著者

宮下 純夫 新井 孝志 長橋 徹

出版者

日本地質学会

雑誌

地質学論集 (ISSN:03858545)

巻号頁・発行日

no.47, pp.307-323, 1997-04-24

被引用文献数

17

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北海道中央部を構成する日高帯には, 周囲の砂泥質堆積岩と同時期に形成された現地性緑色岩が多数分布している。これらは, 日高帯西縁のイドンナップ帯, 日高帯西部, 日高帯東部の3帯の緑色岩に区分される。年代は, イドンナップ帯のものが白亜紀中頃, 日高帯西部は後期白亜紀後半, 日高帯東部は古第三紀暁新世-始新世と推定される。緑色岩の全岩組成はいずれもN-MORBの特徴を示す。これらは, イドンナップ帯においてはユーラシアプレートとイザナギ-クラプレートとの洩れ型トランスフォーム境界, もしくはイザナギ-クラ海嶺, 日高帯西部については沈み込み境界に対して高角な海洋プレート内の洩れ型トランスフォーム断層, 日高帯東部についてはクラ-太平洋海嶺に由来すると推定される。日高帯は, 後期白亜紀後半から古第三紀にかけて海嶺の多重衝突を経験した特異な付加体で, 日高火成・変成作用の発生によりこの付加体は大陸性地殻へと転化した。これは, 海嶺の相次ぐ衝突による付加体深部の異常な温度上昇, 大量の陸源砕屑物の供給による付加体の急激な成長, 東側から古千島弧が接近してきたなどの複合によっていると考えられる。

著者

亀田 純 木村 学 O. A. MELINIKOV 早坂 康隆 橋本 善孝 坂島 隆彦 新井 孝志 芳野 極 鈴木 紀毅

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.109, no.2, pp.235-248, 2000-04-25 (Released:2010-11-18)

参考文献数

21

被引用文献数

4 8

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The region from Sakhalin in Russia to the eastern margin of the Japan Sea has been regarded as a convergent plate boundary zone between the Eurasia and the North America Plates because large earthquakes and active crustal movements are prominent in this zone. These activities along the eastern margin of the Japan Sea to southern Sakhalin are almost consistent with the expected relative plate motion deduced from the Euler pole which is estimated from the magnetic anomaly lineations in the Atlantic Ocean, but the modern tectonic aspect in northern Sakhalin is inconsistent; e.g., 1995 Neftegorsk Earthquake is one of the typical events.As a result of a structural and tectonic study in northern Sakhalin, the NE-SW compressive tectonic feature since the Late Miocene was clarified. In the northernmost area of the Schmidt Peninsula, the early Cretaceous ophiolite thrusts upon the Late Cretaceous sedimentary rocks. The ophiolite has an overturned sequence: serpentinites, gabbros, basaltic rocks, and hemipelagic sediments in descending order. The Cretaceous sediments form a map-scale and NW vergent synclinorium. All the deformation structures in outcrop scale, such as micro-folds, minor reverse and normal faults, axial plane cleavages and bedding slips, are consistent with a large scale folding. These structural relationships suggest only one event of deformation, which appears to be linked to overthrusting of the ophiolitic rocks.A structural investigation of the southeastern part of the Schmidt Peninsula revealed that the Middle Miocene sediments composed of siltstone and sandstone are folded with wavelength of several tens to several hundred meters. Their fold axes trend in the NW direction, which indicates that deformation under the NE compression is the same as the deformation in the northernmost area. The thickness of sedimentary layers are constant everywhere in folding. This fact indicates that the timing of the deformation is after sedimentation, that is, after the Middle Miocene. This deformation event is consistent with modern activity in northern Sakhalin. Therefore, the modern tectonic framework might have started in the Late Miocene time.A plate tectonic model indicates that the modern relative motion between the Eurasia and the North America Plate started at about 11 m. y. ago. The Late Miocene onset of the modern tectonic framework in northern Sakhalin occurred at almost the same time. The most reliable model to explain the discrepancy of sense of movement from the Eurasia-North America retative motion, may be the “extrusion” of the Okhotsk Block toward the Pacific Ocean. The dextral extrusion boundary in northern Sakhalin may be traced along theeastern coast of Sakhalin to the northern edge of the Kuril Basin, where active seismicityhas been observed although a detailed study of focal mechanisms and other tectonic aspects is needed in the future.