Architecture of subduction zone magma reservoirs and origin of primitive arc magmatism:
Petrochronology and geochemistry of the Polaris Alaskan-type ultramafic-mafic intrusion
Magmatism at subduction zones has contributed significantly to the growth of continental crust throughout geologic time. Ore deposits in convergent margins of nickel-copper-platinum group elements (Ni-Cu-PGE) in ultramafic-mafic intrusions, rocks dominated by olivine-pyroxene-hornblende that crystallized from mantle-derived magmas, are gaining global importance as an economic resource, yet remain poorly understood and underexplored (Manor et al., 2016, 2017; Nixon et al., 2015). The Polaris complex exhibits many of the features typical to Ural-Alaskan-type ultramafic-mafic intrusions and is one of the best exposed (mostly alpine) ultramafic-mafic bodies in the Canadian Cordillera, second in size only to the Tulameen complex. The North American Cordillera hosts a considerable number of zoned ultramafic-mafic bodies (e.g., Duke Island, Tulameen, Giant Mascot), variably endowed in Ni-Cu-PGE mineralization, that are interpreted to represent the frozen magmatic conduits of Mg-rich arc lavas. Contributing to the understanding of arc-related magmatic conduit systems is paramount to filling knowledge gaps which currently exist regarding the origin of the zoning and timing of mineralization within the chronology of intrusion assembly and overall relationship to the life cycle of a subduction zone.
In collaboration with the British Columbia Geological Survey (BCGS), this project combines extensive detailed field mapping and sample collection to gain observational and analytical constraints in the development of emplacement mechanism models utilizing geochronometry and geothermometry as basis for model development. Current research at UBC, following established high-precision analytical workflows at the Pacific Centre for Isotopic and Geochemical Research (PCIGR), involves trace element geochemistry and U-Pb geochronology of zircon to constrain petrological processes and to develop a spatio-temporal (4D) emplacement framework for the Polaris intrusion as an arc magmatic conduit system. With the geochronological framework in place, mineral (olivine, clinopyroxene, hornblende) and whole rock geochemistry, including Pb-Sr-Nd-Hf radiogenic isotopes, will be investigated to evaluate variations in source components, parent magma(s) compositions, and differentiation processes with respect to time. These results will aid in evaluation of primitive arc magmatism and the role of mid-crustal magmatic systems through comparison with lesser exposed intrusions throughout the North American Cordillera (Alaska to California) and globally (e.g. Urals). As the age of the Early Jurassic Polaris intrusion coincides with the initial stages of breakup of the Pangea supercontinent and the concurrent initiation of terrain accretion in the Cordillera, this research will contribute to our understanding of Cordilleran tectonics and subduction zone magmatism.
- PhD (candidate) in Geological Sciences: University of British Columbia. Supervisors: Drs. James Scoates; 2019-present
- B.Sc. Geology, Environmental Science Dalhousie University; 2010 - 2015
- B.Sc. Earth Science, Environmental Science (Visiting), University of Victoria; Sept 2013 – Apr 2014
- Culinary Management/Chef Apprentice Basic & Advanced, Confederation College; 2003 - 2005
- NSERC PGS-D (2021)
- NSERC CGS-M (2019)
- Dalhousie University Faculty of Science Dean’s list (2010-2014)
- Dalhousie University Earth Science Department Undergrad Scholarship (2012)
Confederation College First Class Standing (2003-2005)
Nott, J.A., Scoates, J.S., Milidragovic, D., Nixon, G.T., Spence, D.W., 2022d. Primitive arc magma conduits from the zircon petrochronology perspective in the Polaris Alaskan-type intrusion, North American Cordillera. 2022 Goldschmidt Conference.
Spence, D.W., Scoates, J.S., Nott, J.A., Milidragovic, D., Nixon, G.T., 2022c. Olivine in primitive arc magmas from the Polaris Alaskan-type intrusion in the North American Cordillera. 2022 Goldschmidt Conference.
Nott, J.A., Scoates, J.S., Milidragovic, D., Nixon, G.T., 2022b. Petrochronological investigation of the Early Jurassic Polaris ultramafic-mafic Alaskan-type intrusion, north-central British Columbia. Association for Mineral Exploration (AME) Roundup, Vancouver, BC, Jan. 31 – Feb 3, 2022.
Spence, D. W., Crawford, H., Scoates, J. S., Nott, J. A., & Nixon, G. T., 2022a. Mapping ultramafic cumulates at the Tulameen ultramafic-mafic Alaskan-type intrusion, south-central British Columbia, aided by remotely piloted aircraft system photogrammetry. Geological Fieldwork 2021, British Columbia Ministry Of Energy, Mines and Low Carbon Innovation, British Columbia Geological Survey Paper 2022-01, 103–122.
Milidragovic, D., Nixon, G.T., Scoates, J.S., Nott, J.A., Spence, D.W., 2021. Redox-controlled chalcophile element geochemistry of the Polaris Alaskan-type mafic-ultramafic complex, British Columbia, Canada. The Canadian Mineralogist, 59(6), 1627–1660. https://doi.org/10.3749/canmin.2100006
Nixon, G. T., Scoates, J. S., Milidragovic, D., Nott, J., Moerhuis, N., Ver Hoeve, T., J, Manor, M. J., Kjarsgaard, I., & M., 2020. Convergent margin Ni-Cu-PGE-Cr ore systems: U-Pb petrochronology and environments of Cu-PGE versus Cr-PGE mineralization in Alaskan-type intrusions. In Targeted Geoscience Initiative 5: Advances in the Onderstanding of Canadian Ni-Cu-PGE and Cr ore Systems (ed.) W. Blee (Vol. 8722). https://doi.org/10.4095/326897
Nott, J.A., Milidragovic, D., Nixon, G.T., Scoates, J.S., 2020b. Geology of the Polaris Alaskan-type ultramafic-mafic intrusion, north-central British Columbia. British Columbia Ministry of Energy, Mines and Petroleum Resources, British Columbia Geological Survey Open File 2020-04, 1:15,000 scale.
Nott, J., Milidragovic, D., Nixon, G.T., and Scoates, J.S., 2020a. New geological investigations of the Early Jurassic Polaris ultramafic-mafic Alaskan-type intrusion, north-central British Columbia. In: Geological Fieldwork 2019, British Columbia Ministry of Energy, Mines and Petroleum Resources, British Columbia Geological Survey Paper 2020-01, pp. 59-76.