Chapter 6. APPLICATION OF EXPERIMENTAL RESULTS TO C-O-H SPECIES IN NATURAL MELTS

Holloway, John; Blank, Jennifer

doi:10.1515/9781501509674-012

Cited by 185 publications

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“…8a is representative of data for common melt compositions such as rhyolite, andesite, phonolite and basalt (e.g. Holloway and Blank 1994). The majority of data points for H 2 O in Fig.…”

Section: Solubility In Experimental Melt Compositionsmentioning

confidence: 99%

The volatile content of hypabyssal kimberlite magmas: some constraints from experiments on natural rock compositions

et al. 2011

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Kimberlites are volatile rich magmas that ascend from deep in the mantle at high velocities, then as they reach a 'root zone' at 1-3 km in depth they either discharge explosively through to the surface or stall to form dykes and sills. Understanding this eruptive behaviour is difficult due to a lack of data on volatile solubility, particularly at conditions where the magmas enter the 'root zone' . In this study, we perform experiments on some putative primary kimberlite magma compositions to assess the amount of CO 2 and H 2 O retained if these compositions represent magma as it enters the root zone. At the conditions investigated (100-200 MPa and 1,275-1,100°C) the results suggest that none of these particular kimberlite compositions reproduce a magma that can retain the observed high volatile content when intruded at these pressures (∼4-8 km). In our experiments, the low volatile retention is due to a combination of factors including a high proportion of solid phases, none of which are volatilebearing, and inadequate volatile solubilities in the subordinate amounts of melt present. Modelled solubilities also suggest that the dissolved volatile contents remain too low even at super-liquidus temperatures (i.e. 100% melt). For water, the higher values observed in natural rocks can be explained by the addition of H 2 O associated with ubiquitous post-emplacement serpentinization. The high CO 2 contents in hypabyssal rocks are unlikely to be related to alteration. We suggest that most kimberlites originally had lower SiO 2 contents and as such may have been 'transitional' between silicate and carbonate melts. This results in both higher CO 2 solubilities and lower liquidus temperatures. For such compositions, it is possible that both CO 2 and water solubility may first decrease and then increase as magmas decompress and crystallize. Such unusual behaviour can help explain why kimberlite magmas can be very explosive or form shallow hypabyssal intrusions.

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“…8a is representative of data for common melt compositions such as rhyolite, andesite, phonolite and basalt (e.g. Holloway and Blank 1994). The majority of data points for H 2 O in Fig.…”

Section: Solubility In Experimental Melt Compositionsmentioning

confidence: 99%

The volatile content of hypabyssal kimberlite magmas: some constraints from experiments on natural rock compositions

et al. 2011

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“…In order to calculate pressure from measured water contents in the glassy rims we used the solubility model of Holloway and Blank (1994), which is based on the earlier models of Spera and Bergman (1980) and Silver and Stolper (1985). Solubility parameters for H 2 O in basaltic melt were taken from .…”

Section: Estimation Of Eruption Pressures and Ice Thicknessmentioning

confidence: 99%

Constraints on the dynamics of subglacial basalt eruptions from geological and geochemical observations at Kverkfjöll, NE-Iceland

2006

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The Kverkfjöll area, NE Iceland is characterised by subglacial basalt pillow lavas erupted under thick ice during the last major glaciation in Iceland. The water contents of slightly vesiculated glassy rims of pillows in six localities range from 0.85±0.03 to 1.04±0.03 wt %. The water content measurements allow the ice thickness to be estimated at between 1.2 and 1.6 km, with the range reflecting the uncertainty in the CO 2 and water contents of the melt. The upper estimates agree with other observations and models that the ice thickness in the centre of Iceland was 1.5-2.0 km at the time of the last glacial maximum. Many of the pillows in the Kverkfjöll area are characterised by vesiculated cores (40-60% vesicles) surrounded by a thick outer zone of moderately vesicular basalt (15-20% vesicles). The core contains ∼1 mm diameter spherical vesicles distributed uniformly. This observation suggests a sudden decompression and vesiculation of the still molten core followed by rapid cooling. The cores are attributed to a jökulhlaup in which melt water created by the eruption is suddenly released reducing the environmental pressure. Mass balance and solubility relationships for water allow a pressure decrease to be calculated from the observed change of vesicularity of between 4.4 and 4.7 MPa depressurization equivalent to a drop in the water level in the range 440-470 m. Consideration of the thickness of solid crust around the molten cores at the time of the jökulhlaup indicates an interval of 1-3 days between pillow emplacement Editorial responsibility: J. and the jökulhlaup. Upper limits for ice melting rates of order 10 −3 m/s are indicated. This interpretation suggests that jökulhlaups can reactivate eruptions.

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“…In addition, the high abundance of CO 2 in magmatic systems (Carroll and Halloway 1994;Wallace 2005), its low solubility in silicate melts favouring early exsolution at mantle to deep-crustal conditions (Holloway and Blank 1994), and the relatively inert chemical behaviour (at least compared to more reactive species such as SO 2 , or HCl; Symonds et al 2001) make CO 2 an optimal chemical tracer of volcanic degassing processes. This fact, when combined with the large mass-dependent fractionations among its carbon stable isotopes ( 12 C and 13 C; Craig 1953;Chacko et al 2001), has stimulated a large number of isotopic determinations in fumaroles and steaming grounds (Lyon and Hulston 1984;Allard et al 1988;Giggenbach 1997), groundwaters (Allard et al 1997;Caliro et al 1999Caliro et al , 2005Chiodini et al 2000), and in soils on the surroundings of active volcanoes (Chiodini et al 2008).…”

Section: Introductionmentioning

confidence: 99%

First 13C/12C isotopic characterisation of volcanic plume CO2

et al. 2010

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We describe analytical details and uncertainty evaluation of a simple technique for the measurement of the carbon isotopic composition of CO 2 in volcanic plumes. Data collected at Solfatara and Vulcano, where plumes are fed by fumaroles which are accessible for direct sampling, were first used to validate the technique. For both volcanoes, the plume-derived carbon isotopic compositions are in good agreement with the fumarolic compositions, thus providing confidence on the method, and allowing its application at volcanoes where the volcanic component is inaccessible to direct sampling. As a notable example, we applied the same method to Mount Etna where we derived a 0.27‰ (Bocca Nuova and Voragine craters). The comparison of our measurements to data reported in previous work values of Etna CO 2 from~−4‰, in the 1970's and the 1980's, to~−1‰ at the present time (2009). This shift toward more positive δ 13 C values matches a concurrent change in magma composition and an increase in the eruption frequency and energy. We discuss such variations in terms of two possible processes: magma carbonate assimilation and carbon isotopic fractionation due to magma degassing along the Etna plumbing system. Finally, our results highlight potential of systematic measurements of the carbon isotopic composition of the CO 2 emitted by volcanic plumes for a better understanding of volcanic processes and for improved surveillance of volcanic activity.

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Chapter 6. APPLICATION OF EXPERIMENTAL RESULTS TO C-O-H SPECIES IN NATURAL MELTS

Cited by 185 publications

References 0 publications

The volatile content of hypabyssal kimberlite magmas: some constraints from experiments on natural rock compositions

The volatile content of hypabyssal kimberlite magmas: some constraints from experiments on natural rock compositions

Constraints on the dynamics of subglacial basalt eruptions from geological and geochemical observations at Kverkfjöll, NE-Iceland

First 13C/12C isotopic characterisation of volcanic plume CO2

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