⁴⁰Ar/³⁹Ar and K–Ar age constraints on shear zone evolution, southern Taltson magmatic zone, northeastern Alberta

Abstract

New 40Ar/39Ar analyses of hornblende, muscovite, biotite, and K-feldspar constrain the timing of deformation and cooling of the southern Taltson magmatic zone, which underwent lower granulite to upper amphibolite grade deformation, in part synchronous with voluminous 1.99–1.92 Ga magmatism. New data are combined with existing K–Ar dates into a regional cooling framework to provide thermotemporal constraints on the deformational history. 40Ar/39Ar hornblende ages of ca. 1900 Ma are interpreted to record relatively rapid cooling following ductile thrusting on the Andrew Lake shear zone, and younger anatectic magmatism. These data, with published K–Ar and U–Pb data, support relatively rapid cooling of the Taltson magmatic zone from monazite closure temperature of 725 °C at ca. 1930 Ma to 525 °C at ca. 1900 Ma. Cooling rate estimates are about 7 °C/Ma, which suggests moderate exhumation rates during the high-grade part of the deformational history. A muscovite 40Ar/39Ar plateau age of 1803 ± 11 Ma is consistent with the mean muscovite K–Ar age of 1792 Ma, indicating regional cooling through about 350 °C at ca. 1800 Ma. 40Ar/39Ar ages from magmatic biotite of 1856 and 1799 Ma also suggest slow cooling during greenschist grade deformation, which can be no older than ca. 1860 Ma. A K-feldspar 40Ar/39Ar age of 1681 Ma provides a lower limit for the time of greenschist grade deformation. Cooling rate estimates during amphibolite to greenschist grade deformation are 1.75–2.25 °C/Ma.

Evolution of migmatitic granulite complexes: Implications from Lapland Granulite Belt, Part II: Isotopic dating

“…However, arc magmatism and deformation of about the same age or slightly older as in the LGB are found in the Taltson-Thelon magmatic zone in the Western part of the Canadian Shield (Bostock & van Breemen, 1994;Plint & McDonough, 1995;Ross et al, 1995) and in the Aldan Shield (Frost et al, 1998). In the western Canadian Shield, 2.3 − 2.0 Ga juvenile crust is present in the Wopmay orogen, which could be potential a provenance for the sedimentary protoliths of the LGB metapelites (Hoffman, 1988).…”

⁴⁰AR/³⁹AR geochronology of biotite from ductile shear zones of the Ellesmere-Devon crystalline terrane, Nunavut, Canadian Arctic

“…Ages similar to those observed in this study mark the latest deformation in the Thelon tectonic zone. Plint and McDonough (1995) Aside from similar age affinity, ductile shear zones dated in this study strongly resemble the orientation and kinematics of larger shear zones within the Thelon tectonic zone. Additionally, many shear zones within the Thelon tectonic zone cut similar metamorphic facies.…”

“…Magmatic biotite ages of 1856 and 1799 Ma suggest cooling during greenschist-facies, with deformation no older than ca. 1860 Ma(Plint and McDonough, 1995) Hanmer et al (1992). report granulite-and lower amphibolite-facies mylonite ages in the Southwest segment of the Great Slave Lake shear zone younger than ca.…”

40AR/39AR GEOCHRONOLOGY OF BIOTITE FROM DUCTILE SHEAR ZONES OF THE ELLESMERE-DEVON CRYSTALLINE TERRANE, NUNAVUT, CANADIAN ARCTIC

“…Ages similar to those observed in this study mark the latest deformation in the Thelon tectonic zone. Plint and McDonough (1995) and clinopyroxene bearing tonalites, granodiorites and granites (Hanmer et al, 1992).…”