Crustal structure and implications for the tectonic evolution of the Archean Western Superior craton from forward and inverse gravity modeling

Abstract

The distribution of mass anomalies within the crust of the Archean Western Superior Province has been investigated with forward and inverse gravity modeling routines. The gravity models indicate that in most of the Western Superior Province, significant mass anomalies occur only within the top 10 km of the crust, where they are generally related to dense metavolcanic rocks and low‐density granitoid plutons, and at the crust‐mantle boundary, where they are linked to undulations of this interface. An exception is the region encompassing the central Wabigoon Subprovince and the segments of the Quetico and Wawa belts south of it, where implied large intracrustal mass anomalies are associated with a segment of denser lower crust, and with overlying depressions of the interfaces between the main crustal layers. We interpret the predominant lateral mass homogeneity observed at deep crustal levels as evidence of mass redistribution processes associated with a major postaccretionary episode of thermal softening of the Western Superior crust. The incongruent presence of a denser lower crustal segment may reflect the subsequent modification of the lower crust through magmatic intra and underplating, possibly in relation with the Mesoproterozoic midcontinent rifting event.

Instability of the southern Canadian Shield during the late Proterozoic

“…4). Nitescu et al (2006) hypothesize that the oceanic slab argument is not conclusive and that continuity in lower crustal densities align more with a model of post-accretion thermal softening and lower crustal reworking. They argue that the mass anomalies within the lower crust of the Wabigoon Province and those terranes to the south instead represent dense underplated, anisotropic mafic rocks from MCR extension and magmatism.…”

“…This later magmatism produced a >15 km underplated, thickened crust at the MCR, which tapers to approximately ≤10 km thickness to the north in the western Superior Province, based on the aforementioned studies showing a high velocity lower crustal layer (e.g. Musacchio et al, 2004;Nitescu et al, 2006).…”

“…1.26 Mackenzie dike swarm originating in the Slave craton up to 3000 km to the northwest. The dark red dashed line near the southern NCT boundary is the approximate high seismic velocity region from White et al (2003); Musacchio et al (2004) and gravity anomalies of Nitescu et al (2006) interpreted as a result of MCR underplating. Red dashed circle is the region that could theoretically be affected by topographic doming up to 650 km away from the MCR nucleus, from Allen (1992).…”

Lateral constrictional flow of hot orogenic crust: Insights from the Neoarchean of south India, geological and geophysical implications for orogenic plateaux

“…The properties of LCF exposed above may account for the salient geological characteristics of lower crustal exposures of hot Precambrian orogens, such as (1) horizontal isogrades and absence of major reverse metamorphic pressure breaks, suggesting minor topographic gradients, (2) synconvergence HT‐LP metamorphism, and (3) dominance of orogen‐parallel stretching and transcurrent kinematics [ Cagnard et al , 2006b; Chardon et al , 2009; Gapais et al , 2009]. Numerous studies of hot orogens are implicitly or explicitly suggestive of LCF (Precambrian examples: Ehlers et al [1993], Dirks et al [1997], Passchier et al [1997], Vassallo and Wilson [2002], Davis and Maidens [2003], Gapais et al [2005, 2008], Cagnard et al [2006b], Nitescu et al [2006], Duclaux et al [2007], Hamilton [2007], Dumond et al [2010], and Lana et al [2010]; Phanerozoic examples: Aerden [1998], Franke et al [2011], Klepeis and Crawford [1999], Andronicos et al [2003], and Denèle et al [2007]). LCF is also required to operate in three‐dimensional experiments on the shortening of weak lithospheres [ Cagnard et al , 2006b; Cruden et al , 2006; Rey and Houseman , 2006; Duclaux et al , 2007].…”

New insights into the lithosphere beneath the Superior Province from Rayleigh wave dispersion and receiver function analysis

“…Kay et al 1999b; Musacchio et al 2004), though the Vp / Vs ratio is considerably lower to the east and west. A high‐density feature is also modelled at depth in a similar region by 3‐D Bouguer gravity inversion (Nitescu et al 2006).…”