New Age Constraints on Crust Formation, Provenance and Timing of Sedimentation, Boothia Peninsula-Somerset Island, Nunavut, Canada.Wednesday, November 21, 2018 - 09:40 to 09:59 Theatre 1
One of the major geological features of the Canadian Arctic is the ‘Boothia Uplift’, an outlier of Precambrian basement exposed for > 900 km from Taloyoak to northwestern Somerset Island. This under-explored frontier region was last mapped in 1962 (Blackadar, 1967, GSC Bulletin 151) and 1986-1992 (Frisch, 2011, OF 6051, https://doi.org/10.4095/287896). In order to improve the geoscience knowledge base of this region and assess its mineral potential, detailed bedrock mapping supported by new high-resolution aeromagnetic data was conducted in 2017 and 2018 as part of the Geomapping for Energy and Minerals (GEM2) program.
Preliminary results reveal that the oldest basement rocks of Boothia Peninsula are voluminous upper-amphibolite to granulite-facies biotite-garnet K-feldspar porphyroclastic quartz monzonite, and lesser tonalite-trondjhemite gneiss with crystallization ages of ca. 2.56 Ga and 2.53 Ga, respectively.
Metasedimentary rocks across Boothia Peninsula yield detrital zircon that indicate the presence of at least two distinct clastic sequences. Widespread garnet-sillimanite semipelite to inhomogeneous diatexite have a maximum depositional age of ca. 2.50 Ga (Sequence I) with a prominent mode at ca. 2.52 Ga and lack detrital zircon older than 2.55 Ga. Lesser garnet-bearing psammite, quartzite and marble, exposed on northwestern Boothia Peninsula, have a maximum depositional age of ca. 1.95 Ga (Sequence II) with prominent modes at 1.963 Ga, 1.975 Ga, and 1.992 Ga with a minor mode at ca. 2.50 Ga, and no detritus older than 2.53 Ga. The detrital zircon U-Pb data suggest Boothia basement rocks are a likely source for Sequence I, while a prominent source for Sequence II appears to be the Thelon magmatic arc, which, according to the aeromagnetic data, may be 200km west of Boothia Peninsula.
Sequence I is cut by a voluminous intermediate to mafic plutonic suite dominated by diorite and quartz diorite with crystallization ages of ca. 2.49-2.48 Ga, establishing a minimum depositional age for this sedimentary package.
Fieldwork in 2018 on Somerset Island revealed that high-grade tonalitic to granodioritic rocks, associated with minor diorite, are more abundant than supracrustal rocks, the latter comprising clastic rocks often associated with tectonically thinned metacarbonate. It is not yet known if the clastic sequence associated with metacarbonate rocks on Somerset Island is correlative with Sequence I or Sequence II.
In summary, the new results indicate that (i) felsic and intermediate plutonic basement rocks of Boothia-Somerset formed between 2.56-2.48 Ga, a period that historically is not represented in Rae craton evolution; (ii) Neoarchean-Early Paleoproterozoic clastic Sequence I is not sourced from 2.6-2.97 Ga crust of the Rae craton, and (iii) Thelon magmatic arc rocks are not exposed on Boothia Peninsula, as previously suggested, but may constitute Sequence II clastics. Collectively, GEM2 data are revealing an absence of rocks typical of Rae craton throughout the Boothia-Somerset region, suggesting the “Boothia uplift” may be an exotic terrane accreted to the Rae, or a ca. 2.56-2.48 Ga magmatic arc complex built on thinned Rae crust. It also reveals that mineral exploration strategies for Rae craton may not be applicable to the Boothia-Somerset region.