Variations of oxygen isotopic compositions of silicate spherules collected from Antarctic blue ice

Introduction: Recent works suggest that unmelted, phillosilicate-bearing micrometeorites and hydrous interplanetary dust particles (IDPs) collected at stratosphere are related to hydrated carbonaceous chondrites [1], [2], which are supposed to be derived from C-, P-, D-, or T-type asteroids [3, 4]. Anhydrous IDPs are supposed to be cometary origin because of their high D/H ratios and characteristic mineralogy that are distinct from any meteorites [5]. It is difficult to clarify precursor materials of melted cosmic spherule, because of loss of their original mineralogy due to severe heating during atmospheric entry. Oxygen isotopic signature is useful for identification of planetary materials [6]. In order to clarify the precursor of cosmic spherules, we analyzed oxygen isotopes of individual 37 cosmic spherules with an ion probe. Part of this work was briefly reported in [7], here we report a series of results in detail.