The Caledonian suture in the high Arctic? New Data from the Chukchi Borderland, Amerasia Basin

• Main Authors: O'Brien, T M, Brumley, Kelley, Miller, E L, Mayer, Larry A.
• Format: Text
• Language: unknown
• Published: University of New Hampshire Scholars' Repository 2013
• Subjects: amerasia basin; caledonian suture; chukchi; Oceanography and Atmospheric Sciences and Meteorology; Sedimentology; Arctic; Arctic Ocean; Amerasia Basin; Chukchi Borderland; Chukchi
• Online Access: https://scholars.unh.edu/ccom/698; http://abstractsearch.agu.org/meetings/2013/FM/T13B-2522.html

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. ...