論文

査読有り 本文へのリンクあり
2008年

Magnetic fabric of the Siwalik sediments (Nepal): implications to the time-space evolution of the stress field

Journal of Nepal Geological Society
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回数 : 212
  • ゴータム ピタンバル

38
開始ページ
39
終了ページ
48
記述言語
英語
掲載種別
研究論文(学術雑誌)

Magnetic fabric data based on the anisotropy of magnetic susceptibility (AMS) of the sediments constituting the Siwalik<br />
sections (Karnali R., Amilia–Tui Road, Surai R., Tinau R., and Rato R.) in Nepal have been analysed for the variability of<br />
magnetic lineation and the implications to the time-space evolution of the stress field in this region during the last 16 myrs.<br />
This involved compilation of (i) the magnetic polarity data that constrain the depositional age of the Nepalese Siwaliks to<br />
ca. 16 to 1 Ma, and (ii) the declination of characteristic magnetic remanence to reveal the relative tectonic rotations (17°<br />
CCW at Butwal to 9° CW at Amilia). The magnetic fabric, defined mainly by alignment of paramagnetic minerals, corresponds<br />
to an oblate ellipsoid with foliation parallel to bedding plane, implying a sedimentary-compactional origin. The magnetic<br />
lineations show well defined clusters (confined in or close to the bedding plane). Being subparallel to the fold axes/bedding<br />
strikes/thrust fronts, these lineations are assumed to originate from a secondary mild deformation process related to the<br />
compression tectonics in the Siwalik foredeep and therefore correspond to the active direction of the minimum principal<br />
horizontal stress active during foredeep deposition. Hence, the direction of compression is orthogonal to the mean lineation.<br />
The compression direction in the palaeogeographic coordinates can be obtained by introducing an additional correction for<br />
the tectonic rotation about the vertical, using the palaeomagnetic declination. Available AMS-based lineations, corrected for<br />
rotation about vertical using palaeomagnetic declinations, reveal that the compression direction in the Himalayan foreland<br />
remained in general N to NNE with significant deviations in its far western part, in particular around the Amilia–Tui section<br />
where the direction was N58o<br />
E.

リンク情報
URL
http://www.cris.hokudai.ac.jp/rso/gautam/siwfab-gautam2008.pdf

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