HR: 0830h
AN: GP11C-0266    [PDF]
TI: Paleointensity Determination on the Late Jurassic Lavas in Northeastern China
AU: * Shi, R
EM: rpshi@mail.igcas.ac.cn
AF: Paleomagnetism Laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
AU: Zhu, R
EM: rxzhu@mail.igcas.ac.cn
AF: Paleomagnetism Laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
AU: Pan, Y
EM: yxpan@mail.igcas.ac.cn
AF: Paleomagnetism Laboratory, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
AB: The variations in the strength of the geomagnetic field over geologic time is crucial to a complete understand of the workings of Earth­_s dynamo. While many paleointensity data were recently reported and hence enhancing our understanding of the geodynamo, few data except one datum from SBG in the present paleointensity database were obtained from the late Jurassic by passing certain criteria (Thellier method with system p-TRM check and so on) and, in particular, the lack of data from East Asia. We recently carried out an integrated paleomagnetic, rock-magnetic and paleointensity study of the late Jurassic volcanic succession from Beipiao in the west of Liaoning province, northeastern China. A total of 19 lava flows were sampled. The eruption ages of these lava flows were dated by SHRIMP, about 145Ma. Detailed rock magnetic experiments of thermomagnetic curves and hysteresis loops show the primary carrier of remanence to be pseudo-single domain hematite. Stepwise alternating field and thermal demagnetizations isolated a well-defined direction of characteristic remanent magnetization in all studied lava flows. The modified version (Coe, 1967) of Thellier method with system p-TRM check was used to determine paleointensity. Eight out of nineteen lava flows met the selection criteria (positive p-TRM check, at least three points in a line) and the paleointensity and corresponded VDM values were calculated. An average of about fifth of the present day magnetic field, (1.5+/-0.6)E+22 Am2, was recorded by the eight lava flows. This is the first paleointensity results obtained from the Chinese lava flows erupted in the late Jurassic and well-consistent with the results from SBG (Juarez et al., 1998), suggesting the MDL into the late Jurassic, and further confirming the inverse relationship between reversal frequency and paleointensity.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1519 Magnetic mineralogy and petrology
DE: 1521 Paleointensity
DE: 1540 Rock and mineral magnetism
DE: 1560 Time variations--secular and long term
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting