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TitleNumerical constraints on degassing of metamorphic CO2 during the Neoproterozoic Franklin large igneous event, Arctic Canada
AuthorNabelek, P I; Bédard, J H; Rainbird, R HORCID logo
SourceGeological Society of America Bulletin vol. 126, no. 3-4, 2014 p. 759-772,
Alt SeriesEarth Sciences Sector, Contribution Series 20130487
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf
ProvinceNorthwest Territories
NTS77G; 77H; 78A; 78B; 87G; 87H; 88A; 88B
AreaVictoria Island; Minto Inlet
Lat/Long WENS-120.0000 -107.0000 73.0000 71.0000
Subjectsmathematical and computational geology; igneous and metamorphic petrology; carbon dioxide; metamorphism; metamorphism, contact; pressure; pore pressures; porosity; permeability
Illustrationslocation maps; plots
ProgramGEM: Geo-mapping for Energy and Minerals PGE/Base Metals - Victoria Island (NWT and Nunavut)
Released2014 03 06
AbstractGabbroic sills of the widespread, ca. 720 Ma Franklin large igneous event intruded sedimentary strata of the Neoproterozoic Shaler Supergroup exposed in the Minto Inlier on Victoria Island in the western Arctic. The mafic magmatism occurred during breakup of the supercontinent Rodinia and preceded Sturtian glaciation. Calc-silicate metamorphic reactions produced CO2 from decameter-scale contact aureoles in carbonate rocks containing variable amounts of silicates. Numerical modeling of the reactions and fluid flow was done for host-rock permeabilities (k) ranging from 10-18 to 10-14 m2. Metamorphic assemblages and aureoles widths are best reproduced with k between 10-18 and 10-17 m2; however, the lower k produces much broader fracture zones next to the sills than those observed in the field. When k ? 10-16 m2, the contribution of advective heat transport produces aureoles that are too thick. With k = 10-17 m2, the contribution of CO2 to the atmosphere from the aureole of one 50-m-thick sill with an area of 50,000 km2 would have been only 8 ppm (by weight) during the 600 yr metamorphic episode. The sedimentary basin would have to have been more permeable for a higher flux of metamorphic CO2 to the atmosphere. The results demonstrate that host-rock permeability must be considered before changes in the budgets of atmospheric carbonic gases can be attributed to metamorphic degassing from sedimentary basins.
Summary(Plain Language Summary, not published)
The effect of a basaltic intrusion on limestone country rocks was investigated. Modeling implies that the low permeability of most calcareous host rocks prevents significant degassing of CO2, despite the large volume of intruded basalt, and so is unlikely to have significantly perturbed the Proterozoic climate.

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