- journal_title：Geology
- Contributor：Wilfred A. Elders ; Guðmundur Ó Friðleifsson ; Robert A. Zierenberg ; Emily C. Pope ; Anette K. Mortensen ; Ásgrímur Guðmundsson ; Jacob B. Lowenstern ; Naomi E. Marks ; Lara Owens ; Dennis K. Bird ; Mark Reed ; Nellie J. Olsen ; Peter Schiffman
- Publisher：Geological Society of America
- Date：2011-
- Format：text/html
- Language：en
- Identifier：10.1130/G31393.1
- journal_abbrev：Geology
- issn：0091-7613
- volume：39
- issue：3
- firstpage：231
- section：Articles
Magma flowed into an exploratory geothermal well at 2.1 km depth being drilled in the Krafla central volcano in Iceland, creating a unique opportunity to study rhyolite magma in situ in a basaltic environment. The quenched magma is a partly vesicular, sparsely phyric, glass containing ∼1.8% of dissolved volatiles. Based on calculated H2O-CO2 saturation pressures, it degassed at a pressure intermediate between hydrostatic and lithostatic, and geothermometry indicates that the crystals in the melt formed at ∼900 °C. The glass shows no signs of hydrothermal alteration, but its hydrogen and oxygen isotopic ratios are much lower than those of typical mantle-derived magmas, indicating that this rhyolite originated by anhydrous mantle-derived magma assimilating partially melted hydrothermally altered basalts.