HR: 0800h
AN: T11B-0378    [Abstracts]
TI: Dating Deformation in the Anyui-Chukotka Fold Belt, Northeastern Arctic Russia
AU: * Katkov, S M
EM: sergkat@yandex.ru
AF: Moscow State University, Geological Institute, Pyzhevsky 7, Moscow, 119017 Russian Federation
AU: Strickland, A
EM: strick@pangea.stanford.edu
AF: Stanford University, Dept. Geological and Environmental Sciences, Stanford, CA 94305
AU: Miller, E L
EM: miller@pangea.Stanford.EDU
AF: Stanford University, Dept. Geological and Environmental Sciences, Stanford, CA 94305
AU: Podgorny, I I
EM: n/a
AF: Moscow State University, Geological Institute, Pyzhevsky 7, Moscow, 119017 Russian Federation
AU: Toro, J
EM: jtoro@wvu.edu
AF: West Virginia University, Dept. Geology and Geography, Morgantown, WV 26506
AB: The Anyui-Chukotka fold-belt is a regionally extensive zone of folding and lesser thrust-faulting that extends from 162°W longitude to the Bering Strait along the Russian Arctic coast. The southern border of this fold-belt is the South-Anyui suture zone. The South-Anyui suture zone is generally interpreted as the result of Early Cretaceous collision of Eurasia with the Chukotka microcontinent during the closure of the Anyui Ocean and may be the along-strike continuation of the Angayucham suture in Arctic Alaska. Despite its regional extent and significance in terms of Arctic tectonics, there is little published data on the style, geometry and the age of deformation within the Anyui-Chukotka fold-belt. Structural and geochronologic studies were carried out north of Bilibino, east of the Alarmaut Uplift, and south of Pevek. Strata involved in deformation are thick basinal sequences of Triassic slate and fine-grained quartzite that overlie a basement of Permian (?), Carboniferous, and Devonian (?) platformal strata. Two main deformational episodes are distinguished: 1) D1 involved regional folding and minor thrust-faulting associated with penetrative cleavage (S1) that is steeply dipping. Folds range from outcrop-scale to map-scale and are oriented WNW-ESE. D1 structures are best preserved along a belt north of the South Anyui suture. D1 is interpreted as result of regional shortening. Onset of D1 is indirectly dated by the deposition of syn-orogenic turbidites that have sparse Jura-Cretaceous fossils and detrital zircons as young as ~160-180 Ma. 2) D2 affects a region of at least 3000 km2 along and east of the Alarmaut massif, dies out structurally upwards and to the south and east. A well-developed foliation (S2) is gently dipping and recumbently folds quartz veins, bedding and S1. Boudinage and pinch-and-swell structures together with isoclinal folds and transposition of previous fabrics indicate locally high strains during D2. Stretching lineations are locally developed within S2 but are not pervasive or consistent. D2 formed as a result of vertical shortening or flattening coeval with intrusion of widespread granitoid plutons such as those forming the Alarmaut Massif as suggested by metamorphic fabrics and isograds where grade is highest along the flanks of the massif. Post D2 kink folds are present but are only locally systematic and account for lesser strain. Six intrusive bodies were dated by the U-Pb method on zircon with the SHRIMP-RG. The Alarmaut massif or batholith consists of plutons and intrusive phases that yield ages of 117±1.9 Ma, 115.7±1.9 Ma and 112±1.3 Ma. Small bodies of foliated leucogranites intruded into the surrounding country rocks yield an age of 112.8±1.3Ma. Two separate plutons, the Koivel granite massif north of Bilibino and one west of the Mirgovaam River yield ages of 112.4±1.1 and 114.7±1.3. These data are the first to establish a firm age for granitic magmatism in this part of Chukotka, document a post-collisional, extension or crustal-collapse related deformation across NE Arctic Russia, and a means of directly comparing ages of deformation from Arctic Russia to Alaska.
DE: 1115 Radioisotope geochronology
DE: 8012 High strain deformation zones
DE: 8178 Tectonics and magmatism
DE: 9315 Arctic region (0718, 4207)
DE: 9610 Cretaceous
SC: Tectonophysics [T]
MN: Fall Meeting 2005