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Queen Maud Block: a Newly Recognized Paleoproterozoic (2.4–2.5 Ga) Terrane in Northwest Laurentia

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Queen Maud Block: a Newly Recognized Paleoproterozoic (2.4–2.5 Ga) Terrane in Northwest Laurentia Queen Maud block: A newly recognized Paleoproterozoic (2.4–2.5 Ga) terrane in northwest Laurentia Michael E.J. Schultz Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Thomas Chacko Alberta T6G 2E3, Canada Larry M. Heaman Hamish A. Sandeman Northwest Territories Geoscience Offi ce, Yellowknife, Northwest Territories X1A 2R3, Canada Antonio Simonetti Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada Robert A. Creaser ABSTRACT An alternative model (Chacko et al., 2000) pro- The Queen Maud block of Arctic Canada is central to understanding the Proterozoic tec- poses that the Slave and Churchill Provinces tonic history of northwestern Laurentia, but its crustal history is largely unknown. Results were not separated ca. 2.0 Ga, but were together of an in situ U-Pb zircon, monazite, and whole-rock Sm-Nd study through the central and in the earliest Paleoproterozoic or Archean. eastern Queen Maud block indicate: (1) widespread 2.46–2.50 Ga magmatism derived from Thus the Taltson-Thelon magmatic zone is simi- Neoarchean source rocks, (2) an extensive NE-trending 2.44–2.39 Ga sedimentary belt char- lar to present-day plate interior mountain belts acterized by 2.45–2.50 Ga detritus, and (3) regional ca. 2.39 Ga granulite metamorphism. of Central Asia (e.g., Tian Shan). If the Queen There is no evidence of metamorphic or magmatic activity at 1.9–2.0 Ga, concurrent with oro- Maud block represents a Tibetan-style orogenic genesis in the adjacent Taltson-Thelon belt. We propose that the eastern Queen Maud block plateau, there should have been extensive meta- was the site of an incipient continental rift ca. 2.5 Ga. Exhumation of 2.46–2.50 Ga granitoids morphic and tectonic reworking of mid-crustal produced in the early stages of rifting provided detritus to a short-lived basin that underwent levels ca. 1.9–2.0 Ga. In contrast, the second granulite metamorphism ca. 2.39 Ga. model predicts that the Queen Maud block should have been little affected at 1.9–2.0 Ga Keywords: Queen Maud block, Paleoproterozoic, U-Pb zircon, Sm-Nd, Laurentia. and should largely preserve earlier periods of magmatism, metamorphism, and deformation. INTRODUCTION Two tectonic models currently exist for the To test these models, we conducted the fi rst The Queen Maud block of Arctic Canada occu- origin of the Queen Maud block. The fi rst main- extensive geochronological and isotopic study pies the keystone tectonic position between the tains that the Slave and Churchill Provinces of the Queen Maud block and adjacent Churchill Archean Slave and Churchill Provinces (Fig. 1), were separated by an ocean basin that closed Province. Our results mandate a reinterpretation but due to its remote location has received neg- by subduction beneath the Churchill Province, of the Queen Maud block and its role in the ligible research attention. As a result, Laurentia- followed by a Himalayan-style collision at assembly of northwestern Laurentia. scale geotectonic models incorporating the Queen 1.9–2.0 Ga (Hoffman, 1987). In this model, the Maud block are generally based on research Taltson-Thelon magmatic zone is analogous to REGIONAL GEOLOGY conducted in surrounding tectonic domains, or the modern-day Himalayas and the Queen Maud The Churchill Province comprises variably through use of remotely sensed geophysical data. block to a deeply eroded Tibetan Plateau (Fig. 1). reworked Archean continental crust bound to the west by the 2.0–1.9 Ga Taltson-Thelon magmatic 83°W 68°N zone (e.g., Hoffman, 1989) and to the southeast 120°W 68°N by the 1.9–1.8 Ga Trans-Hudson orogen (Fig. 1). Coronation 100° The province is divided along the Snowbird Supergroup TTMz tectonic zone into the Rae and Hearne domains Queen Maud CBb (Hoffman, 1989; Hanmer et al., 2004). Rocks of Kilohigok Wopmay Basin Block the north-central Rae domain consist of 2.73– Orogen Rae 64°N 2.68 Ga greenstone belts, underlain by slightly Domain 83°W Slave older basement that is largely obscured by Neo- Thelon Craton Basin archean granitoids; Sm-Nd model ages indicate Hudson 3.0–2.8 Ga crustal precursors at depth (Skulski Paleozoic Bay Cover et al., 2003). A widespread Neoarchean granitoid bloom occurred at 2.62–2.58 Ga (Skulski et al., 60°N 2003), after which granitoid magmatism gener- 120°W Talston-Thelon Hearne Magmatic Zone ally ceased in the northern Rae domain until 1.85– Domain 1.81 Ga plutonism associated with Trans-Hudson 200 km (TTMz) orogenesis (Peterson et al., 2002). The majority of Athabasca the Churchill Province has also been subjected to Basin Wathaman Batholith greenschist to upper amphibolite facies metamor- phism associated with Trans-Hudson orogenesis. Trans-Hudson Orogen Older metamorphic events from 2.3 to 2.4 Ga are 56°N Superior Craton 56°N 112°W 95°W recorded in the Committee Bay belt of the north- central Rae domain (Berman et al., 2005) and in Figure 1. Tectonic elements of northwestern Laurentia including major cratonic blocks, sur- rounding Paleoproterozoic orogens, and Proterozoic sedimentary basins (modifi ed after the southwestern Rae domain, accompanied by Hanmer et al., 2004). Area of Queen Maud block investigated for this study is outlined and plutonic activity (Bostock and van Breemen 1994; detailed in Figure 2. CBb is Committee Bay belt. McNicoll et al., 2000; Hartlaub et al., 2007). © 2007 The Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. GEOLOGY,Geology, August August 2007; 2007 v. 35; no. 8; p. 707–710; doi: 10.1130/G23629A.1; 4 fi gures; Data Repository item 2007182. 707 100°W 96°W GEOLOGY OF THE QUEEN 68°N 68°N MAUD BLOCK The Queen Maud block is on the northwest Queen Maud Gulf Sherman margin of the Rae domain (Fig. 1). Reconnais- Basin sance mapping determined that the block com- BT-5 prises largely high-grade, quartzofeldspathic gneisses, granitoids, and metavolcanic and ST-7 NT-8 BT-4 metasedimentary rocks (Heywood, 1961; Fraser 1964). Further subdivision is based on aeromag- BT-3 WMHWMH NT-7 EMHEMH netic data (Geological Survey of Canada, 2006) NT-3 that outline three N- to NE-trending domains CMLCML ST-4 (Fig. 2), including an eastern magnetic high, a ST-3 uniform central magnetic low (blue in Fig. 2), NT-1 and an internally complex western magnetic high. ST-1 Field work conducted during this study demon- 25 km strates that magnetic high domains are dominated 68°N 67°N by deformed tonalites to granodiorites, most of 100°W 96°W which contain orthopyroxene. The central mag- Figure 2. Aeromagnetic map of northeastern and north-central Queen Maud block show- netic low is dominated at the surface by migma- ing sample locations described in text. Magnetic domains: WMH—western magnetic high; tized pelitic and semipelitic metasedimentary CML—central magnetic low; EMH—eastern magnetic high. Magnetic highs comprise rocks characterized by garnet-bearing melt leu- deformed granitoids; magnetic low is mainly metasedimentary rocks. Dashed line is our cosomes. This NE-trending belt of supracrustal proposed boundary between Queen Maud block and Rae domain. rocks is here termed the Sherman Group. Mafi c dikes were identifi ed in the eastern high and mafi c (2457 ± 24 Ma), NT-3a (2490 ± 29 Ma), and narrow range from 2432 to 2608 Ma and pri- xenoliths in the two westerly domains. The occur- NT-7 (2497 ± 19 Ma), yield ages between 2.46 mary node at 2496 Ma (Fig. 4). The youngest rence of the garnet–cordierite–potassium feldspar and 2.50 Ga, distinct from known ages of the zircon grain exhibiting oscillatory growth zoning assemblage in pelitic rocks indicates regional, north-central Rae domain (Skulski et al., 2002). yielded an age of 2452 Ma, interpreted to be the low- to moderate-pressure granulite facies meta- Whole-rock Sm-Nd isotopic data were also maximum depositional age of the protolith. Zir- morphism. Samples of the main lithologies were obtained for these samples and yield depleted cons isolated from BT-5d are similar to sample collected from the three aeromagnetic domains mantle model ages of 2.8–3.1 Ga (calculated ST-3a, with slender, elongate grains dominating. and the adjacent Rae domain (Fig. 2). using the depleted mantle model of Goldstein The detrital zircon U-Pb ages defi ne a narrow et al.[1984]; Tables DR1 and DR3). range from 2345 to 2513 Ma and primary node at IN SITU U-Pb ZIRCON, MONAZITE, Three metasedimentary samples were investi- 2480 Ma (Fig. 4). The youngest grain exhibiting AND WHOLE-ROCK Sm-Nd ANALYSES gated using in situ U-Pb monazite geochronology clear oscillatory growth zoning yielded an age of Zircon and monazite were analyzed for their to delimit timing of regional metamorphism (Fig. 2438 Ma, interpreted to be the maximum pos- U-Pb isotopic composition (see GSA Data DR1). Sample ST-3a reveals a two-part history. sible depositional age of the protolith. Given the Repository Table DR21) in standard petrographic Two grains have cores that exhibit patchy compo- ca. 2.39 Ga high-grade metamorphism identifi ed thin sections by laser ablation–multicollector sitional variations mantled by homogeneous rims by U-Pb monazite dating, zircon grains yielding inductively coupled plasma–mass spectrometry (Fig. 3). Analyses from patchy cores yield a com- ages younger than 2390 Ma must have undergone using a novel in situ technique (Simonetti et al., posite weighted mean 207Pb/206Pb age of 2481 ± Pb loss or new growth during younger events. 2006). Age calculations were made using Iso- 7 Ma, coeval with 2.46–2.50 Ga zircon ages of the plot Version 3.0 (Ludwig, 2003), and are sum- granitoids.
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