ヒマラヤのテクトニクス  [in Japanese] Tectonics of the Himalayas  [in Japanese]

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Author(s)

    • 酒井 治孝 Sakai Harutaka
    • 京都大学大学院理学研究科地球惑星科学専攻地質学鉱物学教室 Department of Geology and Mineralogy, Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University

Abstract

<p>ヒマラヤの4つの地質帯を画するプレート境界断層の活動が,北から南へと移動するのに伴い山脈は上昇・隆起してきた.大陸衝突以前に深度100kmを超えるマントルまで沈み込んだテチス海の海洋プレートがslab break-offしたことにより,約50~35Maにチベット前縁山地が急激に上昇した.次にインド亜大陸の北縁の上部原生界の地層が沈み込み,地下約40kmに達し中圧型の変成作用を被ったが,デラミナーションを起こし,22~16 Maに急激に上昇した.約15Maに地表に露出した変成帯は上昇を続け,南方のレッサーヒマラヤを構造的に覆い変成岩ナップを形成したが,その運動は11~10Maに停止した.それ以降ナップと下盤の弱変成したレッサーヒマラヤ堆積物は,その先端から北方に向け約10km/Myrの速度で冷却した.また運動停止後,その前縁に生じたMBTに沿ってインドプレートの沈み込みが始まり,3~2.5Maには南方のMFTに移動し,それによってヒマラヤ前縁山地とシワリク丘陵が誕生した.</p>

<p>The Himalayan range was formed and uplifted in association with the southward migration of plate boundary thrusts that separate the Himalaya into four belts. Initially, during 50-35 Ma, the Tibetan marginal mountain range was uplifted after slab break-off of the Tethyan oceanic plate, which was subducted under the Asian continent to depths of up to 100 km. During the second stage at ~35-25 Ma, the Mesoproterozoic sediments deposited on the northern passive margin of the Greater India were subducted and underwent moderate-pressure metamorphism at depths of ~40 km. Subsequent to metamorphism, metamorphosed continental crust was separated from the underlying mantle by delamination, and its rapid exhumation and associated amphibolite facies metamorphism occurred during 22-16 Ma. Partially melted metamorphic rocks generated granitic melt that intruded both metamorphic rocks and Tibetan Tethys sediments during the Miocene. Exhumation of the metamorphic belt continued after its exposure at ~15 Ma, forming an extensive metamorphic nappe covering the Lesser Himalayan sediments. After ceasing movement at 11-10 Ma, the Indian plate started to subduct along the Main Boundary Thrust (MBT), which was newly formed in front of the southern margin of the metamorphic nappe. At the same time, the nappe and weakly metamorphosed underlying Lesser Himalayan sediments started to cool laterally from the southern front to the root zone at a rate of ~10 km/Myr. At 3-2.5 Ma, the plate boundary fault shifted to the Main Frontal Thrust (MFT) to the south of the MBT, causing rapid uplift of the marginal range of the Lesser Himalaya and the Siwalik Hills. Today, the Indian Plate is converging with the Asian Continent at the rate of 58 mm/yr, and half of this convergence is consumed by uplift of the Siwalik Hills along the MFT.</p>

Journal

  • The Journal of the Geological Society of Japan

    The Journal of the Geological Society of Japan 123(6), 403-421, 2017

    The Geological Society of Japan

Codes

  • NII Article ID (NAID)
    130005858623
  • NII NACSIS-CAT ID (NCID)
    AN00141768
  • Text Lang
    JPN
  • ISSN
    0016-7630
  • NDL Article ID
    028363888
  • NDL Call No.
    Z15-174
  • Data Source
    NDL  J-STAGE 
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