Fertility of metapelites and metagraywackes during leucogranite generation: an example from the Black Hills, U.S.A.

Nábělek, Peter I.; Bartlett, Cindy D.

doi:10.1130/0-8137-2350-7.1

Cited by 8 publications

(10 citation statements)

References 38 publications

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“…A greywacke rather than pelitic source is also consistent with the mineralogy and geochemistry of the exposed granites; a pelitic source would be expected to produce leucogranite with higher modal abundances of muscovite and limited occurrences of ferromagnesian minerals along with lower Sr and Ba but higher Rb (Pickering and Johnston, 1998). The source characteristics required for the most primitive G3 melts are consistent with a metagreywacke that had previously undergone melt extraction following muscovite-dominated partial melting (Harris et al, 1995;Nabelek and Bartlett, 1999).…”

Section: Two-mica Muscovite Biotite and Tourmaline Granites (G1-g4)mentioning

confidence: 56%

“…Harris et al, 1995), source variation (e.g. Nabelek and Bartlett, 1999) and magma mixing (e.g. Patiño-Douce, 1999).…”

Section: Petrogenetic Modellingmentioning

confidence: 99%

“…Partial melting modelling was performed with Ba, Sr, Rb and REE for the G1-G2, G3-G4 and G5 granites using the modal mineral abundances for metagreywackes and metapelites of Nabelek and Bartlett (1999). Metagreywackes are distinguished from metapelites by their lower abundance of micas and higher proportion of plagioclase relative…”

Section: Source Compositional Characteristicsmentioning

confidence: 99%

“…Nabelek and Bartlett, 1999), varying degrees of partial melting (e.g. Harris et al, 1995), incorporation of restite material or a peritectic phase (e.g.…”

Section: Introductionmentioning

confidence: 99%

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The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

Simons

Shail

Andersen

2016

Lithos

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The Early Permian Cornubian Batholith was generated during an extensional regime following Variscan convergence within the Rhenohercynian Zone of SW England. Its component granites can be classified, using mineralogical, textural and geochemical criteria, into five main types, all of which are peraluminous (A/CNK >1.1): G1 (two-mica), G2 (muscovite), G3 (biotite), G4 (tourmaline) and G5 (topaz). G1 granites formed through up to 20% muscovite and minor biotite dehydration melting of a metagreywacke source at moderate temperatures and pressures (731-806°C, >5 kbar). Younger G3 granites formed through higher temperature, lower pressure (768-847°C, <4 kbar) biotite-dominated melting of a similar source. Partial melting was strongly influenced by the progressive lower-mid crustal emplacement of mafic igneous rocks during post-Variscan extension and a minor (<5-10%) mantle-derived component in the granites is possible. Two distinct fractionation series, G1-G2 and G3-G4, are defined using whole rock geochemical and mineral chemical data.Variations in the major elements, Ba, Sr and Rb indicate that G1 and G3 granites underwent 15-30% fractionation of an assemblage dominated by plagioclase, alkali feldspar and biotite to form, more evolved G2 and G4 granites respectively. Decreasing whole rock abundances of Zr, Th and REE support fractionation of zircon, monazite, apatite and allanite. Subsolidus alteration in G2 and G4 granites is indicated by non-primary muscovite and tourmaline and modification of major and trace element trends for G3-G4 granites, particularly for P 2 O 5 and Rb. Topaz (G5) granites show low Zr, REE and extreme enrichment in Rb (up to 1530 ppm) and Nb (79 ppm) that cannot be related in a straightforward manner to continued differentiation of the G1-G2 or G3-G4 series. Instead, they are considered to represent partial melting, mediated by granulite facies fluids, of a biotite-rich restite following extraction of

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Section: Two-mica Muscovite Biotite and Tourmaline Granites (G1-g4)mentioning

confidence: 56%

“…Harris et al, 1995), source variation (e.g. Nabelek and Bartlett, 1999) and magma mixing (e.g. Patiño-Douce, 1999).…”

Section: Petrogenetic Modellingmentioning

confidence: 99%

Section: Source Compositional Characteristicsmentioning

confidence: 99%

“…Nabelek and Bartlett, 1999), varying degrees of partial melting (e.g. Harris et al, 1995), incorporation of restite material or a peritectic phase (e.g.…”

Section: Introductionmentioning

confidence: 99%

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The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

Simons

Shail

Andersen

2016

Lithos

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“…%. These granites are enriched in Rb, Zr, Ba and Pb and depleted in Ni, Cr, V, Nd, Sr, Y, Nb, and have REE contents comparable to S-type granites (Brown 1994;Harris et al 1995;Bea 1996b;Patiño Douce 1999;Nabelek & Bartlett 2000;Healy et al 2004;Stevens et al 2007;Villaros et al 2009;García-Arias et al 2012;Moyen et al 2017). Low concentrations of Ni, Cr, V, Sr, Y, Nb, and REE indicate that they probably remained in the residuum (metapelitic xenoliths) during partial melting and segregation.…”

Section: Rock Geochemistrymentioning

confidence: 99%

Geochemical characteristics and conditions of formation of the Chah-Bazargan peraluminous granitic patches, ShahrBabak, Iran

Fazlnia¹

2017

Geologica Carpathica

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Xenoliths of garnet-biotite-kyanite schist from the Qori metamorphic complex (southern part of the Sanandaj-Sirjan zone, northeast Neyriz, Zagros orogen in Iran) in the 173.0±1.6 Ma Chah-Bazargan leuco-quartz diorite intrusion were studied. This intrusion caused these schist xenoliths to be metamorphosed to the pyroxene hornfels facies (approximately 4.5±1.0 kbar and 760±35 °C), converting them to diatexite migmatite as a result of partial melting of the xenoliths. These melts are granites in composition. Melt volumes of 20 to 30 vol. % were calculated for small patches of the peraluminous granites. It is possible that anatectic melting affected only the leucosome, such that melting was more than 20 to 30 vol. %. It is possible that a large amount of melt was not extracted due to balanced in situ crystallization, the adhesion force between melt and crystal (restite), and high viscosity of the leucosome. The Chah-Bazargan peraluminous granites are depleted in trace elements such as REEs, HFSE (Ti, Zr, Ta, Nb, Th, U, Hf, Y), Ba, Pb, and Sr. These elements are largely insensitive to source enrichment, but sensitive to the amounts of main and accessory minerals. These elements were hosted by minerals such as garnet, biotite, muscovite, K-feldspar, plagioclase, ilmenite, apatite, monazite, and zircon in the source (diatexitic migmatitic xenoliths).

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Petrologic and thermal constraints on the origin of leucogranites in collisional orogens

Nábělek¹,

Liu

2004

Earth and Environmental Science Transactions of the Royal Socie

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Leucogranites are typical products of collisional orogenies. They are found in orogenic terranes of different ages, including the Proterozoic Trans-Hudson orogen, as exemplified in the Black Hills, South Dakota, and the Appalachian orogen in Maine, both in the USA, and the ongoing Himalayan orogen. Characteristics of these collisional leucogranites show that they were derived from predominantly pelitic sources at the veining stages of deformation and metamorphism in upper plates of thickened crusts. Once generated, the leucogranite magmas ascended as dykes and were emplaced within shallower parts of their source sequences. In these orogenic belts, there was a strong connection between deformation, metamorphism and granite generation. However, the heat sources needed for partial melting of the source rocks remain controversial. Lack of evidence for significant intrusion of mafic magmas necessary to cause melting of upper plate source rocks suggests that leucogranite generation in collisional orogens is mainly a crustal process.The present authors evaluate five types of thermal models which have previously been proposed for generating leucogranites in collisional orogens. The first, a thickened crust with exponentially decaying distribution of heat-producing radioactive isotopes with depth, has been shown to be insufficient for heating the upper crust to melting conditions. Four other models capable of raising the crustal temperatures sufficiently to initiate partial melting of metapelites in thickened crust include: (1) thick sequences of sedimentary rocks with high amounts of internal radioactive heat production; (2) decompression melting; (3) thinning of mantle lithosphere; and (4) shear-heating. The authors show that, for reasonable boundary conditions, shear-heating along crustal-scale shear zones is the most viable process to induce melting in upper plates of collisional orogens where pelitic source lithologies are usually located. The shear-heating model directly links partial melting to the deformation and metamorphism that typically precede leucogranite generation.

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Fertility of metapelites and metagraywackes during leucogranite generation: an example from the Black Hills, U.S.A.

Cited by 8 publications

References 38 publications

The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England

Geochemical characteristics and conditions of formation of the Chah-Bazargan peraluminous granitic patches, ShahrBabak, Iran

Petrologic and thermal constraints on the origin of leucogranites in collisional orogens

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