Precambrian U–Pb ages of igneous rocks, Wrangel Complex, Wrangel Island, USSR

Abstract

Proterozoic rocks exposed in an anticlinorium at the centre of Wrangel Island are among some of the few exposures of Precambrian strata around Canada Basin. U–Pb zircon dating of samples collected during joint Canadian–Soviet fieldwork on the island has provided crystallization ages of [Formula: see text] on a volcanic rock, 699 ± 2 Ma on a porphyritic granite sill, and a very imprecise age of ca. 0.7 Ga on a small leucogranite. Broadly similar 600–750 Ma, mostly metamorphic, ages are known from both the Arctic Alaska and northern Chukotkan parts of what is called the Arctic Alaska – Chukotka Ancestral Plate, supporting the hypothesis that they were once a single entity. By contrast, potential Late Proterozoic equivalents in the Canadian Arctic Islands include a deeply buried and relatively undeformed seismically defined succession of hypothesized Late Proterozoic age, now at greenschist-facies metamorphic grade, and the unmetamorphosed 725 Ma Franklin mafic sills, dykes, and volcanic rocks. The differences in metamorphic and igneous ages between the Arctic Alaska–Chukotka Ancestral Plate and the Canadian Arctic Islands suggest that these two areas have fundamentally different Precambrian rocks. If so, this challenges the fundamental assumption of most paleogeographic models of the pre-Canada Basin Arctic that the two areas once formed a single continuous plate. Earlier K–Ar dates together with major unconformities in Phanerozoic successions on Wrangel Island suggest early Paleozoic orogenic events.

The Grenville–Sveconorwegian orogen in the high Arctic

“…Cecile et al . (1991) obtained U–Pb dates on tectonized granites of c . 700 Ma, and on an acid subvolcanic porphyry of c .…”

Bioapatite 87Sr/86Sr of the last woolly mammoths—Implications for the isolation of Wrangel Island

“…They are felsic to intermediate volcanic and clastic strata, intruded by several mafi c and felsic bodies (Kos'ko et al, 1993). The crystallization of these bodies has been U-Pb dated to 630-700 Ma (Cecile et al, 1991). The Wrangel Complex is surrounded by Silurian-Triassic clastic and carbonate rocks.…”

Neoproterozoic basement history of Wrangel Island and Arctic Chukotka: integrated insights from zircon U–Pb, O and Hf isotopic studies

“…Several additional episodes of crustal growth from magmatic addition and subduction accretion have occurred along the margin since Late Cretaceous time (e.g., Hourigan et al, 2009). This obscured boundary of Arctic Chukotka is proposed to cross the Bering shelf south of Saint Lawrence Island and link up with the Angayucham suture zone that delineates the southern boundary of the Alaskan part of the AAC (Churkin and Trexler, 1981;Nokleberg et al, 2000;Amato et al, 2015). The oldest dated meta-igneous basement rocks in the AAC are the 968±5 Ma Ernie Lake orthogneiss, located in the southern Brooks Range (BR, Fig.…”

“…elucidating paleotectonic associations of the AAC with other basement complexes in the circum-Arctic realm. The AAC contains numerous exposures of Neoproterozoic metamorphic and igneous basement overlain by a Paleozoic and Mesozoic sedimentary cover sequence (e.g., Cecile et al, 1991;Patrick and McClelland, 1995;Amato et al, 2009Amato et al, , 2014Till et al, 2014a;Akinin et al, 2015). This paper focuses on the geochronology and isotope geochemistry of Neoproterozoic basement rocks from two localities (western Chukotka and Wrangel Island; Figs.…”