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The episodic variation of the seawater [sup 87]Sr/[sup 86]Sr ratio has been attributed to either variations in the Sr flux or the Sr-isotopic composition of the riverine-dissolved load derived from weathering of the continental crust. The discovery that Himalayan rivers are characterized by high concentrations of dissolved Sr concentrations with high [sup 87]Sr/[sup 86]Sr ratios has raised the possibility that collisional orogens play a critical role in moderating the variations in seawater [sup 87]Sr/[sup 86]Sr ratios. Here we describe Himalayan carbonates and calc-silicates from Garhwal, the headwaters of the Ganges, with extreme [sup 87]Sr/[sup 86]Sr ratios (> 1.0). Elevated Sr-isotope ratios result from exchange with Rb-rich silicate material during both Himalayan and pre-Himalayan metamorphic episodes, and the carbonates contribute a significant fraction to the Ganges [sup 87]Sr flux. Particularly elevated [sup 87]Sr/[sup 86]Sr ratios are found in calc-silicates from the Deoban Formation of the Lesser Himalaya. A detailed traverse of shales and calc-silicates from this unit confirms that carbonate horizons have increased [sup 87]Sr/[sup 86]Sr ratios as a result of isotopic exchange over length scales of 10-30 cm. We conclude that metamorphism of carbonates may cause elevation of their [sup 87]Sr/[sup 86]Sr ratios and that uplift of metamorphosed carbonates may be a consequence of collisional orogens, which contributes to the elevation of seawater [sup 87]Sr/[sup 86]Sr ratios. [ABSTRACT FROM AUTHOR]