Showing papers by "Michael R. Carroll published in 1999"
TL;DR: In this article, the authors investigated the ascent rates required to maintain bubble-melt equilibrium in high-silica rhyolitic melts at 200 MPa and 825°C, and decompressed to lower pressures at constant rates of 0.025, 0.25,0.5, and 1.0 MPa s−1.
225 citations
TL;DR: In this article, the authors investigated the CO2 solubility and speciation in melts along the NaAlO2-SiO2 join from Ne (NaAlSiO4) to a model rhyolite (Ry) composition (NAlSi6O14) as a function of pressure (10 to 25 kb) and temperature (1450 to 1700°C).
116 citations
TL;DR: In this article, the authors used an ultra-violet laser ablation microprobe (UVLAMP) technique to measure the diffusion properties of a crystal with simple microtextures, over a range of temperatures.
97 citations
TL;DR: Moncrieeff et al. as discussed by the authors derived a simple relationship between magma oxidation state and sulphur speciation using the peak shift of S-Kcz radiation relative to a pyrite standard.
Abstract: D. H. S. MONCRIEFF AND M. R. CARROLL Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, B S8 1R J, UK New data on sulphur valence and magmatic oxidation state for Central Andean volcanic rocks, in combination with published data for experimental and natural samples, allow derivation of a simple relationship between magma oxidation state and sulphur speciation. For a number of highly oxidized Central Andean volcanic rocks fo2 has been calculated using magnetite-ilmenite or olivine-spinel pairs and the sulphur valence in glasses has been measured using the peak shift of S-Kcz radiation relative to a pyrite standard. Previously published experimental and natural data have been incorporated with a wider range in f% and S valence. The variation in sulphur speciation (as S 2 or SO ] ) as a function of log fo2 is described by an empirical polynomial fit which reproduces the data to within _+ 0.5 log units and allows use of electron microprobe measurements of the S-Kcz wavelength shift for estimation of magmatic oxygen fugacities. This approach is applicable for fo2 between FMQ-2 and FMQ+6, encompassing most terrestrial magmas. The method has been used to calculate the fo2 conditions under which melt inclusions were trapped in andesitic magmas before magma mixing in two Central Andean volcanoes, and to calculate the oxygen fugacity of a slowly-cooled pyroclastic flow in which the Fe-Ti oxide phases have subsequently re-equilibrated. In combination with Fe-Ti oxide data, two distinct trends emerge for Lascar volcano. Basaltic andesite-andesitic magma chambers follow T-fo2 trends which parallel the FMQ buffer curve, indicating ferrous-ferric iron buffering of oxygen fugacity. Dacitic anhydrite-bearing magmas with admixed basaltic andesite and andesite follow trends of increasing fo2 with decreasing temperature, indicative of buffering offo2 by SO2-H2S in a co-magmatic gas phase. This trend continues into the metamorphic aureole of the magma chamber, resulting in highly oxidized (close to magnetite-hematite) conditions.
66 citations