Dynamic model of dehydration melting motivated by a natural analogue: applications to the Ivrea–Verbano zone, northern Italy

Barboza, Scott A.; Bergantz, George W.

doi:10.1130/0-8137-2315-9.23

Cited by 6 publications

(3 citation statements)

References 58 publications

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“…Models of heat transfer between mafic magma and crust have typically involved a single mafic sill instantaneously emplaced in contact with crustal rocks (Barboza & Bergantz 1996;Bergantz 1989;Huppert & Sparks 1988;Jackson et al 2003;Raia & Spera 1997). The amount of crustal melt generated in these models depends on the thickness of the mafic sill, and on the initial temperatures and physical properties of the mafic magma and crust.…”

Section: Progressive Emplacement Of Mafic Magmamentioning

confidence: 99%

The sources of granitic melt in Deep Hot Zones

Annen¹,

Blundy

Sparks

2008

Transactions of the Royal Society of Edinburgh: Earth Sciences

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A Deep Hot Zone develops when numerous mafic sills are repeatedly injected at Moho depth or are scattered in the lower crust. The melt generation is numerically modelled for mafic sill emplacement geometries by overaccretion, underaccretion or random emplacement, and for intrusion rates of 2, 5 and 10 mm/yr. After an incubation period, melts are generated by incomplete crystallisation of the mafic magma and by partial melting of the crust. The first melts generated are residual from the mafic magmas that have low solidi due to concentration of H 2 O in the residual liquids. Once the solidus of the crust is reached, the ratio of crustal partial melt to residual melt increases to a maximum. If wet mafic magma, typical of arc environments, is injected in an amphibolitic crust, the residual melt is dominant over the partial melt, which implies that the generation of I-type granites is dominated by the crystallisation of mafic magma originated from the mantle and not by the partial melting of earlier underplated material. High ratios of crustal partial melt over residual melt are reached when sills are scattered in a metasedimentary crust, allowing the generation of S-type granites. The partial melting of a refractory granulitic crust intruded by dry, high-T mafic magma is limited and subordinate to the production of larger amount of residual melt in the mafic sills. Thus the generation of A-type granites by partial melting of a refractory crust would require a mechanism of selective extraction of the A-type melt.

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Section: Progressive Emplacement Of Mafic Magmamentioning

confidence: 99%

The sources of granitic melt in Deep Hot Zones

Annen¹,

Blundy

Sparks

2008

Transactions of the Royal Society of Edinburgh: Earth Sciences

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“…Partial melting is a process of fundamental importance to the evolution of the continental crust because it exerts a strong control on crustal rheology (e.g. Barboza & Bergantz, 1996;Raia & Spera, 1997;Vanderhaeghe & Teyssier, 2001;Vanderhaeghe, 2009) and thermal structure (e.g. De Yoreo et al, 1989;Depine et al, 2008) and causes crustal differentiation (e.g.…”

Section: Introductionmentioning

confidence: 99%

Anatectic melt volumes in the thermal aureole of the Etive Complex, Scotland: the roles of fluid‐present and fluid‐absent melting

Droop¹,

Brodie²

2012

Journal Metamorphic Geology

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Pelitic hornfelses within the inner thermal aureole of the Etive igneous complex underwent limited partial melting, generating agmatic micro‐stromatic migmatites. In this study, observed volume proportions of vein leucosomes in the migmatites are compared with modelled melt volumes in an attempt to constrain the controls on melting processes. Petrogenetic modelling in the MnNCKFMASHT system was performed on the compositions of 15 analysed Etive pelite samples using THERMOCALC. Melt modes were calculated at 2.2 kbar (the estimated pressure in the southern Etive aureole) from solidus temperatures to 800 °C for both fluid‐absent and fluid‐present conditions. Volume changes accompanying fluid‐absent melting at 2.2 kbar were also calculated. P–T pseudosections reproduce the zonal sequence of the southern Etive aureole fairly well. The modelled solidus temperatures of silica‐rich pelitic compositions are close to 680 °C at 2.2 kbar and, in the absence of free fluid, melt modes in such compositions rise to between 12 and 29% at 800 °C, half of which is typically produced over the narrow reaction interval in which orthopyroxene first appears. Silica‐poor compositions have solidus temperatures of up to ∼770 °C and yield <11.4% melt at 800 °C under fluid‐absent conditions. For conditions of excess H2O, modelled melt modes increase dramatically within ∼13 °C of the solidus, in some cases to >60%; by 800 °C they range from 61 to 88% and from 29 to 74% in silica‐rich and silica‐poor compositions, respectively. Calculated volume changes for fluid‐absent melting are positive for all modelled compositions and reach 4.5% in some silica‐rich compositions by 800 °C. Orthopyroxene formation is accompanied by a volume increase of up to 1.48% over a temperature increase of as little as 2.7 °C, supporting the arguments for melt‐induced ‘hydrofracturing’ as a viable melt‐escape mechanism in low‐P metamorphism. Mineral assemblages in the innermost aureole support previous conclusions that partial melting took place predominantly under fluid‐absent conditions. However, vein leucosome proportions, estimated by image analysis, do not show the expected correlation with grade, and are locally greatly in excess of melt modes predicted by fluid‐absent models, particularly close to the melt‐in isograd. Melting of interlayered psammites, addition of H2O from interlayered melt‐free rocks, and metastable persistence of muscovite are ruled out as major causes of the excess melt anomaly. The most likely cause, we believe, is that local variations existed in the amount of fluid available at the onset of melting, promoted by focussing of fluid released by dehydration in the middle and outer aureole; however, some redistribution of melt by compaction‐driven flow through the vein channel network cannot be ruled out. The formation of melt‐filled fractures in the inner Etive aureole was assisted by stresses that caused extension at high angles to the igneous contact. The fractures were probably caused either by transient pressure reduction in the ...

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“…Other authors, e.g. [Barboza & Bergantz, 1996] have put forward theories that result in flow rates of the order of millimetres per year (or less) and these were associated with buoyancy effects. The same order of magnitude is recovered here in connection with average tectonic strain rates.…”

Section: Discussionmentioning

confidence: 99%

Quantitative analysis and scaling of sheared granitic magmas

Koenders

Petford

2000

Geophysical Research Letters

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We present a quantitative treatment of the macroscopic behaviour of a sheared granitic magma using Biot's theory [Biot, 1941] and a shear‐dilatancy sensitive material model for the solids. The calculations are relevant to a magma in the solidosity range 0.55–0.7. The resulting excess pore pressure distribution is a function of the position and the time. Results are presented in graphical form. A scaling emerges that enables the results to be presented in non‐dimensional form. A sensitivity study is carried out of the parameters describing the rheology of the solid matrix (including permeability features). The model enables the estimate of pressure and flow rates, thus opening a way of understanding the features in the granite crystal mush that are caused by upflowing magma. At high strain rates (10−10S−1) flow rates due to shear far exceed melt movement due to buoyancy effects.

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Dynamic model of dehydration melting motivated by a natural analogue: applications to the Ivrea–Verbano zone, northern Italy

Cited by 6 publications

References 58 publications

The sources of granitic melt in Deep Hot Zones

The sources of granitic melt in Deep Hot Zones

Anatectic melt volumes in the thermal aureole of the Etive Complex, Scotland: the roles of fluid‐present and fluid‐absent melting

Quantitative analysis and scaling of sheared granitic magmas

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