Abstract
Strontium isotopes have been analyzed in a typical calcrete profile developed on granite in the Toledo mountains, Central Spain. The pedogenic carbonates show clear petrographic evidence of pseudomorphic replacement of the weathered parent granite. Calcretes display 87Sr/ 86Sr ratios between 0.70961 and 0.71059 in sharp contrast to the granite whole rock (0.72856) and minerals (0.71359 to 0.91351). This difference shows that the contribution of Sr from the granite to the calcretes is at most 33% and may be as low as 3%. Direct measurements in rains and aerosols show that the allochtonous source of Ca and Sr is clearly related to the atmospheric input, mainly as dry deposit. A slight decrease of Sr concentration is observed from the upper horizon composed of continuous calcrete to the deeper calcrete veins in the saprolite. This may be due to a kinetic control of the Sr/Ca fractionation, and different crystallization rates of the carbonates in the different units of the profile. Finally, local groundwaters have Sr isotopic compositions similar to the calcretes and the atmospheric input, very different from waters running on the granite.
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