Carbon dioxide in petrogenesis III: role of volatiles in the ascent of alkaline magma with special reference to xenolith-bearing mafic lavas

Spera, Frank J.

doi:10.1007/bf00380167

Cited by 232 publications

(108 citation statements)

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“…The vapors may enhance crack propagation, permitting rapid uprise of the kimberlite magma. Many intrusions from this level will solidify through thermal death before rising far [Spera, 1984], but others will enter the crust as kimberlite intrusions [Artyushkov and Sobolev, 1984]. Figure 32).…”

Section: Cratons and Kirnberlitesmentioning

confidence: 99%

Magma genesis, plate tectonics, and chemical differentiation of the Earth

Wyllie¹

1988

Reviews of Geophysics

130

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Magma genesis, migration, and eruption have played prominent roles in the chemical differentiation of the Earth. Plate tectonics has provided the framework of tectonic environments for different suites of igneous rocks and the dynamic mechanisms for moving masses of rock into melting regions. Petrology is rooted in geophysics. Petrological and geophysical processes are calibrated by the phase equilibria of the materials. The geochemistry of basalts and mantle xenoliths demonstrates that the mantle is heterogeneous. The geochemical reservoirs are related to mantle convection, with interpretation of a mantle layered or stratified or peppered with blobs. Seismic tomography is beginning to reveal the density distribution of the mantle in three dimensions, and together with fluid mechanical models and interpretation of the geoid, closer limits are being placed on mantle convection. Petrological cross sections constructed for various tectonic environments by transferring phase boundaries for source rocks onto assumed thermal structures provide physical frameworks for consideration of magmatic and metasomatic events, with examples being given for basalts, andesites, and granites at ocean-continent convergent plate boundaries, basalts and nephelinites from a thermal plume beneath Hawaii, kimberlites in cratons, nephelinites from continental rifts, and anorogenic granites. The fluid dynamics of rock-melt-vapor systems exerts strong control on igneous processes and chemical differentiation. Unravelling the processes during subduction remains one of the major problems for understanding mantle heterogeneities and the evolution of continents. INTRODUCTIONThe Union Lecture on which this review is based was pre- the magmatic processes occurring nearer the source of magma generation. There remains a gap between volcanoes, their plutonic roots, and the magma sources which has to be filled by indirect studies including geophysics, geochemistry, and fluid dynamics. Lavas reach the surface through volcanoes, and lavas can provide information about the source rocks from which they were derived if the materials and processes can be suitably calibrated in the laboratory. The calibration involves the geochemistry of major, minor, and trace element distributions (including isotopes) between minerals and melts and the conditions for melting of the various source materials under various conditions. Some lavas also bring to the surface samples of the host rocks from which they were derived by partial melting or of the rocks through which they rose. The lavas release gases to the atmosphere and hydrosphere which also provide clues about the nature of the source material at depth.The theme common to the different parts of this review relates to the conditions for melting, transfer, storage, and eruption of melts. The approach is as follows. Plate tectonics provides a framework of tectonic environments and internal processes, which can be calibrated by laboratory experiments at high pressures. Within this framework I next outline the developm...

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Section: Cratons and Kirnberlitesmentioning

confidence: 99%

Magma genesis, plate tectonics, and chemical differentiation of the Earth

Wyllie¹

1988

Reviews of Geophysics

130

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“…Some magma becomes volatile-saturated at depths extending well into the lithosphere. For example, kimberlitic magmas owe their rapid (Spera, 1984;Kelley and Wartho, 2000) ascent rates to their low density and viscosity and high compressibility imparted by their signi¢cant volatile content. Similarly, the conversion of pressure^volume expansion work into kinetic energy is dramatically apparent during the eruption of H 2 O-rich magma from shallow crustal magma bodies characteristic of explosive volcanism.…”

Section: Introductionmentioning

confidence: 99%

Shear viscosity of rhyolite-vapor emulsions at magmatic temperatures by concentric cylinder rheometry

Stein

Spera

2002

Journal of Volcanology and Geothermal Research

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The viscosity of natural rhyolitic melt from Lipari, Aeolian Islands and melt-bubble emulsions (30^50 vol% porosity) generated from Lipari rhyolite have been measured in a concentric cylinder rheometer at temperatures and shear rates in the range 925^1150 ‡C and 10 33^1 0 31:2 s 31 , respectively, in order to better understand the dependence of emulsion shear viscosity on temperature and shear rate in natural systems. Bubble-free melt exhibits NewtonianÂ rrhenian behavior in the temperature range 950^1150 ‡C with an activation energy of 395 þ 30 kJ/mol; the shear viscosity is given by log R m = 38.320+20624/T. Suspensions were prepared from natural rhyolite glass to which small amounts of Na 2 SO 4 were added as a 'foaming agent'. Reasonably homogeneous magmatic mixtures with an approximate log-normal distribution of bubbles were generated by this technique. Suspension viscosity varied from 10 6:1 to 10 8:37 Pa s and systematically correlates with temperature and porosity in the shear stress range (10 4:26^1 0 5:46 Pa) of the experiments. The viscosity of melt-bubble emulsions is described in terms of the relative viscosity, R r = R e / R m where R e is the emulsion viscosity and R m is the viscosity of melt of the same composition and temperature. The dependence of relative viscosity on porosity for magmatic emulsions depends on the magnitude of the capillary number CarG/(cr 31 b R 31 m ), the ratio of viscous forces acting to deform bubbles to interfacial forces resisting bubble deformation. For inviscid bubbles in magmatic flows three regimes may be identified. For Ca 6 0.1, bubbles are nearly spherical and relative viscosity is an increasing function of porosity. For dilute systems, R r = 1+P given by the classical result of Taylor [Proc. R. Soc. London A 138 (1932) 41^48]. For Ca in the range 0.1 6 Ca 6 10, emulsions behave as power law fluids and the relative viscosity depends on shear rate (or Ca) as well as porosity. At high Ca (Ca s 10) an asymptotic regime is reached in which relative viscosity decreases with increasing porosity and is independent of Ca. Our experiments were carried out for 30 6 Ca 6 925 in order to quantify the maximal effect of bubbles in reducing the viscosity of magmatic emulsions relative to single-phase melt at identical conditions of shear rate and temperature. The viscosity of a 50 vol% emulsion is a factor of five smaller than that of melt alone. Rheometric measurements obtained in this study are useful in constraining models of magma transport and volcanic eruption mechanics relevant to transport of volatile-saturated magma in the crust and upper mantle. ß 2002 Elsevier Science B.V. All rights reserved.Keywords: magmatic emulsion; magma rheology; melts and bubbles; relative viscosity 0377-0273 / 02 / $^see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 7 -0 2 7 3 ( 0 1 ) 0 0 2 6 0 -8

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“…Spera, 1984;Endo et al, 1996, Geschwind and Rutherford, 1995, Rutherford and Devine 2003, Proussevitch and Sahagian, 2005. Szramek et al, 2006Toramaru, 2006;Castro andDingwell, 2009, Ruprecht and.…”

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confidence: 99%