U‐Pb geoehronology and evolution of the English River Subprovince, an Archean low P‐high T metasedimentary belt in the Superior Province

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Abstract
U‐Pb isotopic data for zircon, monazite, and titanite are used to assess the evolution of the late Archean English River Subprovince (ERS) and adjacent domains of the Winnipeg River Subprovince in the northern Superior Province, Ontario. The ERS consists of turbiditic metasedimentary rocks, deposited during the final stages of magmatic and tectonic accretion within the greenstone‐granite Uchi Subprovince to the north at around 2720 to 2710 Ma. The sedimentary rocks were intruded by a suite of calc‐alkalic plutons at 2698 Ma. Major regional deformation, amphibolite to granulite facies metamorphism, anatexis, and emplacement of an extensive peraluminous granitic suite culminated at 2691 Ma. Late episodes of metamorphism, metasomatism, and emplacement of pegmatites occurred locally at circa 2680 and 2669 Ma. In contrast, the Winnipeg River Subprovince to the south consists of widespread tonalitic suites formed mainly between 3200 and 2800 Ma and granodioritic to granitic intrusions formed between 2710 and 2690 Ma. Metamorphism occurred at around 2710 Ma in southern domains, and a distinct granulite facies event at around 2680 Ma affected central and northern domains of the Winnipeg River Subprovince. The rapid sequence of events recorded in the ERS supports the notion that metamorphism was caused by thermal perturbations related to injection of granitic magmas. These melts were generated through partial melting of the lower crust by a thermal anomaly presumably caused by mantle upwelling related to collapse of the inactivated subducting plate. The short‐lived nature of the metamorphic events and their cyclicity follow the behaviour predicted by recent models linking the evolution of strain rates to episodes of segregation and upward magma transfer in the course of prolonged orogenic events.

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