Thrust Sheets, Tectonic Windows, and Intermontane Basins in the Nepal Himalaya

2020 ◽  
pp. 233-254
Author(s):  
Megh Raj Dhital ◽  
Basanta Raj Adhikari
Keyword(s):  
Nepal Himalaya ◽  
Thrust Sheets ◽  
Intermontane Basins ◽  
Tectonic Windows

Strain partitioning within thrust sheets of tectonic windows: Insights from eastern Himalaya

2021 ◽  
Author(s):  
Jyoti Das ◽  
Kathakali Bhattacharyya
Keyword(s):  
Finite Strain ◽  
Strain Analysis ◽  
Eastern Himalaya ◽  
Strain Partitioning ◽  
Transport Direction ◽  
Thrust Sheets ◽  
Strain Magnitude ◽  
Far Eastern ◽  
Tectonic Windows ◽  
The Impact

<p>In a fold-thrust belt (FTB), penetrative strain within thrust sheets vary in its magnitude, orientation and type. Addressing variation in magnitude and orientation of strain from major thrust sheets in a FTB, both along the transport direction and along-strike, enable us to understand the complexity of strain partitioning during orogeny. Tectonic windows provide an opportunity to understand the impact of footwall structures on finite strain geometry and orientations of the overlying thrust sheets. In this study, we investigate how penetrative strain is partitioned from the internal to the external major thrust sheets in the Siang window in far-eastern Arunachal Himalayan FTB. We also compare these results with similar thrust sheets from well preserved tectonic windows in the eastern Himalaya, i.e., the Teesta window of the Sikkim and Kuru Chu window of the Bhutan Himalayan FTB.</p><p>We conduct finite strain analysis on quartz grains using R<sub>f</sub>-φ, normalized Fry and Shape Matrix Eigenvector methods. The studied lithologies are gneiss for the internal Pelling-Munsiari-Bomdilla thrust (PT) sheet, while quartzite and sandstone dominantly comprise the external Main Boundary thrust (MBT) and the Main Frontal thrust (MFT) sheets. The rocks north of the PT sheet are not accessible. Results from this study indicate that all the studied rocks record an overall flattening strain. Magnitude of the finite penetrative strain decreases from the internal PT sheet to the external MBT, MFT sheets in the Siang window. The long axes of the finite strain ellipsoids (X) generally have a low plunge and vary in bearing, irrespective of the structural positions of the different thrust sheets. Finite strain ellipses are folded along with the thrust sheets indicating that the penetrative strain developed prior to folding of the thrust sheets. The results also indicate that the footwall structures affect the strain geometry in the interior part of the Himalayan wedge. The grain scale shortening percentage is highest for internal PT sheet and it progressively decreases towards the external MFT sheet. The results indicate greater contribution of thrust-parallel stretch than thrust-perpendicular component, in both internal and external thrust sheets in the Siang window. Preliminary results also suggest that the strain magnitude and grain-scale shortening percentage are the lowest, and orientations of X-axes are more variable with respect to the regional transport direction in the far-eastern Siang window as compared to the other westerly lying regional transects of the Himalayan FTB.</p>

scholarly journals Transverse faults and block movements in Nepal Himalaya: results from satellite interpretation

1998 ◽  
Vol 17 ◽  
Author(s):  
P. Hoppe
Keyword(s):  
Satellite Images ◽  
Aerial Photographs ◽  
Indian Plate ◽  
Lesser Himalaya ◽  
Local Pressure ◽  
Regional Trend ◽  
Nepal Himalaya ◽  
Tectonic History ◽  
Thrust Sheets ◽  
History Of

The study of aerial photographs and satellite images has revealed the youngest tectonic history of Nepal Himalaya. The nappes and thrust sheets piled up during the Alpinie orogeny are now breaking into smaller blocks and slide aside the northward pushing and subducting Indian Plate. Since the Pleistocene, faults are opening perpendicularly or obliquely to the regional trend, and blocks are moving laterally. Local pressure structures were developed by these movements. There is selective erosion in the regional synclines and anticlines of the Lesser Himalaya. The upper sections of the Higher Himalayan Crystalline and Tibetan Series are generally preserved in depressions on top of the Lesser Himalaya. The Lesser Himalayan rocks themselves are mainly outcrop in the antlclinal areas.

Ecological relationships at a near-natural treeline, Rolwaling Valley, Nepal Himalaya: Implications for the sensitivity to climate change

Erdkunde ◽  
2020 ◽  
Vol 74 (1) ◽  
pp. 15-44
Author(s):  
Niels Schwab ◽  
Karolina Janecka ◽  
Ryszard J. Kaczka ◽  
Jürgen Böhner ◽  
Ram Prasad Chaudhary ◽  
...  
Keyword(s):  
Climate Change ◽  
Nepal Himalaya ◽  
Ecological Relationships

scholarly journals Kinematic and tectonic significance of microstructures and crystallographic fabrics within quartz mylonites from the Assynt and Eriboll regions of the Moine thrust zone, NW Scotland

1986 ◽  
Vol 77 (2) ◽  
pp. 99-125 ◽  
Author(s):  
R. D. Law ◽  
M. Casey ◽  
R. J. Knipe
Keyword(s):  
Strain Path ◽  
Extensional Flow ◽  
Crystallographic Preferred Orientation ◽  
X Ray ◽  
Tectonic Significance ◽  
Thrust Zone ◽  
Thrust Sheets ◽  
Strain Paths ◽  
Tectonic Loading ◽  
Microstructural Studies

ABSTRACTUsing a combination of optical microscopy and X-ray texture goniometry, an integrated microstructural and crystallographic fabric study has been made of quartz mylonites from thrust sheets located beneath, but immediately adjacent to, the Moine thrust in the Assynt and Eriboll regions of NW Scotland. A correlation is established between shape fabric symmetry and pattern of crystallographic preferred orientation, a particularly clear relationship being observed between shape fabric variation and quartza-axis fabrics.Coaxial strain paths dominate the internal parts of the thrust sheets and are indicated by quartzc- anda-axis fabrics which are symmetrical with respect to foliation and lineation. Non-coaxial strain paths are indicated within the more intensely deformed quartzites located near the boundaries of the sheets by asymmetricalc- anda-axis fabrics. These kinematic interpretations are supported by microstructural studies. At the Stack of Glencoul in the northern part of the Assynt region, the transition zone between these kinematic (strain path) domains is located at approximately 20 cm beneath the Moine thrust and is marked by a progression from symmetrical cross-girdlec-axis fabrics (30cm beneath the thrust), through asymmetrical cross-girdlec-axis fabrics to asymmetrical single girdlec-axis fabrics (0·5 cm beneath the thrust).Tectonic models (incorporating processes such as extensional flow, gravity spreading and tectonic loading) which may account for the presence of strain path domains within the thrust sheets are considered, and their compatibility with local thrust sheet geometries assessed.

Slope denudation and the supply of debris to cones in Langtang Himal, Central Nepal Himalaya

Geomorphology ◽  
1998 ◽  
Vol 26 (1-3) ◽  
pp. 185-197 ◽  
Author(s):  
Teiji Watanabe ◽  
Liu Dali ◽  
Takayuki Shiraiwa
Keyword(s):  
Nepal Himalaya ◽  
Central Nepal
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