Geochronology of Crustal Xenoliths and Detrital Zircons from the De Long Islands

Henning Lorenz

We present new ages from the basement underlying the De Long Plateau, New Siberian Islands, and possible correlations to other Arctic areas. Henrietta Island is the northernmost De Long Island, located about 600 km north of the Russian mainland and 250 km south of the continental break to the Amerasia Basin. It is mainly composed of calc-alkaline magmatic rocks (basalts, gabbros, diorites, some andesites), dated to c. 440 Ma (Ar-Ar on diorites, Kaplan et al. 2001) and siliciclastic sediments. Zhokhov Island, located about 150 km to the southwest, is the remnant of an eroded Miocene to Pleistocene intraplate volcano (6.1-0.53 Ma; K-Ar, Silantyev et al. 2004). Basalts are rich in mantle xenoliths and carry crustal xenoliths. Granitic boulders along with psammite and conglomerate up to 25-30 cm across can be found on the island and are considered by us to be xenoliths weathered from the lava flows. Two granitic rocks and a sandstone xenolith from Zhokhov and a sandstone from Henrietta were analysed by ion-microbe U-Th-Pb dating at the NordSIM facility in Stockholm. Dating of the granitic rocks resulted in concordia ages of 535.5±2.6 Ma and 577.0±3.1 Ma. 101 detrital zircons were analyzed from the sandstone xenolith. A distinct peak at c. 650 Ma dominates the age spectrum, followed by a c. 1300 - 900 Ma age assemblage. Some zircons have both a Mesoproterozoic or early Neoproterozoic and a late Neoproterozoic age domain. The age spectrum of the sandstone xenolith from Zhokhov resembles very much that of the sandstone from Henrietta: Here 86 zircons were analyzed, resulting in a dominant c. 650 Ma peak and a broader c. 1700 - 900 Ma assemblage. We preliminarily conclude that the Paleozoic rocks exposed on Henrietta Island are likely to continue beneath the De Long Plateau, where they were incorporated as xenoliths in the young volcanics of Zhokhov Island. In similarity with other high Arctic areas, sediment was derived from Meso- to Early Neoproterozoic (Grenville-Sveconorwegian) and late Neoproterozoic sediment sources. At least a part of the source area was affected by magmatism/metamorphism in both periods. Latest Neoproterozoic to early Cambrian (Timanian) ages are absent in the sedimentary rocks, but the ages of the granitic rocks suggest a Timanian age component in the basement below the De Long Plateau. The age signatures from the De Long Plateau resemble closely those reported from the Donjek assemblage in the Alexander Terrane (Beranek et al. 2013). The latter has faunal affinities to Baltica and Siberia and the analyzed clastic rocks are associated with arc volcanics (as on Henrietta, however somewhat older). Also, the late Neoproterozoic magmatism and Meso- to Neoproterozoic detrital zircon ages in the Arctic Alaska-Chukotka Terrane (c.f. Amato et al. 2009) bear resemblance to the new data from the De Long Islands. The similar history of these terranes and their link to the Timanian domain need to be further investigated.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013