Geochemical and Sm/Nd Isotopic Characterization of Post-Tectonic Granitoids of Boothia Peninsula, NU: Implications for the Extent of the Hudson GranitesWednesday, November 21, 2018 - 10:00 to 10:19 Theatre 1
Bedrock mapping on Boothia Peninsula in 2017 as part of Natural Resource Canada’s GEM-2 program, has revealed extensive 2.50-2.56 Ga tonalite-granodiorite to garnet monzogranite basement rocks, which are interfolded with widespread granulite-facies metasedimentary rocks. In southeast Boothia Peninsula, these metasedimentary rocks are cut by 1.84 -1.82 Ga weakly foliated to massive biotite-orthopyroxene monzogranite (charnockite) and hornblende-biotite quartz syenite to syenogranite. Although the weak fabric in this younger granitoid suite coincides with the general SW-striking regional fabric seen in eastern Boothia Peninsula, the low degree of strain implies late-stage emplacement with respect to regional deformation.
The 1.84-1.82 Ga granitoids have an A- and I-type major-element composition, which is dominantly ferroan with variable SiO2 (55 – 78%). The trace-element discrimination diagrams classify these rocks as transitional between within-plate and collisional granites. LREEs, however, are more enriched in the syenogranites compared to the charnockites. This difference combined with a larger negative Eu anomaly suggests the syenogranites are more evolved than the charnockites. We have investigated the Sm/Nd isotopic compositions of both suites on Boothia Peninsula to access the degree of interaction with Archean crust, therefore furthering our understanding of the granitoids origin and tectonic setting.
The ɛNd1.83 Ga values (-7.0 to -8.0) obtained for 1.84-1.82 Ga granitoid rocks of Boothia Peninsula suggest two distinct crustal sources in their genesis: the hornblende-biotite syenogranite suite (ɛNd1.83 Ga = -7.0 to -7.1, tDM = ~ 2.5-2.6 Ga) and the charnockite suite (ɛNd1.83 Ga = -7.3 to -8.0, tDM = ~ 2.8 Ga). The Nd data for the charnockite suite can be explained by partial melting of late Mesoarchean to early Neoarchean basement rocks, which is typical of Rae craton. The less negative ɛNd1.83 Ga values and younger model ages of the syenogranite suite suggest either derivation from a comparatively younger late Neoarchean crustal source or is a result of contributions from both typical Rae Basement and a slightly more juvenile source.
Geochemically, the 1.84-1.82 Ga granitoids on Boothia Peninsula are broadly comparable to other 1.85-1.80 Ga post-tectonic granites, the Hudson suite, which are widespread across the mainland Rae and Hearne cratons. Elsewhere in the Rae craton, this 1.85-1.80 Ga magmatism has been linked to Au/Cu base metal and uranium mineralization1. If correlative, the 1.82-1.84 Ga granitoids of Boothia Peninsula would mark the northernmost occurrence of Hudson granitoids, highlighting a distribution over nearly 1000 km. Revealing the extent of the Hudson granites may have larger implications for understanding the tectonic settings behind the extensive reworking of Rae and Hearne Cratons during the Paleoproterozoic.
LeCheminant, A. N., Miller, A. R., LeCheminant, G. M. 1987. In Geochemistry and Mineralization of Proterozoic Volcanic Suites, 33: 219-240