The relationship between length and width of plutons within the crustal-scale Cobequid Shear Zone, northern Appalachians, Canada

Koukouvelas, Ioannis; Pe‐Piper, Georgia; Piper, David J. W.

doi:10.1007/s00531-006-0077-7

Cited by 18 publications

(8 citation statements)

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“…In several studies, the size-frequency distributions and spacing of plutons show powerlaw distributions; these distributions have been used to argue that magmatic systems are selforganized from the bottom up Cruden and McCaffrey, 2001;Cruden, 2006;Koukouvelas et al, 2006). This view is consistent with multiple studies of relict anatectic systems (Brown and Solar, 1998a;Brown, 2005Brown, , 2010aHall and Kisters, 2012;Yakymchuk et al, 2012) and results from modeling (Petford and Koenders, 1998;Bons and van Milligen, 2001;Ablay et al, 2008;Hobbs and Ord, 2010) that suggest melt extraction may be a self-organized critical phenomenon.…”

Section: Current Views On Melt Segregation and Extractionsupporting

confidence: 55%

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: Current Views On Melt Segregation and Extractionsupporting

confidence: 55%

Granite: From genesis to emplacement

Brown

2013

Geological Society of America Bulletin

522

219

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“…Emplacement of granitic bodies along crustal-scale structures has been documented in many regions worldwide. Major shear zones were considered to be controlling factors in both magma ascension and pluton emplacement processes (Brown, 1994; Vigneresse, 1995; Koukouvelas, Pe-Piper & Piper, 2006; Rosenberg, 2004). Although magmatic intrusions are considered to be controlled mostly by extensional deformation, many studies have recognized that magmatic intrusions frequently occur along regional strike-slip faults (Aydin, Schultz & Campagna, 1990; Johnston, 1999; Olivier et al .…”

Section: Introductionmentioning

confidence: 99%

Is there a link between faulting and magmatism in the south-central Aegean Sea?

Κοκκάλας

Aydin

2012

Geol. Mag.

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A distinct spatial relationship between surface faulting, magmatic intrusions and volcanic activity exists in the Aegean continental crust. In this paper, we provide detailed structural observations from key onshore areas, as well as compilations of lineament maps and earthquake locations with focal plane solutions from offshore areas to support such a relationship. Although pluton emplacement was associated with low-angle extensional detachments, the NNE- to NE-trending strike-slip faults also played an important role in localizing the Middle Miocene plutonism, providing ready pathways to deeper magma batches, and controlling the late-stage emplacement and deformation of granites in the upper crust. Additionally, the linear arrangements of volcanic centres, from the Quaternary volcanoes along the active South Aegean Volcanic Arc, are controlled primarily by NE-trending faults and secondarily by NW-trending faults. These volcanic features are located at several extensional settings, which are associated with the main NE-trending faults, such as (i) in the extensional steps or relay zones between strike-slip and oblique-normal fault segments, (ii) at the overlap zones between oblique-normal faults associated with an extensional strike-slip duplex and (iii) at the tip zone of a NE-trending divergent dextral strike-slip zone. The NE trend of volcano-tectonic features, such as volcanic cone alignments, concentration of eruptive centres, hydrothermal activity and fractures, indicates the significant role of tectonics in controlling fluid and magma pathways in the Aegean upper crust. Furthermore, microseismicity and focal mechanisms of earthquakes in the area confirm the activity and present kinematics of these NE- trending faults.

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“…The size, shape and spatial distribution of plutons in the middle-to-upper crust reflect melting processes in the middle-to-lower crust, and the sizefrequency distributions and spacing of plutons in several studies show power-law distributions that have been used to argue that magmatic systems are selforganized from the bottom up (Bons & Elburg 2001;Cruden & McCaffrey 2001;Cruden 2006;Koukouvelas et al 2006). This view is consistent with studies of relict anatectic systems (e.g.…”

Section: The View From the Top Down: Granites In The Middle-to-upper 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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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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The relationship between length and width of plutons within the crustal-scale Cobequid Shear Zone, northern Appalachians, Canada

Cited by 18 publications

References 50 publications

Granite: From genesis to emplacement

Granite: From genesis to emplacement

Is there a link between faulting and magmatism in the south-central Aegean Sea?

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

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