HR: 1340h
AN: GP43C-1488    [Abstracts]
TI: Late Paleozoic History of the Kazakhstan orocline
AU: Van der Voo, R
EM: voo@umich.edu
AF: Department Geological Sciences, University of Michigan, 1100 North University, Ann Arbor, MI 48109-1005, United States
AU: * Abrajevitch, S
EM: alexabra@umich.edu
AF: Department Geological Sciences, University of Michigan, 1100 North University, Ann Arbor, MI 48109-1005, United States
AU: Bazhenov, M L
EM: mibazh@mail.ru
AF: Geological Institute, Russian Academy of Sciences, Pyzhevsky Lane 7, Moscow, 109017, Russian Federation
AU: Levashova, N M
EM: mibazh@mail.ru
AF: Geological Institute, Russian Academy of Sciences, Pyzhevsky Lane 7, Moscow, 109017, Russian Federation
AB: Kazakhstan, located in the center of the Eurasian continent, is made of younger crust sandwiched between the old cratons of Siberia, Baltica and Tarim. A prominent geologic feature of Kazakhstan consists of two concentric horse-shoe shaped volcanic arcs, which are Devonian and late Paleozoic in age and with the youngest arc on the inside. Recent paleomagnetic studies in the region show that in the Middle Devonian the volcanic arc, which is now curved, was nearly straight and NW-SE trending. This arc marked the NE margin of the block that some have called Kazakhstania. The southern arm of the curved structure shows no significant changes in its relative orientation since the Middle Devonian, while its northern arm (in present day coordinates) underwent ~ 180 degrees of rotation. To constrain the timing of the rotation we conducted a paleomagnetic study of the Early Permian (295-290 Ma) subduction related volcanics from the central limb of the orocline. Declinations of the primary as well as secondary (Triassic) components isolated in studied rocks agree well with the Baltica reference directions indicating that the bending was essentially over by the earliest Permian. An initial bending of the orocline was probably caused by dextral shear motion of Siberia that affected the northern (Chingiz Range) end of Kazakhstania, while the collision of Tarim with Kazakhstania's southern corner (Tien Shan) created a back-stop. Continued subduction under the northern and southern limbs with an estimated subduction velocity of less than 1 cm/yr eventually led to closure of the intervening Balkhash-Ili ocean and tightening of the orocline. By the early Permian the Balhash-Ili represented a narrow oceanic basin with two subduction zones of opposite polarity, likely similar to the modern Molucca Sea subduction system.
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8157 Plate motions: past (3040)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting