Paleomagnetism of mid-Cretaceous red beds in west-central Kyushu Island, southwest Japan: paleoposition of Cretaceous sedimentary basins along the eastern margin of Asia
Paleomagnetism of mid-Cretaceous red beds in west-central Kyushu Island, southwest Japan: paleoposition of Cretaceous sedimentary basins along the eastern margin of Asia
复制标题
DOI：
10.1016/s0012-821x(02)00691-x
复制
发表时间：
2002-07
影响因子：
5.3
通讯作者：
K. Kodama;Tetsuichi Takeda
中科院分区：
文献类型：
--
作者：
K. Kodama;Tetsuichi Takeda
对日本西南部九州岛中西部白垩纪中期沉积地层进行了古地磁研究，以阐明白垩纪亚洲大陆边缘沿着沉积盆地的成因。我们收集了古地磁样品，共34个地点的白垩纪中期五所之浦组，浅海碎屑沉积在九州中西部，和特征reversium磁化被确认从18个层位的红层。热退磁揭示了红层包含三个磁化分量，具有低（<240°C）、中（240-480°C）和高（480-680°C）的解除阻塞温度。低解块温度分量为现场粘性磁化，中间分量解释为磁赤铁矿所携带的化学还原磁化，磁赤铁矿可能是由碎屑磁铁矿的后折叠、部分氧化形成的。岩石磁性和岩相学研究表明，高解除阻断温度的成分主要存在于赤铁矿（马氏体和黑赤铁矿）和部分磁赤铁矿。由于正的褶皱试验，这种高温分量可被视为原始的碎屑回复磁化。高温分量经倾斜校正后的平均方向为Dec=65°，Inc=63°，α95=5°，古磁极为39°N，186°E，A95=8°。该极与日本西南部晚白垩世岩石的组合定义了一个明显的极移路径（APWP），其特征是晚白垩世和古近纪之间的尖点。与同时代的东北亚古地磁极相比较，该古地磁极在白垩纪后发生了约50°的顺时针旋转和18±8°的南移。白垩纪盆地的南移表明，原日本弧起源于其现在的位置以北。我们建议，这个大陆块的海岸平行平移是由右旋运动的走滑断层，以前的地球动力学模型解释为左旋通过中生代。走滑运动的变化可能是由于中生代鄂霍次克微大陆等外来陆块与亚洲东北部的碰撞和侵入所致。
A paleomagnetic study was carried out on the mid-Cretaceous sedimentary strata in west-central Kyushu Island, southwest Japan, to elucidate the origin of sedimentary basins along the Asian continental margin in the Cretaceous. We collected paleomagnetic samples from a total of 34 sites of the mid-Cretaceous Goshonoura Group, shallow-marine clastic deposits in west-central Kyushu, and characteristic remanent magnetizations were recognized from 18 horizons of red beds. Thermal demagnetization has revealed that the red beds contain three magnetization components, with low (<240°C), intermediate (240–480°C), and high (480–680°C) unblocking temperatures. The low unblocking temperature component is present-field viscous magnetization, and the intermediate one is interpreted as chemical remanent magnetization carried by maghemite that was presumably formed by post-folding, partial oxidation of detrital magnetite. Rock magnetic and petrographic studies suggest that the high unblocking temperature component resides largely in hematite (martite and pigmentary hematite) and partly in maghemite. Because of the positive fold test, this high temperature component can be regarded as primary, detrital remanent magnetization. The tilt-corrected mean direction of the high temperature component is Dec=65°, Inc=63° with α95=5°, which yields a paleomagnetic pole at 39°N, 186°E and A95=8°. A combination of this pole with those of the Late Cretaceous rocks in southwest Japan defines an apparent polar wander path (APWP), which is featured by a cusp between the Late Cretaceous and the Paleogene. A comparison of this APWP with the coeval paleomagnetic pole from northeast Asia suggests an approximately 50° post-Cretaceous clockwise rotation and 18±8° southward drift with respect to northeast Asia. The southward transport of the Cretaceous basin suggests that the proto-Japanese arc originated north of its present position. We propose that the coast-parallel translation of this landmass was caused by dextral motion of strike-slip faults, which previous geodynamic models interpreted to be sinistral through the Mesozoic. The change in strike-slip motion may have resulted from Mesozoic collision and penetration of exotic terranes, such as the Okhotsk microcontinent, with the northeastern part of Asia.