『Abstract
The Brahmaputra is a major river system draining the Himalaya.
The concentration of Sr and its 87Sr/86Sr
have been measured in dissolved and particulate phases of the
Brahmaputra and its tributaries in India to trace the sources
of dissolved Sr. Dissolved Sr ranges from 250 to 1050 nM with
87Sr/86Sr from 0.71298 to 0.75975. The Sr
data along with the available concentrations of major ions in
the samples show that major contributors of Sr in the Brahmaputra
system are the silicates and carbonates of the Himalaya and the
Transhimalaya and carbonates and evaporites of the Tibetan basin.
Silicate Sr in the Brahmaputra river system ranges from 20％ to
80％ with an average of 〜45％. The silicate component of Sr in the
Brahmaputra system is similar or marginally higher than that in
the Ganga system due to contribution from the Transhimalayan calc-alkaline
plutonic rocks which have higher concentration of Sr. Evaporites
of the Tibetan sub-basin and hot springs along the Indus Tsangpo
Suture could be the other significant contributors to the dissolved
Sr budget of the Brahmaputra. Contribution from evaporite dissolution
decouples the total dissolved Sr flux from the Tibetan basin from
atmospheric CO2 consumption. Radiogenic Sr
of the Brahmaputra system is derived from the Himalayan silicates
whereas other Sr sources tend to dilute its radiogenic signature.
The 87Sr/86Sr of the dissolved phase shows
significant correlation with indices of silicate weathering, indicating
that 87Sr/86Sr can serve as a proxy of silicate
weathering. At their outflow, the Brahmaputra is less radiogenic
(〜0.72) compared to the Ganga (〜0.73), however, the flux of 87Sr
from the Brahmaputra is similar to that of the Ganga.
Keywords: Himalaya; Brahmaputra; 87Sr/86Sr;
Weathering』
1. Introduction
2. Brahmaputra river system
3. Sampling
4. Results and discussion
4.1. General observations
4.2. Dissolved Sr and its relation to major ion chemistry
4.3. 87Sr/86Sr to the Brahmaputra river
system
4.4. 87Sr/86Sr as a proxy of silicate weathering
4.5. Fluxes of Sr from different Sub-basins
5. Conclusion
Acknowledgements
References