorphic peak at 680–720 °C and 11–13 kbar. A subsequent decrease to 600–645 °C and 8–9 kbar is inferred from the late growth of staurolite in some samples. Conventional thermobarometric calculations (inverse modelling) on 18 samples with the inferred peak assemblage garnet + plagioclase + muscovite + biotite + quartz + rutile ± ilmenite ± kyanite are associated with large 2σ uncertainties, and absolute pressures calculated for all samples are statistically indistinguishable. However, calculations constraining relative pressure differences (ΔP) between samples sharing a common mineral assemblage are associated with much smaller uncertainties and yield pressure differences that are statistically meaningful. Although the overall pattern is complicated, the results suggest a pressure gradient of up to 3 kbar across the shear zone that is consistent with volume loss and a model of exhumation related to slab extraction for the Plattengneiss shear zone. |
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| Keywords: | exhumation Koralpe mineral equilibria modelling relative thermobarometry slab extraction |
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