The strontium isotopic budget of Himalayan rivers in Nepal and Bangladesh

Journal Article · Thu Jul 01 04:00:00 EDT 1999 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(99)00081-2· OSTI ID:687707

Galy, A ^[1]; France-Lanord, C ^[1]; Derry, L A ^[2]

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1. CNRS, Vandoeuvre-les-Nancy (France). Centre de Recherches Petrographiques et Geochimiques
2. Cornell Univ., Ithaca, NY (United States). Dept. of Geological Sciences

Himalayan rivers have very unusual Sr characteristics and their budget cannot be achieved by simple mixing between silicate and carbonate even if carbonates are radiogenic. The authors present Sr, O, and C isotopic data from river and rain water, bedload, and bedrock samples for the western and central Nepal Himalaya and Bangladesh, including the monsoon season. Central Himalayan rivers receive Sr from several sources: carbonate and clastic Tethyan sediments, High Himalayan Crystalline (HHC) gneisses and granitoids with minor marbles, carbonates and metasediments of the Lesser Himalaya (LH), and Miocene-Recent foreland basin sediment from the Siwaliks group and the modern flood plain. In the Tethyan Himalaya rivers have dissolved [Sr] {approx} 6 {micro}mol/l and {sup 87}Sr/{sup 86}Sr {approx} 0.717, with a large contribution from moderately radiogenic carbonate. Rivers draining HHC gneisses are very dilute with [Sr] {approx} 0.2 {micro}mol/l and {sup 87}Sr/{sup 86}Sr {approx} 0.74. Lesser Himalayan streams also have low [Sr] {approx} 0.4 {micro}mol/l and are highly radiogenic ({sup 87}Sr/{sup 86}Sr {ge} 0.78). Highly radiogenic carbonates of the LH do not contribute significantly to the Sr budget because they are sparse and have very low [Sr]. In large rivers exiting the Himalaya, Sr systematics can be modeled as a mixture between Tethyan rivers, where slightly radiogenic carbonates (mean {sup 87}Sr/{sup 86}Sr {approx} 0.715) are the main source of Sr, and Lesser Himalaya waters, where extremely radiogenic silicates (> 0.8) are the main source of Sr. HHC waters are less important because of their low [Sr]. Rivers draining the Siwaliks foreland basin sediments have [Sr] {approx} 4 {micro}mol/l and {sup 87}Sr/{sup 86}Sr {approx} 0.725. Weathering of silicates in the Siwaliks and the flood plain results in a probably significant radiogenic (0.72--0.74) input to the Ganges and Brahamputra (G-B), but quantification of this flux is limited by uncertainties in the hydrologic budget. The G-B in Bangladesh show strong seasonal variability with low [Sr] and high {sup 87}Sr/{sup 86}Sr during the monsoon. Sr in the Brahmaputra ranges from 0.9 {micro}mol/l and 0.722 in March to 0.3 {micro}mol/l and 0.741 in August. The authors estimate the seasonally weighted flux from the G-B to be 6.5 {times} 10{sup 8} mol/yr with {sup 87}Sr/{sup 86}Sr = 0.7295.

• OSTI ID: 687707
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 13-14 Vol. 63; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
BANGLADESH
ECOLOGICAL CONCENTRATION
HIMALAYAS
NEPAL
POLLUTION SOURCES
RIVERS
STRONTIUM
WATERSHEDS