HR: 0800h
AN: GP41A-0813    [Abstracts]
TI: Deformation History of Central Chukotka (Alarmaut Uplift) Northeastern Arctic Russia
AU: * Katkov, S M
EM: sergkat@yandex.ru
AF: Geological Institute, Pyzhevsky 7, Moscow, 119017 Russian Federation
AU: Miller, E E
EM: miller@pangea.stanford.edu
AF: Dept. Geological and Environmental Sciences, Stanford University,, Stanford, 94305, Stanford, CA 94305 United States
AU: Podgorny, I I
EM: podgorny@ginras.ru
AF: Geological Institute, Pyzhevsky 7, Moscow, 119017 Russian Federation
AU: Toro, J
EM: jtoro@wvu.edu
AF: Dept. Geology and Geography, West Virginia University,, Morgantown WV 26506, Morgantown, WV 26506 United States
AB: The Anyui-Chukotka fold-belt is a regionally extensive zone of folding and lesser thrust-faulting that extends from 162ø W longitude to the eastern end of Chukotka along the Russian Arctic coast. The southern border of this fold-belt is the South-Anyui suture zone. Most investigators consider the South-Anyui suture as a result of Early Cretaceous collision of Eurasia with the Chukotka microcontinent during the closure of the Anyui Ocean. Despite its regional extent and significance in terms of regional tectonics, there is little published data on the style and geometry of deformation within the Anyui-Chukotka fold-belt and there are few age constraints on its development. Structural data was collected within the Anyui-Chukotka fold-belt in area located north of Bilibino, east of the Alarmaut Uplift, and south of Pevek. Strata involved in deformation are mostly thick sequences of Triassic slate and fine-grained quartzite, but locally Permian (?), Carboniferous, and Devonian (?) strata are also exposed locally. Three deformational episodes are distinguished: 1) The earliest deformation (D1) was regional folding and minor thrust-faulting associated with penetrative cleavage (S1) that is steeply dipping where the effects of younger deformation are absent. Folds range from outcrop-scale to map-scale and are oriented WNW-ESE. D1 structures are best preserved along a belt parallel to the South Anyui suture in the southern part of the study area. D1 is the result of the first compression phase, which is likely the main collisional deformation in the area. Abundant quartz veins formed during this phase of deformation. 2) The second deformation phase (D2), which affects a region of at least 3000 km2 along and east of the Alarmaut massif, dies out structurally upwards and to the south. D2 produced a strong high-strain foliation (S2) which is mostly gently dipping to flat. Quartz veins were deformed and folded, bedding and S1 are isoclinally folded, with the axial plane of these folds being parallel to S2. Boudinage and pinch-and-swell structures are also evident, and together with the isoclinal folds and transposition of previous fabrics argue for very high strains. Stretching lineations are locally developed within S2 but are not common. Near the granitic batholith of the Alarmaut massif, new-formed biotite grows within the S2 cleavage. Our interpretation is that D2 formed as a result of vertical shortening or flattening, but its regional significance is not clear, except that it post-dates upright folding in the Chukotka fold belt and may be coeval with intrusion of widespread granitoid plutons (undated). 3) Finally, there are small and outcrop-scale kink folds formed during D3 that fold S2, and there is local development of late-stage crenulation cleavage. Both sets of structures represent small strains.
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 5475 Tectonics (8149)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting