Hybridization of shoshonitic lamprophyre and calc-alkaline granite magma in the early Proterozoic Mt Bundey igneous suite, Northern Territory
Titel:
Hybridization of shoshonitic lamprophyre and calc-alkaline granite magma in the early Proterozoic Mt Bundey igneous suite, Northern Territory
Auteur:
Sheppard, S.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 42 (1995) nr. 2 pagina's 173-185
Jaar:
1995-04
Inhoud:
The Mt Bundey igneous suite (1831 ± 6Ma) intrudes deformed and low-grade metasedimentary rocks of the Early Proterozoic Pine Creek Inlier. The suite consists of a composite pluton of calc-alkaline granite (Mt Bundey Granite) and shoshonitic syenite (Mt Goyder Syenite), and a swarm of spatially, temporally and probably genetically associated, K-rich shoshonitic lamprophyre dykes. Grey, ovoid to tabular lamprophyric enclaves, up to about 1 m in length, are widespread within the syenite. The enclaves have the same mineralogy as, and similar mineral and whole-rock compositions to, the lamprophyre dykes. These features, in conjunction with textural studies, imply that the enclaves represent lamprophyre magma injected into a partly crystalline syenite magma. Lamprophyre dykes, lamprophyric enclaves and syenite contain numerous, widely dispersed uralitized clinopyroxenite enclaves 0.5-5.0 mm in diameter, suggesting that magma mingling was preceded by hybridization of lamprophyric and granitic magmas. The syenite, granite and lamprophyre dykes have near-identical trace element abundance patterns on MORB- and chondrite-normalized plots, and define linear arrays on homologous element plots. Least-squares mixing calculations indicate that the syenite could have been generated by hybridization of lamprophyric and granitic magmas, with some superimposed accumulation of K-feldspar. Hybridization probably occurred at or near the source region of the granite magma precursor to the Mt Goyder Syenite, with further injection of lamprophyre magma at depth of emplacement.
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