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The Paleoproterozoic Hottah terrane is the westernmost exposed bedrock of the Canadian Shield and a critical component for understanding the evolution of the Wopmay Orogen. Thirteen new high-precision U-Pb zircon crystallization ages are presented and support field observations of a volcano-plutonic continuum from Hottah terrane through to the end of the Great Bear magmatism, from >1950 to 1850 Ma. The new crystallization ages, new geochemical data, and newly published detrital zircon U-Pb data are used to challenge hitherto accepted models for the evolution of the Hottah terrane as an exotic arc and microcontinent that arrived over a west-dipping subduction zone and collided with the Slave craton at ca. 1.88 Ga. Although the Hottah terrane does have a tectonic history that is distinct from that of the neighbouring Slave craton, it shares a temporal history with a number of domains to the south and east - domains that were tied to the Slave craton by ca. 1.97 Ga. It is interpreted herein that Hottah terrane began to the south of its current position and evolved in an active margin over an always east-dipping subduction system that began prior to ca. 2.0 Ga and continued to ca. 1.85 Ga, and underwent tectonic switching and migration. The stratigraphy of the ca. 1913-1900 Ma Hottah plutonic complex and Bell Island Bay Group includes a subaerial rifting arc sequence, followed by basinal opening represented by marginal marine quartz arenite and overlying ca. 1893 Ma pillowed basalt flows and lesser rhyodacites. We interpret this stratigraphy to record Hottah terrane rifting off its parental arc crust - in essence the birth of the new Hottah terrane. This model is similar to rapidly rifting arcs in active margins - for example, modern Baja California. These rifts generally occur at the transition between subduction zones (e.g., Cocos-Rivera plates) and transtensional shear zones (e.g., San Andreas fault), and we suggest that extension-driven transtensional shearing, or, more simply, terrane translation, was responsible for the evolution of Bell Island Bay Group stratigraphy and that it transported this newly born Hottah terrane laterally (northward in modern coordinates), arriving adjacent to the Slave craton at ca. 1.88 Ga. Renewed east-dipping subduction led to the Great Bear arc flare-up at ca. 1876 Ma, continuing to ca. 1869 Ma. This was followed by voluminous Great Bear plutonism until ca. 1855 Ma. The model implies that it was the westerly Nahanni terrane and its subducting oceanic crust that collided with this active margin, shutting down the >120 million year old, east-dipping subduction system. [ABSTRACT FROM AUTHOR]

Field evidence, map compilation, geochemistry, geochronology, and potential field data document six intervals of Cretaceous magmatism in the central Sverdrup Basin. These are: (1) Hauterivian (ca. 130 Ma) vol-caniclastic deposition in the lower Isachsen Formation; (2) 126.6 ± 1.2 Ma (U-Pb zircon) gabbroic intrusion; (3) 120.8 ± 0.8 Ma (U-Pb baddeleyite) diabasic intrusion; (4) 105.40 ± 0.22 Ma (U-Pb detrital zircon) pyroclastic deposition at the top of the Invincible Point Member, Christopher Formation; (5) upper Albian (ca. 103 Ma) pillow and hydroclastic breccia in the upper Christopher Formation; and (6) uppermost Albian (ca. 101 Ma) volcanic breccia and scoria in the Hassel Formation. Whole-rock geochemical data show that these magmatic rocks are similar to previously documented High Arctic large igneous province tholeiitic basalts, but analyses of fresh glass in tuffs reveal evolved ferroandesite to dacite compositions not recorded in whole-rock data. Approximate ages of saucer-shaped sills inferred from the relationship of sill width to depth of emplacement suggest at least three intervals of sill emplacement between 130 and 120 Ma. The new data show that volcanism in the Sverdrup Basin was of greater spatial extent, and that magmatism occurred more frequently, than was previously recognized. Comparison of the new central Sverdrup Basin data and interpretations with other data sets from the Sverdrup Basin, Svalbard, and Franz Josef Land suggests that High Arctic large igneous province magmatism occurred over a more extended period of time in the central Sverdrup Basin than in other regions. [ABSTRACT FROM AUTHOR]

New U-Pb zircon dates from gneissic xenoliths in an Early Cambrian lamprophyre point to late Mesoproterozoic metamorphism and magmatism in the crust beneath northern Yukon. The data indicate a previously unrecognized thermal event in Yukon and extend the recognition of widely spaced 1.3-1.0 Ga igneous, metamorphic and tectonic events along the western margin of Laurentia. Together, these events demonstrate that the north-western margin of Laurentia was thermally active during a period of traditionally inferred tectonic quiescence. The tectonic setting, intensity and general nature of this late Mesoproterozoic tectonothermal activity are poorly constrained, but their recognition is key to expanding our understanding of the Proterozoic geology of North America. The recognition of this event places new constraints on the palaeotectonic reconstructions of the supercontinent Rodinia. [ABSTRACT FROM AUTHOR]

Terra Nova, 23, 92-99, 2011 Abstract Zircon crystallization ages for a syntectonic granite and an associated dyke along the Tangtse strand of the Karakorum fault are 18.5 ± 0.2 and 18.6 ± 0.2 Ma, respectively. A dyke cross-cutting the foliation in the Karakorum shear zone (Ksz) yielded an age of 16.0 ± 0.6 Ma. These data show that the Ksz was associated with significant granitic magmatism and was active before 16 Ma, since at least c. 18.5 Ma. Consideration of other data along the Karakorum fault suggests that the fault has most likely been active since c. 22.7-25 Ma at a rate of 8-13 mm a−1. This study conducted in the frontal part of the Himalayan orogen shows that large continental strike-slip faults can be linked with magmatism and be stable for more than 20 Ma, even in the hottest part of the orogen where strain localization is supposed to be at a minimum. [ABSTRACT FROM AUTHOR]

Iron oxide copper-gold (IOCG) and associated iron-oxide apatite (IOA) styles of metallic mineralization are recognized throughout the Paleoproterozoic Great Bear magmatic zone of the northwest Canadian Shield. The Great Bear magmatic zone was constructed between ca. 1876 and 1855 Ma on top of the older Hottah terrane, which preserves continental arc magmatism that began around ca. 2.0 to 1.97 Ga and continued between ca. 1.93 and 1.89 Ga. The Great Bear represents the final stages of ca. 150 million years of intermittent and pulsed magmatism related to an evolving continental orogenic belt. The preserved geology supports a dramatic geodynamic change in the subduction zone process at ca. 1875 Ma, a key driving mechanism for magma and metal mobilization, and was rapidly followed by a large-scale introduction of felsic-intermediate plutons. The overall tectonic setting is partially constrained from new and previously published geochemical data that show that the volcanic and plutonic rocks are high-K calc-alkaline to shoshonitic in nature (e.g., high K 2 O, Th/Yb, and Ce/P 2 0 5 ). They also have suprasubduction-zone geochemical signatures, including primitive mantle normalized positive Th and negative Nb, P, and Ti anomalies. The data support the primary melts were derived from a GLOSS-modified mantle wedge. Three-dimensional rendering of geophysical datasets suggest that two (of four) preserved surfaces within the upper mantle lithosphere, at 70 to 120 km depths, represent frozen, subducted oceanic slabs, and likely were the drivers for the bulk of Hottah and Great Bear arc magmatism. The older slab is northwest-striking and dips 12° to 15° northeast, whereas the younger is deeper and north-striking, dipping 13° east. The geometry of the surfaces are comparable with 4D modeling, where a subduction zone is temporarily shut down due to plateau collision, and then steps oceanward and re-initiates; there is no need for polarity reversal of the subduction system. This new geometry and the related inferences about process should be the focus of future research in the region, but for the time-being it can be stated that these subduction and collisional processes were the first order control on lithospheric evolution, and therefore metallic mineralization. Overall, the Great Bear magmatic zone IOCG and related mineralization is not comparable to other Proterozoic IOCG belts, such as those in Australia. However, the complexity of mineralization styles, the spatial-temporal relationship between IOA and IOCG mineralization, the suprasubduction zone environment, and a major change in tectonic regime are features similar to Andean-type IOCG mineralization, as well as Cordilleran alkali porphyry Cu-Au deposits. This further establishes the linkages between subduction zone processes and IOCG formation, as well as relationships in the IOCG-porphyry deposit continuum model. [ABSTRACT FROM AUTHOR]

• The Makkovik orogeny is part of the Great Paleoproterozoic Accretionary Orogen. • New U-Pb ages constrain the Paleoproterozoic magmatism the Makkovik orogen. • Samples from the Aillik Group yield magmatic between 1883 ± 7 Ma and 1858 ± 3 Ma. • Magmatism consisted of significant crustal reworking, and minor preserved juvenile crustal growth. The convergent margin of southeastern Laurentia consists of reworked continental crust as well as accretion of continental ribbons and juvenile arc terranes forming part of the Great Proterozoic Accretionary Orogen. The Makkovik orogen, in Labrador, preserves evidence of the timing, duration and complexities of these accretionary events during the interval 1.88–1.78 Ma. New regional bedrock geological mapping combined with new U-Pb zircon SHRIMP ages constrain the Paleoproterozoic felsic magmatism in the Aillik Group of the Makkovik orogen. Nine samples from the Aillik Group yield magmatic 207Pb/206Pb ages between 1883 ± 7 Ma and 1858 ± 3 Ma. The ages extend the previously documented ages of felsic volcanism, providing evidence for periodic volcanism spanning 35 m.y. with the most prolific volcanic activity occurring ca. 1860 Ma. Combined with previous studies, the Aillik Group is now constrained between 1883 ± 7 and 1848 ± 2.7 Ma. Development of a pervasive planar fabric associated with the northwestward thrusting of the Aillik Group (D 3) occurred after 1848 Ma. Lithotectonic evolution in the Makkovik Province comprised significant crustal reworking, magmatism, and minor preserved juvenile crustal growth between ca. 1883 and 1848 Ma. The revised model for formation of the Aillik Group proposed herein suggests that the Aillik Group formed in a continental back-arc setting. These new ages further refine the timing of the accretionary events as well as characterizing the age of the crustal root of the arc, which could be a juvenile substrate (Neoarchean/Paleoproterozoic) or reworked Archean crust, possibly the 2.3–2.6 Ma Mistinibi-Raude crust of the Southeast Churchill Province. [ABSTRACT FROM AUTHOR]

Abstract: The western Churchill Province of the Canadian Shield experienced a prolonged and complex formation history (ca. 4.04 to 1.70Ga), with evidence for multiple episodes of orogenesis and regional magmatic activity. Here we report on the oxygen isotopic compositions of garnet and zircon recovered from lower crustal xenoliths, which have U–Pb ages between ca. 3.5 and 1.7Ga. Overall, zircon from four metabasite xenoliths from the Rankin Inlet sample suite have δ 18O values ranging from +5.5 to +8.6‰. Zircon from three metatonalite/anorthosite xenoliths and five metabasite xenoliths from the Repulse Bay sample suite have δ 18O values of +5.6 to +8.3‰. High δ 18O values (>+6.0‰) for the oldest igneous zircon cores (ca. 3.5Ga and 3.0–2.6Ga) indicate that their metatonalite/anorthosite protolith magmas were generated from, or had assimilated, supracrustal rocks that interacted previously with surface-derived fluids. Igneous zircon cores (ca. 2.9–2.6Ga) from one metabasite xenolith have δ 18O values of +5.6 to +6.4‰, which suggests a formation from a mantle-derived basaltic/gabbroic magma. Metamorphic zircon cores (ca. 2.0–1.9Ga) from one metabasite xenolith commonly have δ 18O values between +6.0 and +6.3‰, which is indicative of a basalt/gabbro protolith and localized reworking of the lower crust caused by regional-scale plate convergence. The wide range of δ 18O values (+5.5 to +8.3‰) for ca. 1.75–1.70Ga metamorphic zircon rims (identified in all xenoliths) indicates regional transient heating and reworking of mantle- and supracrustal-derived crust, induced by magmatic underplating along the crust–mantle boundary. [Copyright &y& Elsevier]