The Caledonian suture in the high Arctic? New Data from the Chukchi Borderland, Amerasia Basin
The Chukchi Borderland (CB) is a bathymetric high in the Arctic Ocean that is extended by N-S and E-W striking faults. Based on sediment cores of talus slope fragments at the base of the Northwind Ridge (NWR), basement of the CB was previously interpreted as a Paleozoic platform sequence comparable to passive margin strata of western Laurentia (Grantz et al., 1998). The discovery of Silurian (~430 Ma) orthogneiss dredged from a fault scarp in the central CB suggests instead that the CB is a displaced fragment of the Caledonian orogen (Brumley et al., 2008). U-Pb geochronology of zircon suites from rocks dredged from the NWR and central CB fault scarps help resolve the make-up of the CB basement. Samples from the central CB are believed to represent the country rocks of the previously dated Silurian orthogneiss. They consist mostly of paragneiss and lesser orthogneiss intruded by leucosomal segregations, all deformed and metamorphosed to amphibolite facies with assemblages Qtz Kfs Plag Bt Grt ± Ms ± Chl (retrograde) with accessory zircon, sphene and apatite. The abundance of Kfs Plag Bt in paragneiss samples suggest a volcanogenic sediment protolith. Dynamic recrystallization of quartz by grain-boundary migration and recrystallization/myrmekite development along the edges of feldspar crystals suggest final deformation at temperatures of ~450 C. U-Pb geochronology of zircon from an orthogneiss sample from the central CB yields an age of 499.2 ± 0.9 Ma with late Neoproterozoic (600 Ma) and Mesoproterozoic - early Paleoproterozoic (1100-1700 Ma) grains. Detrital zircon geochronology from four paragneiss samples show a broad range of ages between 480-650 Ma with a dominant age peak ~500 Ma. Lesser, mostly discordant, Mesoproterozoic and Paleoproterozoic zircons are also present. The paragneiss sampled represent an arc-proximal sediment intruded by Silurian granitoids. Dredge samples from the NWR consist of deformed and metamorphosed calcareous sandstones, low-grade phyllites and highly altered but undeformed basalts. Low-grade (sub to greenschist facies) deformation is indicated by pressure solution cleavage in phyllites and minor recrystallization of quartz in sandstones. Detrital zircons from a silty phyllite from the NWR display age peaks of 1070-1170, 1600-2000 and 2300-3000 Ma. These peaks are known to be characteristic of sediments deposited along the northern passive margin of Laurentia, developed as the result of the breakup of Rodinia in the Late Precambrian and existing as a passive margin until the onset of the Caledonian orogeny. The contrasting rock types and geochronology from this study of dredged bedrock from the CB suggest the juxtaposition of a Cambro-Ordovician volcanic arc terrane intruded by Silurian granitoids with sedimentary rocks representing the northern margin of Laurentia, thus providing a more accurate geologic tie point of the Chukchi Borderland back to the region of Pearya, Lomonosov Ridge and Svalbard. This new data argues against previous interpretations of the CB as part of the Proterozoic to Jurassic passive margin of western Laurentia (Grantz et al. 1998) as well as the restoration of CB to the Chukotka margin of Russia (Lawver et al. 2011).
Journal or Conference Title
Fall Meeting, American Geophysical Union (AGU)
9-13 December, 2013
San Francisco, CA, USA
American Geophysical Union Publications
O'Brien, T., Brumley, K. Miller, E., and Mayer, L.A., The Caledonian suture in the high Arctic? New data from the Chukchi Borderland, Amerasia Basin, Abstract T13B-2522 presented at 2013 Fall Meeting, AGU, San Francisco, Calif., 9-13 Dec. 2013.