Baltican crustal provenance for Cambrian–Ordovician sandstones of the Alexander terrane, North American Cordillera: evidence from detrital zircon U–Pb geochronology and Hf isotope geochemistry

Abstract

Detrital zircon U–Pb geochronology and Hf isotope geochemistry allow us to decipher the crustal provenance of Cambrian–Ordovician backarc basin strata of the Alexander terrane, North American Cordillera, and evaluate models for its origin and displacement history relative to Baltica, Gondwana, Siberia, and Laurentia. Quartzose shallow-marine sandstones of the Alexander terrane contain a range of Neoproterozoic to Neoarchaean detrital zircons with the most dominant age groupings c . 565–760, 1000–1250, 1450, and 1650 Ma. Subordinate volcaniclastic sandstones yield Cambrian and Ordovician detrital zircons with a prominent age peak at 477 Ma. The detrital zircon age signatures resemble coeval strata in the Eurasian high Arctic, and in combination with faunal and palaeomagnetic constraints suggest provenance from local magmatic rocks and the Timanide orogenic belt and Fennoscandian Shield of NE Baltica. The Hf isotopic compositions of Palaeozoic to Neoarchaean detrital zircons strongly favour Baltican crustal sources instead of similar-aged domains of Gondwana. The Alexander terrane formed part of an arc system that fringed the Uralian passive margin, and its position in the Uralian Seaway allowed faunal exchange between the Siberian and Baltican platforms. The available evidence suggests that the Alexander terrane originated in the Northern Hemisphere and migrated to the palaeo-Pacific Ocean by travelling around northern Laurentia. Supplementary material: U–Pb and Lu–Hf data tables are available at www.geolsoc.org.uk/SUP18557 .

Neoproterozoic–early Paleozoic provenance evolution of sedimentary rocks in and adjacent to the Farewell terrane (interior Alaska)

“…Detrital zircon data provide useful information that bears on terrane definitions and aids in interpreting terrane associations and histories within the complex tectonic collage of Alaska. Our data suggest modifications to previously proposed paleogeographic positions of the Farewell terrane (Colpron and Nelson, 2011;Beranek et al, 2013a) during the early Paleozoic.…”

“…Recently published detrital zircon data from the Alexander terrane ( Figs. 16A-16G; Beranek et al, 2013aBeranek et al, , 2013bTochilin et al, 2014;White et al, 2015) show similarities and differences with data from the Farewell terrane. Quartzose sandstones from the upper Cambrian-Middle Ordovician Donjek assemblage (northern Alexander terrane) yielded predominant age populations ranging from 760 to 565 Ma ( Fig.…”

“…Quartzose sandstones from the upper Cambrian-Middle Ordovician Donjek assemblage (northern Alexander terrane) yielded predominant age populations ranging from 760 to 565 Ma ( Fig. 16G; Beranek et al, 2013a), which overlap ages of the Neoproterozoic detrital zircon components in our Lone and Windy Fork Formation samples, but also contain more Mesoproterozoic grains . Statistical comparison of the Donjek quartzose sandstones and the Lone Formation produces a PDP cross-correlation coefficient of 0.58 (Table S3 [footnote 1]; Saylor and Sundell, 2016), suggesting that they are fairly similar.…”

“…16F; Beranek et al, 2013a). The peak age is slightly younger than the major peaks in the Post River Formation and Livengood Dome Chert samples (Figs.…”

“…The few speculative reconstructions that include displaced Arctic terranes discussed herein typically show the Farewell terrane more closely associated with Siberia through much of the Paleozoic (Colpron and Nelson, 2011;Beranek et al, 2013a). The Arctic Alaska-Chukotka and Alexander terranes are more commonly shown in association with the Timanide orogen, a late Neoproterozoic belt that formed along the eastern margin of Baltica (e.g., Gee and Pease, 2004;Amato et al, 2009;Beranek et al, 2013a;Ayuso and Till, 2014;Till et al, 2014a).…”