Evidence from Rb-Sr microsampling geochronology for the timing of Alpine deformation in the Sonnblick Dome, SE Tauern Window, Austria

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Authors:Cliff, R. A.; Meffan-Main, S.
Author Affiliations:Primary:
University of Leeds, School of Earth Sciences, Leeds, United Kingdom
Australian National University, Australia
University of Bern, Switzerland
Volume Title:Geochronology; linking the isotopic record with petrology and textures
Volume Authors:Vance, Derek, editor; Müller, Wolfgang; Villa, Igor M.
Source:Geochronology; linking the isotopic record with petrology and textures, edited by Derek Vance, Wolfgang Müller and Igor M. Villa. Geological Society Special Publications, Vol.220, p.159-172. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0305-8719. ISBN: 1-86239-146-7
Publication Date:2003
Note:In English. 32 refs.; illus., incl. 1 table, sketch maps
Summary:The Sonnblick Dome forms a large antiformal structure within the Pennine of the SE Tauern Window. The structural and metamorphic evolution of this area is relatively well constrained. However, mineral age determinations of the Alpine event within the Zentralgneis granitoid basement remain ambiguous due to a lack of isotopic equilibration during the Alpine event. In this paper we use a newly developed technique, namely Rb-Sr microsampling, in an attempt to place more reliable age constraints upon Alpine deformation. The new age determinations range between c. 22 Ma and 28 Ma. The oldest ages are interpreted to result from shearing related to the earliest stages of dome formation while the youngest ages probably represent late fabric development during uplift of the Zentralgneis complex. A clustering of six fabric ages around 25.5±0.3 Ma is thought to represent the peak of deformation activity associated with formation of the dome. These new data can be fitted into a model for the metamorphic and structural evolution of the SE Tauern Window. In most of the rocks studied isotopic disequilibrium is apparent between and within minerals. It is clear that large feldspar augen did not attain isotopic equilibrium despite amphibolite facies metamorphism. In fact, even where chemical equilibrium was achieved isotopic homogenization did not always occur. The Rb-Sr data from white mica suggest that isotopic equilibration may occur during isochemical rotation of grains suggesting differing mechanisms for chemical and isotopic movement within grains. The data presented herein suggest that small-scale, in-situ sampling methods may provide the most reliable method for deformation chronology in basement gneisses.
Sections:Age determination; Petrology
Subjects:Absolute age; Alpine Orogeny; Cenozoic; Deformation; Faults; Gneisses; Granites; Igneous rocks; Metamorphic rocks; Orogeny; Plutonic rocks; Rb/Sr; Sampling; Shear zones; Tectonics; Tertiary; Alps; Austria; Central Alps; Central Europe; Europe; Pennine Alps; Tauern Window; Sonnblick Dome
Abstract Numbers:04M/1196
Record ID:2004052040
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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