@article{StuebnerGrujicDunkletal.2017, author = {St{\"u}bner, Konstanze and Grujic, Djordje and Dunkl, Istvan and Thiede, Rasmus Christoph and Eugster, Patricia}, title = {Pliocene episodic exhumation and the significance of the Munsiari thrust in the northwestern Himalaya}, series = {Earth \& planetary science letters}, volume = {481}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2017.10.036}, pages = {273 -- 283}, year = {2017}, abstract = {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 to constrain a distinct episode of rapid Pliocene to Present exhumation; north and south of this belt, zircon (U-Th)/He ages are older ( to ). 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.}, language = {en} } @article{GrujicGovinBarrieretal.2018, author = {Grujic, Djordje and Govin, Gwladys and Barrier, Laurie and Bookhagen, Bodo and Coutand, Isabelle and Cowan, Beth and Hren, Michael T. and Najman, Yani}, title = {Formation of a Rain Shadow}, series = {Geochemistry, geophysics, geosystems}, volume = {19}, journal = {Geochemistry, geophysics, geosystems}, number = {9}, publisher = {American Geophysical Union}, address = {Washington}, issn = {1525-2027}, doi = {10.1029/2017GC007254}, pages = {3430 -- 3447}, year = {2018}, abstract = {We measure the oxygen and hydrogen stable isotope composition of authigenic clays from Himalayan foreland sediments (Siwalik Group), and from present day small stream waters in eastern Bhutan to explore the impact of uplift of the Shillong Plateau on rain shadow formation over the Himalayan foothills. Stable isotope data from authigenic clay minerals (<2 μm) suggest the presence of three paleoclimatic periods during deposition of the Siwalik Group, between ∼7 and ∼1 Ma. The mean δ18O value in paleometeoric waters, which were in equilibrium with clay minerals, is ∼2.5 per mille lower than in modern meteoric and stream waters at the elevation of the foreland basin. We discuss the factors that could have changed the isotopic composition of water over time and we conclude that (a) the most likely and significant cause for the increase in meteoric water δ18O values over time is the "amount effect," specifically, a decrease in mean annual precipitation. (b) The change in mean annual precipitation over the foreland basin and foothills of the Himalaya is the result of orographic effect caused by the Shillong Plateau's uplift. The critical elevation of the Shillong Plateau required to induce significant orographic precipitation was attained after ∼1.2 Ma. (c) By applying scale analysis, we estimate that the mean annual precipitation over the foreland basin of the eastern Bhutan Himalayas has decreased by a factor of 1.7-2.5 over the last 1-3 million years.}, language = {en} }