Low-latitude and Southern Hemisphere origin of Anisian (Triassic) bedded chert in the Inuyama area, Mino terrane, central Japan
Low-latitude and Southern Hemisphere origin of Anisian (Triassic) bedded chert in the Inuyama area, Mino terrane, central Japan
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DOI：
10.1029/2000jb900305
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发表时间：
2001-02-10
影响因子：
3.9
通讯作者：
Kojima, S
中科院分区：
文献类型：
--
作者：
Ando, A;Kodama, K;Kojima, S
对日本中部矿区南部犬山地区中三叠世至早侏罗世放射虫层状硅质岩的古地磁和古生物学研究表明，该硅质岩沉积于古纬度在北纬10度至南纬10度之间的赤道地区，特别是中、下安尼期硅质岩沉积盆地位于南半球。硅质岩具有四个特征的剩磁分量。由赤铁矿携带的最高阻断温度分量表现为正向褶皱和反向测试，被认为是沉积后获得的初始回复磁化。其他三个组成部分被解释为目前的字段叠印和两个折叠后重磁化。对于中三叠世至最早侏罗纪时代的所有样品，主要成分的绝对倾斜校正倾角小于20度，下至中阿尼西亚燧石的平均倾角为11.0度+/- 4.3度。古地磁极性反转观察到的低到中的阿尼西亚硅质岩与欧洲三叠纪的部分，在古生物学年龄的限制下，使用放射虫和牙形刺，假设阿尼西亚硅质岩在犬山沉积在南半球。这一结论不仅对日本，而且对亚洲沿着东缘含硅质岩增生杂岩的古地理演化具有重要的意义。
Paleomagnetic and paleontologic studies of Middle Triassic to earliest Jurassic radiolarian bedded chert in the Inuyama area, southern Mine terrane of central Japan, have shown that the chert was deposited in an equatorial region with a paleolatitude between 10 degreesN and 10 degreesS, and in particular, the lower to middle Anisian chert depositional basin was situated in the Southern Hemisphere. The chert has four characteristic components of remanent magnetization. The highest blocking temperature component, carried by hematite, shows positive fold and reversal tests and is regarded as the primary remanent magnetization acquired just after deposition. The other three components are interpreted as a present field overprint and two postfolding remagnetizations. The absolute, tilt-corrected inclinations of the primary component are less than 20 degrees for all the samples of Middle Triassic to earliest Jurassic age, with the mean inclination of the lower to middle Anisian chert being 11.0 degrees +/- 4.3 degrees. Paleomagnetic polarity reversals observed for the lower to middle Anisian chert are well correlated with those of the European Triassic sections, under paleontologic age constraints using radiolarians and conodonts, provided that the Anisian chert in Inuyama was deposited in the Southern Hemisphere. This conclusion illuminates the paleogeographic evolution of the chert-bearing accretionary complexes not only in Japan but along the eastern margin of Asia as well.