Tholeiitic andesite of high-pressure origin from the tweed shield volcano, northeastern New South Wales

Duggan, M. B.; Wilkinson, J. F. G.

doi:10.1007/bf00376467

Cited by 14 publications

(8 citation statements)

References 28 publications

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“…Clearcolored glass bands averaged 77.57 ± 1.14% for SiO 2 , 0.98 ± 0.43% for FeO, and 0.56 ± 0.20% for CaO (Table 1). The SEM glass results are consistent with an XRF analysis of a bulk glass separate reported by Duggan (1974); all elemental oxides measured by SEM are, within our estimated 2σ uncertainties, indistinguishable from the XRF results. The same observation holds for the mean (anhydrous) wholerock values reported in Duggan (1974), which is consistent with the aphyric nature of the Minyon Falls Rhyolite.…”

Section: Glass and Mineral Chemistrysupporting

confidence: 89%

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Pre-eruptive temperatures and eruption dynamics of rhyolite lava, Nimbin rhyolite, eastern Australia

Campo

2020

33rd Keck Proceedings Volume

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Section: Glass and Mineral Chemistrysupporting

confidence: 89%

“…These results are in excellent agreement with available EMPA results. Duggan (1974) reported phenocryst cores and rims with average anorthite contents of 23 ± 3 mol% and and 22 ± 1 mol%, respectively, and groundmass plagioclase with an average anorthite content of 48% ± 2 mol%.…”

Section: Glass and Mineral Chemistrymentioning

confidence: 99%

Pre-eruptive temperatures and eruption dynamics of rhyolite lava, Nimbin rhyolite, eastern Australia

Campo

2020

33rd Keck Proceedings Volume

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“…We are not aware of documented occurrences of spinel megacrysts in tholeiites, and high-pressure subcalcic clinopyroxenes and orthopyroxenes in tholeiitic hosts are extremely rare (Duggan and Wilkinson 1973;Nicholls and Lorenz 1973). Note, however, that some Cr-diopside pyroxenites have been interpreted as crystal segregations from tholeiitic magmas rather than from alkaline or transitional types (e.g.…”

Section: (I) Pyroxene and Spinel Megacrysts In Ma®c Volcanicsmentioning

confidence: 99%

Subcalcic clinopyroxenites and associated ultramafic xenoliths in alkali basalt near Glen Innes, northeastern New South Wales, Australia

Wilkinson

Stolz

1997

Contributions to Mineralogy and Petrology

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An alkali basalt near Glen Innes, northeastern New South Wales, contains a suite of Cr-diopside group ultrama®c xenoliths which includes some spinel peridotites but which is dominated by a diverse spinel pyroxenite assemblage. Pyroxenite xenoliths range from subcalcic clinopyroxenites (composed largely of unmixed prismatic subcalcic clinopyroxene megacrystals and lesser orthopyroxene megacrystals) to equant mosaic textured websterites (orthopyroxene and Ca-rich clinopyroxene AEspinel. Rare orthopyroxenite xenoliths also occur. The pyroxenite xenoliths are characterised by high 100MgaMg Fe 2 ratios (M$ 90 and low concentrations of Ti, K, P, La, Ce and Zr. The websterites are mineralogically and chemically similar to many spinel pyroxenites occurring as layers or dykes in peridotite massifs such as those at Ronda in southern Spain and at ArieÁ ge (French PyreÂ neÂ es). a estimates indicate crystallization temperatures of 1250±1350°C for subcalcic clinopyroxene-orthopyroxene megacrystal pairs and 900± 1000°C for the equilibrated mosaic textured websterites and associated peridotites at pressures of 9±13 kbar. Subcalcic clinopyroxene megacrystals, websterites and orthopyroxenites have LREE-depleted chondrite-normalised REE abundances with La/Yb CN`1 and their convex-upwards REE patterns are typical of subcalcic clinopyroxene-dominated cumulates. The pyroxenites are not residua from partially melted pyroxenite layers or dykes in mantle peridotites nor are they completely crystallized protobasaltic or protopicritic magmas. They are interpreted as high-pressure crystal segregations from basaltic magmas (probably mildly alkaline or transitional)¯owing within narrow mantle conduits (the¯ow crystallization model of Irving, 1980). The parental magma(s) was Ti-poor (0.6±0.7% TiO 2 ) and relatively Mg-rich (M $ 74À70. Pyroxenite genesis was a two-stage process involving crystallization of tschermakitic subcalcic clinopyroxenes and orthopyroxenes AEspinel as liquidus or near-liquidus phases at 1250±1350°C and 9± 13 kbar to yield``primary'' subcalcic clinopyroxenites which then re-equilibrated at 900±1000°C and similar pressures to produce the mosaic textured``secondary'' websterites. The pyroxenites show a wide range of 143 Nda 144 Nd and 87 Sra 86 Sr values (0.513298±0.512473 and 0.702689±0.704659, respectively). Their isotopic ratios appear to have been variably modi®ed by exchange with adjacent mantle peridotites or migrating basaltic melts.Editorial responsibility: R.A. Binns Petrography and mineralogy of pyroxenite xenolithsPetrography Four basic mineralogical and textural types of pyroxenite can be distinguished.

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“…The petrology and geochemistry of the volcanic succession comprising the northern flank of the volcano was examined by Ewart et al (1977) and Ewart (1982). The stratigraphy of the southern flank of the volcano is presented in Duggan and Mason (1978) and a detailed evaluation of the petrogenesis was untaken by Duggan (1974). The generalized volcanic succession comprises an early mafic succession followed by rhyolitic lavas and tuffs that are in turn overlain by a younger mafic sequence.…”

Section: Geological Backgroundmentioning

confidence: 99%

Using 3D petrography of microlites and bubbles in obsidian to assess factors governing eruptive style for rhyolitic magmas

Knesel

2020

33rd Keck Proceedings Volume

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Tholeiitic andesite of high-pressure origin from the tweed shield volcano, northeastern New South Wales

Cited by 14 publications

References 28 publications

Pre-eruptive temperatures and eruption dynamics of rhyolite lava, Nimbin rhyolite, eastern Australia

Pre-eruptive temperatures and eruption dynamics of rhyolite lava, Nimbin rhyolite, eastern Australia

Subcalcic clinopyroxenites and associated ultramafic xenoliths in alkali basalt near Glen Innes, northeastern New South Wales, Australia

Using 3D petrography of microlites and bubbles in obsidian to assess factors governing eruptive style for rhyolitic magmas

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