The Eastern Himalayan syntaxis
The Eastern Himalayan Syntaxis (EHS) is a structure located at the conjunction of the Indian Plate, the Eurasian Plate and the Burma platelet. This boundary with the Burma platelet resulted in the termination of the Himalayan mountain belt (at the convergence of the Indian and Eurasian plates) and formed the EHS. The presence of the platelet also results in dextral strike-slip motion in the faults along the plate boundary; here, the collision boundary becomes a transform fault.
There are three main geologic units in the EHS. The Himalayan terrane is composed of the Tethys-Himalayan sequence and the High Himalayan crystalline sequence, and is part of the Indian Plate. The Tethys-Himalayan sequence is mainly composed of low-grade metasedimentary rocks as well as Paleozoic and Mesozoic sediments, while the High Himalayan crystalline sequence is composed of high-grade metamorphic rocks. The Indus-Tsangpo Suture zone is the suture zone created by the convergence of the Indian and Eurasian plates; it is folded around the EHS, and separates the Himalayan terrane from the south Lhasa terrane. The Lhasa terrane is formed of two geologic units: the granulite facies metamorphic unit, which has granulitic lenses or blocks within the amphibolite facies country rock, and the amphibolite facies metamorphic unit, which consists of amphibolite, gneiss, schist, and some marble and quartzite. It also contains a Gangdese batholith chain. The map below (Figure 1) depicts the rock types present in the EHS.
These two terranes came together at the convergence of the Indian and Eurasian plates, which first began to converge approximately 50 million years ago.
There are three main geologic units in the EHS. The Himalayan terrane is composed of the Tethys-Himalayan sequence and the High Himalayan crystalline sequence, and is part of the Indian Plate. The Tethys-Himalayan sequence is mainly composed of low-grade metasedimentary rocks as well as Paleozoic and Mesozoic sediments, while the High Himalayan crystalline sequence is composed of high-grade metamorphic rocks. The Indus-Tsangpo Suture zone is the suture zone created by the convergence of the Indian and Eurasian plates; it is folded around the EHS, and separates the Himalayan terrane from the south Lhasa terrane. The Lhasa terrane is formed of two geologic units: the granulite facies metamorphic unit, which has granulitic lenses or blocks within the amphibolite facies country rock, and the amphibolite facies metamorphic unit, which consists of amphibolite, gneiss, schist, and some marble and quartzite. It also contains a Gangdese batholith chain. The map below (Figure 1) depicts the rock types present in the EHS.
These two terranes came together at the convergence of the Indian and Eurasian plates, which first began to converge approximately 50 million years ago.
The EHS consists of a fold structure as well as a fault structure. The fold is antiformal, and occurs in the Indus-Tsangpo Suture zone (shown in yellow in Figure 1 above), as well as in the Himalayan terrane rocks (both of which are represented in shades of light pink in the map above). In addition, in the colored map below this text, there is a shear zone around the Himalayan terrane rock antiform known as the Yarlung-Tsangpo shear zone. Although this shear zone appears to correspond to the Indus-Tsangpo Suture zone, it is associated with older Himalayan events.
The final structure shown on the geologic maps (best shown in Figure 3) is the dextral faulting around the rock of the Himalayan terrane.
The final structure shown on the geologic maps (best shown in Figure 3) is the dextral faulting around the rock of the Himalayan terrane.
The deformation that created this feature originated from the collision of the Indian Plate with the Eurasian Plate and the Burma platelet. Both of these collisions were sources of strain that deformed the Indian Plate. The force of both of them acting on the Himalayan rocks created the antiformal fold. However, the dextral faulting was created by the force of the Indian plate pushing past the Burmese platelet.
references
Booth, A. L., C. P. Chamberlain, W. S.f. Kidd, and P. K. Zeitler. "Constraints on the Metamorphic Evolution of the Eastern Himalayan Syntaxis from Geochronologic and Petrologic Studies of Namche Barwa." Geological Society of America Bulletin 121, no. 3/4 (2009): 385-407.
Holt, William E., James F. Ni, Terry C. Wallace, and A. J. Haines. "The Active Tectonics of the Eastern Himalayan Syntaxis and Surrounding Regions." Journal of Geophysical Research 96, no. B9 (1991): 14595-4632. Accessed March 30, 2015. http://onlinelibrary.wiley.com/doi/10.1029/91JB01021/abstract.
Lang, Karl A. “The Persistence of Rapid Exhumation in the Eastern Himalayan Syntaxis.” PhD diss., University of Washington, 2014.
Liu, Y., Z. Berner, H-J Massonne, and X. Xiao. "Geology of the Eastern Himalayan Syntaxis." Himalayan Journal of Sciences 2, no. 4 (2004): 197-98.
Quanru, Geng, Pan Guitang, Lailin Zheng, Zhiliang Chen, Richard D. Fisher, Zhiming Sun, Chunsheng Ou, Han Dong, Xiaowei Wang, Sheng Li, Xiongying Lou, and Heng Fu. "The Eastern Himalayan Syntaxis: Major Tectonic Domains, Ophiolitic Mélanges and Geologic Evolution." Journal of Asian Earth Sciences 27, no. 3 (2006): 265-85. Accessed March 30, 2015. http://www.sciencedirect.com/science/article/pii/S1367912005000878.
Rowley, David. "Age of Initiation of the India-Asia Collision." Age of Initiation of the India-Asia Collision. Accessed March 31, 2015. http://geosci.uchicago.edu/~rowley/Rowley/Collision_Age.html.
Zhang, Z. M., G. C. Zhao, M. Santosh, J. L. Wang, X. Dong, and J. G. Liou. "Two Stages of Granulite Facies Metamorphism in the Eastern Himalayan Syntaxis, South Tibet: Petrology, Zircon Geochronology and Implications for the Subduction of Neo-Tethys and the Indian Continent beneath Asia." Journal of Metamorphic Geology, 2010, 719-33.
Holt, William E., James F. Ni, Terry C. Wallace, and A. J. Haines. "The Active Tectonics of the Eastern Himalayan Syntaxis and Surrounding Regions." Journal of Geophysical Research 96, no. B9 (1991): 14595-4632. Accessed March 30, 2015. http://onlinelibrary.wiley.com/doi/10.1029/91JB01021/abstract.
Lang, Karl A. “The Persistence of Rapid Exhumation in the Eastern Himalayan Syntaxis.” PhD diss., University of Washington, 2014.
Liu, Y., Z. Berner, H-J Massonne, and X. Xiao. "Geology of the Eastern Himalayan Syntaxis." Himalayan Journal of Sciences 2, no. 4 (2004): 197-98.
Quanru, Geng, Pan Guitang, Lailin Zheng, Zhiliang Chen, Richard D. Fisher, Zhiming Sun, Chunsheng Ou, Han Dong, Xiaowei Wang, Sheng Li, Xiongying Lou, and Heng Fu. "The Eastern Himalayan Syntaxis: Major Tectonic Domains, Ophiolitic Mélanges and Geologic Evolution." Journal of Asian Earth Sciences 27, no. 3 (2006): 265-85. Accessed March 30, 2015. http://www.sciencedirect.com/science/article/pii/S1367912005000878.
Rowley, David. "Age of Initiation of the India-Asia Collision." Age of Initiation of the India-Asia Collision. Accessed March 31, 2015. http://geosci.uchicago.edu/~rowley/Rowley/Collision_Age.html.
Zhang, Z. M., G. C. Zhao, M. Santosh, J. L. Wang, X. Dong, and J. G. Liou. "Two Stages of Granulite Facies Metamorphism in the Eastern Himalayan Syntaxis, South Tibet: Petrology, Zircon Geochronology and Implications for the Subduction of Neo-Tethys and the Indian Continent beneath Asia." Journal of Metamorphic Geology, 2010, 719-33.