Geology and U–Pb geochronology of the Neoarchean Snare River terrane: tracking evolving tectonic regimes and crustal growth mechanisms

Abstract

U–Pb zircon crystallization ages determined by isotope dilution – thermal ionization mass spectrometry (ID–TIMS) and laser ablation microprobe – inductively coupled plasma – mass spectrometry (LAM–ICP–MS) for 13 intrusive units in the Neoarchean Snare River terrane (SRT) provide tight constraints on the timing of crust formation and orogenic evolution. Seven metaluminous plutons were emplaced over ~80 Ma from ca. 2674 to 2589 Ma, whereas six peraluminous bodies were emplaced in a ~15 Ma interval from ca. 2598 to 2585 Ma. A detrital zircon study yielded an age spectrum with peaks correlative with known magmatic events in the Slave Province, with the ca. 2635 Ma age of the youngest detrital zircon population providing a maximum estimate for the onset of sedimentation. This age contrasts with evidence for pre-2635 Ma sedimentation elsewhere in the SRT, indicating that sedimentation was protracted and diachronous. Evolution of the SRT can be subdivided into four stages: (i) 2674–2635 Ma — formation of a metaluminous protoarc in a tonalite–trondhjemite–granodiorite (TTG) – granite–greenstone tectonic regime (TR1) and coeval with early turbidite sedimentation; (ii) 2635–2608 Ma — continued turbidite sedimentation, D1/M1 juxtaposition of turbidites and protoarc lithologies prior to ~2608 Ma, and metaluminous granitoid plutonism; (iii) 2608–2597 Ma — onset of TR2, collision of Snare protoarc with Central Slave Basement Complex, D2/M2 crustal thickening and mid-crustal granulite-facies metamorphism, sychronous with metaluminous and peraluminous plutonism; and (iv) 2597–2586 Ma — orogenic collapse, D3/M3 mid-crustal uplift, granulite-facies metamorphism, and waning metaluminous and peraluminous plutonism. The distribution of igneous rocks yields an "orogenic stratigraphy" with an older upper crust underlain by a younger synorogenic mid-crust. These data can be used to provide constraints for the interpretation of the Slave – Northern Cordillera Lithospheric Evolution (SNORCLE) Lithoprobe transect.