HR: 09:45h
AN: T11E-08    [Abstracts]
TI: Geology of Wrangel Island, Arctic Russia, Revisited
AU: * Miller, E L
EM: miller@pangea.stanford.edu
AF: Stanford University, Dept. Geological and Environmental Sciences, Stanford, CA 94305, United States
AU: Gehrels, G
EM: ggehrels@geo.arizona.edu
AF: University of Arizona, Department of Geosciences., Tucson, AZ 85721, United States
AU: Soloviev, A
EM: solov@ginras.ru
AF: Russian Academy of Sciences, Geological Institute, Moscow, 119017, Russian Federation
AB: It has long been suggested that Wrangel Island represents the western continuation of the Brooks Range fold and thrust belt of northern Alaska. It is thus a unique exposure to test for the continuity of structures, lithologies and facies from Alaska to Russia across the Chukchi Sea, however no new structural and geochrononologic data has emerged since the thorough overview of Kos'ko et al. (1993, Geol. Surv.Canada Bull. 461). In 2006, an international team of geologists (S.Sokolov, M.Tuchkova, V.Verzhbitsky, E.Miller and V.Pease) visited the island with the help and logistic support of the director and scientific staff of the Wrangel Island Wildlife Preserve. Strata on Wrangel Island are highly deformed and metamorphosed, but may match part of the section described for the Hannah Trough, Alaska (Sherwood et al., 2002 GSA Spec.Paper 360): Coarse clastic strata overlie late Precambrian basement (630-700 Ma Kos'ko et al. (1993)), followed by a succession of mid to Late Paleozoic limestone, shale and lesser clastic rocks. Wrangel Island differs from the N.Slope and Brooks Range in that a thick sequence of basinal Triassic clastics constitutes the upper part of the section. Comparison of single grain U-Pb ages of detrital zircons from the Triassic of Wrangel to the Russian Arctic mainland and to the Lisburne Hills, Alaska, suggests basin continuity and similar source regions between these three regions (but not the N. Slope) in the Triassic. Single grain ages as young as 215 Ma validate the inferred Triassic age of these sediments on Wrangel Island. Penetrative deformation, increasing in strain and metamorphic grade with depth in the section, is defined by a foliation that dips south and a pronounced N-S mineral elongation or stretching lineation. The structural style of deformation is unlike the style of folding and thrusting in the external (northern) part of the Brooks Range, but similar to that of the internal (southern) zone of the Brooks Range. Limited thin section observations suggest that this deformation may have been superimposed on an earlier, lower strain event but its evidence has been largely obliterated. The main foliation is axial planar to tight to isoclinal folds in all units; these folds (and associated thrust faults) intricately involve the sediment-basement interface (no brittle detachment). Low-angle faults and map-scale boudinage omit section and structurally thin the stack of folded rocks. Low greenschist facies metamorphism (chlorite-white mica) transitional to mid-greenschist (biotite) accompanied deformation. Fifteen oriented thin sections show that the high strain in these rocks was accompanied by formation of mylonitic textures in quartz: subgrain formation, grain size reduction, grain boundary migration and syn-tectonic recrystallization. Fabrics indicate mostly flattening perpendicular to foliation and stretching in a NS direction; they are not highly asymmetric. The excellent preservation of deformation-related structures in quartz suggests that the observed deformation may be related to unroofing rather than to (thrust) burial. Apatite fission track ages from structurally deepest crystalline basement rocks (samples provided by M. Cecile, GSC) are 82.9 +/- 6.7 and 82.5 +/- 6.4 Ma (1 sigma errors) and have relatively long (14 micron) unimodal track lengths, supporting this possibility.
DE: 8005 Folds and folding
DE: 8038 Regional crustal structure
DE: 8110 Continental tectonics: general (0905)
DE: 8169 Sedimentary basin processes
SC: Tectonophysics [T]
MN: 2007 Fall Meeting