Sr isotopes in rivers of India and Pakistan: a Reconnaissance study

Abstract

It is well established that the isotopic composition of Sr in sea water has oscillated on different time scales during the past similar to 600 Ma. These oscillations result from changes in the relative contributions of dissolved Sr to sea water from its two major sources, continental weathering and hydrothermal interactions, with their characteristic ⁸⁷Sr/ ⁸⁶Sr. The continental input via fluvial weathering is generally more radiogenic (average ⁸⁷Sr/ ⁸⁶Sr 0.7119 ref. 2) compared to the hydrothermal ⁸⁷Sr/ ⁸⁶Sr of 0.7035 (ref. 2). The Sr flux and ⁸⁷Sr/ super(86)Sr of different river systems vary widely and in some way are related to the lithology of the drainage basin, the intensity of weathering and the efficiency with which they transport their dissolved load. We have measured the dissolved Sr concentrations and ⁸⁷Sr/ ⁸⁶Sr of the major rivers draining India and Pakistan. These measurements provide data on the flux of Sr isotopes transported by these rivers to the ocean and their impact on the Sr isotope evolution of the oceans. Further, as the river basins sampled comprise a diverse set of lithologic, tectonic and climatic regimes, they provide an opportunity to study the controls of these factors place in determining the Sr isotopic systematics of rivers.