Diachronous Palaeoproterozoic deformation and metamorphism in the Committee Bay belt, Rae Province, Nunavut: insights from ⁴⁰Ar–³⁹Ar cooling ages and thermal modelling

Abstract

Regional-scale 40 Ar-39 Ar data presented in this paper reveal significant across-strike and along-strike age differences in the Committee Bay belt (CBb), Rae Province, Nunavut, Canada, that complement variations in observed monazite ages. 40 Ar-39 Ar hornblende ages are c. 1795, 1775, and 1750 Ma in the western, eastern and central parts of the Prince Albert Group (PAG) domain respectively. The migmatite domain and Walker Lake intrusive complex are characterized by c. 1750-1730 40 Ar-39 Ar hornblende ages without significant along-strike variation. The 40 Ar-39 Ar data provide important constraints on the cooling history and on thermal modelling that elucidates the controls on diachroneity and metamorphic patterns within the belt. In the western CBb, prograde monazite growth occurred 26 ± 10 Myr earlier in the migmatite domain (1864 ± 9 Ma; peak P-T = 5 kbar)700°C) than in the PAG domain (1838 ± 5 Ma; peak P-T = 5 kbar)580°C). Calculations indicate that this earlier monazite growth results from tectonic thickening of higher heat productivity Archean lithologies in the migmatite domain, which undergoes more rapid prograde heating than the less radiogenetic and lower grade rocks of the PAG domain. Granite generation via biotite dehydration melting at 800°C and 20 km depth is predicted to occur c. 1835 Ma, in agreement with geochronological constraints. The tectonic burial of crustal domains with contrasting radiogenic properties also explains the general congruence of lower to upper amphibolite facies metamorphic zones generated during the two main orogenic cycles (i.e. M 2 -D 1 and M 3 -D 2 ). The modelled timing of prograde monazite growth in the migmatite domain suggests that D 2 tectonic thickening began at 1872 ± 9 Ma, some 8 ± 3 Myr before monzazite growth, coeval with the inferred time of collision of the Meta Incognita terrane with the southern Rae Province. Along-strike diachroneity, reflected in 25 Myr younger monazite and 40 Ar-39 Ar hornblende ages in the eastern relative to the western PAG domain, cannot be accounted for by heat productivity contrasts along the belt. Instead the younger deformation and metamorphism in the eastern CBb was driven by its proximity to the eastern promontory of the Superior Province which collided with the Rae Province at c. 1820 Ma. The 40 Ar-39 Ar data presented here support the interpretation that the youngest monazite in the CBb crystallized at c. 1790 Ma in the central CBb when this part of the belt was downfolded into a gentle synformal structure while the western part of the belt cooled through 40 Ar-39 Ar hornblende closure. The results of this study illustrate the important influence of contrasting rock properties on the thermal evolution of orogenic belts and on the temporal record of this evolution.

Genesis of Multifarious Uranium Mineralization in the Beaverlodge Area, Northern Saskatchewan, Canada

“…200°C. Stage 1 chlorite reflects exhumation and retrograde metamorphism to lower greenschist facies in the basement rocks during the late stages of the Arrowsmith orogen (Hartlaub et al, 2007;Berman et al, 2010). Retrograde metamorphic fluids associated with stage 1 chlorite are relatively Ca-rich, have high F and Mg contents and likely result from interaction between fluids and Ca-Mg-F-rich rocks in the basement.…”

The Hudson Bay Lithospheric Experiment (HuBLE): insights into Precambrian plate tectonics and the development of mantle keels

“…The most widespread tectonic/ metamorphic reworking of the Hudson Bay region occurred during the 1.9-1.8 Ga Hudsonian orogeny (e.g. Hoffman 1988;Berman et al 2010b) when accretion of microcontinents to the SE flank of the Rae craton occurred c. 1.9-1.87 Ga. These tectonic events are known collectively as the Snowbird phase of the Hudsonian orogeny (Berman et al 2007).…”

Neoarchean continental crust formation and Paleoproterozoic deformation of the central Rae craton, Committee Bay belt, Nunavut

“…1815 Ma), and even earlier (ca. 1.86 Ga) in the northwest migmatite domain (Berman et al 2010a(Berman et al , 2010b.…”

“…Rather, this structural analysis underscores significant shortening of the region accommodated via northwest-directed tectonic thickening. One-dimensional thermal modeling (Berman et al 2010b) suggests thermal incubation during D 2 thickening led to low-pressure metamorphism of the Committee Bay belt, with monazite growth at ca. 1.86 Ga in more radiogenic rocks of the migmatite domain, and at ca.…”

“…The presence of such a ribbon terrane between the colliding western Churchill and Superior cratons, and its collision at ca. 1.87 Ga with the southeastern Rae ± Hearne margin, may have been the driver for crustal thickening, which according to thermal modelling (Berman et al 2010b) would have resulted in metamorphism across the region ϳ10-30 million years later.…”