New Mexico Geological Society Annual Spring Meeting — Abstracts

Thirty-eight samples of palagonitic hyaloclastites formed in submarine, subaerial, and subglacial environments from Antarctica (33), Iceland (2), and N.Z. (3) were analysed for hydrogen isotope (δD) and Br content. Differentiating between submarine and subglacially formed hyaloclastites is critical in deciphering Antarctic glacial history. Poor exposure and near ubiquitous palagonitization of Antarctic hyaloclastites often obscures environmentally distinctive characteristics. The heavy δD - high Br content of marine water and light δD - low Br content of glacial waters are thought to be reflected tn the composition of palagonite.

Dried (> 200 C) palagonites have δD values ranging from -37 to -233 per mil and show good agreement within a sample locality. Br contents ranged from 0.1 and 71.0 ppm with a median of 0.9 ppm. Palagonites from the same locality had similar Br contents.

Six important factors affect D and Br composition of palagonite: 1) initial sideromelane δD and Br content; 2) palagonitizing fluid composition; 3) fractionation of δD and Br; 4) temperature of palagonitization; 5) degree of palagonitization; 6) OH-Halogen (Br) exchange reactions. These factors must be evaluated before δD and Br analyses of palagonite can be used in differentiating between submarine and subglacial eruptive environments of palagonitized volcaniclastic deposits.