Abstract
In the polymetamorphic Austroalpine Matsch Unit (European Eastern Alps) Cretaceous upper greenschist facies metamorphism overprinted Variscan and Permian magmatic and metamorphic assemblages. Mineral compositional and (micro-)structural data of metapelites and metapegmatites document different mechanisms of interrelated deformation and (re-)equilibration during Cretaceous overprinting: i) Microfractures in relic garnet represented pathways for material transport, and thus established material exchange between intragranular domains and the matrix. Major element equilibration by fast diffusion along microfractures contrasts with limited volume diffusion in adjacent host garnet. ii) Syn-tectonic breakdown of staurolite initially to paragonite, then chloritoid allows correlating reaction progress with the formation of different fracture sets. iii) Syn-tectonic mineral growth with shape-preferred orientation in foliation domains contrasts with radial growth in microlithons and strain shadows of the mylonitic foliation. iv) Syn-tectonic unmixing of pre-existing oligoclase (an14–16) produced fine-grained aggregates of two supposedly coexisting plagioclase-phases (an3–6 and an20–25) in strain shadows of the oligoclase-clasts. v) Pre-existing deformation-induced heterogeneities in the spatial distribution of phases and their preferred orientation influence the kinetics of phase equilibration. Understanding the mechanisms of the mutual interrelation between deformation and phase equilibration is a prerequisite for deducing PT-constraints from strained metamorphic rocks. New garnet—whole rock Sm-Nd data from metapegmatites indicate their emplacement at 263–280 Ma and provide an important age constraint on the interrelated deformation and re-equilibration processes.











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Acknowledgement
The study has been funded by the Austrian Science Fund FWF in the projects P15644-GEO (fieldwork, sampling, (micro-)structural investigations, geochronology, EPMA-analyses) and T319-N10 (EPMA-analyses, thermodynamic modelling, data-compilation). The authors thank the Dept. for Lithospheric Research at the University of Vienna (Austria) for providing the facilities for project execution, major element analysis (EPMA) and isotopic investigations (ID-TIMS). T. Ntaflos and F. Kiraly are thanked for technical assistance with EPM-analytics. J. Selverstone and an anonymous reviewer are thanked for their critical comments, which helped to significantly improve the manuscript.
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Habler, G., Thöni, M. & Grasemann, B. Cretaceous metamorphism in the Austroalpine Matsch Unit (Eastern Alps): The interrelation between deformation and chemical equilibration processes. Miner Petrol 97, 149 (2009). https://doi.org/10.1007/s00710-009-0094-x
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DOI: https://doi.org/10.1007/s00710-009-0094-x