Sr isotope composition of island-surface dolomites at Kita-daito-jima, northern Philippine Sea

Abstract

We present strontium (Sr) isotope data for island-surface dolomites at Kita-daito-jima, northern Philippine Sea. The ⁸⁷Sr/⁸⁶Sr ratios of 50 samples fall within a wide range from 0.709037 to 0.709079, corresponding to 4.9-2.1 Ma. This wide range in Sr ages reflects the fact that the island-surface dolomites comprise variable mixtures of geochemically distinct, diachronous, dolomite crystal phases. Our results indicate that the Sr isotope ages of multi-generational dolomites on carbonate islands such as Niue and Little Bahama Bank, as well as Kita-daito-jima, should be re-examined employing a new method that determines the Sr isotope ratio of individual crystal phases.