The Darby Lake - Arrowsmith River area, southwest of Pelly Bay and southeast of Chantrey Inlet, is readily divided into three northeast-trending lithotectonic subdomains all of which are dominated by granitoid rocks, but contain uncommon, dispersed remnants of
upper greenschist- to amphibolite-facies Archean supracrustal rocks dominated by psammite and semipelite with rare mafic and ultramafic units.
Greenschist-facies supracrustal rocks are associated in the northwest and southeast by widespread tonalite, granodiorite, and monzogranite. Along the central axis of the map area, a wide range of moderately to strongly deformed, commonly L>S medium-grained to megacrystic granodiorite to
dominant monzogranite tectonite bodies at amphibolite facies, grade into biotite±garnet and biotiteorthopyroxene± garnet-bearing granitoid rocks. These granitoid rocks all contain abundant screens, rafts, and schlieren of tonalite,
biotite±garnet±hornblende±sillimanite-bearing metasedimentary rocks, and cospatial metasedimentary metatexite and diatexite. Small cupolas of massive biotite±magnetite monzogranite crosscut these rocks
The thrust bounded McLeod Road -Birch Lake sequence (MB sequence) occurs within the Paleoproterozoic Snow Lake arc assemblage (SLA) of the Flin Flon Belt. Stratigraphic correlation of volcanic strata of the MB sequence with strata of the thrust bounded Chisel sequence, indicates that distinctive, submarine, eruption-fed, pyroclastic flow deposits are more extensive and voluminous than previously recognized (>10 km 3 ). These voluminous felsic pyroclastic deposits define a distinct magmatic and explosive volcanic event during bimodal volcanism that accompanied rifting of the Snow Lake arc. The felsic pyroclastic deposits define the remnants of a basin, or of nested basins, that formed during arc rifting and subsidence, and their eruption immediately preceded formation of the Chisel sequence volcanogenic massive sulfide (VMS) deposits. Although the Chisel sequence ore interval is recognized in the MB sequence, the lack of VMS-related alteration indicates that VMS hydrothermal activity was restricted to the Chisel portion of the basin. However, the MB sequence is host to the younger Snow Lake gold mine, a 1.4M oz. (43,699kg) gold producer.The overlying MORB-like Birch Lake Basalts, if conformable with the MB sequence, may represent a progression from a rifted-arc to a back-arc setting, however if thrust fault bounded they may represent the initial phases of arc-rifting, prior to the voluminous felsic pyroclastic eruptions. Correlation and integrity of stratigraphy between the thrust bounded MB and the SLA sequences indicates that the bounding thrust faults, which developed during accretionary processes, have less regional significance than previously interpreted.
The Neoarchean is generally considered to have been the final era of major crust formation and may have been characterized by the onset of modern plate tectonics. The Neoarchean may also have been the time interval during which subduction processes prevailed and became global. Evidence from individual cratons around the world suggests that this transition in geodynamic processes may have included diachronous and episodic major changes (i.e., turning points) and a more gradual evolution at the global scale, possibly largely driven by the secular cooling of the mantle and increasing stability of the lithosphere. The Superior craton, Canada, is the largest and best-preserved Archean craton in the world, making it an ideal location in which to investigate the occurrence (or absence) of turning points in the Neoarchean. This contribution examines the changes in geodynamic and magmatic processes that occurred during the Neoarchean, using geochemical data and new insights garnered from isotopic surveys from the southern part of the Superior craton. We summarize current understanding of the evolution of the youngest (southern) part of the Superior craton that led to the stabilization (cratonization) of this continental lithosphere and how this evolution aligns with local and global geodynamic processes.
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