U–Pb geochronology of the central Uchi Subprovince, Superior Province

Abstract

U–Pb zircon and titanite ages for rocks of the central Uchi Subprovince in northwestern Ontario indicate a late Archean magmatic and tectonic development spanning over 200 Ma. An early period at 2900–2800 Ma formed volcano-plutonic complexes, presumably linked to 3.1–2.8 Ga terrains of the northwestern Superior Province. A later period of southward growth by magmatic and tectonic accretion occurred at 2750–2710 Ma and was concluded by large scale compression and plutonism at 2700 Ma.The oldest 2890–2860 and 2840–2820 Ma components occur in the Pickle Lake and Meen–Dempster greenstone belts and as gneisses in the Seach–Achapi and the Lake St. Joseph batholiths in northern and central sectors of the region. Together with distinct 2750–2740 Ma volcano-plutonic complexes they form a collage assembled by multiple episodes of tectonic juxtaposition and magmatic accretion. Plutons of 2730–2710 Ma age are intrusive into these older, northern domains, whereas their volcanic counterparts compose the Lake St. Joseph and Miminiska – Fort Hope greenstone belts to the south. Late-tectonic to posttectonic granitoid rocks intruded a region extending from the northern Berens River Subprovince to the southern English River Subprovince at 2700 Ma. These plutons were cut by regional scale faults formed by residual north-northwest directed shortening. The timing of this movement seems to be recorded by titanite ages of 2690–2670 Ma. Reactivation of the same faults may account for Proterozoic Pb loss observed in some of the zircon populations. The age patterns are consistent with crustal growth along a continental margin in a north-dipping subduction environment.

Age structure and orogenic significance of the Berens River composite batholiths, western Superior Province

“…1 and 2 for sample locations. Published ages are from Corfu and Ayres (1984), Corfu et al (1985), Corfu and Wallace (1986), Corfu and Wood (1986), Corfu and Andrews (1987), Noble (1989), Schärer (1989), Turek et al (1989), Corfu and Ayres (1991), Corfu andStott (1993a, 1993b), and Stevenson (1995). likely to be the fortuitous combination of complex inheritance and multiple Pb loss events, the pattern supports other evidence for reactivation of the fault during the Hudsonian event (Corfu and Ayres 1984;Corfu and Stott 1993b).…”

“…Volcanic assemblages of the Uchi Subprovince show a general southward-younging trend (Corfu and Stott 1993b;Stott and Corfu 1991), and, at the subprovince scale, plutons correlative with each volcanic assemblage intruded older domains to the north. The volcanic-plutonic zonation appears to reflect largely the progressive migration of a magmatic arc over a retreating subduction zone, but it is also likely that the original geometry was modified by earlier thrusting, tectonic amalgamation of arc sequences, and faulting (Noble 1989;Stott and Corfu 1991).…”

Variable unroofing in the western Superior Province - metamorphic evidence and possible origin

“…These studies have indicated that the region is characterized by an abundance and variety of granitoid intrusives, with ages that range between 2745 and 2690 Ma. In the south of Berens River subprovince, close to the north of central Uchi subprovince, the ages of plutonic rocks are concentrated between 2705 and 2690 Ma (Corfu and Ayres 1984;Stott and Corfu 1991;Corfu and Stott 1993a;Corfu and Stone 1998a). It is, therefore, likely that most of the pressure estimates provided in this study reflect burial depths at ca.…”

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

“…Some early models [e.g., Langford and Morin , 1976] and most of the tectonic interpretations in the past two decades [e.g., Hoffman , 1989; Card , 1990; Williams , 1990; Williams et al , 1992; Card and Poulsen , 1998] suggest on the basis of observations derived from geochronological, geochemical and field studies (e.g., generally southward younging Neoarchean magmatism, deformation and sedimentation; compositional and geochemical similarities between greenstone belt sequences and modern volcanic arcs) that the growth of the WS occurred mainly through progressive lateral accretion of arc and microcontinental fragments to the southern margin of a Mesoarchean continental block, termed the North Caribou protocraton [ Thurston et al , 1991]. The Neoarchean development of the Berens River and Uchi belts on the southern margin of the North Caribou protocraton appears comparable with that of an Andean‐type continental margin [ Corfu and Stott , 1993; Corfu and Stone , 1998]. The volcano‐plutonic complexes of the Uchi Subprovince record episodic growth between circa 2900 and 2700 Ma, which ended with their deformation between 2720 and 2700 Ma [ Corfu and Stott , 1993].…”

“…The Neoarchean development of the Berens River and Uchi belts on the southern margin of the North Caribou protocraton appears comparable with that of an Andean‐type continental margin [ Corfu and Stott , 1993; Corfu and Stone , 1998]. The volcano‐plutonic complexes of the Uchi Subprovince record episodic growth between circa 2900 and 2700 Ma, which ended with their deformation between 2720 and 2700 Ma [ Corfu and Stott , 1993]. The deformation of the Uchi crust was likely caused by far‐field stresses transmitted through the Winnipeg River terrain, following the juxtaposition of Neoarchean volcanic assemblages of the western Wabigoon Subprovince with the Winnipeg River belt at circa 2717 Ma [ Melnyk et al , 2006].…”