Extreme O-18 Depletion In Calcite And Chert Clasts From The Elephant Moraine On The East Antarctic Ice-Sheet

Two large morain es are presently forming near the margin of the East Antarctic ice sheet west of Victoria Land where the flow of the ice sheet is disturbed by subglacial bedrock ridges of the Transantarctic Mountains (Fig. 1). During the 1983–84 search for meteorites in this area several clasts, composed of black acicular calcite crystals, were collected from the Elephant Moraine (76°17'35 S and 157°20'05 E) where they are ablating out of the ice1–3. Additional samples of this calcite were later collected from the Elephant Moraine during the 1984–85 and 1986–87 field seasons, but none were found at the Reckling Moraine at 76° 15' S and 158°40' E4–6. The calcite clasts are strongly depleted in 18O (δ 18O = –20.5 ±0.4%) with reference to standard mean ocean water, SMOW and in 13C (S13C =–22.6 ±0.1% with reference to the PDB standard) in addition to being enriched in radiogenic 87Sr (87Sr/86Sr = 0.71417 ±0.00002) relative to sea water. These results suggest that the calcite precipitated from aqueous solutions discharged by hotsprings under the East Antarctic ice sheet.