⁴⁰Ar/³⁹Ar phlogopite and U – Pb perovskite dating of lamprophyre dykes from the eastern Lake Superior region: evidence for a 1.14 Ga magmatic precursor to Midcontinent Rift volcanism

Abstract

Thin lamprophyre dykes are abundant in the vicinity of the ca. 1.1 Ga Midcontinent Rift System and the late Archean – Early Proterozoic Kapuskasing Uplift in the Canadian Shield northeast of Lake Superior. However, the relationship between these dykes and spatially associated alkalic-carbonatite complexes has been unclear. To ascertain the temporal relationship between the two, we have determined, by 40Ar/39Ar and U–Pb dating, precise emplacement ages for six lamprophyre dykes from the region. The [Formula: see text] Ma U–Pb date for perovskite from the western Marathon and Wawa areas is indistinguishable from the 1144 ± 7 Ma 40Ar/39Ar date for phlogopite from the eastern Kapuskasing Uplift, and it is concluded that these dykes are part of a regional 1.14 Ga swarm that extends over 300 km. These dykes were therefore emplaced some 35 Ma prior to the 1109 Ma commencement of Midcontinent Rift volcanism and coeval alkaline-complex activity, but essentially simultaneously with emplacement of the 1141 ± 2 Ma Abitibi diabase dyke swarm. It is suggested that these widespread 1144 Ma lamprophyre dykes and the Abitibi diabase dykes represent the first magmatic response of initiation of the Midcontinent rifting event, and were precursors to the main rift magmatism at 1109 Ma.

Paleomagnetism and Geochemistry of ~1144‐Ma Lamprophyre Dikes, Northwestern Ontario: Implications for the North American Polar Wander and Plate Velocities

“…The ~1144‐Ma ultramafic lamprophyre dikes (Queen et al, ) and the ~1142 Abitibi diabase dikes (Krogh et al, ) that crop‐out northeast of Lake Superior (Ontario, Canada; Figure ) represent the earliest magmatic events related to MCR (Table ). For both suites, local dike trends form a fan pattern radiating from a common center in the Lake Superior basin (Figure ).…”

“…For both suites, local dike trends form a fan pattern radiating from a common center in the Lake Superior basin (Figure ). Based on similar age and radiating dike trends, Queen et al () suggested that the lamprophyre and Abitibi dikes represented the incipient magmatic activity of the Midcontinent rifting, preceding the main rift magmatism by ~35 Ma.…”

“…Sample ID refers to the name used in the geochronology study, or, in parentheses, the site name studied for paleomagnetism in this study (lamprophyres) and in Ernst and Buchan (; Abitibi dikes). Lat and Long are the approximate site latitude and longitude; Ref stands for the age reference: 1, Queen et al (); 2, L. M. Heaman, unpublished data cited in Sage (), and 3, Krogh et al ().…”

Kimberlites from the Wawa area, Ontario

“…It is intruded by Proterozoic diabase dykes. The youngest igneous rocks of the Wawa area are carbonatites and lamprophyres with ages of 1000-1140 Ma (Gittins et al 1967;Sage 1996;Queen et al 1996;Sage and Crabtree 1997).…”

Petrogenesis of lamprophyres from Chhota Udepur area, Narmada rift zone, and its relation to Deccan magmatism

“…Despite their relatively small-volume, increasing significance is being attached to the studies on lamprophyres owing to their (i) role in understanding of the large-scale geodynamic processes such as continental extension (e.g., Larsen and Rex, 1992;Queen et al, 1996;Tappe et al, 2006), mantle plume-lithosphere interactions (e.g., Gibson et al, 2006;Orejana et al, 2008;Kerr et al, 2010), continental break-ups and collisions (e.g., Foley et al, 2002;O'Leary et al, 2009;Rocchi et al, 2009) and mantle-enrichment processes (e.g., Beard et al, 1996;Guo et al, 2004;Srivastava and Chalapathi Rao, 2007), (ii) entrapped lower-crustal and mantle xenoliths which serve as snapshots to the lower portions of the 1367-9120/$ -see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2011.09.009…”