U-Pb geochronology of the Grenville Orogen of Ontario and New York: constraints on ancient crustal tectonics |
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| Authors: | K Mezger E J Essene B A van der Pluijm A N Halliday |
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| Institution: | (1) Department of Geological Sciences, 1006 C.C. Little Building, University of Michigan, 48109-1063 Ann Arbor, MI, USA;(2) Max-Planck-Institut für Chemie, Saarstrasse 23, Postfach 3060, W-6500 Mainz, Germany |
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| Abstract: | Based on lithological, structural and geophysical characteristics, the Proterozoic Grenville Orogen of southern Ontario and New York has been divided into domains that are separated from each other by ductile shear zones. In order to constrain the timing of metamorphism, U-Pb ages were determined on metamorphic and igneous sphenes from marbles, calc-silicate gneisses, amphibolites, granitoids, skarns and pegmatites. In addition, U-Pb ages were obtained for monazites from metapelites and for a rutile from an amphibolite. These mineral ages constrain the timing of mineral growth, the duration of metamorphism and the cooling history of the different domains that make up the southern part of the exposed Grenville Orogen. Based on the ages from metamorphic minerals, regional and contact metamorphism occurred in the following intervals:Central Granulite Terrane:Adirondack Highlands: 1150 Ma; 1070–1050 Ma; 1030–1000 MaCentral Metasedimentary Belt:Adirondack Lowlands 1170–1130 MaFrontenac domain 1175–1150 MaSharbot Lake domain ca. 1152 MaFlzevir domain: 1240 Ma; 1060–1020 MaBancroft domain: ca. 1150 Ma; 1045–1030 MaCentral Gneiss Belt: ca. 1450 Ma; ca. 1150 Ma; 1100–1050 MaGrenville FrontTectonic Zone ca. 1000 Ma.Combination of mineral ages with results from thermobarometry indicates that metamorphic pressures and temperatures recorded by thermobarometers were reached polychronously in the different domains that are separated by major shear zones. Some of these shear zones such as the Robertson Lake shear zone and the Carthage-Colton shear zone represent major tectonic boundaries. The Grenville Orogen is made up of a collage of crustal terranes that have distinct thermal and tectonic histories and that were accreted laterally by tectonic processes analogous to those observed along modern active continental margins. The subsequent history of the orogen is characterized by slow time-integrated cooling rates of 3±1°C/Ma and denudation rates of 120±40m/Ma. |
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