Correlation by Rb-Sr geochronology of garnet growth histories from different structural levels within the Tauern Window,Eastern Alps |
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| Authors: | John N Christensen Jane Selverstone John L Rosenfeld Donald J DePaolo |
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| Institution: | (1) Department of Earth and Space Sciences, University of California, Los Angeles, 90024 Los Angeles, CA, USA;(2) Center for Isotope Geochemistry, Department of Geology and Geophysics, University of California, 94720 Berkeley, CA, USA;(3) Earth Sciences Division, Lawrence Berkeley Laboratory, 94720 Berkeley, CA, USA;(4) Department of Geological Sciences, University of Colorado, 80309-0250 Boulder, CO, USA;(5) Present address: Department of Geological Sciences, University of Michigan, 1006 C. C. Little Bldg, 48109 Ann Arbor, MI, USA |
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| Abstract: | In order to evaluate rates of tectonometamorphic processes, growth rates of garnets from metamorphic rocks of the Tauern Window, Eastern Alps were measured using Rb-Sr isotopes. The garnet growth rates were determined from Rb-Sr isotopic zonation of single garnet crystals and the Rb-Sr isotopic compositions of their associated rock matrices. Garnets were analyzed from the Upper Schieferhülle (USH) and Lower Schieferhülle, (LSH) within the Tauern Window. Two garnets from the USH grew at rates of 0.67
–0.13
+0.19
mm/million years and 0.88
–0.19
+0.34
mm/million years, respectively, indicating an average growth duration of 5.4±1.7 million years. The duration of growth coupled with the amount of rotation recorded by inclusion trails in the USH garnets yields an average shear-strain rate during garnet growth of 2.7
–0.7
+1.2
×10-14 s-1. Garnet growth in the sample from the USH occurred between 35.4±0.6 and 30±0.8 Ma. The garnet from the LSH grew at a rate of 0.23±0.015 mm/million years between 62±1.5 Ma and 30.2±1.5 Ma. Contemporaneous cessation of garnet growth in both units at  30 Ma is in accord with previous dating of the thermal peak of metamorphism in the Tauern Window. Correlation with previously published pressure-temperature paths for garnets from the USH and LSH yields approximate rates of burial, exhumation and heating during garnet growth. Assuming that theseP — T paths are applicable to the garnets in this study, the contemporaneous exhumation rates recorded by garnet in the USH and LSH were approximately 4
–2
+3
mm/year and 2±1 mm/year, respectively. |
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