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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Paleomagnetism of mid-Cretaceous red beds in west-central Kyushu Island, southwest Japan: paleoposition of Cretaceous sedimentary basins along the eastern margin of Asia
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Paleomagnetism of mid-Cretaceous red beds in west-central Kyushu Island, southwest Japan: paleoposition of Cretaceous sedimentary basins along the eastern margin of Asia

机译：日本西南部九州岛中西部白垩纪中部红层古磁性：亚洲东部边缘白垩纪沉积盆地的古沉积

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摘要

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 ℃), intermediate (240-480 ℃), and high (480-680 ℃) 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 α_(95) = 5°, which yields a paleomagnetic pole at 39°N, 186°E and A_(95) = 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.
机译：在日本西南部九州中西部白垩纪中部沉积地层进行了古磁研究，以阐明白垩纪亚洲大陆边缘沉积盆地的起源。我们从白垩纪中部五所群的总共34个地点，九州中西部的浅海碎屑沉积物中收集了古磁性样品，并从18个红层中识别出了特征性的剩余磁化强度。热退磁显示，红层包含三个磁化分量，分别为低（<240℃），中（240-480℃）和高（480-680℃）解锁温度。较低的疏松温度成分是当前磁场的粘性磁化强度，中间的磁化强度被解释为由磁赤铁矿携带的化学剩余磁化强度，该磁化赤铁矿大概是由碎屑磁铁矿的后折叠，部分氧化形成的。岩石磁性和岩石学研究表明，高解块温度成分主要存在于赤铁矿（马氏体和颜料赤铁矿）中，部分存在于赤铁矿中。由于进行正向折叠测试，因此该高温分量可以被视为主要的，碎屑性的剩余磁化强度。高温分量的倾斜校正平均方向为Dec = 65°，Inc = 63°（α_（95）= 5°），这在39°N，186°E和A_（95）= 8时产生了古磁极°。该极点与日本西南部晚白垩世岩石的极点组合，形成了一条明显的极地游走路径（APWP），其特征是晚白垩世与古近纪之间的尖端。将该APWP与来自东北亚的同代古地磁极进行比较，发现白垩纪后约顺时针旋转约50°，相对于东北向南漂移18±8°。白垩纪盆地的向南输送表明，原始日本弧起源于其当前位置的北部。我们认为，该陆块的海岸平行平移是由走滑断层的右旋运动引起的，以前的地球动力学模型通过中生代将其解释为左旋。走滑运动的变化可能是由于中生代碰撞和与亚洲东北部的鄂霍次克微大陆等奇异地形的渗透所致。

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