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Opis bibliograficzny

Autorzy (3)

• AGHDumańska-Słowik Magdalena
• AGHPowolny Tomasz
• Khac Giang Nguyen

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Dane bibliometryczne

ID BaDAP	148406
Data dodania do BaDAP	2023-09-20
Tekst źródłowy	URL
DOI	10.1093/petrology/egad042
Rok publikacji	2023
Typ publikacji	artykuł w czasopiśmie
Otwarty dostęp
Creative Commons
Czasopismo/seria	Journal of Petrology

Abstract

The alkaline Cho Don complex in NE Vietnam comprises several mafic-felsic suites related to the widespread magmatism developed during the early Permian-late Triassic. The contribution explores the petrogenesis of nepheline syenite from the Bang Phuc massif and its petrogenetic relationship with cogenetic scapolite-rich gabbro. The nepheline syenite formed through fractional crystallization of pristine mantle-derived basaltic melt modified by subduction-related components (chiefly sediment-derived melts), as shown by, e.g. low Ba/Th and high Th/Nb ratios of the rocks. The transition from gabbro to syenite follows a within-plate enrichment trend (e.g. increasing Ta/Yb, Nb/Yb, and Th/Yb ratios) that might reflect switch from post-orogenic to intra-plate regimes, accompanied by subduction-collision-extension events related to the Indosinian Orogeny. Furthermore, magma evolution involved the progressive contribution of asthenospheric-derived melts that resulted in the appearance of OIB-like signatures (e.g. high Nb/La ratios) in the nepheline syenite. Fractional crystallization of fluorapatite and mafic phases, as well as assimilation of carbonate wall rocks ultimately led to the decrease of LREE contents and/or modification of Zr/Hf ratios. Magmatic phases of the nepheline syenite include nepheline, sodalite, oligoclase, orthoclase, and annite, as well as accessory fluorapatite, fluorite, and minor amounts of zircon and metamict allanite-Ce. The nepheline equilibrated at temperatures ranging between 850°C and 700°C, which reflects protracted residence at a higher temperature. Later, it has been locally altered to cancrinite, dawsonite, and natrolite via CO2- and alkali-rich fluid influx. The fluid-rock interactions were also manifested by the presence of chessboard-twinned albite and coarsening of braid-perthite into patch-perthite, as well as recrystallization of primary orthoclase into microcline. The orthoclase→microcline conversion, albeit fairly indiscrete under a polarizing microscope and confirmed by Raman micro-spectroscopy, is followed by the change of cathodoluminescence colours, i.e. from light-blue (activated by Ti4+ and/or Al-O - Al centres) in orthoclase towards brownish and/or greenish (activated by Mn2+ and structural defects) in microcline.

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