The Benkar Fault Zone: An Orogen-Scale Cross Fault in the Eastern Nepal Himalaya
The Benkar Fault Zone (BFZ) is a recently recognized, NNE-striking, brittle to ductile, cross fault that cuts across the dominant metamorphic fabric of the Greater Himalayan Sequence (GHS) and the Lesser Himalayan Sequence (LHS) in eastern Nepal. 40Ar/39Ar-muscovite cooling ages along a transect acr...
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GeoScienceWorld
2024-10-01
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| Series: | Lithosphere |
| Online Access: | https://pubs.geoscienceworld.org/gsw/lithosphere/article-pdf/doi/10.2113/2024/lithosphere_2023_299/7009727/lithosphere_2023_299.pdf |
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| author | Bibek Giri Mary Hubbard Christopher S. McDonald Neil Seifert Bishal KC |
| author_facet | Bibek Giri Mary Hubbard Christopher S. McDonald Neil Seifert Bishal KC |
| author_sort | Bibek Giri |
| collection | DOAJ |
| description | The Benkar Fault Zone (BFZ) is a recently recognized, NNE-striking, brittle to ductile, cross fault that cuts across the dominant metamorphic fabric of the Greater Himalayan Sequence (GHS) and the Lesser Himalayan Sequence (LHS) in eastern Nepal. 40Ar/39Ar-muscovite cooling ages along a transect across the BFZ in the GHS indicate movement younger than 12 Ma. To understand the mode of genesis, and seismo-tectonic implications of the BFZ, we mapped this fault from the Everest region in the upper Khumbu valley toward the south, across the Main Central Thrust, into the LHS and the Greater Himalayan Nappe. We recognize a series of cross faults segments, which we interpret the BFZ system. The currently mapped section of the BFZ is >100 km long, and its width is up to 4 km in the LHS. The BFZ is semi-ductile in the GHS region but is brittle in the south, where it is expressed as gouge zones, tectonically brecciated zones, sharp fault planes, and segments of nonpenetrative brittle deformation zones. From petrographic and kinematic analysis, we interpret largely a right-lateral, extensional sense of shear. Our work did not continue into the Sub-Himalaya, but the BFZ may continue through this zone into the foreland as documented in other Himalayan cross faults. While several genetic models have been proposed for cross faults in the Himalaya and other convergent orogens, we suggest that the BFZ may be related to extensional structures in Tibet. Understanding cross faults is not only important for the tectonic history of the Himalaya but due to the co-location of cross faults and seismogenic boundaries, there may be a causal relationship. Cross faults also follow many of the north-south river segments of the Himalaya and weakened fault rocks on the valley walls may enhance the landslide hazard in these areas. |
| format | Article |
| id | doaj-art-275d500bb7eb4f4f8a90a2f8d79c3fb8 |
| institution | OA Journals |
| issn | 1941-8264 1947-4253 |
| language | English |
| publishDate | 2024-10-01 |
| publisher | GeoScienceWorld |
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| series | Lithosphere |
| spelling | doaj-art-275d500bb7eb4f4f8a90a2f8d79c3fb82025-08-20T02:12:11ZengGeoScienceWorldLithosphere1941-82641947-42532024-10-012024410.2113/2024/lithosphere_2023_299The Benkar Fault Zone: An Orogen-Scale Cross Fault in the Eastern Nepal HimalayaBibek Giri0https://orcid.org/0000-0002-3388-9761Mary Hubbard1Christopher S. McDonald2Neil Seifert3Bishal KC4Department of Earth Sciences, Montana State University, Bozeman, MT, USADepartment of Earth Sciences, Montana State University, Bozeman, MT, USAGroup 18 Laboratories, School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USATeck Resources Limited, Vancouver, BC, CanadaAustralian Institute of Management and Commerce, Sydney, NSW, AustraliaThe Benkar Fault Zone (BFZ) is a recently recognized, NNE-striking, brittle to ductile, cross fault that cuts across the dominant metamorphic fabric of the Greater Himalayan Sequence (GHS) and the Lesser Himalayan Sequence (LHS) in eastern Nepal. 40Ar/39Ar-muscovite cooling ages along a transect across the BFZ in the GHS indicate movement younger than 12 Ma. To understand the mode of genesis, and seismo-tectonic implications of the BFZ, we mapped this fault from the Everest region in the upper Khumbu valley toward the south, across the Main Central Thrust, into the LHS and the Greater Himalayan Nappe. We recognize a series of cross faults segments, which we interpret the BFZ system. The currently mapped section of the BFZ is >100 km long, and its width is up to 4 km in the LHS. The BFZ is semi-ductile in the GHS region but is brittle in the south, where it is expressed as gouge zones, tectonically brecciated zones, sharp fault planes, and segments of nonpenetrative brittle deformation zones. From petrographic and kinematic analysis, we interpret largely a right-lateral, extensional sense of shear. Our work did not continue into the Sub-Himalaya, but the BFZ may continue through this zone into the foreland as documented in other Himalayan cross faults. While several genetic models have been proposed for cross faults in the Himalaya and other convergent orogens, we suggest that the BFZ may be related to extensional structures in Tibet. Understanding cross faults is not only important for the tectonic history of the Himalaya but due to the co-location of cross faults and seismogenic boundaries, there may be a causal relationship. Cross faults also follow many of the north-south river segments of the Himalaya and weakened fault rocks on the valley walls may enhance the landslide hazard in these areas.https://pubs.geoscienceworld.org/gsw/lithosphere/article-pdf/doi/10.2113/2024/lithosphere_2023_299/7009727/lithosphere_2023_299.pdf |
| spellingShingle | Bibek Giri Mary Hubbard Christopher S. McDonald Neil Seifert Bishal KC The Benkar Fault Zone: An Orogen-Scale Cross Fault in the Eastern Nepal Himalaya Lithosphere |
| title | The Benkar Fault Zone: An Orogen-Scale Cross Fault in the Eastern Nepal Himalaya |
| title_full | The Benkar Fault Zone: An Orogen-Scale Cross Fault in the Eastern Nepal Himalaya |
| title_fullStr | The Benkar Fault Zone: An Orogen-Scale Cross Fault in the Eastern Nepal Himalaya |
| title_full_unstemmed | The Benkar Fault Zone: An Orogen-Scale Cross Fault in the Eastern Nepal Himalaya |
| title_short | The Benkar Fault Zone: An Orogen-Scale Cross Fault in the Eastern Nepal Himalaya |
| title_sort | benkar fault zone an orogen scale cross fault in the eastern nepal himalaya |
| url | https://pubs.geoscienceworld.org/gsw/lithosphere/article-pdf/doi/10.2113/2024/lithosphere_2023_299/7009727/lithosphere_2023_299.pdf |
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