Integrated potential-field and seismic constraints on the structure of the Archean metasedimentary English River belt, Western Superior craton, Canada

The building and stabilization of an Archean Craton in the Superior Province, Canada, from a heat flow perspective

“…to the boundary between the Uchi domain and the English River belt which marks the southern edge of the craton core [Sol et al, 2002;White et al, 2003;Musacchio et al, 2004]. The seismic reflection profiles do not show imbrication of the English River and Uchi-North Caribou crusts [White et al, 2003].…”

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

“…The most prominent gravity anomaly observed in the WS is a gravity high (>25 mGal) largely coincident with the English River belt (E in Figure 2). Although initially interpreted as the effect of a thick package of metasediments on the basis of a positive surface density contrast (∼40–50 kg/m 3 ) observed between the English River metasedimentary rocks and the felsic rocks of the neighboring domains [e.g., Gupta and Barlow , 1984; Gupta and Wadge , 1986], the English River anomaly is likely not an effect of the metasedimentary rocks, since it also extends over felsic intrusions and tonalitic gneisses of the metaplutonic Winnipeg River belt [ Nitescu and Cruden , 2001; Nitescu et al , 2006]. A recent integrated analysis of magnetic, seismic and gravity information in the English River belt [ Nitescu et al , 2006] suggests that this gravity anomaly is caused by a dense charnockitic unit formed within an extensive suite of circa 2698 Ma felsic plutons that intrude the metasedimentary rocks, in response to high‐grade metamorphic conditions attained at circa 2691 Ma.…”

“…Although initially interpreted as the effect of a thick package of metasediments on the basis of a positive surface density contrast (∼40–50 kg/m 3 ) observed between the English River metasedimentary rocks and the felsic rocks of the neighboring domains [e.g., Gupta and Barlow , 1984; Gupta and Wadge , 1986], the English River anomaly is likely not an effect of the metasedimentary rocks, since it also extends over felsic intrusions and tonalitic gneisses of the metaplutonic Winnipeg River belt [ Nitescu and Cruden , 2001; Nitescu et al , 2006]. A recent integrated analysis of magnetic, seismic and gravity information in the English River belt [ Nitescu et al , 2006] suggests that this gravity anomaly is caused by a dense charnockitic unit formed within an extensive suite of circa 2698 Ma felsic plutons that intrude the metasedimentary rocks, in response to high‐grade metamorphic conditions attained at circa 2691 Ma. Another significant gravity anomaly produced by a source that is not exposed at surface occurs in the Winnipeg River Subprovince between 93.3°W and 94.3°W (W in Figure 2), in an area that is mostly underlain by a large late orogenic granitic intrusion characterized by lower densities compared to the surrounding rock bodies [e.g., Gupta and Barlow , 1984].…”

“…The modeling results also show that the large gravity high associated with the Red Lake greenstone belt is consistent with a 3‐km‐thick body of mafic metavolcanic rocks. For the modeling of the large residual gravity high observed in the English River Subprovince, which is considered to represent the effect of a dense charnockitic unit within a suite of shallow tonalitic plutons that intrude the English River metasediments [ Nitescu et al , 2006], we assumed a source of cross‐sectional geometry, depth and density contrast similar to those suggested by Nitescu et al [2006]. In addition, the gravity contributions of the thicker packages of metasediments (up to 2 km thick) that flank this intrusion, and which were interpreted on the basis of magnetic and seismic data [ Nitescu et al , 2006], were also considered.…”

“…However, it was observed that the inversion of the gravity data using this initial reference model would produce density distributions characterized by significant tails at depth for some of the upper crustal mass anomalies in the Wabigoon Subprovince, and therefore the depth extents of those mass anomalies in the reference density model were subsequently adjusted to 5 km in the case of greenstone belts and to 10 km in the case of low‐density granitoid bodies. For the source of the English River gravity anomaly, it was assumed that it has a density contrast of 200 kg/m 3 and that it extends between 1 and 3 km depth, based on its characteristics inferred by Nitescu et al [2006]. In the case of the source of the Winnipeg River anomaly we assumed, consistent with the forward gravity model obtained along Lithoprobe line 2b (Figure 6), that it is produced by a 10‐km‐thick upper crustal layer characterized by a positive density contrast of 20 kg/m 3 .…”