Volcanic Events of Ross Island, Antarctica, Based on the Stable Isotope Studies of Drilled Volcanic Rocks

Abstract

In 1973, DVDP 3 drill hole near McMurdo Station, Ross Island penetrated lava flows and pyroclastics composed of alkaline basalts and reached 381 m. The basal 214 m thick pyroclastic unit consists of basaltic hyaloclastites. Cores contain permafrost ice as layers, filling the vesicles and cementing pyroclastics. Thenardite and calcite are also present mainly along the icerock interface. The origin of ice and salts was investigated using compositions of stable isotopes to disclose the volcanic events occurred in geologic time. For these purposes, δD, δ^C, δ^S and δ^O were measured using the above-mentioned samples. Theδ^O of ice samples increases substantially with increasing depth, ranging from -35.3‰ near the ground surface to +1.1 ‰ at the bottom of the drill hole. δ^S, δ^O andδ^C values for thenardite and calcite can be divided readily into three groups according to their depth. From the above results, the following conclusions can be obtained. 1) Basaltic hyaloclastites found at a depth of 200 to 381 m were erupted in the submarine volcanism. 2) Lavas and pyoclastics found at a depth of 100 to 200 m were formed under a subglacial and brackish condition, and have undergone strong hydrothermal alteration. 3) Samples from 0 to 100m downhole were erupted in environment quite different from volcanic rocks beneath, suggesting subaerial flow or eruptions.