Geodynamic Models of Melt Generation and Extraction at Mid-Ocean Ridges

Gregg, P. M.; Hebert, L. B.; Montési, Laurent G. J.; Katz, Richard F.

doi:10.5670/oceanog.2012.05

Cited by 14 publications

(8 citation statements)

References 53 publications

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“…Hirschmann, 2010). Because the LAB represents a permeability barrier, melts are expected to migrate upward buoyantly and focus at depressions in the LAB if the slope towards that dip is sufficiently high, until they are extracted in veins (Gregg et al, 2012). In fact, craton edges and other zones with weaker cratonic signatures (slower velocities, lower elastic thickness and resistivity compared to intact roots), such as intra-cratonic boundaries, have been identified as the locus of preferred kimberlite magmatism (Poudjom Djomani et al, 2005;Malkovets et al, 2007;Artemieva, 2009;Begg et al, 2009;Faure et al, 2011).…”

Section: Melt Retention and Resupply At The Labmentioning

confidence: 99%

Origins of cratonic mantle discontinuities: A view from petrology, geochemistry and thermodynamic models

Aulbach

Massuyeau

Gaillard

2017

Lithos

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Section: Melt Retention and Resupply At The Labmentioning

confidence: 99%

Origins of cratonic mantle discontinuities: A view from petrology, geochemistry and thermodynamic models

Aulbach

Massuyeau

Gaillard

2017

Lithos

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“…Given regional-scale variations in strain along the length of an orogen, it is likely that the solidus surface in three dimensions is uneven and undulating, with antiformal culminations and synformal troughs. Under these circumstances, the solidus surface may act as a melt-impermeable boundary, or permeability barrier, at the base of the subsolidus crust, analogous to models for melt extraction at mid-ocean ridges (Sparks and Parmentier, 1991;Gregg et al, 2012). Although such a permeability barrier must inevitably be associated with a crystallization front at the solidus, the uneven and undulating nature of the front may allow melt to migrate upslope, driven by buoyancy, to points of melt extraction that form at antiformal culminations in the solidus surface.…”

Section: Focusing Melt For Extractionmentioning

confidence: 99%

Granite: From genesis to emplacement

Brown

2013

Geological Society of America Bulletin

521

219

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At low temperatures (<750 °C at moderate to high crustal pressures), the production of suffi cient melt to reach the melt connectivity transition (~7 vol%), enabling melt drainage, requires an infl ux of aqueous fl uid along structurally controlled pathways or recycling of fl uid via migration of melt and exsolution during crystallization. At higher temperatures, melting occurs by fl uid-absent reactions, particularly hydrate-breakdown reactions involving micas and/or amphibole in the presence of quartz and feldspar. These reactions produce 20-70 vol%, melt according to protolith composition, at temperatures up to 1000 °C. Calculated phase diagrams for pelite are used to illustrate the mineralogical controls on melt production and the consequences of different clockwise pressure-temperature (P-T) paths on melt composition. Preservation of peritectic minerals in residual granulites requires that most of the melt produced was extracted, implying a fl ux of melt through the suprasolidus crust, although some may be trapped during transport, as recorded by composite migmatitegranite complexes. Peritectic minerals may be entrained during melt drainage, consistent with observations from leucosomes in migmatites, and dissolution of these minerals during ascent may be important in the evolution of some crustal magmas. Since siliceous melt wets grains, suprasolidus crust may become porous at only a few volume % melt, as evidenced by microstructures in residual migmatites in which quartz or feldspar pseudomorphs form after melt fi lms and pockets. With increasing melt volume and decreasing effective pressure, assuming the residue is able to deform and compact, the source becomes permeable at the melt connectivity transition. At this threshold, a change from distributed shear-enhanced compaction to localized dilatant shear failure enables melt segregation. The result is a highly permeable vein network that allows transfer of melt to ascent conduits at the initiation of a melt-extraction event. Melt is drained from the anatectic zone via several extraction events, consistent with evidence for incremental construction of plutons from multiple batches of magma. Buoyancy-driven magma ascent occurs via dikes in fractures or via high-permeability zones controlled by tectonic fabrics; the way in which these features relate to compaction and the generation of porosity waves is discussed. Emplacement of laccoliths (horizontal tabular intrusions) and wedge-shaped plutons occurs around the ductile-to-brittle transition zone, whereas steep tabular sheeted and blobby plutons represent back freezing of melt in the ascent conduit or lateral expansion localized by instabilities in the magma-wallrock system, respectively.

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“…At mid-ocean ridges, melt is generated by decompression of the mantle that rises in response to the divergence of plates. Subsequent extraction of melt can be modeled as a three-step process [Sparks and Parmentier, 1991;Mont esi et al, 2011;Gregg et al, 2012]: (1) Melt moves vertically through buoyancy-driven porous flow enhanced by subvertical dissolution channels [e.g., Kelemen et al, 1997]. (2) Melt accumulates in and travels along decompaction channels associated with a permeability barrier at the base of thermal boundary layer [Sparks and Parmentier, 1991;Spiegelman, 1993;Hebert and Mont esi, 2010] generally sloping toward the ridge axes.…”

Section: Introductionmentioning

confidence: 99%

Slip‐rate‐dependent melt extraction at oceanic transform faults

Bai

Montési

2015

Geochem Geophys Geosyst

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Crustal thickness differences between oceanic transform faults and associated mid-ocean ridges may be explained by melt migration and extraction processes. Slow-slipping transform faults exhibit more positive gravity anomalies than the adjacent spreading centers, indicating relative thin crust in the transform domain, whereas at intermediate-spreading and fast-spreading ridges transform faults are characterized by more negative gravity anomalies than the adjacent spreading centers, indicating thick crust in the transform domain. We present numerical models reproducing these observations and infer that melt can be extracted at fast-slipping transforms, but not at slow-slipping ones. Melt extraction is modeled as a three-step process. (1) Melt moves vertically through buoyancy-driven porous flow enhanced by subvertical dissolution channels. (2) Melt accumulates in and travels along a decompaction channel lining a low-permeability barrier at the base of the thermal boundary layer. (3) Melt is extracted to the surface when it enters a melt extraction zone. A melt extraction width of 2-4 km and a melt extraction depth of 15-20 km are needed to fit the tectonic damages associated with oceanic plate boundaries that reach into the upper mantle. Our conclusions are supported by the different degrees of magmatic activities exhibited at fast-slipping and slow-slipping transforms as reflected in geological features, geochemical signals, and seismic behaviors. We also constrain that the maximum lateral distance of crust-level dike propagation is about 50-70 km.

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Geodynamic Models of Melt Generation and Extraction at Mid-Ocean Ridges

Cited by 14 publications

References 53 publications

Origins of cratonic mantle discontinuities: A view from petrology, geochemistry and thermodynamic models

Origins of cratonic mantle discontinuities: A view from petrology, geochemistry and thermodynamic models

Granite: From genesis to emplacement

Slip‐rate‐dependent melt extraction at oceanic transform faults

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