2007 Fiscal Year Final Research Report Summary
Formation mechanism and uplift process of the Kathmandu nappe in the Nepal Himalaya : a geochronological approach
| Project/Area Number |
18540447
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Geology
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| Research Institution | Hokkaido University |
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Principal Investigator |
ARITA Kazunori Hokkaido University, Hokkaido University Museum, Researcher (30091408)
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| Co-Investigator(Kenkyū-buntansha) |
ITAYA Tetsumaru Okayama University of Science, Research Institute of Natural Sciences, Professor (60148682)
OHIRA Hiroto Shimane University, Interdisciplinary Faculty of Science and Engineering, Assistant professor (60273918)
YAMAGUCHI Haruka Hokkaido University, Japan Agency for Marine-Earth Science and Technology, IFREE, Researcher (80359207)
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| Project Period (FY) |
2006 – 2007
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| Keywords | isotopic age dating / nappe / thrust / mountain uplift / Nepal / Himalaya / out-of-sequence thrust |
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| Research Abstract |
The project aimed to elucidate the formational mechanism and uplift process of the Kathmandu nappe in central Nepal on the basis of isotopic age dating, and obtained the following results.
1. The southern limit of the Kathmandu Nappe can be traced in the field. The field observations and laboratory works denied the double-nappe idea for the Kathmandu nappe.
2. The Rb-Sr isochron age determination showed that the mylonitic augen gneisses in the Main Central Thrust (MCT) zone from the southern margin of the Nappe is late Proterozoic in age which is consistent with those found in the MCT zone in the northern root zone.
3. The U-Th age dating for monazites included in garnet of phyllites in the MCT zone was not carried successfully due to lack of monazite, but some age determinations yielded the Miooene ages of 22-13 Ma for the middle part of the MCT zone and the late Pliocene ages of 4-2 Ma for the southern marginal part. This suggests the out-of-sequence thrust cutting the Nappe to be active younger than ca. 13 Ma and older than 4 Ma.
4. FT age datings of zircons and apatites from the Kathmandu Nappe are younging northwards from ca.9 Ma in the southern part to 2-1.5 Ma in the northern part, suggesting the uplift of the Nappe to be caused by the ramp structure in the depth and the splay thrust from the ramp and by the northward wedging of the Indian middle crust.
5. Zircon FT age distribution across the Gosainkund Mountains in the northern part of the Nappe presents that the relationship of the ages and sample altitudes on the southern and northern sides of the mountain is in strong contrast, suggesting that the rocks of the southern side passed through the closure temperature of zircon before ca. 2.6 Ma and then the northern side was uplifted more rapidly.
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Research Products
(15 results)
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[Journal Article] Timing of the Tsergo Ri Landslide, Langtang Himal, Nepal, determined by fission-track dating of pseudotachylyte2007
Author(s)
Takagi, H., Arita, K., Danhara, T., Iwano, H.
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Journal Title
Journal of Asian Earth Sciences 29(2/3)
Pages: 466-472
Description
「研究成果報告書概要(欧文)」より
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