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The Himalayan thrust belt comprises three in-sequence foreland-propagating orogen-scale faults, the Main Central thrust, the Main Boundary thrust, and the Main Frontal thrust. Recently, the Munsiari–Ramgarh–Shumar thrust system has been recognized as an additional, potentially orogen-scale shear zone in the proximal footwall of the Main Central thrust. The timing of the Munsiari, Ramgarh, and Shumar thrusts and their role in Himalayan tectonics are disputed. We present 31 new zircon (U–Th)/He ages from a profile across the central Himachal Himalaya in the Beas River area. Within a ∼40 km wide belt northeast of the Kullu–Larji–Rampur window, ages ranging from 2.4 ± 0.4 Ma to 5.4 ± 0.9 Ma constrain a distinct episode of rapid Pliocene to Present exhumation; north and south of this belt, zircon (U–Th)/He ages are older ( 7.0 ± 0.7 Ma to 42.2 ± 2.1 Ma ). We attribute the Pliocene rapid exhumation episode to basal accretion to the Himalayan thrust belt and duplex formation in the Lesser Himalayan sequence including initiation of the Munsiari thrust. Pecube thermokinematic modelling suggests exhumation rates of ∼2–3 mm/yr from 4–7 to 0 Ma above the duplex contrasting with lower (<0.3 mm/yr) middle-late Miocene exhumation rates. The Munsiari thrust terminates laterally in central Himachal Pradesh. In the NW Indian Himalaya, the Main Central thrust zone comprises the sheared basal sections of the Greater Himalayan sequence and the mylonitic ‘Bajaura nappe’ of Lesser Himalayan affinity. We correlate the Bajaura unit with the Ramgarh thrust sheet in Nepal based on similar lithologies and the middle Miocene age of deformation. The Munsiari thrust in the central Himachal Himalaya is several Myr younger than deformation in the Bajaura and Ramgarh thrust sheets. Our results illustrate the complex and segmented nature of the Munsiari–Ramgarh–Shumar thrust system. [ABSTRACT FROM AUTHOR]

Greenschist to amphibolite grade Haimanta metasediments of the NW Himalaya preserve much of the prograde metamorphic history of Eohimalayan crustal thickening, which has been erased by Oligo-/Miocene migmatization elsewhere in the Himalaya. Our zircon and monazite U/Th–Pb data unravel a multi-stage prograde metamorphic evolution. The earliest evidence of prograde Barrovian metamorphic monazite growth is ~ 41 Ma. Peak metamorphic conditions (~ 8–8.5 kbar, ~ 600–700 °C) were attained at 37–36 Ma and followed by a prolonged evolution at high temperatures with at least three distinct episodes of monazite growth, which may be related to the formation of the northern Himalayan nappes (e.g., Shikar Beh nappe, Nyimaling nappe). Rapid exhumation of the crystalline started at ~ 26 Ma and resulted in cooling through the muscovite 40 Ar/ 39 Ar closure temperature by 21.8 Ma. Although a local continuation of the South Tibetan detachment is not unambiguously identified in central Himachal Pradesh extrusion was likely facilitated by a system of several minor late Oligocene/early Miocene top-to-the-N to NE shear zones. In contrast to the crystalline of Zanskar and eastern Himachal Pradesh, extrusion was not accompanied by widespread decompression melting. [ABSTRACT FROM AUTHOR]

The Pamir mountains at the western end of the Himalaya–Karakorum–Tibet mountain belt are characterized by landscape extremes: The western Pamir has an extreme local relief of >2000 m. The eastern Pamir is a low-relief orogenic plateau at ~4100 m. In most of the Pamir, modern glaciers are small and often are rock glaciers restricted to the north sides of the crests but significant ice caps occur in the eastern Pamir (Muztagh Ata, Kongur Shan) and in the northwestern Pamir, where the Fedchenko glacier is the longest glacier outside the polar regions. Glaciation of the Pamir contrasts with the strong glaciation of the Karakorum ranges farther south reflecting differences in annual precipitation beween the Monsoon-influenced Karakorum and the arid, Westerlies-controlled Pamir.Glacial and glaciogenic sediments that have been mapped throughout the Pamir suggest much more widespread glaciation during the Pleistocene. Cosmogenic radionuclide (CRN) dates indicate that one or several glacial maxima occurred ≥100 ka, but the extent of the mid-Pleistocene ice cover is currently not known. While CRN exposure ages of glacially polished bedrock in the west-Pamir valleys suggest that these may have been formed by mid-late Pleistocene Alpine glaciers there is little record of the glacial advances on the east-Pamir plateau. We present new CRN exposure ages that elucidate the glacial and post-glacial history of the Pamir. We also present a geomorphological analysis focusing on the strong east-west difference in topography and on morphological evidence of glaciation in the eastern Pamir. Our analysis sheds light on the landscape evolution and on the competing effects of fluvial and glacial erosion and mass-wasting processes in an arid mountain environment. [ABSTRACT FROM AUTHOR]

The distribution of tectonic activity within the Himalaya is still disputed. For instance the tectonic processes that ultimately sustain Himalayan topography and the activity of major fault zones within the orogen at geological-timescales remain unknown. In our studies, we study landscape morphology and combine surface exposure,thermochronologic dating methods, thermokinematic modelsto address the spatial and temporal pattern of deformation in the western Himalaya. Of particular interest is a 30 to 40-km-wide orogen-parallel belt of rapid exhumation that extends from central Nepal to the western Himalaya. This belt has been linked to a mid-crustal ramp in the basal décollement, to out-of-sequence basement thrusts, and to the growth of Lesser Himalayan duplex structures. Further goals are constraining fault activity of the Main Boundary Thrust fault (MBT). From our results we conclude that all major deformation zones in western Himalaya are active and some portion of crustal shortening is accommodated by active out of sequence faulting sustaining topography. We have published several new studies containing new apatite fission-track (AFT) and zircon U-Th/He cooling ages from the western Himalayan region, particular in the vicinity of the transition from the central to the western Himalaya (~77°-78°E). We analyzed the spatial distribution of the relative change of river steepness using averaged basin wide river steepness indexes (ksn), both along and across strike to gain information about the regional distribution of differential uplift pattern and relate this to the activity of distinctive fault zones and orogenic segments. Our results recognize three orogenic segments with distinctive landscape morphology, structural architecture, and fault geometry exists along the western Himalaya: Garhwal-Sutlej, Beas-Lahul-Chamba, and Kashmir Himalaya (from east to west). We observe a positive correlation of averaged ksn values with long-term exhumation rates derived from recently published regional thermochronologic datasets combined with 1D and 2D-thermal modelling as well as with millennial timescale denudation rates based on cosmogenic nuclide dating. These results are in agreement with documented significant lateral changes in exhumation between the Dhauladar Range to the west, the Beas-Lahul region, and the Sutlej-Garhwal area to the east. Moreover, our data recognize distinctive fault segments suggesting varying differential uplift along strike of the Main Frontal Thrust (MFT), the Main Boundary Thrust (MBT), and in the vicinity of steep topographic transition between the Lesser and Greater Himalaya. In this region, we relate out-of-sequence deformation along major basement thrust ramps, such as the Munsiari Thrust (MT) combined with deformation along mid-crustal ramp along the basal décollement. Our results allow us to spatially correlate the termination of the rapid exhumation belt with a mid-crustal ramp to the west. In contrast to the Himalayan front farther to the east, exhumation in the far west is focused at the frontal parts of the mountain range, and associated with the hanging wall of the MBT. [ABSTRACT FROM AUTHOR]