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Thrust tectonics of Hidaka Collion Zone and formation of Hidaka Mountains, Hokkaido, Japan

日本北海道日高碰撞带逆冲构造与日高山脉的形成

基本信息

批准号：
08640564
负责人：
ARITA Kazunori
金额：
$ 1.34万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08640564/
关键词：
Hidaka Mountains Hidaka Main Thrust K-Ar dating Fission-track dating Mountain uplift Molasse deposit フイッショントラック年代

项目摘要

Uplift of the Hidaka Mountains has been related to thrusting along the Hidaka Main Thrust by which the Hidaka Metamorphic Belt is thrust over the Poroshiri Ophiolite Belt. In order to educidate the uplift process we decided biotite K-Ar ages on the metamorphic and granitic rocks in the souther Hidaka Metamorphic Belt and on granitic gravels in the Middle Miocene to Lower Pliocene molassses distributed in both sides of the Hidaka Mountains. Fission-track ages also were measured on zircons from central part of the metamorphic belt.K-Ar ages of the metamorphic belt are clearly separeted into eastern and western sides by a possible fault which is situated arond the crest line, that is, around 30Ma in the east and 19-17Ma in the west. These Early Miocne ages have an inverse correlation with the altitude of the sample localities, that is, the higher the localities are, the younger the radiometric ages are. This is completely contrary to the cases in the Himalaya and Alps. In addition K-Ar ages of granitic gravels from the mollases also present quite differnt ages in both sides. In eastern side the ages show the Middle Eocene to Early Oligocene (45.9 to 33.1Ma) , and the higher the stratigraphic horizon of the mollase samples are, the older these Paleogene ages are. On the other hand in the western side the ages are Early Miocene (19-17Ma) , and almost same regardless of the stratigraphic horizon. Zircons from central Hidaka Mountains yield FT ages of 16-12Ma, and also show the inverse correlation with the altitudes of sample localities especially in western side. The peculiar uplift process revealed by the radiometric ages is considered to be caused by rotational uplift due to thrusting of the Hidaka Main Thrust.

日高山的隆起与沿着日高主冲断层的逆冲作用有关，通过该逆冲作用，日高变质带被推覆在Poroshiri蛇绿岩带之上。为了揭示隆升过程，对日高变质带南部的变质岩和花岗质岩石以及分布于日高山两侧的中新世中期至上新世早期的花岗质砾石进行了黑云母K-Ar年龄测定。对变质带中部锆石进行了裂变径迹年龄测定，变质带的K-Ar年龄被一条可能位于山脊线附近的断裂明显地分为东西两侧，即东部约为30 Ma，西部约为19- 17 Ma。这些早中新世年龄与样品地点的海拔高度呈负相关，即地点越高，其年龄越年轻。这与喜马拉雅山和阿尔卑斯山的情况完全相反。此外，两侧软岩中花岗质砾石的K-Ar年龄也存在较大差异。东侧为中始新世-早渐新世（45.9 - 33.1Ma），且磨拉石样品层位越高，古近纪年龄越大。另一方面，在西侧，年龄为早中新世（19- 17 Ma），无论地层层位如何，年龄几乎相同。日高山中部锆石FT年龄为16- 12 Ma，与样品海拔高度呈负相关，尤其是西侧。放射性年龄所揭示的特殊隆升过程被认为是由日高主冲断层的逆冲作用引起的旋转隆升。