HR: 13:55h
AN: GP43C-02    [Abstracts]
TI: Tectonics of NE Russia: Pivotal issues and uncertainties
AU: * Sokolov, S D
EM: sokolov@ginras.ru
AF: Geological Institute, Pyzhevsky 7, Moscow, 119017 Russian Federation
AB: The main feature of the tectonic setup of NE Russia is the existence there of two contrasting tectonic grains: (1) Verkhoyansk-Chukotka orogenic belt (VCOB) with a markedly mosaic tectonic style and predominance of NW trends modified by the "Kolyma loop," and (2) Koryak-Kamchatka orogenic belt (KKOB), with its typical NE-trending linear features, conformable to the general tectonic grain of the Circum-Pacific foldbelts. Such sharp contrast in the tectonic grain can be explained as follows: (i) evolution of the VCOB was dominated by collisional processes, whereas, the KKOA provided the stage for accretionary ones; (ii) the VCOB incorporates terranes with continental crust (microcontinents); (iii) the paleostructures of the VCOB were separated from the Pacific by a convergent boundary, and their origin was not therefore related to the motions of Pacific plates-as was the case with the terranes of the KKOA. The time of inception of the convergent boundary between Eurasia and NW Pacific remains poorly constrained. Reliable reconstructions become feasible starting only from as late as the Late Jurassic. There are two different approaches on the origin and evolution of South Anyui suture (SAS): (1) Late Mesozoic rift; and (2) remnant after the closure of a Pacific re-entrant. The multiplicity of the viewpoints is due to the insufficient knowledge of the region and, primarily, to the lack of reliable data on (i) the structures of the different segments of the SAS and its northern and southern surroundings; (ii) age of the oceanic fragments; (iii) the tectonic position and geodynamic settings of the ophiolites; (iv) timing of the principal geologic events such as metamorphism, island-arc volcanism, granite emplacement, collision, etc.; (v) depositional environments and clastic sources of the Triassic -Early Cretaceous sediments. These white spots in our knowledge of the tectonic setup of the Chukotka Peninsula prevent us from adopting or rejecting the popular tectonic model viewing Chukotka as a microplate that split off Canada's Arctic margin to eventually dock onto the North Asian continent. In the KKOA, the pivotal issue is the original location of terranes, their travel paths, and the timing and mode of their accretion. This applies to the following terranes: (i) Ganychalan, including Early Paleozoic ophiolites that have no counterparts anywhere in NE Asia and that are likely fragments of oceanic lithosphere of the Pacific, Iapetus, or the Paleo-Asian Ocean; and (ii) the terranes carrying Late Paleozoic limestones and Tethyan faunas. Such units are common within the northern Circum-Pacific accretionary complexes (Cache Creek terrane in British Columbia, Akieshi terrane in Japan, etc.), and they are critical to paleotectonic reconstructions; and (iii) the numerous and diverse island arc terranes with both Tethyan and boreal faunas. It should be investigated which island arc terranes provided convergent boundaries to which plates, and by which Pacific plates these terranes were transported. Supported by the Russian Foundation for Basic Research (project 02-05-64217).
DE: 8110 Continental tectonics--general (0905)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting