Vestoid cosmic spherules from the South Pole Water Well and Transantarctic Mountains (Antarctica): A major and trace element study

Abstract

We present major and trace element data of five glass cosmic spherules (CS) with differentiated compositions recovered in the South Pole Water Well and the Transantarctic Mountains, Antarctica. The differentiated CS were first identified using Fe/Mg and Fe/Mn ratios and we have now added high Rare Earth Element concentrations (5 < REE N < 14), and low siderophile element abundances (e.g. Ni = 25 ± 27 ppm) as characteristics. We propose that the siderophile depletions observed in differentiated CS result from the segregation of these elements into the core of their parent body during differentiation. Then, the high Fe/Mg ratios of differentiated CS result from their low MgO contents. Combined with their high level of REE enrichment, this indicates that the precursors formed through basaltic melt extraction from the asteroid/planetary source. As Fe/Mn and Fe/Mg ratios cannot distinguish between a Martian or Vestoid origin, we measured trace elements (zinc, cobalt, and vanadium) whose chemical behavior depends on oxidation state, known to be higher in the Martian than in the Vestoid environment. The compositions of the differentiated CS studied in this work share the characteristics of eucrites for all these indicators, providing further evidence that these differentiated CS are samples of a Vesta-like asteroid. However, their precursors show a considerable diversity in their mineralogy when compared to eucrites, that results in a wider range of major (Ca and Al) and trace element (Ba, Sr, Sc, and V) composition in differentiated CS.