Linkages between the Neoproterozoic Natkusiak basalts and Franklin sills on Victoria Island, Arctic Canada

Charles D Beard1,2, Dominique Weis3, Jean H J Bedard4, James S Scoates2 and Trent A Dell'Oro2, (1)McGill University, Earth & Planetary Sciences, Montreal, QC, Canada, (2)University of British Columbia, Vancouver, BC, Canada, (3)University of British Columbia, PCIGR, Earth, Ocean and Atmospheric Sciences, Vancouver, BC, Canada, (4)Geological Survey of Canada, Quebec, QC, Canada

Contact First Author: Charles D Beard; charles.beard@mail.mcgill.ca

Previously Published Material: Yes, these data were partially presented by J. Bédard at Goldschmidt 2012, also in Montréal. The interpretations have been refined and revised since this date. A manuscript has been prepared from these data, which will be submitted to Journal of Petrology before the end of January 2015.

Abstract ID#: 36218

 

English Abstract:
The 724–716 Ma Franklin Large Igneous Province extends >2500 km from Siberia to Greenland and is associated with break-up of Rodinia. On Victoria Island, the Natkusiak flood basalts cap the carbonate-dominated Shaler Supergroup (also with shale, sandstone and sulphate evaporite), which hosts the coeval Franklin sills. The basal Natkusiak basalt unit (50–100 m) is dominated by discontinuous flows and volcaniclastic rocks, and is overlain by voluminous sheet flow basalts (up to 800 m preserved thickness). The layered Type 1 sills have similar chemistry to the basal basalts, whilst the diabasic Type 2 sills resemble the sheet flow basalts. The former are restricted to deeper parts of the intrusive plumbing system.

Weak continental geochemical signatures, such as negative Nb–Ta anomalies, are ubiquitous in the intrusions and basalts, indicating that the Franklin magmas were pervasively, albeit subtly, contaminated during transit through the lithosphere. The basal basalt unit and Type 1 sills are the most contaminated with the lowest initial εNd and εHf (-6 to +8; -4 to +5). Basal and sheet flow basalt units define separate trends in trace element plots and cannot be related by closed or open system fractional crystallisation or variable degrees of melting of a single mantle source.

The initial εNd and εHf of the northernmost Natkusiak basalts (-6 to +5; -4 to +16) are positively correlated along the OIB mantle array, whereas rocks from three southern volcanic sections are displaced toward more radiogenic Nd compositions (εNd +4 to +12). The isotopic compositions of the Franklin sills exposed in the Minto Inlier correlate with the northern section basalts. The radiogenic Nd signature of the southern basalts is consistent with source contributions from old oceanic crust. We attribute this geographical control on melt composition to a long-lived heterogeneity in the Neoproterozoic mantle source(s) that was preserved in the basalts by a compartmentalized plumbing system.

Back to: Chemical Scene Investigations of Large Igneous Provinces (CSI-LIPs) I