Detrital zircon geochronology and Hf isotope geochemistry of Mesozoic sedimentary basins in south-central Alaska: Insights into regional sediment transport, basin development, and tectonics along the NW Cordilleran margin

Abstract

The Jurassic–Cretaceous Nutzotin, Wrangell Mountains, and Wellesly basins provide an archive of subduction and collisional processes along the southern Alaska convergent margin. This study presents U-Pb ages from each of the three basins, and Hf isotope compositions of detrital zircons from the Nutzotin and Wellesly basins. U-Pb detrital zircon ages from the Upper Jurassic–Lower Cretaceous Nutzotin Mountains sequence in the Nutzotin basin have unimodal populations between 155 and 133 Ma and primarily juvenile Hf isotope compositions. Detrital zircon ages from the Wrangell Mountains basin document unimodal peak ages between 159 and 152 Ma in Upper Jurassic–Lower Cretaceous strata and multimodal peak ages between 196 and 76 Ma for Upper Cretaceous strata. Detrital zircon ages from the Wellesly basin display multimodal peak ages between 216 and 124 Ma and juvenile to evolved Hf compositions. Detrital zircon data from the Wellesly basin are inconsistent with a previous interpretation that suggested the Wellesly and Nutzotin basins are proximal-to-distal equivalents. Our results suggest that Wellesly basin strata are more akin to the Kahiltna basin, which requires that these basins may have been offset ~380 km along the Denali fault. Our findings from the Wrangell Mountains and Nutzotin basins are consistent with previous stratigraphic interpretations that suggest the two basins formed as a connected retroarc basin system. Integration of our data with previously published data documents a strong provenance and temporal link between depocenters along the southern Alaska convergent margin. Results of our study also have implications for the ongoing discussion concerning the polarity of subduction along the Mesozoic margin of western North America.

Geochemical and Stratigraphic Analysis of the Chisana Formation, Wrangellia Terrane, Eastern Alaska: Insights Into Early Cretaceous Magmatism and Tectonics Along the Northern Cordilleran Margin

“…Furthermore, thick successions of siliciclastic strata occur south of the Chisana Formation in the Wrangell Mountains basin and are interpreted to have been deposited in a forearc basin positioned outboard of the Chisana arc (Plafker & Berg, 1994; Trop et al, 2002). The Chisana arc was a major sediment source to this basin during late Early to early Late Cretaceous time judging from compositional and detrital geochronological data (Trop et al, 2002; Fasulo, 2019; Fasulo et al, 2020). The presence of these forearc deposits, together with coeval subduction complex deposits to the south in the Chugach terrane (Amato et al, 2013), are consistent with models that attribute Chisana magmatism to island arc‐formation above an east dipping subduction zone (Figures 10a and 10c–10e).…”

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

“…Since there is no known evidence that the Farewell terrane and Insular superterrane accreted to the Laurentian margin together, our model requires that the Farewell terrane rifted away from the Insular superterrane following their assembly. This event can be inferred to have occurred prior to the Middle Jurassic, when the Insular superterrane (Wrangellia composite terrane) began to collide obliquely with the continental margin in what is now British Columbia, followed by diachronous northward closure of an intervening ocean basin during the Cretaceous (e.g., Beranek et al., 2017; Box et al., 2019; Fasulo et al., 2020; Hampton et al., 2010; McClelland et al., 1992; Ridgway et al., 2002; Romero et al., 2020; Stevens Goddard et al., 2018; Trop et al., 2002, 2005). In the central and western Alaska Range, Upper Triassic‐Lower Jurassic strata of the Farewell terrane (Mystic subterrane) comprise thick sections of pillow basalts and volcanic flows interbedded with minor marine siliciclastic strata (Figure 5f; e.g., Bundtzen et al., 1997; Dumoulin, Jones, Box, et al., 2018).…”

Detrital zircon geochronology of modern river sediment in south-central Alaska: Provenance, magmatic, and tectonic insights into the Mesozoic and Cenozoic development of the southern Alaska convergent margin

“…2). Both of these potential sources contain significant populations of Late Jurassic to Early Cretaceous detrital zircons (e.g., Amato et al, 2013;Day et al, 2016;Fasulo et al, 2020). Early Cretaceous plutons that may have contributed 132-117 Ma detrital zircons in the Copper River watershed have not been documented, aside from sparse Cretaceous-aged plutons that have been mapped in the eastern Alaska Range (e.g., Wilson et al, 2015).…”

“…The source(s) for Early Cretaceous detrital zircons from samples farther downstream are most likely recycled from metasedimentary and sedimentary strata of the Chugach accretionary prism and Wrangell Mountains basin (Fig. 2); both contain similar aged detrital zircons (e.g., Amato et al, 2013;Fasulo et al, 2020). Similar to Early Cretaceous plutons, mid-Cretaceous plutons are also lacking in the Copper River watershed (Fig.…”