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Albite

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Melanie Barboni – 1st expert on this subject based on the ideXlab platform

  • petrogenesis of magmatic Albite granites associated to cogenetic a type granites na rich residual melt extraction from a partially crystallized a type granite mush
    Lithos, 2013
    Co-Authors: Melanie Barboni, Francois Bussy

    Abstract:

    Abstract The uncommon association of cogenetic and nearly contemporaneous potassic K-feldspar A-type granites and sodic Albite granites is observed within the 347 Ma-old bimodal Saint-Jean-du-Doigt (SJDD) intrusion, Brittany, France. A-type granites outcrop as small bodies ( 2 ) of fine-grained, pinkish to yellowish rock or as meter-thick sills in-between mafic layers. They emplaced early within the thermally “cool” part of the SJDD pluton directly beneath the Precambrian host rock, forming the pluton roof. Albite granites are fine-grained hololeucocratic yellowish rocks emplaced slightly after the A-type granites in the thermally mature part of the pluton. They form meter-thick sills that mingle with adjacent mafic layers and represent ca. 1 vol.% of the outcropping part of the pluton. The two granite types are similar in many respects with comparable Sr–Nd–Hf isotope compositions ( 87 Sr/ 86 Sr 347  = 0.7071 for A-type granites vs. 0.7073 for Albite granites; eNd 347  = + 0.2 vs. + 0.3; eHf 347zircon  = + 2.47 vs. + 2.71, respectively) and SiO 2 contents (74.8 vs. 74.4 wt.%). On the other hand, they have contrasting concentrations in K 2 O (5.30 vs. 1.97 wt.%), Na 2 O (2.95 vs. 4.73 wt.%) and CaO (0.48 vs. 2.04, respectively) as well as in some trace elements like Sr (59 vs. 158 ppm in average), Rb (87 vs. 35 ppm), Cr (170 vs. 35 ppm) and Ga (30 vs. 20 ppm). The isotopic composition of the A-type and Albite granites is very distinct from that of the associated and volumetrically dominant mafic rocks (i.e. 87 Sr/ 86 Sr 347  = 0.7042; eNd 347  = + 5.07; eHf 347zircon  = + 8.11), excluding a direct derivation of the felsic rocks through fractional crystallization from the basaltic magma. On the other hand, small volumes of hybrid, enclave-bearing granodiorite within the SJDD lopolith suggest mixing processes within a reservoir located at deeper crustal levels. A-type granites may therefore form by magma mixing between the mafic magma and crustal melts. Alternatively, they might derive from the pure melting of an immature biotite-bearing quartz-feldspathic crustal protolith induced by early mafic injections at low crustal levels. Strong field evidences coupled to mineral chemistry and elemental geochemistry strongly support a magmatic origin for the Albite granite. Sr, Nd, Hf zircon isotope data, U–Pb zircon ages, as well as data on petrography, mineral chemistry and elemental geochemistry attest that A-type and Albite granites are closely related. Our preferred petrogenetic model is to consider the Albite granite magma as a compositionally extreme melt that was extracted from a partially crystallized A-type granite mush at a late stage of crystallization. Alternatively, Albite granites could form by melting of plagioclase-rich layers formed during A-type granite differentiation.

Bin Li – 2nd expert on this subject based on the ideXlab platform

  • molecular dynamics simulation of Albite twinning and pericline twinning in low Albite
    Modelling and Simulation in Materials Science and Engineering, 2013
    Co-Authors: Bin Li, Kevin M Knowles

    Abstract:

    Two twinning laws, the Albite law and the pericline law, are the predominant growth twinning modes in triclinic plagioclase feldspars such as low Albite, NaAlSi3O8, in which the aluminum and silicon atoms are in an ordered arrangement on the tetrahedral sites of the aluminosilicate framework. In the terminology used formally to describe deformation twinning in a triclinic lattice, these twin laws can be described as Type I and Type II twin laws, respectively, with the pericline twin law being conjugate to the Albite twin law. In this study, twin boundaries have been constructed for low Albite according to these two twinning laws and studied by molecular dynamics simulation. The results show that suitably constructed twin boundary models are quite stable for both Albite twinning and pericline twinning during molecular dynamics simulation. The calculated twin boundary energy of an Albite twin is significantly lower than that of a pericline twin, in accord with the experimental observation that Albite twinning is the more commonly observed mode seen in plagioclase feldspars. The results of the molecular dynamics simulations also agree with conclusions from the prior work of Starkey that glide twinning in low Albite is not favoured energetically.

Francois Bussy – 3rd expert on this subject based on the ideXlab platform

  • petrogenesis of magmatic Albite granites associated to cogenetic a type granites na rich residual melt extraction from a partially crystallized a type granite mush
    Lithos, 2013
    Co-Authors: Melanie Barboni, Francois Bussy

    Abstract:

    Abstract The uncommon association of cogenetic and nearly contemporaneous potassic K-feldspar A-type granites and sodic Albite granites is observed within the 347 Ma-old bimodal Saint-Jean-du-Doigt (SJDD) intrusion, Brittany, France. A-type granites outcrop as small bodies ( 2 ) of fine-grained, pinkish to yellowish rock or as meter-thick sills in-between mafic layers. They emplaced early within the thermally “cool” part of the SJDD pluton directly beneath the Precambrian host rock, forming the pluton roof. Albite granites are fine-grained hololeucocratic yellowish rocks emplaced slightly after the A-type granites in the thermally mature part of the pluton. They form meter-thick sills that mingle with adjacent mafic layers and represent ca. 1 vol.% of the outcropping part of the pluton. The two granite types are similar in many respects with comparable Sr–Nd–Hf isotope compositions ( 87 Sr/ 86 Sr 347  = 0.7071 for A-type granites vs. 0.7073 for Albite granites; eNd 347  = + 0.2 vs. + 0.3; eHf 347zircon  = + 2.47 vs. + 2.71, respectively) and SiO 2 contents (74.8 vs. 74.4 wt.%). On the other hand, they have contrasting concentrations in K 2 O (5.30 vs. 1.97 wt.%), Na 2 O (2.95 vs. 4.73 wt.%) and CaO (0.48 vs. 2.04, respectively) as well as in some trace elements like Sr (59 vs. 158 ppm in average), Rb (87 vs. 35 ppm), Cr (170 vs. 35 ppm) and Ga (30 vs. 20 ppm). The isotopic composition of the A-type and Albite granites is very distinct from that of the associated and volumetrically dominant mafic rocks (i.e. 87 Sr/ 86 Sr 347  = 0.7042; eNd 347  = + 5.07; eHf 347zircon  = + 8.11), excluding a direct derivation of the felsic rocks through fractional crystallization from the basaltic magma. On the other hand, small volumes of hybrid, enclave-bearing granodiorite within the SJDD lopolith suggest mixing processes within a reservoir located at deeper crustal levels. A-type granites may therefore form by magma mixing between the mafic magma and crustal melts. Alternatively, they might derive from the pure melting of an immature biotite-bearing quartz-feldspathic crustal protolith induced by early mafic injections at low crustal levels. Strong field evidences coupled to mineral chemistry and elemental geochemistry strongly support a magmatic origin for the Albite granite. Sr, Nd, Hf zircon isotope data, U–Pb zircon ages, as well as data on petrography, mineral chemistry and elemental geochemistry attest that A-type and Albite granites are closely related. Our preferred petrogenetic model is to consider the Albite granite magma as a compositionally extreme melt that was extracted from a partially crystallized A-type granite mush at a late stage of crystallization. Alternatively, Albite granites could form by melting of plagioclase-rich layers formed during A-type granite differentiation.