HR: 0830h
AN: GP41C-0052    [PDF]
TI: Paleomagnetic Study for the Cretaceous Laiyang Basin in the Shandong Province, Northeast China: Tectonic Implications for East Asia
AU: * Koo, W
EM: kwmoe@korea.ac.kr
AF: Korea University, Department of Earth and Environmental Sciences, Seoul, 136-701 Korea, Republic of
AU: Doh, S
EM: sjdoh@korea.ac.kr
AF: Korea University, Department of Earth and Environmental Sciences, Seoul, 136-701 Korea, Republic of
AU: Park, Y
EM:
AF: Korea University, Department of Earth and Environmental Sciences, Seoul, 136-701 Korea, Republic of
AU: Kim, W
EM:
AF: Korea University, Department of Earth and Environmental Sciences, Seoul, 136-701 Korea, Republic of
AU: Oh, C
EM:
AF: Chonbuk National University, Department of Earth and Environmental Sciences, Chonju, 561-756 Korea, Republic of
AU: Zhai, M
EM:
AF: Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
AU: Guo, J
EM:
AF: Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
AU: Ni, Z
EM:
AF: Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
AB: Paleomagnetic investigation has been carried out for the Early Cretaceous Laiyang Group exposed in the eastern part of the Tan-Lu fault of the Shandong Province, Northeast China. A total of 224 independently oriented core samples were obtained from 12 sites for the study. The mean direction of high temperature/coercivity components (HC) in stratigraphic coordinates (D/I=$16.0\deg$/$57.3\deg$, k=140.5, $\alpha_{95}$=$3.7\deg$) is more clustered than that in geographic coordinates (D/I=$18.1\deg$/$56.7\deg$, k=60.0, $\alpha_{95}$=$5.6\deg$), yielding a positive fold test at the 95 % confidence level. Also, the parameter estimating fold test gives the maximum k value at 84.3 % unfolding. These results collectively indicate that the HC of the Laiyang Group might be a primary remanent magnetization component. The Early Cretaceous paleomagnetic pole position calculated from the mean direction of the HC is at Lat./Long.=$77.1\deg$N/$198.8\deg$E (A$_{95}$=$4.7\deg$). This pole position is not statistically distinguishable from coeval pole positions reported from the western part of the Tan-Lu fault within the North China Block (NCB). It indicates that the east of the Tan-Lu fault did not experience the relative movement with respect to the west of the fault since the Early Cretaceous. Thus, it is interpreted that the sinistral motion of the Tan-Lu fault, which was initiated by the collision between the North and South China blocks since the Late Paleozoic, might be ceased before Cretaceous or at least during the Early Cretaceous. To clarify the tectonic relationships of blocks in East Asia since Cretaceous, the reported Early Cretaceous pole positions of the South China Block (SCB), Mongolia, Siberia and Korea were compared with the coeval mean pole position of the NCB ($78.0\deg$N, $196.7\deg$E, A$_{95}$=$5.9\deg$) calculated from paleopoles of the east and west of the Tan-Lu fault including this study. The paleopoles of the SCB ($76.4\deg$N, $211.2\deg$E, A$_{95}$=$6.8\deg$) and Siberia ($74.9\deg$N, $205.6\deg$E, A$_{95}$=$1.9\deg$) are indistinguishable from that of the NCB. On the other hand, the paleopoles of Mongolia ($82.9\deg$N, $249.5\deg$E, A$_{95}$=$5.7\deg$) and the Korean Peninsula ($65.2\deg$N, $202.1\deg$E, A$_{95}$=$3.4\deg$) are displaced westward by about $10\deg$ and eastward by about $17\deg$, respectively, with respect to that of the NCB, indicating the rotations of opposite senses of the two blocks with respect to the NCB. Several previous paleomagnetic studies reported the Cretaceous clockwise rotations of the east of the Tan-Lu fault (e.g., Benxi area of northeast NCB and the Korean Peninsula), which were ascribed to the sinistral motion of the Tan-Lu fault. However, this study shows that the Tan-Lu fault did not experience any strike-slip motion since the Early Cretaceous, suggesting that another mechanism for the rotations might be involved. Recently, Lin et al. (2003) proposed that the clockwise rotation of the Korean Peninsula and the Benxi area might be caused by the fan-shaped intraplate rifting of the Cretaceous basins in the northeastern NCB and eastern Mongolia. The counterclockwise rotation of Mongolia and the no strike-slip motion of the Tan-Lu fault since the Early Cretaceous, identified in this study, could support the model by Lin et al. (2003) for rotations of blocks in East Asia.
DE: 1500 GEOMAGNETISM AND PALEOMAGNETISM
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting