Introduction to a <i>virtual special issue</i> on crustal melting

Brown, Michael

doi:10.1111/j.1525-1314.2012.00976.x

Cited by 6 publications

(5 citation statements)

References 23 publications

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“…It represents the latest in a series of reviews published during the past two decades (Atherton, 1993;Brown, 1994Brown, , 2007Brown, , 2010bPetford et al, 2000;Sawyer et al, 2011), none of which is reviewed herein, but to which the interested reader is referred to follow the development of ideas during the past 20 yr. This article covers material similar to that in the book by Brown and Rushmer (2006), and it includes reference to papers in the Virtual Special Issue on crustal melting in the Journal of Metamorphic Geology (Brown, 2012). "What's past is prologue" is engraved on the National Archives Building in Washington, D.C., and today the phrase is used liberally to mean that history infl uences, and sets the context for, the present.…”

Section: Introductionmentioning

confidence: 99%

Granite: From genesis to emplacement

Brown

2013

Geological Society of America Bulletin

522

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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Section: Introductionmentioning

confidence: 99%

Granite: From genesis to emplacement

Brown

2013

Geological Society of America Bulletin

522

219

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“…The partial melting of deeply subducted eclogite has several very important implications. First, the melt channels that are spaced every 10–20 m represent significant seismic velocity anomalies that should be accounted for in analysis of seismic data for geophysical models of the lithosphere 25 26 Second, the process of melting and melt aggregation from the subgrain scale to the pluton-feeding dike scale can be shown to be closely linked with structural processes, and the melt-enhanced deformation shows how deformation, melting and metamorphism are closely linked 27 28 29 . Third, recognizing melt channels in eclogite is important for understanding mid-to-lower crustal and mantle flow: the melt channels have a much lower viscosity than the surrounding eclogite and can accommodate large amounts of strain, allowing translation of intervening blocks.…”

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confidence: 99%

Partial melting of deeply subducted eclogite from the Sulu orogen in China

et al. 2014

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We report partial melting of an ultrahigh pressure eclogite in the Mesozoic Sulu orogen, China. Eclogitic migmatite shows successive stages of initial intragranular and grain boundary melt droplets, which grow into a three-dimensional interconnected intergranular network, then segregate and accumulate in pressure shadow areas and then merge to form melt channels and dikes that transport magma to higher in the lithosphere. Here we show, using zircon U–Pb dating and petrological analyses, that partial melting occurred at 228–219 Myr ago, shortly after peak metamorphism at 230 Myr ago. The melts and residues are complimentarily enriched and depleted in light rare earth element (LREE) compared with the original rock. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behaviour of subducted lithosphere and its rapid exhumation, controlling the flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust.

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“…Migmatites can also be overprinted by brittle-ductile shear zones, which further complicates the interpretation of migmatitic structures [19,21]. Considering the complex geological history of most migmatites, detailed field mapping and structural analyses are needed to understand the anatectic melt network of migmatites [11,12,18,[22][23][24][25][26] and are crucial for providing insights into the mechanics of melt production, melt segregation, melt migration, and melt redistribution during crustal partial melting accompanying orogenesis [8,10,11,27,28]. However, there is still a poor understanding of the relative roles of deformation versus melt fraction during the transition from metatexite to diatexite in migmatite terranes, but this information is crucial for linking structures in migmatites to the broader evolution of orogenic belts.…”

Section: Introductionmentioning

confidence: 99%

Partial Melting and Crustal Deformation during the Early Paleozoic Wuyi–Yunkai Orogeny: Insights from Zircon U-Pb Geochronology and Structural Analysis of the Fuhuling Migmatites in the Yunkai Region, South China

et al. 2019

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：Migmatites record crucial information about the rheology and tectonothermal evolutionof the deep crust during orogenesis. In the Wuyi–Yunkai orogen in South China, migmatites at Fuhuling record Early Paleozoic high temperatures and associated partial melting. However, the absolute timing and implications for the rheology of the deep crust during orogenesis are poorly constrained. In this contribution, we used spatial analysis of migmatitic leucosomes, structural analysis, and U-Pb geochronology of zircon to elucidate the absolute timing of crustal partial melting, the degree of partial melting, and the role of partial melting on the rheology of the crust during the Wuyi–Yunkai orogeny. Partial melting of the Fuhuling migmatites occurred at c. 440 Ma during Early Paleozoic Wuyi–Yunkai orogenesis. Subsequent lower temperature metamorphism associated with Indosinian movement that caused minor zircon recrystallization was temporally associated with the crystallization of nearby biotite monzogranites, but it did not influence the morphology of the Fuhuling migmatites. The migmatites preserve a morphological transition from metatexite to diatexite with an increasing proportion of leucosome. This transition preserves different structural characteristics that represent the response of the solid framework and melt network to variable melt fractions during partial melting. The large proportion of in situ or in source leucosome in the Fuhuling migmatites suggests that it was a melt-rich crustal horizon during orogenesis, and that a substantial proportion of anatectic melt was retained in the deep crust. The rheological transition documented in the Fuhuling migmatites was caused by changes in the melt fraction, and it is an analogue for the rheological transition characteristics of melt-rich crustal horizons in the Yunkai region during Early Paleozoic Wuyi–Yunkai orogenesis and subsequent orogenic collapse.

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Introduction to a virtual special issue on crustal melting

Cited by 6 publications

References 23 publications

Granite: From genesis to emplacement

Granite: From genesis to emplacement

Partial melting of deeply subducted eclogite from the Sulu orogen in China

Partial Melting and Crustal Deformation during the Early Paleozoic Wuyi–Yunkai Orogeny: Insights from Zircon U-Pb Geochronology and Structural Analysis of the Fuhuling Migmatites in the Yunkai Region, South China

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