James Nott

Petrochronology and emplacement framework of the Polaris ultramafic-mafic Alaskan-type intrusion, north-central British Columbia.

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 will combine 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. Following established high-precision analytical workflows at PCIGR, LA-ICP-MS will be conducted to acquire geochronological and geochemical data via radiogenic systematics, trace elements, and Ti-in-Zircon and Zr-in-Titanite thermometry. Select samples may then be selected for CA-TIMS analysis to efficiently constrain emplacement chronology.