Dt. James et Gr. Dunning, U-Pb geochronological constraints for paleoproterozoic evolution of the core zone, southeastern Churchill Province, northeastern laurentia, PRECAMB RES, 103(1-2), 2000, pp. 31-54
The Core Zone of the Southeastern Churchill Province, northeastern Laurenti
a, is a composite of Paleoproterozoic lithotectonic domains assembled in th
e vise between obliquely colliding Archean Superior and North Atlantic crat
ons between ca. 1860 and 1810 Ma. Detailed geological and U-Pb geochronolog
ical studies of domains in the southern Core Zone highlight significant dif
ferences in Archean and Paleoproterozoic geology between domains, and const
rain timing and models for Paleoproterozoic assembly. In the south-central
part of the Core Zone, Crossroads and Orma domains consist of Late Archean
granite-greenstone terrane crust. Crossroads domain also contains a signifi
cant number of granite-charnockite intrusions belonging to the 1840-1810 Ma
De Pas batholith; magmatism pre-dates and overlaps with ca. 1820-1775 Ma h
igh-grade metamorphism and attendant deformation. In marked contrast, Orma
domain, which occurs to the east of Crossroads domain, contains only local
evidence of Paleoproterozoic (De Pas related?) intrusions and appears to ha
ve mainly escaped Paleoproterozoic metamorphism and penetrative deformation
. A model compatible with available data suggests the De Pas batholith is a
continental magmatic are formed above an east-dipping subduction zone. Pal
eoproterozoic metamorphism and deformation is concentrated in regions conti
guous with are magmatism. West of Crossroads domain, and separated from it
by the Lac Tudor shear zone, McKenzie River domain is dominated by Archean
orthogneiss (> 80 m.y. older than gneisses in Crossroads and Orma domains),
minor amounts of Paleoproterozoic supracrustal rocks (absent in domains to
the east) and 1815 Ma tonalite. It does not contain De Pas intrusions. U-P
b geochronology suggests juxtaposition of the McKenzie River domain with do
mains to the east may have occurred around 1810 Ma. One possible model envi
sages the McKenzie River domain as a piece of reassembled Superior craton c
rust, incompletely rifted from the Superior margin during ca 2.17 Ga riftin
g. Domains occurring east of the Lac Tudor shear zone are interpreted to be
exotic with respect to the Superior craton. (C) 2000 Elsevier Science B.V.
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