Presentation
Differentiating Metamorphic Events in a Polymetamorphic Terrane using Zr-in-Ttn thermometry and Titanite U-Pb Geochronology
American Geophysical Union Fall Meeting 2016
(2016)
Abstract
In polymetamorphic terranes, it is problematic to link ages from geochronometers to metamorphic fabrics and, therefore, to a specific deformation event(s). It is necessary to analyze a mineral which may preserve multiple age domains. Titanite has been shown to retain multiple age and elemental domains in single grains through high-grade metamorphism. In this study, titanite U-Pb geochronology is used to examine whether ages are thermally reset along a sample transect towards a mylonitic shear zone in NW Argentina. This work also seeks to understand the conditions under which titanite resists resetting. A combination of petrographic and electron microprobe analyses reveal the textures and compositional domains in titanite, garnet, and hornblende. Titanite are elongate, wrapped by the mylonitic fabric, and have patchy elemental zoning. Garnet has distinct cores with prograde zoning and thin rims, which appear to be in equilibrium with the fabric defining minerals. Hornblende has inclusion rich cores and thin overgrowth rims in equilibrium with the fabric defining minerals. In-situ U-Pb and trace element data was collected in titanite from four samples, which all preserve lower-intercept ages between ~900Ma and 1.0Ga. We observed no correlation between age and elemental domains; these domains correlate with Al and Nb variations. Zr-in-titanite temperatures preserve upper amphibolite facies conditions, ~660C-710C. Given these results, we conclude that titanite U-Pb ages and temperatures reflect original Grenville metamorphism. 40Ar/39Ar hornblende cooling ages, of 515 Ma, suggested titanite may be reset near the shear zone but overprinting P-T of 560C and 0.8 GPa, fluid infiltration, and deformation did not cause significant Pb loss. Overprinting conditions and cooling ages suggest that rims of garnet and hornblende correlate to Paleozoic metamorphism, while textural evidence and titanite ages suggest garnet and hornblende cores grew during the Proterozoic.
Keywords
- Polymetamorphic terranes
Disciplines
Publication Date
Fall 2016
Location
San Francisco, CA
Comments
Section: Volcanology, Geochemistry, Petrology
Session: Tectonochemistry I Posters
Citation Information
M. Kenney, S. Roeske, S. R. Mulcahy, J.M. Cottle, M. A. Coble, (2016), Differentiating Metamorphic Events in a Polymetamorphic Terrane using Zr-in-Ttn thermometry and Titanite U-Pb Geochronology, Abstract V13D-2888 presented at 2016 Fall Meeting, AGU, San Francisco, Calif., 11-15 Dec.