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Rutherford, M. J.
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Rutherford, M. J.
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- PublicationRestrictedOrigin of basalt fire-fountain eruptions on Earth versus the Moon(2009-03)
; ; ;Rutherford, M. J.; Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA ;Papale, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Fire-fountain eruptions of basaltic magma occur on Earth at centers such as Kilauea (Hawaii), and deposits from apparently similar eruptions have been found on the lunar surface. The driving force for terrestrial fire-fountain eruptions is the exsolution of dissolved CO2 based on gases dissolved in melt inclusions trapped in olivine phenocrysts and the relatively high oxidation state of these magmas. Gases released at the vent show that SO2, and eventually H2O, are partitioned into the CO2-rich gas, adding to the gas volume. In contrast, analytical and experimental studies of lunar samples indicate that the gas phase responsible for driving the lunar eruptions was CO-rich and produced by the oxidation of C (graphite) carried in the slowly ascending low-fO2 basalt. The graphite oxidation occurs when the pressure in the ascending lunar magma reaches that of the graphite-gas reaction surface (40 ± 1 MPa or ~8 km depth for the Apollo 17 orange-glass magma). As graphite is oxidized, some FeO is reduced, potentially forming a Fe-rich metal phase, and Fe-rich metal spherules are present in beads in lunar glass deposits. Other gas species such as S, Cl, and F partitioned variously into CO-rich lunar volcanic gas, and appear in surface coatings on the glass spherules. Modeling of the magma flow from 8 km depth to the lunar surface shows that the gas bubble volume fraction (assuming initial C at 50–500 ppm levels) ranges from 0.5 to 0.8 at the surface, the exit velocity ranges from 15 to 35 m/s, and the low-viscosity magma fragments only as it erupts at the lunar surface.227 22 - PublicationRestrictedThe deep magmatic system of the Campi Flegrei caldera (Italy)(2008)
; ; ; ; ; ; ;Mangiacapra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Moretti, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Rutherford, M.; Department of Geological Sciences, Brown University, Providence, ;Civetta, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Orsi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Papale, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; ; ; ; ; Melt inclusions in phenocrysts of the Minopoli2 shoshonite and Fondo Riccio latite eruptive products (Campi Flegrei caldera; 10.2 to 9.5 ka BP) constrain the nature of deep Phlegraean magmatic fluids, their role in volcanism and give new insights into the magmatic plumbing system. The analyzed melt inclusions show that CO2 is an abundant gaseous species, confirming the results of geochemical studies on the magmatic gas fraction involved in present-day fumarolic emissions. Volatile concentrations within the melt inclusions require gas-melt equilibria between 8 and 9 km depth, and closed-system degassing in presence of ascending CO2-rich fluids of deep provenance. Magmas later re-equilibrate at depths up to 3–2 km, i.e. above the top of the carbonate basement. These observations correlate well with independent geophysical and geochemical evidence and are useful constraints for volcanic hazards assessment at Campi Flegrei.244 32