Evolution of perthite composition and microstructure during progressive metamorphism of hypersolvus granite, Rhode Island, USA

Day, Howard W.; Brown, Vernon

doi:10.1007/bf00371344

Cited by 19 publications

(6 citation statements)

References 11 publications

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“…Alkali feldspar phenocrysts in young rhyolitic ash-flow tuffs are typically cryptoperthitic sanidine (e.g., Boyd, 1961;Scott et al, 1971;Hildreth, 1979;Mahood, 1981). Perthite generally becomes coarser grained with age, longer periods of cooling, or increasing grade of metamorphism (Boyd, 1961;Day and Brown, 1980;Smith, 1988). Day and Brown (1980) describe the textural change in a hypersolvus granite from vein perthite to coarser patch perthite with increasing grade of younger regional metamorphism.…”

Section: Petrographymentioning

confidence: 99%

“…Perthite generally becomes coarser grained with age, longer periods of cooling, or increasing grade of metamorphism (Boyd, 1961;Day and Brown, 1980;Smith, 1988). Day and Brown (1980) describe the textural change in a hypersolvus granite from vein perthite to coarser patch perthite with increasing grade of younger regional metamorphism. Boyd (1961) documented that the cryptoperthite from the Yellowstone Tuff became progressively coarser grained, but remained cryptoperthite, stratigraphically upward in the section and used this as evidence that tuff represented one cooling unit.…”

Section: Petrographymentioning

confidence: 99%

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Compositional zoning of a Neoproterozoic ash-flow sheet of the Mount Rogers Formation, southwestern Virginia Blue Ridge, and the aborted rifting of Laurentia

Novak¹,

Rankin²

2004

Memoir 197: Proterozoic Tectonic Evolution of the Grenville Orogen in North America

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The 760 Ma Wilburn Rhyolite Member of the Mount Rogers Formation, in southwestern Virginia, is a mineralogically and compositionally zoned welded ash-flow sheet at least 660 m thick. Compositional zoning, preserved despite greenshist-facies metamorphism, developed in the pre-eruptive magma chamber and was inverted during eruption of the ash-flow sheet. Microphenocrysts of aegerine and riebeckite occur at the base of the sheet, riebeckite alone or with biotite at higher levels, and Fe-rich biotite at the top. Alkali feldspar phenocrysts are more potassic, and riebeckite and biotite exhibit decreasing Mg/Fe toward the top of the ash-flow sheet; F content of biotite increases toward the base. The ash-flow tuff is a high-silica rhyolite (SiO 2 = 76.6 wt%); the basal one-sixth of the sheet is interpreted as originally peralkaline, whereas the remainder is metaluminous. Major-and trace-element zoning within the sheet is similar to other well-documented ash-flow sheets: SiO 2 , Na 2 O, and F increase toward the base of the sheet, whereas Al 2 O 3 , MgO, CaO, K 2 O, and TiO 2 decrease. Concentrations of Be, Rb, Zr, Nb, Sn, Hf, Ta, Th, U, Tb, and Yb increase toward the base; elements more abundant toward the top include Sc, Sr, Ba, La, Ce, Nd, and Eu. These gradients developed in a high-level silicic magma chamber in which peralkaline high-silica rhyolitic magma overlay metaluminous high-silica rhyolite. The 765-740 Ma Crossnore Complex, which includes the Mount Rogers Formation, in the Grenvillian French Broad massif includes A-type granitoids and is interpreted to reflect aborted rifting of Laurentian continental crust. The locus of aborted rifting migrated northeastward to the Shenandoah massif, where A-type magmatism occurred at 735-680 Ma. Continental breakup and opening of the Iapetus Ocean followed Late Neoproterozoic (ca. 572-554 Ma) rifting. Formation of a voluminous highsilica, partly peralkaline magma chamber indicates that the initial pulse of rifting took place in relatively thick continental crust, perhaps explaining why this pulse did not culminate in continental breakup until ∼ ∼200 m.y. later.

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Section: Petrographymentioning

confidence: 99%

Section: Petrographymentioning

confidence: 99%

Compositional zoning of a Neoproterozoic ash-flow sheet of the Mount Rogers Formation, southwestern Virginia Blue Ridge, and the aborted rifting of Laurentia

Novak¹,

Rankin²

2004

Memoir 197: Proterozoic Tectonic Evolution of the Grenville Orogen in North America

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“…The 'metamorphic fluids' are characterized at lower greenschist facies for protomylonites (>350˚C and 0.6 GPa), and transitional between higher greenschist to lower amphibolite facies (500-550˚C and 1.0 GPa) for medium-grade mylonite rocks, since the pertites would disappear if metamorphic conditions were higher (Day and Brown 1980).…”

Section: A C C E P T E D Accepted Manuscript Feldspars At Intermediatmentioning

confidence: 99%

Rio Maria granodiorite and associated rocks of Ourilândia do Norte – Carajás province: Petrography, geochemistry and implications for sanukitoid petrogenesis

Santos

Oliveira

2016

Journal of South American Earth Sciences

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“…The microstructures and compositional patterns of perthites contain information on cooling rates and have been used for reconstructing the thermal histories of magmatic (Yund and Chapple 1980;Brown et al 1983;Brown and Parsons 1984;Menna et al 2008;Parsons and Gerald 2011) and metamorphic rocks (Day and Brown 1980;Evangelakakis et al 1993;Abart et al 2009b). The dynamics of exsolution by spinodal decomposition can be described by the Cahn-Hilliard theory (Cahn and Hilliard 1958), which was used for modelling spinodal decomposition of alkali feldspar and the successive coarsening (Abart et al 2009b;Abart 2009, 2012).…”

Section: Introductionmentioning

confidence: 99%

Spinodal decomposition in alkali feldspar studied by atom probe tomography

et al. 2020

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We used atom probe tomography to complement electron microscopy for the investigation of spinodal decomposition in alkali feldspar. To this end, gem-quality alkali feldspar of intermediate composition with a mole fraction of a K = 0.43 of the K end-member was prepared from Madagascar orthoclase by ion-exchange with (NaK)Cl molten salt. During subsequent annealing at 550 • C and close to ambient pressure the ion-exchanged orthoclase unmixed producing a coherent lamellar intergrowth of Na-rich and K-rich lamellae. The chemical separation was completed, and equilibrium Na-K partitioning between the different lamellae was attained within four days, which was followed by microstructural coarsening. After annealing for 4 days, the wavelength of the lamellar microstructure was ≈ 17 nm and it increased to ≈ 30 nm after annealing for 16 days. The observed equilibrium compositions of the Na-rich and K-rich lamellae are in reasonable agreement with an earlier experimental determination of the coherent solvus. The excess energy associated with compositional gradients at the lamellar interfaces was quantified from the initial wavelength of the lamellar microstructure and the lamellar compositions as obtained from atom probe tomography using the Cahn-Hilliard theory. The capability of atom probe tomography to deliver quantitative chemical compositions at nm resolution opens new perspectives for studying the early stages of exsolution. In particular, it helps to shed light on the phase relations in nm scaled coherent intergrowth.

show abstract

Evolution of perthite composition and microstructure during progressive metamorphism of hypersolvus granite, Rhode Island, USA

Cited by 19 publications

References 11 publications

Compositional zoning of a Neoproterozoic ash-flow sheet of the Mount Rogers Formation, southwestern Virginia Blue Ridge, and the aborted rifting of Laurentia

Compositional zoning of a Neoproterozoic ash-flow sheet of the Mount Rogers Formation, southwestern Virginia Blue Ridge, and the aborted rifting of Laurentia

Rio Maria granodiorite and associated rocks of Ourilândia do Norte – Carajás province: Petrography, geochemistry and implications for sanukitoid petrogenesis

Spinodal decomposition in alkali feldspar studied by atom probe tomography

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