Wetting Angles, Equilibrium Melt Geometry, and the Permeability Threshold of Partially Molten Crustal Protoliths

Laporte, Didier; Rapaille, Cédric; Provost, Ariel

doi:10.1007/978-94-017-1717-5_3

Cited by 72 publications

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“…contemporaneous deformation and associated pressure gradients lead to a melt connectivity transition that may be significantly lower than the 7 vol% estimated by Rosenberg & Handy (2005) and lower than the upper limit for the percolation threshold of 3.4 vol% suggested by Laporte et al (1997). As figure 4a shows, the distribution of melt is relatively uniform with no tendency to form veins, although most of the former melt occurs as connected arrays up to five grain diameters long located along grain boundaries that lie within 20…”

Section: (B) What Data Do We Have and How May We Use Them?mentioning

confidence: 81%

“…Within the first few per cent of melt production, the melt reaches the melt connectivity transition in all common crustal protoliths (Laporte et al 1997;Rosenberg & Handy 2005), although not necessarily at a common temperature (for a constant pressure or depth) and, therefore, not at the same time. The development of permeability enables advective melt flow from grain boundaries to veins, assuming dilatancy collapse by shear-enhanced compaction of the matrix (Rutter & Mecklenburgh 2006); this may occur earlier in some horizons than in others.…”

Section: (B) From the Initiation Of Melting To The Melt Connectivity mentioning

confidence: 99%

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The spatial and temporal patterning of the deep crust and implications for the process of melt extraction

Brown

2010

Phil. Trans. R. Soc. A.

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Volumetrically significant melt production requires crustal temperatures above approximately 800• C. At the grain scale, the former presence of melt may be inferred based on various microstructures, particularly pseudomorphs of melt pores and grainboundary melt films. In residual migmatites and granulites, evidence of melt-extraction pathways at outcrop scale is recorded by crystallized products of melt (leucosome) and residual material from which melt has drained (melanosome). These features form networks or arrays that potentially demonstrate the temporal and spatial relations between deformation and melting. As melt volume increases at sites of initial melting, the feedback between deformation and melting creates a dynamic rheological environment owing to localization and strain-rate weakening. With increasing temperature, melt volume increases to the melt connectivity transition, in the range of 2-7 vol% melt, at which point melt may escape in the first of several melt-loss events, where each event represents a batch of melt that left the source and ascended higher in the crust. Each contributing process has characteristic length and time scales, and it is the nonlinear interactions and feedback relations among them that give rise to the dissipative structures and episodicity of melt-extraction events that are recorded as variations in the spatial and temporal patterning of the crust. Focused melt flow occurs by dilatant shear failure of low-melt fraction rocks creating melt-flow networks that allow accumulation and storage of melt, and form the link for melt flow from grain boundaries to veins allowing drainage to crustal-scale ascent conduits. Preliminary indications suggest that anatectic systems are strongly self-organized from the bottom up, becoming more ordered by decreasing the number and increasing the width of ascent conduits from the anatectic zone through the overlying subsolidus crust to the ductile-to-brittle transition zone, where the melt accumulates in plutons.

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Section: (B) What Data Do We Have and How May We Use Them?mentioning

confidence: 81%

Section: (B) From the Initiation Of Melting To The Melt Connectivity mentioning

confidence: 99%

The spatial and temporal patterning of the deep crust and implications for the process of melt extraction

Brown

2010

Phil. Trans. R. Soc. A.

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“…Distances between the studied Grt in this rock, therefore, are at least in the range of a few cm. Melt interconnetion in partially melted metasedimentary rocks is expected to occur at the temperatures registered in the migmatites (≥800 ºC; Laporte et al 1997;Clemens 2006, and references therein). However, the interconnected melt is likely to be compositionally heterogeneous due to the sluggish diffusion of Si and Al in melt (Acosta-Vigil et al 2006a, 2012b.…”

Section: Significance Of Glass Compositions In Remelted Nanogranitoidsmentioning

confidence: 99%

The composition of nanogranitoids in migmatites overlying the Ronda peridotites (Betic Cordillera, S Spain): the anatectic history of a polymetamorphic basement

Acosta-Vigil

Barich

Bartoli

et al. 2016

Contrib Mineral Petrol

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The study of the composition of primary melts during anatexis of high-pressure granulitic migmatites is relevant to understand the generation and differentiation of continental crust.Peritectic minerals in migmatites can trap dropless of melt that forms via incongruent melting reactions during crustal anatexis. These melt inclusions commonly crystallize and form nanogranitoids upon slow cooling of the anatectic terrane. To obtain the primary compositions of crustal melts recorded in these nanogranitoids, including volatile concentrations and information on fluid regimes, they must be remelted and rehomogenize before analysis. A new occurrence of nanogranitoids was recently reported in garnets of mylonitic metapelitic gneisses (former high pressure granulitic migmatites) at the bottom of the prograde metamorphic sequence of Jubrique, located on top of the Ronda peridotite slab (Betic Cordillera, S Spain). Nanogranitoids within separated chips of cores and rims of large garnets from these former migmatites were remelted at 15 kbar and 850, 825 or 800 ºC and dry (without added H 2 O), during 24 hours, using a piston cylinder apparatus. Although all experiments show glass (former melt) within melt inclusions, the extent of rehomogenization depends on the experimental temperature. Experiments at 850-825 ºC show abundant disequilibrium microstructures, whereas those at 800 ºC show a relatively high proportion of rehomogenized nanogranitoids, indicating that anatexis and entrapment of melt inclusions in these rocks was likely close to 800 ºC. Electron microprobe and NanoSIMS analyses show that experimental glasses are leucogranitoid and peraluminous, though define two distinct compositional groups. Type I corresponds to K-rich, Ca-and H 2 O-poor leucogranitic melts, whereas type II represents K-poor, Ca-and H 2 O-rich granodioritic to tonalitic melts. Type I and II melt inclusions are found in most cases at the cores and rims of large garnets, respectively. We tentatively suggest that these former migmatites underwent two melting events under contrasting fluid regimes, possibly during two different orogenic periods. This 3 study demonstrates the strong potential of melt inclusions studies in migmatites and granulites in order to unravel their anatectic history, particularly in strongly deformed rocks where most of the classical anatectic microstructures have been erased during deformation.

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“…A parameter of primary importance in this context is the permeability threshold 0c, that is, the volume percentage of fluid at which fluid interconnection is established. and Watson, 1991]; quartz-, biotite-, and hornblende-silicic melt [Laporte, 1994;Laporte and Watson, 1995]; and plagioclase-silicate melt [Longhi and Jurewicz, 1995;Laporte et al, 1997]. The systematic observation of crystal faces indicates that the assumption of isotropic surface energies is not a good one for silicate-fluid systems.…”

Section: Introductionmentioning

confidence: 99%

Equilibrium geometry of a fluid phase in a polycrystalline aggregate with anisotropic surface energies: Dry grain boundaries

Laporte¹,

Provost²

2000

J. Geophys. Res.

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Abstract. The equilibrium distribution of a fluid phase in a rock is controlled by the ratio of grain boundary energy to solid-fluid interfacial energy ("surface energy"). A strong dependence of interfacial energy on interface orientation (anisotropy) is the rule for solidfluid surfaces of geological interest. We investigated the effects of surface energy anisotropy on the equilibrium interface configuration at the junction of two crystals with a fluid in a two-dimensional solid-fluid system. The two major effects are to promote the development of planar solid-fluid interfaces parallel to crystallographic planes of minimum energy and to lead to large variations of the dihedral angle from one triple junction to the other (as a function of the orientation of crystalline lattices relative to the grain boundary). Despite these large variations, the frequency distributions of equilibrium dihedral angles remain unimodal; also the relationship between the mean fluid dihedral angle and the ratio of grain boundary to surface energy is very close to the isotropic law. Even in the most anisotropic systems, the fluid dihedral angle is therefore a parameter of primary importance for predicting the grainscale geometry of a low-volume fraction of fluid and its mobility.

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Wetting Angles, Equilibrium Melt Geometry, and the Permeability Threshold of Partially Molten Crustal Protoliths

Cited by 72 publications

References 0 publications

The spatial and temporal patterning of the deep crust and implications for the process of melt extraction

The spatial and temporal patterning of the deep crust and implications for the process of melt extraction

The composition of nanogranitoids in migmatites overlying the Ronda peridotites (Betic Cordillera, S Spain): the anatectic history of a polymetamorphic basement

Equilibrium geometry of a fluid phase in a polycrystalline aggregate with anisotropic surface energies: Dry grain boundaries

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