advances, the analytical limitations imposed by the inherently young age of Quaternary deposits (i.e., very small amounts of radiogenic 40Ar in-growth and often small amounts of 36Ar) remain. Our current understanding of what factors may be important in determining the suitability of glassy materials for 40Ar/39Ar dating (e.g., magma chemistry, volatile contents, eruption mechanism, degassing behavior, etc.) is limited. In this we investigate 40Ar/39Ar and major volatile contents (H2O, CO2, Cl, F, and S) in a suite of effusion-dominated rhyolites from several subglacial (Torfajökull and Prestahnúkur, Iceland) and one subaerial eruption (Hrafntinnusker, Torfajökull) that are chemically and texturally distinct to better understand the application of the 40Ar/39Ar system to glassy materials. Volatile contents preserved in fresh volcanic glass can provide a estimate of the pre-eruptive volatile contents of the original minimum magma from which they are derived, as well as track and record the degassing history of a body of magma through time (Johnson et al., 1994; Balconne-Boissard et al., 2010). Here, we look at the preserved volatile record to assess variability and the occurrence of poor or incorrect 40Ar/39Ar ages to evaluate the suitability of young, subglacial and subaerially erupted glassy material for 40Ar/39Ar dating. 2. SAMPLE LOCATIONS AND ERUPTION ENVIRONMENT Eruption products from two volcanic centers in Iceland were sampled: (1) predominantly subglacial rhyolites from Torfajökull (Fig. 1a, b) and (2) a small-volume (0.6 km3; McGarvie et al., 2007) subglacial rhyolite eruption of a single magma-batch at Prestahnúkur (Fig. 1a, c). Eruptions at both locations have involved complex volcano-ice interactions (e.g., Tuffen et al., 2001; McGarvie et al., 2006, 2007). 2.1 Torfajökull
advances, the analytical limitations imposed by the inherently young age of Quaternary deposits (i.e., very small amounts of radiogenic 40Ar in-growth and often small amounts of 36Ar) remain. Our current understanding of what factors may be important in determining the suitability of glassy materials for 40Ar/39Ar dating (e.g., magma chemistry, volatile contents, eruption mechanism, degassing behavior, etc.) is limited. In this we investigate 40Ar/39Ar and major volatile contents (H2O, CO2, Cl, F, and S) in a suite of effusion-dominated rhyolites from several subglacial (Torfajökull and Prestahnúkur, Iceland) and one subaerial eruption (Hrafntinnusker, Torfajökull) that are chemically and texturally distinct to better understand the application of the 40Ar/39Ar system to glassy materials. Volatile contents preserved in fresh volcanic glass can provide a minimum estimate of the pre-eruptive volatile contents of the original magma from which they are derived, as well as track and record the degassing history of a body of magma through time (Johnson et al., 1994; Balconne-Boissard et al., 2010). Here, we look at the preserved volatile record to assess variability and the occurrence of poor or incorrect 40Ar/39Ar ages to evaluate the suitability of young, subglacial and subaerially erupted glassy material for 40Ar/39Ar dating. 2. SAMPLE LOCATIONS AND ERUPTION ENVIRONMENT Eruption products from two volcanic centers in Iceland were sampled: (1) predominantly subglacial rhyolites from Torfajökull (Fig. 1a, b) and (2) a small-volume (0.6 km3; McGarvie et al., 2007) subglacial rhyolite eruption of a single magma-batch at Prestahnúkur (Fig. 1a, c). Eruptions at both locations have involved complex volcano-ice interactions (e.g., Tuffen et al., 2001; McGarvie et al., 2006, 2007). 2.1 Torfajökull
CHEMGE_7792_Ms_Revised.docx