著者

山崎 大輔 辻野 典秀 芳野 極 米田 明

出版者

岡山大学

雑誌

基盤研究(A)

巻号頁・発行日

2017-04-01

---

本研究の目的は、深さ~1000 kmの粘性率異常の原因を解明することである。最近のジオイド研究から、下部マントルの深さ1000km付近で粘性率が1-2桁増加することが指摘されている。一方で、地震学的研究において、沈み込んで行くスラブの滞留が、660 kmの下部マントル境界のみならずおおくの場合で1000 kmにあることが見て取れる。すなわち、1000 kmにおける粘性率増加が、マントル対流へ与える影響は660 km不連続面と同程度かそれ以上であること示している。従って、全マントルの運動を理解する上で、この1000 kmの粘性増加が何に起因しているのかを物質学的に明らかにすることは非常に重要な課題である。下部マントルは主にブリッジマナイトとフェロペリクレースの2相混合岩石で構成されている。この2相では粘性率が数桁のオーダーで異なっており、複合岩石としての微細構造やそれぞれの相の量比が全岩の粘性率に影響を与える。すなわち、逆に、観測されている粘性率を与える量比を実験的に明らかにすれば、現在でも問題となっている下部マントルの組成(パイロライト的かコンドライト的か)については、新たな制約を与えることができる。そのため、下部マントル条件を実験的に再現し、ブリッジマナイトとフェロペリクレースの2相混合岩石の粘性率に関する実験を行ってきている。特に、30年度は、2相混合岩石に大変形剪断歪みを与える実験の技術的開発を行い、100%以上の実験に成功した。また、開発した手法を放射光その場観察実験に応用し、変形場での応力その場測定を実施した。

著者

芳野 極

出版者

日本高圧力学会

雑誌

高圧力の科学と技術 (ISSN:0917639X)

巻号頁・発行日

vol.29, no.2, pp.94-102, 2019 (Released:2019-07-18)

参考文献数

31

---

Knowledge of distribution and transport mechanism of melt in the Earth and planetary interiors is important for understanding formation process of stratified structure, estimation of melt fraction in partial molten region, and volatile recycling. In this article, advances in high pressure studies on melt distribution and its transport process were reviewed in terms of surface tension-driven process. Melt migration in solid media is controlled by melt connectivity. A traditional way to determine melt connectivity is determination of dihedral angle by quench experiments. Recently, in situ X-ray radiographic observation or electrical conductivity measurement are developing as effective ways to determine melt morphology. At the end of this article, an example of melt penetration experiments is reported. High pressure experiments on penetration of metallic iron alloy melt into lower mantle phases suggest absence of interaction between core and mantle by surface-tension driven penetration mechanism.

著者

芳野 極 三部 賢治 小野 重明

出版者

一般社団法人 日本地質学会

雑誌

日本地質学会学術大会講演要旨 (ISSN:13483935)

巻号頁・発行日

vol.2002, 2002

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

---

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.