The Bear River dykes (1265–1269 Ma): westward continuation of the Mackenzie dyke swarm into Yukon, Canada

Abstract

The 1.27 Ga Mackenzie dyke swarm, the largest on Earth, radiates from a point in the western Canadian Arctic and extends across much of the Canadian Shield. Possible western extensions of the swarm are largely obscured by younger sedimentary cover. Paleoproterozoic inliers in northern Yukon host the Bear River dykes (BRD), herein dated by U-Pb baddeleyite and zircon methods at 1268.5 ± 1.5 Ma and 1264.6 ± 1.2 Ma. The BRD share similar geochemical and Nd-isotopic characteristics with the Mackenzie dykes and the coeval Coppermine River basalts, and are regarded as products of the same plume. Hydrothermal activity at ∼1270 Ma in breccia of the Nor mineral occurrence, northwest of the BRD, was probably generated by BRD at depth. The BRD generally strike northwest, approximately 90 • to the orientation predicted by the radiating dyke model. This difference may be explained by an anomalous local stress field at the time of BRD emplacement, or reorientation of BRD during subsequent events of Cordilleran deformation. Using the Nor mineral occurrence as the westernmost locale of Mackenzie dyking, and assuming a model of uniform dyke radiation, the arc of the Mackenzie swarm is at least 50 • greater than previously recognized, bringing the total arc of dyke radiation to >150 • .

Ca. 1318 Ma A-type granite on the northern margin of the North China Craton: Implications for intraplate extension of the Columbia supercontinent

“…1318 Ma A-type granite and granitic porphyry in this contribution and the identification of a 1330± 11 Ma to 1313± 17 Ma granite pluton on the northern margin of NCC (Zhang et al, 2011) give felsic magmatic evidence to support an extensional event occurred in the northern NCC in the late Mesoproterozoic. These ages are similar to those in other regions such as Laurentia and Baltica (Anderson and Morrison, 2005;Emslie and Loveridge, 1992), Greenland (Upton et al, 2003), Africa (Mayer et al, 2004), and South America (Bettencourt et al, 1999), with coeval abundant mafic dike swarms (or sills) (Black et al, 1991;Ernst and Buchan, 2001;Ernst et al, 2000Ernst et al, , 2008LeCheminant and Heaman, 1989;Schwab et al, 2004;Upton et al, 2005;shown in Table 4) in these cratons, suggesting intraplate extension of the Columbia supercontinent Zhang et al, 2009;Zhao et al, 2002). The available paleomagnetic data from NCC Pei et al, 2006) show that the NCC shares similar paleomagnetic poles with Laurentia (Emslie et al, 1976;Halls and Heaman, 2000;Harlan and Geissman, 1998;Harlan et al, 1994), Siberia (Ernst et al, 2000), and Baltica Pesonen, et al, 2003) during late Paleoproterozoic to early Mesoproterozoic, indicating that these paleo-continents drifted together or close during this period (Fig.…”

Evidence for late Mesoproterozoic tectonism in northern Yukon and the identification of a Grenville‐age tectonothermal belt in western Laurentia

“…The ‡1.58 event may be linked to Racklan orogeny and subsequent c. 1.60 Ga voluminous hydrothermal brecciation . The 1.27-1.25 Ga ages are likely a reflection of the Bear River dyke emplacement, during the Mackenzie igneous event at c. 1.27 Ga (Schwab et al, 2004).…”

“…The 1.27–1.25 Ga ages are likely a reflection of the Bear River dyke emplacement, during the Mackenzie igneous event at c . 1.27 Ga (Schwab et al. , 2004).…”

Large igneous provinces (LIPs), giant dyke swarms, and mantle plumes: significance for breakup events within Canada and adjacent regions from 2.5 Ga to the PresentThis article is one of a selection of papers published in this Special Issue on the the theme Lithoprobe—parameters, processes, and the evolution of a continent.Lithoprobe Contribution 1482. Geological Survey of Canada Contribution 20100072.

“…6h;Fahrig 1987;Baragar et al 1996). An even greater fan angle (1508) is implied by the identification of coeval Bear River dykes in the Yukon (Schwab et al 2004). The coeval Coppermine Volcanics (up to 2 km thick) and other isolated volcanic rocks (e.g., the Tweed volcanics, Sevigny et al 1991) are the erosional remnants of originally much more widely distributed flood basalts.…”