PROVENANCE AND CORRELATION OF VOLCANICLASTIC MATERIAL FROM THE BRANSFIELD BASIN, ANTARCTICA: PRELIMINARY RESULTS

The Bransfield Basin is a marginal basin west of the Antarctic Peninsula. Within the Basin lie several active volcanic centers including Penguin Island, Bridgeman Island, Deception Island, and Melville Peak on King George Island. Deception Island has been the most active of these centers in historic times, with more than a dozen documented or suspected eruptions since 1800; the most recent documented eruption occurred in 1970. In addition, the Basin is also characterized by a number of submarine volcanic centers that are located along a spreading ridge stretching from Deception Island to Bridgeman Island. Collectively, these subaerial and submarine volcanic centers are believed to have produced most of the abundant volcaniclastic material contained in sediment cores retrieved from the Basin.

We studied volcaniclastic layers in several sediment cores collected from the Bransfield Basin during Operation Deep Freeze in 1982 and found that various layers contained pumice, volcanic rock fragments, and volcanic glass shards singly or in combination. We wanted to determine if the chemical composition of materials contained in these layers could be used 1) to identify associated sources, and 2) to develop a stratigraphic correlation between different cores collected within the Basin.

Using WDS electron microprobe analysis, we determined the chemical composition of various materials separated from the volcanic layers. These analytical data were compared to published analyses of volcanic material from Melville Peak, the seamounts, and from Deception, Bridgeman and Penguin Islands. Preliminary results indicate that it is possible to determine the provenance for many samples, at least in the broad sense of delineating a compositional correlation between an individual layer and the published range of materials produced from individual volcanic sources. However, certain cores contain layers that are compositionally distinctive and are clearly associated with only one particular eruption from one particular source. Conversely, some layers are compositionally heterogeneous, indicating mixing of source material through a variety of possible mechanisms. Provenance determinations have been encouraging, but correlation of layers throughout the basin has not yet been possible.