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Assembly and breakup of Earth's first supercontinent Nuna


Conférence de Mme Sally Pehrsson, chercheure scientifique à la Commission géologique du Canada Assembly and breakup of Earth's first supercontinent Nuna: its impact on formation and preservation of Paleo-Mesoproterozoic mineral deposits

The early Proterozoic is marked by confluence of two major geodynamic events: oxygenation of the atmosphere and assembly of Earth‟s first true supercontinent, Nuna. This confluence profoundly influenced the formation and preservation of world-class metallotects associated with distinct phases of Nuna’s evolution: 1) TransHudsonian VMS; Homestake, Tanami and Pine Creek Gold; Circum-Superior- Baltic Ni-Cu-PGE associated with assembly; 2) Athabasca-Kombolgie unconformity-hosted U associated with stability and 3) BrokenHill, Mt Isa and Sullivan Pb-Zn and Olympic Dam IOCG associated with protracted break-up. New appropriately scaled reconstructions of Nuna can now be used to evaluate the influence of supercontinent formation on its contained mineral endowment.


Nuna was formed by closure of the Manikewan ocean between 2.1 and 1.8 Ga, during which nine Archean cratons and eight ribbon microcontinents were amalgamated along with seven newly assembled cratonic blocks. Orogens and contraction-related ore deposits (VHMS and orogenic lode gold) of Nuna show a lateral age progression reflecting diachronous closure of the Manikewan interior ocean and related seas. Magmatic nickel deposits formed in diverse, broadly back-arc settings immediately following early periods of accretion. Younger 1.7-1.6 Ga VMS (Jerome-Bagdad) formed above or inboard of a subduction zone on Nuna‟s periphery that initiated following termination of assembly-related convergence. Unconformity-U deposits contemporaneously formed in intracontinental basins that underwent alternating transpressive tectonism and subsidence linked to changes in coupling of this long-lived peripheral orogen. A major triple junction between Siberia-Laurentia-Proto-Australia rifted ca. 1.67-1.4 Ga, forming basins (Broken Hill) and a seaway (Sullivan) that hosted major Pb-Zn districts. Its failed northern arm preserved the greater Laurentia configuration, influencing subsequent Rodinia paleogeography.


The difference in assembly between Nuna (introversion) and Rodinia (extroversion) profoundly influenced the character of bounding orogens and their metallogeny and may partially explain the underwhelming mineral endowment of the later, even when scaled for its presently preserved deeper crustal level. Introversion with its younger oceanic lithosphere, abundant pericratonic arcs and minimal subduction erosion allowed rapid obduction, trapping newly formed submarine VMS deposits before they could be consumed. Extroversion with its subduction of older oceanic lithosphere and often strong subduction erosion doomed Rodinia‟s VMS endowment. With nearly double the number of assembled plates and cratons than Rodinia, Nuna preserves a distinctly Archeanesque series of contraction-related metallotects. Importantly the switch to peripheral orogenesis late in Nuna‟s history favoured formation of IOCG and unconformity U metallotects where older ‟introverted‟accretionary structures were intruded, crosslapped or reactivated and ultimately preserved.



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