Basalts From the Chukchi Borderland: ⁴⁰Ar/³⁹Ar Ages and Geochemistry of Submarine Intraplate Lavas Dredged From the Western Arctic Ocean

Abstract

Submarine volcanism in the western Arctic Ocean, known as Amerasia Basin, is attributed to a mantle plume based on geophysics and meager geochemical evidence. Basaltic samples dredged from Chukchi Borderland within the basin have produced minimum 40Ar/39Ar ages for eruption at circa 118–112, circa 105–100, and circa 90–70 Ma, which we use to constrain tectonic models for basin opening. Major oxide and trace element concentrations and Sr, Nd, and Hf isotopic ratios of the lavas show that the circa 118–112 Ma samples from Northwind Ridge are tholeiites (low‐Ti tholeiite I) with low degrees of rare‐earth element (REE) fractionation, high overall heavy rare‐earth element (HREE), and Mg# (Mg‐number), which suggests magma derivation from a garnet‐free source followed by minor crystal fractionation. Strontium, Nd, and Hf isotope systematics for these lavas and ratios of highly incompatible trace elements point toward a lithospheric source. Eruptions at circa 105–100 and circa 90–70 Ma, both at Healy Spur, produced two types of lavas: low‐Ti tholeiite II—which are generally older than high‐Ti tholeiite—both common in continental flood basalt (CFB) provinces and both with trace element abundance patterns typifying a garnet‐free source and significant crystal fractionation for the high‐Ti tholeiite. The isotope characteristics for both groups are common features of asthenospheric sources. Composition‐time relationships for the lavas suggest inception of melting in the subcontinental lithospheric mantle (SCLM)—probably due to introduction of a heat source by a plume—followed later (at ca. 105–100 and ca. 90–70 Ma) by asthenospheric melting possibly triggered by plume rise.

New constraints on the age, geochemistry, and environmental impact of High Arctic Large Igneous Province magmatism: Tracing the extension of the Alpha Ridge onto Ellesmere Island, Canada

“…1). These samples from the steep margins of the Chukchi Borderland, however, all are tholeiitic in composition (Mukasa et al, 2020). The timing and igneous make-up of the Alpha Ridge remains elusive, other than (i) dredged samples of alkaline basalt from the Alpha Ridge that yielded an Ar-Ar age of 90.40 ± 0.26 Ma (Wil-liamson et al, 2019a) and previously 89 ± 1 Ma (Jokat et al, 2013), (ii) ages of 127-110 Ma suggested for volcanic samples dredged at the Siberian end of the Mendeleev Ridge (Nikishin et al, 2020), and (iii) ages of ca.…”

“…118-112 Ma, ca. 105-100 Ma, and 90-70 Ma for dredge samples of the Chuckchi borderland (Mukasa et al, 2020). The compositions of the few dredged samples of the Alpha Ridge, with the exception of Van Wagoner et al (1986), have only been reported in abstracts without access to the whole rock data.…”

New Constraints on the Age, Geochemistry, and Environmental Impact of High Arctic Large Igneous Province Magmatism: Tracing the Extension of the Alpha Ridge Onto Ellesmere Island, Canada

“…118-112 Ma, ca. 105-100 Ma, and 90-70 Ma for dredge samples of the Chuckchi borderland (Mukasa et al, 2020). The compositions of the few dredged samples of the Alpha Ridge, with the exception of Van Wagoner et al (1986), have only been reported in abstracts without access to the whole rock data.…”

Canada’s maritime frontier: the science legacy of Canada’s extended continental shelf mapping for UNCLOS

“…The general consensus from these samples is that Alpha Ridge was emergent or shallowly submerged. The in-situ samples consist predominantly of continental flood basalts derived from melting in the subcontinental lithospheric mantle and volcaniclastic sedimentary rock formed subaerially and shallow marine (e.g., Brumley 2009;Mukasa et al 2020) which also accounts for the limestone.…”