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Are there any fossil seismic zone in an accretionary complex ? -A thermochronologic study-

增生杂岩中是否存在化石地震带？

基本信息

批准号：
11640446
负责人：
HASEBE Noriko
金额：
$ 2.37万
依托单位：
KANAZAWA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-11640446/
关键词：
fission track method Shimanto Belt faults accretionary complex earthquake 九州延岡断層

项目摘要

Accretionary prisms develop along subducted continental margins by the offscraping and underplating of the mixture of oceanic sediments and trench fill continental deposits. Because subduction zones, where accretionary prisms develop, is the area of large earthquakes at the depth of 10-30km, the thermal energy radiated by earthquakes could cause various geological events to surrounding accretionary complexes, as is detected by the fission track (FT) method from rocks around the active Nojima Fault, Awaji Island, central Japan.The Shimanto accretionary complex in northeastern Kyusyu, southwest Japan, is divided into four units based on microfossiles and rock facies. The degree of heating by regional metamorphism is estimated for each units using fission track method and vitrinite reflectance. The thermal disturbance within Mikado formation, which exists south of the Nobeoka thrust, becomes higher from south to north according to FT ages and track-length distribution. The FT age of the sample collected from thrust gouge of the Nobeoka thrust fault shows higher thermal disturbance than that of hanging Kitagawa unit and the lower Mikado formation. The FT age, 31.2±5.7 Ma, may indicate the time of heating by the thrust fault activity. The time range between sedimentation and the obtained FT age is less than 5 million years. Provided the velocity and the angle of subduction to be 50 mm/yr and 13°, respectively, underthrusted sediments reach the depth, where plate-boundary earthquakes occur, within a few million years. Hence the obtained time of thrust activity may cause a large earthquake at the plate boundary. Other faults show no evidenceof heating in FT data. This means that the degree of heating may vary along the fault plane.

增生棱柱体是大洋沉积物和海沟充填大陆沉积物混合物的刮离和底侵作用，沿沿着俯冲大陆边发育。在日本中部淡路岛野岛活动断层周围的岩石中，裂变径迹（FT）方法发现，由于俯冲带是10- 30 km深度的大地震活动区，地震辐射的热能可对周围的增生杂岩引起各种地质事件。根据微相和岩相可划分为四个单元。利用裂变径迹法和镜质体反射率估算了各单元区域变质作用的加热程度。根据FT年龄和径迹长度分布，位于野冈逆冲断层以南的天皇组内的热扰动由南向北逐渐增大。从野冈逆冲断层的冲断层泥中采集的样品的FT年龄显示出比上北川单元和下天皇组更高的热扰动。FT年龄为31.2± 5.7Ma，反映了逆冲断层活动的加热时间。从沉积作用到获得FT年龄的时间范围小于500万年。假设俯冲速度和俯冲角度分别为50毫米/年和13°，下冲沉积物在几百万年内到达发生板块边界地震的深度。因此，所获得的逆冲活动时间可能会在板块边界引起大地震。其他断层在FT数据中没有显示加热的证据。这意味着加热的程度可以沿着断层面变化。