Geologic map of the Marsyandi drainage, central Nepal digitized from the combined maps of Searle & Godin (2003) and Colchen et al. (1986). Solid lines represent the Main Central Thrust and South Tibetan Detachment (STD) as mapped by Searle & Godin (2003). The dashed line is the STD as mapped by Colchen et al. (1986). U^Pb zircon age distributions are shown for samples of river sediment taken from either tributaries draining single geologic units (A, C, D, F, H and I) or the main stem Marsyandi (B, E, G and K). 

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... ¢rst part of our study focuses on the Marsyandi drai- nage, where six modern sand samples (A, C, D, F, H and I) were taken from small tributaries to de¢ne the contribu- tion from speci¢c formations (Fig. 4). Additionally, four sand samples were taken from the Marsyandi River where it crosses the STD (B), the Formation I^II contact (E), the MCT (G) and just above the con£uence with the Trisuli River (K). These samples were deliberately taken just downstream of where the Marsyandi crosses formational boundaries and were used to determine ...

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... tethyan strata (n = 962) (1986) and Fuchs (1980), with priority given in that order where features were inconsistent between maps (Fig. 4). Such a combination of maps was necessary because the oldest map was too large in scale and lacked su⁄cient de- tail in the Marsyandi region, while the younger two were not spatially extensive enough to cover the entire ¢eld area. As a result, the locations of features within the Marsyandi drainage are highly accurate, whereas some ...

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... distributions from the Marsyandi drainage show clear downstream trends re£ecting the input of zircons from successive formations (Fig. 4). Sample B characterizes the age distribution of the Marsyandi as it emerges from post- Ordovician Tethyan units. The trunk river then receives contributions from Formations II and III, which, based on their similarity, are treated as a single source in mixing calculations. Downstream of Formation II, sample E con- tains a large ...

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... II and III, which, based on their similarity, are treated as a single source in mixing calculations. Downstream of Formation II, sample E con- tains a large proportion of ages o700 Ma and a relative paucity of ages 41000 Ma, suggesting a larger contribu- tion from Formation II/III than would be expected based on its limited exposure area (Fig. 4 and Table 4). Further downstream, sample G shows a strong peak between 900 and 1000 Ma, and more ages 41000 Ma indicating a mod- erate, but not dominant, contribution from Formation I (sample F; Fig. 4). Samples H and I (Fig. 4) characterize Lesser Himalayan age distributions that are in excellent agreement with pre- viously reported ...

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... paucity of ages 41000 Ma, suggesting a larger contribu- tion from Formation II/III than would be expected based on its limited exposure area (Fig. 4 and Table 4). Further downstream, sample G shows a strong peak between 900 and 1000 Ma, and more ages 41000 Ma indicating a mod- erate, but not dominant, contribution from Formation I (sample F; Fig. 4). Samples H and I (Fig. 4) characterize Lesser Himalayan age distributions that are in excellent agreement with pre- viously reported ages shown in Fig. 3 (DeCelles et al., 2000; Martin et al., 2005).The contribution of Lesser Himalayan zircons is clear in sample K (Fig. 4) from the lowest Mar- syandi, which contains large peaks at ...

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... Ma, suggesting a larger contribu- tion from Formation II/III than would be expected based on its limited exposure area (Fig. 4 and Table 4). Further downstream, sample G shows a strong peak between 900 and 1000 Ma, and more ages 41000 Ma indicating a mod- erate, but not dominant, contribution from Formation I (sample F; Fig. 4). Samples H and I (Fig. 4) characterize Lesser Himalayan age distributions that are in excellent agreement with pre- viously reported ages shown in Fig. 3 (DeCelles et al., 2000; Martin et al., 2005).The contribution of Lesser Himalayan zircons is clear in sample K (Fig. 4) from the lowest Mar- syandi, which contains large peaks at $1800 and 2400 Ma. The ...

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... a mod- erate, but not dominant, contribution from Formation I (sample F; Fig. 4). Samples H and I (Fig. 4) characterize Lesser Himalayan age distributions that are in excellent agreement with pre- viously reported ages shown in Fig. 3 (DeCelles et al., 2000; Martin et al., 2005).The contribution of Lesser Himalayan zircons is clear in sample K (Fig. 4) from the lowest Mar- syandi, which contains large peaks at $1800 and 2400 Ma. The importance of the Tethyan Series and Formation II/ III contributions to sample K is apparent in the high age probability between $480 and 700 Ma. This interpreta- tion is con¢rmed by comparison with sample J, which contains noTethyan or Formation II/III ...

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... from generalizing from speci¢c sites to broader areas. For example, in the present study we treat the Tethyan Series as a single unit, even though it com- prises carbonates and siliclastics that have highly contrast- ing zircon concentrations. We de¢ne the zircon age distributions based on two samples from catchments with- in theTethyan rocks (Fig. 4).We did not speci¢cally sample Cambro -Ordovician Tethyan strata, and yet we now sus- pect that they contain an age signal that is more equivalent to that of Formation II than to that of the 'Tethyan' popula- tion that we ...