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[1] This research presents the first multitechnique provenance study of the Siwalik Group in the Himalayan foreland basin in India, using the Jawalamukhi section, magnetostratigraphically dated at 13-5 Ma. Combined with provenance data from a Dharamsala Formation sedimentary section (21-13 Ma) located close by, it forms the longest temporally continuous record of Himalayan erosion in the Indian foreland basin. Sandstone petrography and heavy mineral analysis, conglomerate clast composition, Ar-Ar dating of detrital white micas, and Sm-Nd analyses on siltstones, conglomerate matrix and conglomerate clasts was undertaken to determine (1) shifts in source region through time and (2) changes in detrital lag times related to exhumation rates in the hinterland, together interpreted in the light of thrusting events. We interpret the data to show a slow down in exhumation rate of the Higher Himalaya by 16-17 Ma, after which time the locus of thrusting propagated south of the Main Central Thrust, and erosion of the low grade Haimanta Formation to the south became significant. The nonmetamorphosed Inner Lesser Himalaya breached its Haimanta cover by 9 Ma with the metamorphosed Inner Lesser Himalaya (Lesser Himalayan Crystalline Series) exhuming to surface by 6 Ma. This event caused sufficient disruption to established drainage patterns that all Higher Himalayan material was diverted from this location at this time. Citation: Najman, Y., M. Bickle, E. Garzanti, M. Pringle, D. Barfod, N. Brozovic, D. Burbank, and S. Ando (2009), Reconstructing the exhumation history of the Lesser Himalaya, NW India, from a multitechnique provenance study of the foreland basin Siwalik Group, Tectonics, 28, TC5018, doi: 10.1029/2009TC002506.

The 18-14 Ma Kamlial Formation Himalayan foreland basin sedimentary rocks in the Chinji Village region, Potwar Plateau, Pakistan, are characterized by: (1) lithofacies indicative of deposition by a large river; (2) a dominant magmatic arc provenance completely unlike the 'recycled orogen' foreland basin deposits stratigraphically below, above, or coeval with these rocks; and (3) subordinate contribution from a rapidly exhuming source, interpreted as either the Nanga Parbat Haramosh Massif or the southern margin of the Asian crust. The start of Kamlial Formation deposition at this locality at 18 Ma marks a major break with the older Murree Formation rocks, which were deposited by rivers draining predominantly the Himalayan thrust stack south of the arc. We interpret this change as the result of diversion of the paleo-Indus River to its present position, which crosses the Kohistan arc and Himalayas and debouches into the foreland. If the rapidly exhuming subordinate source region were the Nanga Parbat Haramosh Massif, then initiation of its uplift would have resulted in significant arc detritus to the basin as the overlying arc carapace was exhumed. As the carapace was progressively breached, arc material would have become a less substantial component of detritus to the basin, consistent with the reported petrography of the overlying Siwalik deposits. Keywords: Himalaya, Indus River, detrital minerals, exhumation, foreland basin, Nanga Parbat.

Weathering fluxes from four small catchments in the Himalayas, one forested, one agricultural, and two glacial, have been calculated by quantifying stream discharge, deposition, and biomass uptake of major ions. These fluxes were partitioned between silicate and carbonate sources by using a mineral mass-balance model. This approach provides the first well-defined estimates of Himalayan weathering fluxes from small catchments. Silicate weathering rates are highest in the favorable weathering environment of the Middle Hills catchments, despite higher dissolved fluxes in the High Himalayas attributed to high carbonate weathering. The silicate weathering fluxes for High Himalayan small catchments are similar to estimates from the chemistry of large rivers draining the same regions. Much higher silicate weathering intensity for the Ganges basin indicates that the silicate material eroded from the High Himalayas undergoes up to six times as much weathering in the Ganges Plain as in the High Himalayan mountains. Himalayan silicate weathering rates are higher than in equivalent continental settings and, on an area-normalized basis, are comparable to fluxes from weathering of basalts on ocean islands and tropical volcanic provinces. Keywords: catchment, erosion, flux, Himalayas, weathering.

Nd and Sr isotope systematics may provide important constraints on the location of major thrust systems that separate lithologically similar sedimentary sequences. The potential of the technique is illustrated by this isotopic study of the Main Central thrust system of the Himalaya. Nd isotope data from the Garhwal Himalaya indicate that metasedimentary rocks from the Vaikrita Group ((mathematical expression not reproducible in ASCII) = -14 to-19) correlate closely with those from the High Himalayan Crystalline Series, which constitutes the hanging-wall lithologies of the Main Central thrust. In contrast, metasedimentary rocks from the Munsiari Group ((mathematical expression not reproducible in ASCII) = -23 to-28) show marked similarities to the Lesser Himalayan Series in the footwall of the Main Central thrust. Sr isotopes support the correlations in that the Vaikrita Group shows partial reequilibration at 500 Ma, whereas the Munsiari Group has not undergone Sr isotope homogenization since 1800 Ma. Thus, the Vaikrita thrust that juxtaposes these two formations is recognized as the Main Central thrust in Garhwal Himalaya. The thrust coincides, approximately, with the location of the kyanite isograd, confirming that inverted metamorphism is characteristic of both hanging wall and footwall of the Main Central thrust. Along the Tons thrust (known locally as the Srinagar thrust) 50 km south of the Main Central thrust, low-grade quartzarenites with Nd-Sr isotope and trace element characteristics typical of Lesser Himalayan formations have been emplaced on phyllites and siltstones with geochemical characteristics of the High Himalayan Crystalline Series. The field relationships most probably result from out-of-sequence thrusting in which Lesser Himalayan Series rocks to the north were emplaced over low-grade equivalents of the High Himalayan Crystalline Series preserved in the external part of the orogen. This study establishes the value of isotope data for lithostratigraphic correlations within orogenic belts. Keywords: correlation, Himalayan orogeny, isotope geochemistry, Main Central thrust, metasedimentary rocks.

The injected brine solutions had an initial dye concentration of Graph $c 0 = 3.00 \pm 0.05$ g l Graph $^{-1}$ and an initial density Graph $\rho 0 = 1.030$ or 1.070 g cm Graph $^{-3}$, assuming a water temperature of 20 Graph $^{\circ }$ C (Green & Southard 2019). The injected fluid spreads below an impermeable horizontal baffle containing a fault of gap width Graph $d f$, thickness Graph $h f$, permeability Graph $k f$ and porosity Graph $\phi f$ which abuts the boundary. Less dense CO Graph $ 2$ is injected at a constant rate of 0.1 Mt yr Graph $^{-1}$ at the bottom of layer 1, and assumed to have constant density Graph $\rho = 790$ kg m Graph $^{-3}$ and dynamic viscosity Graph $\mu = 6.9 \times 10^{-5}$ Pa s, calculated at typical storage reservoir conditions of 15 MPa and 40 Graph $^{\circ }$ C (Dubacq, Bickle & Evans 2013). Figure 2( I b i ) shows three height profiles at Graph $\tilde {t}=0.5$, Graph $\tilde {t}=5$ and Graph $\tilde {t}=50$ (solid lines), where the extent and height of the profiles have been normalised by the maximum extent Graph $\tilde {x} N$ and the thickness of the current at Graph $\tilde {x}=0$, Graph $\tilde {h} 0$. In diffusion dominated flows, where Graph ${\textit {Pe}} \ll 1$, the transport coefficient Graph $D\simeq D d/\tau$ is constant whereas in advection dominated flows, where Graph ${\textit {Pe}} \gg 1$, Graph $D\simeq d 0U$ is dependent on the flow speed. [Extracted from the article]