Magmatic processes

Marsh, Bruce D.

doi:10.1029/rg025i005p01043

Cited by 26 publications

(9 citation statements)

References 347 publications

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“…Mass balance relations, based upon major and trace element data and isotope systematics, comprise the major geochemical criteria, along with the relevant constraints from phase equilibria. Recent years have seen an increasing number of studies emphasizing the physics of magmatic processes (see Marsh [1987] for a recent review). Analysis of petrologic processes, with regard to their physical plausibility, has produced new insights into processes such as the rate of ascent and heat transfer for molten diapirs [cf.…”

Section: Introductionmentioning

confidence: 99%

Rheology of subliquidus magmas: 1. Picritic compositions

Ryerson¹,

Weed²,

Piwinskii³

1988

J. Geophys. Res.

188

128

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The relationship between the rheology and phase equilibria of a picritic basalt from Kilauea Iki has been investigated at 1 atm along the QFM buffer. Between 1270 ø and 1180øC olivine and minor spinel are the only liquidus phases, and the melt volume decreases from 85 to 74 vol %. At the ol-sp-pc-cpx cotectic, melt is consumed more rapidly dropping to 47 vol % at 1139øC. The rheology of the magma is non-Newtonian, is characterized by time-dependent, pseudoplastic behavior, and is consistent with power law flow or Bingham pseudoplastic behavior. Non-Newtonian effects are most apparent when the crystal volume is greater than 25% and the shear rate is increasing. Once stirred, the magma approaches Newtonian rheology with decreasing shear rate. At 1170øC (approximately 25% suspended crystals) the apparent activation energy (calculated at unit shear rate) increases from 123 + 10 kcal mol-• to 452 + 21 kcal mol-X. When the change in liquid composition along the liquidus is included, the observed viscosities are in good agreement with those calculated from the Einstein-Roscoe equation for a serial size distribution of crystals. A quadratic fit to the shear stress-strain rate data yields a nonzero intercept indicative of a finite yield strength. The apparent yield strength increases with decreasing temperature reaching • 800 Pa at 1149øC. These extrapolated (and model dependent) values are in good agreement with those determined by other methods (Shaw et al., 1968' McBirney andMurase, 1984). The yield strengths can be fit by a power law expression, ao = 6500• b2'85, where ao is the yield strength and •b the crystal volume fraction. This expression recovers the yield strength estimates for other basalts, suggesting that it may be generally applicable to magmas in which the melt is of broadly basaltic composition. The magmas exhibit heating due to viscous dissipation during shearing. However, this effect is not large enough to produce the observed pseudoplasticity. We conclude that the non-Newtonian behavior in these magmas is due to reorientation of solids in the flow field and solid-solid interactions. We develop a model in which the time-dependent pseudoplasticity and yield strengths are produced by the relationship between solid phase contiguity (the fraction of solid internal surface area shared with other solids) and grain dispersive pressure due to shearing. Increased contiguity is related to increased apparent viscosities and yield strengths, while increased grain dispersive pressure due to shearing acts to diminish contiguity. Paper number 7B7035. 0148-0227/88/007B-7035505.00 cooled liquids (cf. Bockris and Lowe [1953, 1954], Bockris et al. [1955], Shaw [1963], Cukierrnan and Uhlmann [1973, 1974], Cranmer and Uhlmann [1981], and Urbain et al. [1982], among others). The variables investigated in these studies are temperature and bulk composition. Using these variables empirical models for the estimation of viscosity have been formulated [Shaw, 1972; Bottinga and Weill, 1972]. Other studies have concentrated upon th...

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Section: Introductionmentioning

confidence: 99%

Rheology of subliquidus magmas: 1. Picritic compositions

Ryerson¹,

Weed²,

Piwinskii³

1988

J. Geophys. Res.

188

128

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“…At low crystal concentrations (Φ s < 25 vol.%), crystal-bearing magmas can be approximated as Newtonian fluids [19,21,59,60] …”

Section: Comparison With Previous Studiesmentioning

confidence: 99%

Experimental investigation of magma rheology at 300 MPa: From pure hydrous melt to 76 vol.% of crystals

Champallier

Bystricky

Arbaret

2008

Earth and Planetary Science Letters

100

102

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The rheological behaviour of synthetic crystal-bearing magmas containing up to 76 vol.% of crystals (0 ≤ φ S ≤ 0.76) has been investigated experimentally at a confining pressure of 300MPa and temperatures between 475 and 1000°C at shear rates between 10 -4 and 2x10 -3 s -1 .Starting hydrated crystal-bearing glasses were synthesized from a dry haplogranitic glass For pure hydrated melt and for 16 vol.% of crystals, the rheology is found to be newtonian. At higher crystal contents, the magmas exhibit shear thinning behaviour (pseudoplastic). TheEinstein-Roscoe equation adequately estimates viscosities of the crystal-bearing magmas at low crystal contents (φ S ≤~ 0.25), but progressively deviates from the measured viscosities with increasing crystal content as the rheological behaviour becomes non-newtonian. On the basis of a power-law formulation, we propose the following expression to calculate the viscosity as a function of temperature, crystal content and applied stress (or shear rate):where γ& is shear rate (s -1 ), τ is shear stress (MPa), Φ is the crystal volume fraction, T is temperature (K), Φ m is the relative maximum packing density, R is the gas constant, Q = 231 kJ.mol -1 is the activation energy of the viscous flow and A 0 , K, K 1 and K 2 are empirical parameters.

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“…8a-c, 9c, 12a). We suggest that as blocks sink through a crystal-rich magma, mafic material accumulates along the lower margin and fabrics form parallel to this surface as it pushes through the magma, similar to a fi lter-pressing mechanism (Marsh 1987, Sawyer 1994). …”

Section: Evidence That Xenoliths Are Stoped Blocksmentioning

confidence: 95%

Voluminous Stoping in the Mitchell Peak Granodiorite, Sierra Nevada Batholith, California, Usa

Pignotta¹,

Paterson²

2007

The Canadian Mineralogist

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The Mitchell Peak Granodiorite, Sierra Nevada, California, has an outcrop exposure of nearly 50% stoped blocks in its youngest intrusive phase and an estimated 20% exposure of stoped blocks throughout the entire pluton. In this pluton, stoping thus is an important process. It is an excellent locale to study the effect of stoping on the evolution of magmatic systems. Preliminary work in the Mitchell Peak area has shown a complex pattern of stoping at pluton margins, with abundant evidence for mechanical disintegration of the granodiorite blocks. Preserved blocks range in size from hundreds of meters across down to K-feldspar xenocrysts. Many stoped blocks have a sharp contact with the surrounding pluton; rare examples have a diffuse, partially melted contact. Abundant xenocrysts derived from the stoped blocks provide evidence of contamination. In addition, a variety of magmatic features concentrated along the margin of stoped blocks, such as swarms of microgranitoid enclaves, schlieren layering, aplite intrusive bodies and orbicular granodiorite, suggests that these are areas of repeated injection or pulsing of magma. We speculate that repeated injection of magma plays an important role in the mechanical and chemical breakdown of host-rock margins and of stoped blocks. Stoping may play an important role in the thermal, mechanical, and chemical contamination of magmas in arcs, and deserves further attention.

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Magmatic processes

Cited by 26 publications

References 347 publications

Rheology of subliquidus magmas: 1. Picritic compositions

Rheology of subliquidus magmas: 1. Picritic compositions

Experimental investigation of magma rheology at 300 MPa: From pure hydrous melt to 76 vol.% of crystals

Voluminous Stoping in the Mitchell Peak Granodiorite, Sierra Nevada Batholith, California, Usa

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