On the archean geologic history of eastern Hall Peninsula, Baffin Island, Nunavut, Canada
From, Richard Eric
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Eastern Hall Peninsula on southeastern Baffin Island, lies at the junction of a complex Paleoproterozoic collision between the Rae craton, Meta Incognita microcontinent and the North Atlantic craton from ca. 1.88 to 1.80 Ga. The original configuration of these cratons is not well understood because eastern Hall Peninsula, which lies at the triple junction between these plates, lacks detailed geoscience mapping and geochemical data. Consequently, detailed mapping was conducted in eastern Hall Peninsula and zircons separated from selected samples were analyzed for U-Pb and Lu- Hf isotopes. Magmatic zircons yielded U-Pb crystallization ages between ca. 2976 to 2720 Ma and metamorphic zircons record tectonothermal disturbances between ca. 2740 to 2700 Ma, a period coinciding with metamorphism documented in adjacent crustal blocks. Magmatic rocks older than ca. 2740 Ma yielded positive εHf(t) and consistent model ages of ca. 3.1 to 3.0 Ga, indicating the time that protolith melt was extracted from the mantle. The oldest, granodioritic crust crystallized at ca. 2976 Ma and was then reworked periodically at ca. 2.93, 2.84-2.81 and 2.77-2.69 Ma, forming other rock units. Two rock units younger than ca. 2740 Ma yielded negative εHf(t) model ages of ca. 3.4 and 3.3 Ga respectively, indicating derivation from an older crustal source yet to be identified in outcrop on Hall Peninsula. Zircons from a suite of relatively undeformed magnetite-bearing granites yielded UPb magmatic ages between ca. 2750 to 2612 Ma. Sm-Nd data from these granites outline a spatial trend across eastern Hall Peninsula with negative εNd(t) in the west becoming more positive εNd(t) to the east. This trend outlines an increase of crustal reworking and recycling in the west compared with more mantle-derived, juvenile crust towards the east, delineating a boundary between Paleoproterozoic rocks of Meta Incognita microcontinent and Archean rocks of eastern Hall Peninsula. Synthesizing all data we propose a new regional correlation model that incorporates previous models and other recent studies. This new model groups eastern Hall Peninsula, southern Cumberland Peninsula and southern Aasiaat domain into a “core zone” that shared a geologic history prior to 1.90 Ga and potentially prior to 2.75 Ga.