Metapelites record two episodes of decompressional metamorphism in the Himalayan orogen

The 1714 Bhutan earthquake was one of the largest in the Himalaya in the last millennium. We show that the surface rupture caused by this earthquake extended further to the east than previously known, it was at least 175 km long, with slip exceeding 11 m at our study site. The age of the surface rupture was constrained by a combination of radiocarbon and traditional optically stimulated luminescence dating of affected river sediments. Computations using empirical scaling relationships, fitting historical observations and paleoseismic data, yielded a plausible magnitude of Mw 8.1 ± 0.4 and placed the hypocentre of the 1714 Bhutan earthquake on the flat segment of the Main Himalayan Thrust (MHT), the basal décollement of the Himalayan orogen. Calculations of Coulomb stress transfer indicate that great earthquakes along the leading part of the MHT would cause surface rupture. In contrast, distal earthquakes may not immediately trigger surface rupture, although they would increase the stresses in the leading part of the MHT, facilitating future surface-rupturing earthquakes. Frontal earthquakes would also transfer stress into the modern foreland basin facilitating southward propagation of the MHT as a blind basal décollement. In conclusion, studies of surface-rupturing events alone likely underestimate the seismic slip along the Himalayan megathrust.

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Comment on “Channel flow, tectonic overpressure, and exhumation of high-pressure rocks in the Greater Himalayas” by Marques et al. (2018)

Solid Earth ◽

10.5194/se-10-357-2019 ◽

2019 ◽

Vol 10 (1) ◽

pp. 357-361 ◽

Cited By ~ 1

Author(s):

John P. Platt

Keyword(s):

Boundary Condition ◽

High Pressure ◽

Shear Strength ◽

Channel Model ◽

Permanent Deformation ◽

Gravity Anomalies ◽

Return Flow ◽

Lithostatic Pressure ◽

Himalayan Orogen ◽

Upper Boundary

Abstract. The upward-tapering channel model proposed by Marques et al. (2018) for the Himalayas has a “base” that forms part of the subducting footwall and therefore does not close the channel. This configuration does not produce return flow, and no dynamic overpressure develops in the channel. The geometrical and kinematic configuration they actually use for their calculations differs from this and is both geologically and mechanically improbable. In addition, the fixed upper boundary condition in their models is mechanically unrealistic and inconsistent with geological and geophysical constraints from the Himalayan orogen. In reality, the dynamic pressures calculated from their model, which exceed lithostatic pressure by as much as 1.5 GPa, would cause elastic flexure or permanent deformation of the upper plate. I estimate that a flexural upwarp of 50 km of the upper plate would be required to balance forces, which would lead to geologically unrealistic topographic and gravity anomalies. The magnitude of the dynamic overpressure that could be confined is in fact limited by the shear strength of the upper plate in the Himalayas, which is likely to be < 120 MPa.

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From tectonically to erosionally controlled development of the Himalayan orogen

Geology ◽

10.1130/g21483.1 ◽

2005 ◽

Vol 33 (8) ◽

pp. 689 ◽

Cited By ~ 71

Author(s):

Rasmus C. Thiede ◽

J Ramón Arrowsmith ◽

Bodo Bookhagen ◽

Michael O. McWilliams ◽

Edward R. Sobel ◽

...

Keyword(s):

Himalayan Orogen

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Miocene high-temperature leucogranite magmatism in the Himalayan orogen

Geological Society of America Bulletin ◽

10.1130/b35691.1 ◽

2020 ◽

Author(s):

Peng Gao ◽

Yong-Fei Zheng ◽

Matthew Jason Mayne ◽

Zi-Fu Zhao

Keyword(s):

High Temperature ◽

Partial Melting ◽

Plate Boundary ◽

Source Rocks ◽

Eastern Himalaya ◽

Maximum Temperature ◽

Himalayan Orogen ◽

Metasedimentary Rocks ◽

Se Tibet ◽

Zircon Thermometry

Himalayan leucogranites of Cenozoic age are generally attributed to partial melting of metasedimentary rocks at low temperatures of <770 °C. It is unknown what the spatial distribution and characteristics of high-temperature (>800 °C) leucogranites are in the Himalayan orogen. The present study reports the occurrence of such leucogranites in the collisional orogen. We use the Ti-in-zircon thermometry in combination with the thermodynamically calibrated relationships of T-aSiO2-aTiO2 to retrieve crystallization temperatures of Miocene (ca. 17 Ma) two-mica granites from Yalaxiangbo, in the eastern Himalaya, SE Tibet. The results give the maximum temperature as high as ∼850 °C for granite crystallization, providing a significant constraint on the nature of thermal sources. Phase equilibrium modeling using metasedimentary rocks as the source rocks indicates that felsic melts produced at ∼850 °C and 6−10 kbar can best match the target leucogranites in lithochemistry. In this regard, the anatectic temperatures previously obtained for the production of Himalayan leucogranites would probably be underestimated to some extent. Such high temperatures are difficult to explain purely by the internal heating of the thickened orogenic crust. Instead, they require an extra heat source, which would probably be provided by upwelling of asthenospheric mantle subsequent to thinning of the orogenic lithospheric mantle by foundering along the convergent plate boundary. Therefore, the Himalayan leucogranites of Miocene age would be derived from partial melting of the metasedimentary rocks in the post-collisional stage.

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