HR: 0800h
AN: GP11D-0861    [Abstracts]
TI: Magnetostratigraphy and Rock Magnetism of the Neogene Yaha Section (Northwest China) and Possible Late Cenozoic Uplift of the Tianshan by 11 Ma
AU: * Charreau, J
EM: julien.charrea@univ-orleans.fr
AF: Institut des Sciences de la Terre d'Orl‚ans, Bƒtiment G‚osciences, rue de Saint Amand, Orleans, 45000 France
AU: Chen, Y
EM: yan.chen@univ-orleans.fr
AF: Institut des Sciences de la Terre d'Orl‚ans, Bƒtiment G‚osciences, rue de Saint Amand, Orleans, 45000 France
AU: Gilder, S
EM: gilder@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris; Laboratoire de Pal‚omagnetisme, 4 place Jussieu, Paris, 75252 France
AU: Dominguez, S
EM: dominguez@dstu.univ-montp2.fr
AF: Laboratoire Dynamique de la LithosphŠre, Bƒtiment 22 (cc. 60) Place Bataillon,, Montpellier, 34095 France
AU: Avouac, J
EM: avouac@gps.caltech.edu
AF: California Institute of Technology;, Division of Geological and Planetary Sciences, Pasadena CA, 91125 United States
AU: Sen, S
EM: sen@cimrs1.mnhn.fr
AF: Museum of Natural History, Paris Cedex 5, 43 rue Buffon, Paris, 75005 France
AU: Li, Y
AF: Institute of Geology & Mineral Resource, Bureau of Geology & Mineral Resources of Xinjiang Uygur Autonomous Region, Urumqi, 000 China
AB: In order to better constrain the timing of the Cenozoic uplift history of the Tianshan due to the India-Asia collision, we carried out a magnetostratigraphic study at the Yaha section, on the southern flank of the Tianshan range (northwest China). 1069 samples were collected from a 2814-m-thick section composed mainly of fluvio-lacustrine sandstone and conglomerate mapped as the Neogene Kuqa Formation. Rock magnetic experiments show that the magnetic remanence is principally carried by magnetite yet hematite is also abundant . Stepwise thermal demagnetization isolated a linear magnetization component that decays univectorally toward the origin. Based on a positive fold test and the equal proportion of magnetic polarities, the isolated direction likely represents a primary magnetization. Eighteen magnetic polarity changes were identified. They correlate between ~5.2 and ~12.6 Ma with the reference magnetic polarity time scale. We also measured the anisotropy of magnetic susceptibility of the samples. Before ~ 11 Ma the average shape parameter T of the AMS is around 0 meaning the grains are spherical in shape and far-traveled. By ~11 Ma, T strongly increases to values strictly greater than 0 meaning that the magnetic grains are oblate in shape and traveled less far. The timing of this change in the T parameter is strongly correlated to a decrease in the bulk susceptibility that likely signals a modification of the source rock. From the rock magnetic parameters, together with the acceleration of the sedimentation rate, we conclude that the uplift of the Tianshan mountains started by ~ 11 Ma.
DE: 1520 Magnetostratigraphy
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting