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Tectonic Growth of the Late Paleozoic‐Middle Mesozoic Northwestern Margin of Laurentia and Implications for the Farewell Terrane: Stratigraphic, Structural, and Provenance Records From the Central Alaska Range

B. Keough,K. Ridgway

Published 2021 in Tectonics

ABSTRACT

Analysis of upper Paleozoic‐Jurassic strata in the central Alaska Range provides new insights into the following: the configuration of Late Triassic‐Jurassic depocenters along the northwestern Laurentian margin, the late Paleozoic paleogeographic position of the Farewell terrane, and the timing of accretion of the Farewell terrane to the Laurentian margin. Results from geologic mapping, stratigraphic analysis, and U‐Pb detrital zircon geochronology document two juxtaposed Paleozoic‐Jurassic stratigraphic assemblages. The Southern package consists of Permian‐Middle Triassic submarine fan strata and Upper Triassic pillow basalts that can be correlated with the Farewell terrane of the western Alaska Range. This package yields Ordovician‐Silurian and Late Pennsylvanian‐Early Permian detrital zircons linked to the Alexander and Wrangellia terranes. This detrital connection suggests that the Farewell terrane most likely collided with the Insular terranes in the paleo‐Pacific basin during the late Paleozoic. The Northern package, in contrast, consists of Upper Triassic‐Jurassic submarine fan strata deposited along the northwestern margin of Laurentia. An abundance of Neoproterozoic and early Paleozoic detrital zircons suggests recycling of Caledonian and Baltican zircons from the Ellesmerian clastic wedge of northwestern Canada. An influx of Late Triassic‐Early Jurassic detrital zircons in Upper Jurassic strata of the Northern package records the development of Mesozoic arc magmatism along the continental margin. Our findings document deformation consistent with latest Jurassic‐earliest Cretaceous accretion of the Farewell terrane to the Laurentian margin. Our results also suggest that the Farewell terrane may underlie much of the central Alaska Range, and played an important role in the construction of the northern Cordillera.

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