HR: 1340h
AN: GP43C-1485    [Abstracts]
TI: Paleomagnetism of the Early Cretaceous island arc complex from the north Sakhalin Island: implications to the Cretaceous paleogeography of the Pacific
AU: Bazhenov, M
EM: mibazh@mail.ru
AF: Geological Institute, Russian Academy of Sciences, Pyzhevsky Lane, 7, Moscow, 119017, Russian Federation
AU: * Levashova, N
EM: namile2007@rambler.ru
AF: Geological Institute, Russian Academy of Sciences, Pyzhevsky Lane, 7, Moscow, 119017, Russian Federation
AB: Several paleomagnetic studies of Late Cretaceous island arc complexes from the Northwest Pacific demonstrated that the corresponding island arcs had originally been far away from the Eurasian margin and docked to it in the Cenozoic. Hence the Late Cretaceous paleogeography of the Northwest Pacific was very different from the modern one and resembled what we now see in Polynesia. In contrast, the Early Cretaceous subduction-related volcanism is confined to the Okhotsk-Chukotka volcanic belt along the NE coast of the Sea of Okhotsk; both geological and paleomagnetic data firmly indicate that the belt did not move with respect to Eurasia. Thus a drastic difference in paleogeography of the Northwest Pacific in the Early and Late Cretaceous epochs appears to be indicated, and the existence of remote intra-oceanic island arcs becomes of crucial importance. We studied basalt flows of island arc affinity and basalt cobbles from intra-formational conglomerate at the northernmost tip of the Sakhalin Island (54.3°N, 142.2°E); according to radiolaria from silicic intercalations, the complex is of Valanginian-Albian age. Upon stepwise thermal cleaning, a well-defined dual-polarity characteristic magnetization was isolated from all 14 sites studied. This remanence shows about five-fold decrease in dispersion upon tilt correction, thus rendering the fold test positive. The reversal and conglomerate tests are positive too, and the dual-polarity magnetization is most likely to be primary. Its tilt-corrected mean direction (D = 279.3°; I = 54.2°; k=35, a95 = 6.3°, N = 14) corresponds to a paleolatitude of 35° +/- 6°, which is by more than 20° lower than what is expected for the Eurasian plate. In our presentation, we will discuss different implications of these data on paleogeography of the Northwest Pacific in Early Cretaceous time.
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 8104 Continental margins: convergent
DE: 8125 Evolution of the Earth (0325)
DE: 8155 Plate motions: general (3040)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting