Main Boundary Thrust
{{Short description|Geological fault in the Himalayas}}
{{Infobox fault
| name = Main Boundary Thrust
| other_name = Main Boundary Fault
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| location = Himalayas
| country = India, Nepal, Pakistan, Bhutan
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| range = Himalayan Mountains
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| length = {{cvt|2400|km|abbr=on}}
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| type = Thrust (formerly), Normal (present)
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| orogeny = Himalayan
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The Main Boundary Thrust (MBT), also known as the Main Boundary Fault, is a discontinuous series of seismic faults in the Himalayas which form the structural boundary between the Outer Himalayas and Lower Himalayan Range. The MBT is itself part of a series of thrusts which helped to accommodate the deformation when the Indian Plate collided with the Eurasian Plate in the Cenozoic. The MBT fault system began forming in the Miocene. The MBT consists of multiple segments, and is composed from west to east of the Murree and Drang thrust faults, the Krol thrust fault, the Surkhet-Ghorahi thrust fault, the Kathmandu thrust, and the Gondwana/Garu thrust. Despite originating as a thrust fault in the collision of India and Eurasia, the MBT system has reactivated as a normal faulting system.
Tectonic setting
{{Main|Paleogeography of the India–Asia collision system|l1=India-Asia collision}}
The MBT was formed as a result of the collision of the Indian continent with Asia. It developed to relieve stresses from the compression of the continental collision. When the MBT initially formed around 10-25 million years ago,{{sfn|Meigs|Burbank|Beck|1995|p=423, 425}} it was a system of thrust faults which accommodated stresses from the compression of the continental collision which led to Himalayan uplift. The Main Himalayan Thrust is the root Décollement structure, and results in similar fault system splays such as the Main Himalayan Thrust, Main Central Thrust, and the South Tibetan Detachment. These faults accommodated stresses parallel to the MBT and helped the Himalayan mountains grow.{{sfn|Thiede|Robert|Stübner|Dey|2017|p=716, 717}} Each of these faults served as the primary reliever of strain in the Himalayan Orogeny until being abandoned in a successive chain of intracontinental thrust faults.{{sfn|Meigs|Burbank|Beck|1995|p=423}} Currently, the Main Frontal Thrust is the main thrust fault in the system.{{sfn|Patra|Saha|2019}}
Segments
The Main Boundary Thrust consists of multiple segments spanning {{cvt|2400|km|abbr=on}} in the Himalayas.
=Murree/Drang thrust=
The Murree fault is a thrust fault which lies in Kashmir. To its southeast, the Drang thrust continues as an extension of the Murree thrust in Himachal.{{sfn|Valdiya|1980|p=329}}
=Krol thrust=
To the southeast of the Murree and Drang faults, the Krol thrust is the main strand of the MBT and has "caused great shattering, inversion
and imbricate thrusting".{{sfn|Valdiya|1980|p=329, 331}}
=Surkhet-Ghorahi fault=
The Surkhet-Ghorahi thrust fault is a northwest trending fault in Central Nepal.{{sfn|Malinconico|Lillie|Nakata|1989|p=253-254}} It stretches from Surkhet to Ghorahi in over an extent of {{cvt|90-120|km|abbr=on}}.{{sfnm|1a1=Mugnier|1a2=Huyghe|1a3=Chalaron|1a4=Mascle|1y=1994|1p=200|2a1=Malinconico|2a2=Lillie|2a3=Nakata|2y=1989|2p=253}} At the western bank of the Bheri River, the fault slips at a rate of {{cvt|0.75|mm|abbr=on}}/yr.{{sfn|Malinconico|Lillie|Nakata|1989|p=256}} The fault shows vertical fault scarp of {{cvt|30|m|abbr=on}}.{{sfn|Riesner|Bollinger|Hubbard|2021}}
=Kathmandu thrust=
=Gondwana/Garu thrust=
The Gondwana thrust fault system runs from west of Thimphu passing through Bhutan before terminating in West Kameng. In the east it is termed the Garu thrust, though it is a part of the Gondwana thrust.{{sfn|Valdiya|1980|p=329, 334}}
Modern reactivation
After acting as a thrust fault initially, the Surkhet-Ghorahi may have reactivated as a normal fault—moving the opposite direction of a thrust fault.{{sfn|Mugnier|Huyghe|Chalaron|Mascle|1994|p=205, 210}}
References
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Sources
{{refbegin}}
- {{cite journal |last1=Meigs |first1=Andrew J. |last2=Burbank |first2=Douglas W. |last3=Beck |first3=Richard A. |title=Middle-late Miocene (>10 Ma) formation of the Main Boundary thrust in the western Himalaya |journal=Geology |date=May 1, 1995 |volume=23 |issue=5 |pages=423–426 |doi=10.1130/0091-7613(1995)023<0423:MLMMFO>2.3.CO;2 |bibcode=1995Geo....23..423M |url=https://pubs.geoscienceworld.org/gsa/geology/article-abstract/23/5/423/206310/Middle-late-Miocene-gt-10-Ma-formation-of-the-Main |access-date=15 May 2024|url-access=subscription }}
- {{cite book |last1=Malinconico |first1=Lawrence L. Jr.|last2=Lillie |first2=Robert J. |last3=Nakata |first3=Takashi |title=Tectonics of the western Himalayas |date=January 1, 1989 |publisher=Geological Society of America |isbn=9780813722320 |doi=10.1130/SPE232-p243 |volume=232 |pages=243–264 |url=https://pubs.geoscienceworld.org/gsa/books/book/371/chapter-abstract/3796943/Active-faults-of-the-Himalaya-of-India-and-Nepal?redirectedFrom=PDF |access-date=24 May 2024 |chapter=Active faults of the Himalaya of India and Nepal}}
- {{cite journal |last1=Mugnier |first1=Jean-Louis |last2=Huyghe |first2=Pascale |last3=Chalaron |first3=Edouard |last4=Mascle |first4=Georges |title=Recent movements along the Main Boundary Thrust of the Himalayas: Normal faulting in an over-critical thrust wedge? |journal=Tectonophysics |date=15 November 1994 |volume=238 |issue=1–4 |pages=199–215 |doi=10.1016/0040-1951(94)90056-6 |bibcode=1994Tectp.238..199M |url=https://www.sciencedirect.com/science/article/abs/pii/0040195194900566 |access-date=24 May 2024|url-access=subscription }}
- {{cite journal |last1=Patra |first1=Abhijit |last2=Saha |first2=Dilip |title=Stress regime changes in the Main Boundary Thrust zone, Eastern Himalaya, decoded from fault-slip analysis |journal=Journal of Structural Geology |date=March 2019 |volume=120 |pages=29–47 |doi=10.1016/j.jsg.2018.12.010 |bibcode=2019JSG...120...29P |url=https://www.sciencedirect.com/science/article/abs/pii/S0191814118303225 |access-date=20 May 2024|url-access=subscription }}
- {{cite journal |last1=Riesner |first1=M. |last2=Bollinger |first2=L. |last3=Hubbard |first3=J. |title=Localized extension in megathrust hanging wall following great earthquakes in western Nepal |journal=Scientific Reports |date=2 November 2021 |volume=11 |issue=21521 |page=21521 |doi=10.1038/s41598-021-00297-4 |pmid=34728644 |pmc=8563945 |bibcode=2021NatSR..1121521R }}
- {{cite journal |last1=Thiede |first1=Rasmus |last2=Robert |first2=Xavier |last3=Stübner |first3=Konstanze |last4=Dey |first4=Saptarshi |last5=Faruhn |first5=Johannes |title=Sustained out-of-sequence shortening along a tectonically active segment of the Main Boundary thrust: The Dhauladhar Range in the northwestern Himalaya |journal=Lithosphere |date=July 14, 2017 |volume=9 |issue=5 |pages=715–725 |doi=10.1130/L630.1 |bibcode=2017Lsphe...9..715T |url=https://pubs.geoscienceworld.org/gsa/lithosphere/article/9/5/715/350190/Sustained-out-of-sequence-shortening-along-a |access-date=15 May 2024}}
- {{cite journal |last1=Valdiya |first1=K. S. |title=The two intracrustal boundary thrusts of the Himalaya |journal=Tectonophysics |date=10 July 1980 |volume=66 |issue=4 |pages=323–348 |doi=10.1016/0040-1951(80)90248-6 |bibcode=1980Tectp..66..323V |url=https://www.sciencedirect.com/science/article/abs/pii/0040195180902486 |access-date=5 June 2024|url-access=subscription }}
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