Evolution of the Komiji Syncline in the North Fossa Magna, central Japan: Paleomagnetic and K–Ar age insights
Evolution of the Komiji Syncline in the North Fossa Magna, central Japan: Paleomagnetic and K–Ar age insights
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日本中部北大窝小美地向斜的演化：古地磁和 K-Ar 见解时代
DOI：
10.1046/j.1440-1738.2003.00397.x
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发表时间：
2003
期刊：
影响因子：
1.5
通讯作者：
Kazuo Saito
中科院分区：
文献类型：
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作者：
S. Niitsuma;N. Niitsuma;Kazuo Saito
摘要我们对日本中部北大窝新近纪安山质熔岩和志贺见组岩床进行了古地磁测量和K-Ar定年。Shigarami组分布在北大窝西南部褶皱带小见寺向斜的轴部。结果表明，小见寺向斜形成于上新世（4.42 ± 0.12 Ma）之后不久。 Shigarami组的沉积岩由浅海和河流沉积组成。在浅海沉积物中发现安山岩岩床侵入体，在河流沉积物中发现两个安山岩熔岩流。定向样品取自四个地点的岩床和三个地点的熔岩。通过分步交变磁场和热退磁，样品产生了稳定的剩磁。正褶曲测试结果表明，在根据沉积岩层理方向进行校正后，稳定的逆磁化强度集中在平均反极性169.0°、倾角-58.5 °和95%置信限9.0°附近。 从古地磁测量样品中选取了4个新鲜样品进行K-Ar定年。从岩床上取的3个样品的基底年龄分别为4.42 ± 0.12，4.49 ± 0.22和4.69 ± 0.13Ma，而从下部熔岩中取的样品的基底年龄为5.91 ± 0.26Ma。 我们认为，小见寺向斜是在该地区的熔岩和岩床侵位后形成的，因为下降的中新世地层与Shigarami组一致地褶皱。上新世和更新世地层不整合于褶皱地层之上。变形可能在上新世进行，然后在早更新世减缓。研究结果表明，菲律宾海板块的北西运动和丹泽地块的碰撞不仅影响了南大窝，也影响了北大窝。
Abstract We carried out paleomagnetic measurements and K–Ar dating on Neogene andesitic lavas and sills of the Shigarami Formation in North Fossa Magna, central Japan. The Shigarami Formation is distributed in the axial part of the Komiji Syncline in the folding zone of the southwestern North Fossa Magna. Results of the present study indicate that the Komiji Syncline was formed shortly after 4.42 ± 0.12 Ma during the Pliocene. The sedimentary rocks of the Shigarami Formation consist of shallow marine and fluvial deposits. Intrusions of andesitic sills are found in the shallow marine deposits and two andesitic lava flows are present in the fluvial deposits. Oriented samples were taken from the sills at four sites and from the lavas at three sites. The samples produced stable remanent magnetization through stepwise alternating field and thermal demagnetizations. Results of a positive fold test indicate that the stable remanent magnetizations concentrate around a mean reversed polarity of declination = 169.0°, inclination = −58.5° and 95% confidence limit = 9.0° after corrections have been made according to the direction of the bedding of the sedimentary rocks. Four fresh samples were selected for K–Ar dating from the samples used for paleomagnetic measurements. The groundmass of three samples taken from the sills yield ages of 4.42 ± 0.12, 4.49 ± 0.22 and 4.69 ± 0.13 Ma, whereas the one taken from the lower lava has an age of 5.91 ± 0.26 Ma. We believe that the Komiji Syncline was formed after the emplacement of lavas and sills in the area, because the descending Miocene strata were folded concordantly with the Shigarami Formation. The Pliocene and Pleistocene strata rest unconformably on the folded strata. The deformation might have progressed during the Pliocene, then slowed down in the Early Pleistocene. Our results suggest that the northwestward motion of the Philippine Sea Plate and the collision of the Tanzawa Block affected not only the South Fossa Magna, but also the North Fossa Magna.
DOI：
10.1098/rspa.1953.0064
发表时间：
1953-01-01
影响因子：
--
作者：
FISHER, R
通讯作者：
FISHER, R