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TitleCreating the Canadian Shield and the 'greatest' unconformity: enhanced crustal erosion during Rodinia breakup and snowball earth glaciations
AuthorMcDannell, KORCID logo; Pinet, N; Currie, LORCID logo; O'Sullivan, P; Zeitler, P; Metcalf, J
SourceGSA 2019 - Geological Society of America, Annual Meeting 2019, technical programs; Geological Society of America, Abstracts With Programs vol. 51, no. 5, 79-12, 2019 p. 1, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20190293
PublisherGeological Society of America
MeetingGSA 2019 - Geological Society of America, Annual Meeting; Phoenix, AZ; US; September 22-25, 2019
DocumentWeb site
Mediaon-line; digital
File formathtml; pdf (Adobe® Reader®)
ProvinceAlberta; Manitoba; Newfoundland and Labrador; Northwest Territories; Nunavut; Ontario; Quebec; Saskatchewan
NTS12; 13; 14; 15; 16; 21; 22; 23; 24; 25; 26; 27; 28; 29; 31; 32; 33; 34; 35; 36; 37; 38; 39; 41; 42; 43; 44; 45; 46; 47; 48; 49; 52; 53; 54; 55; 56; 57; 58; 59; 63; 64; 65; 66; 67; 73; 74; 75; 76; 77; 85; 86; 87
Lat/Long WENS-120.0000 -56.0000 84.0000 44.0000
Subjectsgeochronology; Science and Technology; Nature and Environment; geological history; tectonic history; glacial history; thermal history; burial history; depositional history; crustal evolution; erosion; weathering; glaciation; unconformities; radiometric dating; uranium lead dating; argon argon dating; strontium strontium ratios; fission-track dates; bedrock geology; basement geology; modelling; Archean; Canadian Shield; Great Unconformity; Rodinia; Snowball Earth; Laurentia; Genville Province; Phanerozoic; Paleozoic; Cambrian; Precambrian; Proterozoic
ProgramGEM2: Geo-mapping for Energy and Minerals TransGEM
Released2019 09 01
AbstractCentral tenets of the snowball Earth hypothesis are that mantle upwelling and widespread igneous magmatism during equatorial supercontinent breakup led to increased silicate weathering, CO2 consumption, and biosphere feedbacks that drove Neoproterozoic low-latitude glaciation [1-4]. The synchronicity of these events is key to this hypothesis, yet the timing of significant Canadian Shield planation and weathering of Precambrian cratonic rocks remains an important unresolved question. Stratigraphic evidence for Neoproterozoic continental denudation is lacking because Paleozoic sedimentary rocks unconformably overlie Archean basement - a gap of >2 billion years coinciding with the Great Unconformity. New and published apatite U-Pb, 40Ar/39Ar K-feldspar MDD, apatite fission-track, and zircon/apatite (U-Th)/He data from greter than or equal to 1.8 Ga crystalline basement rocks across the Canadian Shield (e.g. W. Superior Province, ON and Baffin Island) constrain temperatures below ~450ºC and collectively address the broad time-temperature range required for constraining significant exhumation over such protracted histories. Modelled thermal histories indicate that parts of the Laurentian interior were at temperatures of ~150-200ºC at ca. 1.1-0.95 Ga due to minor Grenvillian burial [5] and/or residence at crustal depths of up to ~7 km. Cooling ensued ca. 0.90-0.70 Ga, coincident with initial Rodinia breakup. Major cooling and exhumation began after ca. 0.7 Ga and concluded when rocks were at near-surface conditions during Paleozoic platform sedimentation. Our interpretations agree with seawater 87Sr/86Sr compilations [4] that advocate a shift from mantle (hydrothermal/submarine) to continental flux during this time interval. Further support comes from Archean detrital zircons in Cambrian sandstones from the Laurentian rift-margin[6-8] and interior basins[9]. The observed regional cooling signal indicates large-magnitude unroofing that directly opposes inferred long-term cratonic stability and suggests a large area of the Canadian Shield was exhumed in the Neoproterozoic. This supports a model where renewed Neoproterozoic crustal weathering set the conditions for snowball Earth.
References: [1] Hoffman & Schrag 2002; [2] Goddéris et al. 2003; [3] Donnadieu et al. 2004; [4] Cox et al. 2016; [5] Rainbird et al. 1992; [6] Cawood et al. 2007; [7] Matthews et al. 2017; [8] McMechan et al. 2017; [9] Lovell & Bowen 2013
Summary(Plain Language Summary, not published)
Integrated age dates and information about thermal conditions are used as proxies for erosion and burial on the Canadian Shield. These data imply that a large region of Canada was eroded during supercontinent Rodinia breakup in the Neoproterozoic, beginning approximately 750 million years ago. The low-latitude position of Laurentian North America, vertical continental uplift from the mantle during breakup, and the large flux of eroded sediment drove greater carbon dioxide consumption in the atmosphere and set the conditions for snowball Earth and global-scale, large ice sheet glaciation.

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