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During the last 40Ma the marine 87 Sr/ 86 Sr record shows a rapid rise (from 0 7078 to 0 7092) [1] , a trend which has been linked to the Himalayan Orogeny [2] . Indeed, many Himalayan rivers, principally those of the Ganges|Brahmaputra system, display high 87 Sr/ 86 Sr relative to [Sr] [3] . Theories concerning the cause of this radiogenic Sr enrichment are diverse, but our results suggest that Lesser Himalayan carbonate|rich lithologies play a vital role [4,5] .The Bhote Kosi originates in Tibet at ca.5km elevation from Tibetan Sedimentary Series (TSS) bedrock, before traversing the High Himalayan Crystalline Series (HHCS) and Lesser Himalaya (LH) of eastern Nepal, joining the Indrawati (at ca.0 6km elevation) to form the Sun Kosi, part of the Ganges system. Carbonates, calc|silicates and silicates have been identified from the TSS, HHCS and LH, and the Bhote Kosi provides an opportunity to study the influence of these upon fluvial chemistry. Interest is focused on the cause of a rapid rise in riverine Sr|isotope ratios immediately downstream of the Main Central Thrust (MCT) and the role of carbonate|rich lithologies exposed in this section. Similar lithologies are lacking in the catchment of a second Nepalese river system, the Lantang Khola—Trisuli, sampled during the same period, and used as a baseline indicator for the effect of LH carbonates on the dissolved load of the Bhote Kosi.
Indeed, many Himalayan rivers, principally those who had been linked to the Himalayan Orogeny [2]. During the last 40Ma of the Marine 87 Sr / 86 Sr record shows a rapid rise (from 0 7078 to 0 7092) [1] of the Ganges | Brahmaputra system, display high 87 Sr / 86 Sr relative to [Sr] [3]. Theories concerning the cause of this radiogenic Sr enrichment are diverse, but our results suggest that Lesser Himalayan carbonate | rich lithologies The Bhote Kosi originates in Tibet at ca.5km elevation from Tibetan Sedimentary Series (TSS) bedrock, before traversing the High Himalayan Crystalline Series (HHCS) and Lesser Himalaya (LH) of eastern Nepal, joining the Indrawati (at ca.0km elevation) to form the Sun Kosi, part of the Ganges system. Carbonates, calc | silicates and silicates have been identified from the TSS, HHCS and LH, and the Bhote Kosi provides an opportunity to study the influence of these upon f luvial chemistry. Interest is focused on the cause of a rapid rise in riverine Sr | isotope ratios immediately downstream of the Main Central Thrust (MCT) and the role of carbonate | rich lithologies exposed in this section. Similar lithologies are lacking in the catchment of a second Nepalese river system, the Lantang Khola-Trisuli, sampled during the same period, and used as a baseline indicator for the effect of LH carbonates on the dissolved load of the Bhote Kosi.