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B10210ZÁVADA ET AL.: EXTREME DUCTILITY OF FELDSPAR AGGREGATESB10210activity of basal hai and prism hai slip systems [Lister andHobbs, 1980]. This CPO pattern is typical of constrictionaltype of deformation that is consistent with prolate symmetryof quartz aggregates from this sample [Passchier andTrouw, 1996].Figure 5. BSE image of the type 3 (mylonite) bandedmicrostructure. Note the circular inclusions of K-feldspar inquartz. Scale bar is 500 mm. Inset shows plagioclasecomposition (Or, orthoclase component; Ab, albite component).Rhombs indicate band-forming plagioclase ofoligoclase composition. Triangles indicate interstitial albitein K-feldspar aggregates or oligoclase rims. Mineralabbreviations are after Kretz [1983].5. Melt Topology[17] Investigation of melt topology is important for understandingthe possible influence of melt phase on operativedeformation mechanisms of its host aggregates. Melttopology also reflects grain-scale melt migration pathways[Marchildon and Brown, 2001; Rosenberg, 2001]. Sawyer[2001] reviewed criteria for recognition of former presenceof melt on grain scale in deformed rocks. A typical featureof some rapidly quenched melting experiments is thedevelopment of melt pools with cuspate margins [Jurewiczand Watson, 1984] or thin melt films along crystal faces[Daines and Kohlstedt, 1997]. Melt phase crystallized asalbite, quartz or K-feldspar grains at triple point junctions orat crystal faces in residual aggregates have been commonlyreported from natural examples and interpreted in terms ofmelt topology in partially molten granite [e.g., Brown et al.,1999; Rosenberg and Riller, 2000; Marchildon and Brown,2001; Rosenberg, 2001].[18] In our study, polygonal mosaic of K-feldspar grainscontains numerous interstitial quartz and albite grains up to50 mm wide (Figures 5 and 6a) that extend along singleK-feldspar facets in the XZ section. Locally, narrowalbites (An 0.02 ) margin residual oligoclase (An 0,17 ) grainsFigure 6. Details of BSE images (type 3, mylonite) showing microstructures interpreted to mimic thetopology of crystallized interstitial melt. (a) Interstitial grains of quartz and albite between grains of K-feldspar aggregate developed especially on grain boundaries perpendicular to lineation (L). K-feldspar,light grey; quartz and albite, dark grey; scale bar 500 mm; XZ section. (b) Scarce triangular grain of K-feldspar between mica and oligoclase grain. Note fine exsolution lamella of albite adjacent to oligoclasegrain (arrow). K-feldspar, white; scale bar 250 mm; XZ section. (c) Albite rims on residual oligoclasegrains adjacent to K-feldspar aggregates (arrow 1), partial replacement of oligoclase grain by K-feldspar(arrow 2), amoeboid quartz grains at triple point junctions of plagioclase, adjacent to K-feldsparaggregates (arrow 3). Scale bar 250 mm; XZ section. (d) K-feldspar in host plagioclase grains (arrow 1),wedge-shaped albite grains within muscovite grains (arrow 2). Dark patches, holes in the specimen; scalebar 250 mm; XZ section. Mineral abbreviations are after Kretz [1983].6of15284
B10210ZÁVADA ET AL.: EXTREME DUCTILITY OF FELDSPAR AGGREGATESB10210Figure 7. Block diagram of the mylonite sample microstructure.The melt field in the legend represents grains ofphases assumed to have crystallized from interstitial melt.Note the melt topology; grain face pockets in XZ sectionand triple-point pockets in YZ section. Mineral abbreviationsare after Kretz [1983].(Figure 6c). Numerous interstitial round quartz grains withhigh dihedral angle occur in triple point junctions of thehost plagioclase aggregates often close to adjacent K-feldspar bands (Figure 6c). We suggest that these grainsdo not represent crystallized melt but resulted from annealingof disintegrated myrmekite fronts [Hanmer, 1982]. Locally,triangular K-feldspar grains with thin albitic ‘‘exsolution’’rim adjacent to oligoclase grains occur in plagioclasebands (Figure 6b). Thin wedge-shaped albite grains aredeveloped along (001) cleavage planes of muscovite grainsin plagioclase aggregates (Figure 6d). Plagioclase grainsadjacent to muscovite grains exhibit a rectangular networkof K-feldspar and albite, which is interpreted in terms ofmelt penetration along the cleavage planes of plagioclase(Figure 6d) [Mehnert et al., 1973; Dell’Angelo and Tullis,1988]. Quartz–K-feldspar boundaries show cuspate-lobateshapes and these boundaries are decorated with numeroussmall amoeboid grains of K-feldspar with high dihedral angleadjacent to the K-feldspar cusps (Figure 5).[19] Quartz and albite grains in K-feldspar aggregate,albite rims and scarce K-feldspar ‘‘pools’’ with albite‘‘exsolutions’’ in plagioclase bands, K-feldspar in plagioclasegrains, together with albite grains within mica crystalsand amoeboid grains of K-feldspar in quartz bands satisfythe criteria for presence of crystallized mineral phasesassumed to mimic residual melt topology [Rosenberg andRiller, 2000; Sawyer, 2001] and will be designated as ‘‘themelt’’ for simplicity. K-feldspar component crystallizedfrom melt probably grew mostly onto the older grainswithin K-feldspar bands, which would also explain theirperthite-free margins [Zulauf et al., 2002]. The crystallizationof melt as unlike phases in residual aggregates commonlyresults in disappearance of the banded rock texture.Transitions from a banded orthogneiss into a homogeneousnonfoliated rock can be observed on a single outcrop in thestudied area. However, in type 2 and type 3 samples, themelt distributes preferentially in K-feldspar bands.[20] The SEM imagery allowed identifying melt topologyalong intergranular voids as well as in intragranular fractures(Figures 5 and 6a). Quantitative analysis of meltpockets and their orientations allows creating a threedimensional(3-D) geometrical reconstruction of melt distributionin K-feldspar aggregates and analysis. Furthermore,we can define the geometrical relationship of intragranularfractures with crystal orientation and rock fabric.5.1. Intergranular Melt Topology[21] In order to depict and evaluate in detail the grainscalemelt distribution, grain boundaries on backscatteredelectron (BSE) images were traced and digitized from bothXZ and YZ sections (Figure 7). In moderately deformedorthogneiss type 2, melt in K-feldspar aggregate in XZsection occupies triple point junctions and extends into thinwedge-shaped melt films (maximum 30 mm in width) alonggrain faces perpendicular to the stretching lineation. Inhighly deformed orthogneiss type 3, the intergranular meltpockets (or seams [Rosenberg and Riller, 2000]) of aspectratio 2–3 show two submaxima in R f /f graph inclined at±20° relative to the apparent Z axis of the rock fabricellipsoid (Figure 8). Melt topology in YZ section of type3 orthogneiss is characterized by presence of melt ‘‘droplets’’at triple point junctions of K-feldspar grains. Rarely,the melt forms seams (30 mm in width) that line grainboundaries perpendicular to the foliation. These wide pocketsare likely to result from oblique sections of seamsoriented at high angle to the principle stretching direction.The melt topology from two perpendicular sections allowscreating a simplified 3-D geometrical model of interstitialmelt distribution in K-feldspar aggregate. This model ischaracterized as an interconnected network marked bymelt walls parallel to YZ plane, connected by tubes parallelto X direction along triple point boundaries between threegrains (Figure 9).5.2. Intragranular Fractures Locally Filled by Melt[22] A closer observation of XZ section BSE images ofthe type 3 (mylonite) sample revealed that some K-feldspargrains are crosscut by intragranular fractures (Figure 10a)and some of these fractures are filled with wedge-shapedmelt films. Orientations of traces in XZ section of theseFigure 8. R f /f diagram of the intergranular melt pocketswithin the K-feldspar aggregate from the XZ section.7of15285
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“It strikes me that all our knowl
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Contentsviii4.7 Schulmann, Konopás
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Dedicated to my wife Markéta, daug
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Foreword 2First topic “Quantitati
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Foreword 4source and freely availab
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1. Quantitative analysis of deforma
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Chapter 2Mechanisms of lower crusta
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2. Mechanisms of lower crustal flow
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Chapter 3Quantitative analyses ofme
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3. Quantitative analyses of metamor
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Bibliography 42Culshaw, N., Beaumon
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Bibliography 44sources and trigger
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Bibliography 46Skrzypek, E., Štíp
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Journal of Structural Geology 23 20
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JOURNAL OF GEOPHYSICAL RESEARCH, VO
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DTD 5ARTICLE IN PRESSJournal of Str
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DTD 5ARTICLE IN PRESSL. Baratoux et
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Table 1Statistical values of the qu
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Table 2Summary of parameters derive
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J. metamorphic Geol., 2008, 26, 273
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EXHUMATION IN LARGE HOT OROGEN 275m
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Probabi l irequencyProbabi l ireque
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EXHUMATION IN LARGE HOT OROGEN 279y
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EXHUMATION IN LARGE HOT OROGEN 281N
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EXHUMATION IN LARGE HOT OROGEN 283w
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EXHUMATION IN LARGE HOT OROGEN 285a
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EXHUMATION IN LARGE HOT OROGEN 287w
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EXHUMATION IN LARGE HOT OROGEN 289T
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EXHUMATION IN LARGE HOT OROGEN 291O
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EXHUMATION IN LARGE HOT OROGEN 293r
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EXHUMATION IN LARGE HOT OROGEN 295B
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EXHUMATION IN LARGE HOT OROGEN 297R
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J. metamorphic Geol., 2011, 29, 79-
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HEAT SOURCES AND EXHUMATION MECHANI
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ORIGIN OF FELSIC MIGMATITES 49stron
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ORIGIN OF FELSIC MIGMATITES 51Cmı
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ORIGIN OF FELSIC MIGMATITES 53easte
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104 J. FRANĚK ET AL.in terms of th
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106 J. FRANĚK ET AL.Fig. 2. Struct
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108 J. FRANĚK ET AL.(a)perthite po
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112 J. FRANĚK ET AL.Table 1. Repre
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130 J. FRANĚK ET AL.Southern Bohem
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