Monday, 6 October 2008
George R. Brown Convention Center, Exhibit Hall E
The Afro-Arabian Flood Volcanic Province in Yemen and Ethiopia was erupted during the Oligocene (~26-30 Ma). It is a compositionally bimodal province, containing significant volumes of silicic eruptive units. Previous studies have correlated individual silicic units from onland sites in Yemen to tephra deposits found in Ocean Drilling Project sites (~2700 km SE of Yemen) in the Indian Ocean, making them some of the largest silicic eruptions in Earth's history with inferred volumes >1,000 km3. This project investigates the petrogenetic origins of these large-volume silicic magmas and their potential environmental impacts through study of rehomogenized melt inclusions hosted in plagioclase phenocrysts. Preliminary major element and volatile (S, Cl, F) data will be presented from four onshore ignimbrite units in Yemen. These data will be used to evaluate the robustness of the rehomogenization technique for plagioclase-hosted melt inclusions. Comparisons of elemental compositions of melt inclusions with previously reported tephra shard data will be made to determine the roles of crystallization and mixing in the compositional evolution of the silicic magmas. This data will also be used to evaluate the silicic magma origins through either extreme fractional crystallization or melting of underplated basalts. Pre-eruptive volatile compositions will be utilized to obtain an estimate of atmospheric loading of volatiles for the individual eruptions. Sulfur data will then be compared with predictions from sulfur solubility experiments from Scaillet & Macdonald (2006) who suggest that peralkaline silicic melts (such as Yemen-Ethiopian) should be richer in sulfur than metaluminous silicic melts (such as Parana-Etendeka).