Petrogenesis of the Boothia Ferroan Granite Complex, Boothia Peninsula, Nunavut

  • Author / Creator
    Osinchuk, Alix M.
  • Reconnaissance regional mapping as part of the Geological Survey of Canada’s Geomapping for Energy and Minerals (GEM-2) project documented three voluminous, massive to weakly foliated felsic plutons in Boothia Peninsula, Nunavut. Uranium-lead zircon and monazite geochronology reveals this magmatism, herein called the Boothia Ferroan Granite Complex (BFGC), occurred between 1841 and 1823 Ma, an age range scarcely reported within this region. The emplacement of the BFGC is contemporaneous with widespread Paleoproterozoic granite ‘blooms’ in the Churchill Province associated with the late-accretion to post-collisional stages of the Trans-Hudson orogeny (Peterson et al., 2002; 2015b), and extends the northern limit of tectonothermal effects linked to the orogen to > 1400 km from the orogenic front. A comprehensive study of the granitoids involving U-Pb geochronology, whole-rock and mineral geochemistry, samarium-neodymium and lutetium-hafnium isotope geochemistry, and geothermobarometry was conducted to determine the petrogenesis of the BFGC. This research allows us to investigate potential tectonic mechanisms responsible for this widespread granitic within the Churchill Province, and in turn provides important insights into the nature of late- to post-tectonic magmatism associated with continental collisions. The BFGC comprises four suites of granitoids: the fayalite, charnockite, hornblende-biotite and garnet-biotite suites. These granitoids are dominantly ferroan (high Fe/Mg) and potassic, include both metaluminous and peraluminous varieties, and are relatively enriched in incompatible elements. This study reveals: 1) the BFGC represents high-temperature (> 800°C to up to 950°C), reduced, and relatively H2O-poor magmatic rocks, as evidenced by amphibole-plagioclase, titanium-in-zircon and zircon saturation geothermometric constraints and the presence of high-temperature anhydrous minerals (fayalite, orthopyroxene, inverted pigeonite); 2) the BFGC was emplaced at mid-crustal pressures between 5.1-6.3 kbar (~18-22 km depth) in an overthickened (50-60 km) crust, partially assimilating semi-pelitic country rock during emplacement; 3) BFGC magmatism is spatially associated with shearing associated with far-field stresses of the Trans-Hudson orogen; and 4) strongly negative initial Nd1.83Ga (-7.1 to -8.3) and zircon-derived Hf1.83Ga (-8.4 to -10.8) values, which overlap those of basement rocks in the Boothia Peninsula. However, geochemical and isotopic variations within the BFGC granitoid suites suggest their derivation from two main source rocks, a mixed Boothia basement source, comprising 2.56-2.52 Ga Boothia porphyroclastic granites and 2.48 Ga Boothia basement mafic rocks, and a light rare earth element-enriched mafic source rock, not exposed at the surface in Boothia Peninsula but hypothesized to be present at lower crustal depths. I propose that BFGC magmatism was triggered by a partial lithospheric delamination event that occurred across the Churchill Province hinterland during the late stages of the Trans-Hudson orogen. Mantle upwelling associated with this event, along with radiogenic heating associated with crustal thickening in the hinterland, provided the heat required to generate high-temperature magmas within the lower crust and a previously metasomatized sub-continental lithospheric mantle. The generation of LREE-enriched mantle melts and coeval granitic magmatism through lithosphere delamination is also the proposed petrogenesis of ~1.83 Ga ultrapotassic magmas that intruded synchronously with widespread Hudson granite magmatism in the Churchill Province (Peterson et al., 2002; Cousens et al., 2001; Sandeman and Hadlari, 2010). The data obtained in the present study in conjunction with data collected from widespread ca. 1.83 Ga magmatism elsewhere in the Churchill Province implies lithospheric delamination within a collisional orogen has the capacity to produce a 1) ~1400 km extent of synchronous magmatism in the hinterland orogenic plateau, and 2) high-temperature partial melts distal from the orogenic front.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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