Vibroseis Seismic Reflection Profiling, Crustal Strructure and Tectonics of Hidaka Collion Zone, Hokkaido, Japan

日本北海道日高碰撞带的可控震源地震反射剖面、地壳结构和构造

• 批准号: 06402018
• 负责人: ARITA Kazunori
• 金额: $ 21.63万
• 依托单位: HOKKAIDO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (A)
• 财政年份: 1994
• 资助国家: 日本
• 起止时间: 1994 至 1995
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-06402018/
• 关键词: Vibroseis reflection profiling; Hidaka collision zone; Crustal structure; Hidaka Main Thrust; Buogrer anomalies; Magnetotelluric method; Collision tectonics; Reflector; 日高変成帯; 反射法地震探査; 地殻構造; バイブロサイス

We tried to image the crustal structure of the Hidaka collision zone (Hidaka metamorphic belt : HMB) along a 20km-long measurement line on Route 236 across the zone by using Vibroseis seismic reflection method (Hidaka vibroseis 94), gravity survey and magnetotelluric observations. The following conclusions are rearched :(1) The Hidaka Main Thrust (HMT) which shows steep dip at the surface dips NNE at 45ﾟ beneath the HMB,and dips more gently at about 7-km depth beneath the eastern part of the HMB.The HMT is a listric fault. This suggests the HMB to cut the lithology boundary and schistosity of the HMB(2) Although the Hidaka Western Thrust (HWT) separating the Poroshiri ophiolite belt from the Idon'nappu melange belt is not seen at the upper part, a reflectior is detected 1km below the HMT reflector. The part between these two reflectors is inferred to be the Poroshiri ophiolite.(3) The shallow portion of the don'nappu melange belt at front of the collision zone has a number of NNE-dipping reflections, indicative of a fold-and-thrust structure.(4) There is a subhorizontal reflector at 13-km depth only in the NNE part of the seismic profile. This reflector may correspond to the velocity boundary (5.9-6.6 km/s) obtained from seismic refraction profiling in the northern HMB.(5) The gravity data in the area including profiling line show large positive Buoguer anomalies along the Hidaka Mountains, suggesting an existance of high-density material at shallow part of the HMB.(6) Based on magnetotelluric data a high resistivity (10,000 ohm-m) layr of the Hidaka metamorphic rocks reaches about 8km in thickness. Below the layr there is a 2-km thick relatively conductive (100 ohm-m) layr which is underlan by a very high resistivity (150,000 ohm-m) layr.

利用可控震源地震反射法（日高94型可控震源）、重力测量和大地电磁观测，沿着236国道20 km长的测线，对日高碰撞带（日高变质带：HMB）的地壳结构进行了成像。（1）日高主冲断层在地表上呈陡倾，在其下方45 °处倾向北北东，在其东部约7 km处倾向较缓，为铲形断层。（2）虽然在上部没有看到分隔Poroshiri蛇绿岩带和Idonnappu混杂岩带的日高西逆冲断层（HWT），但在HMT反射层以下1 km处检测到一个反射层。这两个反射体之间的部分被推断为Poroshiri蛇绿岩。(3)碰撞带前部的唐纳普混杂岩带的浅部具有多个NNE向倾斜的反射，指示褶皱-冲断构造。(4)仅在地震剖面的北北东向部分，在13公里深度处存在一个近水平反射层。该反射层可能对应于从北方HMB的地震折射剖面获得的速度边界（5.9-6.6 km/s）。(5)包括剖面线在内的该区重力资料显示，沿着日高山脉存在较大的Buoguer正异常，表明在HMB的浅部存在高密度物质。(6)根据大地电磁数据，日高变质岩的高电阻率（10，000 ohm-m）层厚约8 km。在该层之下有一个2公里厚的相对导电（100欧姆-米）层，其下是一个非常高的电阻率（150,000欧姆-米）层。