Titus, J.P., 2020, Geologic mapping and detrital zircon U-Pb geochronology of the Ernie Lake area of central Brooks Range in Alaska: Implications for Pre-Mississippian basement and Brooks Range architecture: University of Floria, M.S. thesis, 113 p.
The Brooks Range in northern Alaska was formed as a result of Cretatceous arc-continent collisions that formed the northwestern part of the North American Cordillera. The Ernie Lake region lies in the Central Belt (Hammond subterrane) of the Brooks Range (Till et al., 2008), one of two complexly deformed metamorphic belts in the southern Brooks Range metamorphic core. Previous mapping of the area at a scale of 1:250,000 suggested the possible presence of a sub-Mississippian unconformity, which has important implications for the architecture of the Cretaceous orogen. Furthermore, the presence of a previously dated ca. 970 Ma orthogneiss suggests that the study area exposes the oldest rock sin the metamorphic core. Therefore, the Ernie Lake area presents a unique opportunity to study "basement" rocks that can be compared to other circum-Arctic terranes to provide improved constraints on pooly understood pre-Cretaceous tectonic evolution of the Arctic. To address these issues I dated an additional orthogneiss body using U-Pb geochronology and performed U-Pb detrital zircon geochronology on metasedimentary units that were tied to mapping at a scale of 1:34,000. Four samples of the Ernie Lake granite (ELG) yield crystallization ages between 621 Ma ± 2 and 644 Ma ± 2. Although in close proximity to the previously dated ca. 970 Ma orthogneiss 12 body, the new data suggest that there are two distinct Neoproterozoic magmatic events in the area. The new ages suggest ties to southwestern Svalbard, suggesting the pre-Devonian rocks of the Ernie Lake region formed near rocks presently exposed on Svalbard and northern Ellesmere Island. Detrital zircon geochronology yielded two distinct groupings on age populations. Five samples below the proposed Mississippian rocks yield age populations dominated by peaks between ~1.0 and 1.9 Ga with or without a grouping around 900 ? 920 Ma. Samples from possible Mississippian rocks yielded dominantly Late Ordovician to Middle Devonian age populations, with maximum depositional ages of ~360 Ma in some samples. The detrital ages are consistent with a major sub-Mississippian unconformity.
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