An analcime mugearite-megacryst association from north-eastern New South Wales: implications for high-pressure amphibole-dominated fractionation of alkaline magmas

Wilkinson, J. F. G.; Hensel, H. D.

doi:10.1007/bf00306482

Cited by 23 publications

(6 citation statements)

References 61 publications

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“…Mugearites are relatively rare on Earth, and we do not have a good analogue for its low‐grade metamorphic phases. However, analcime‐rich mugearites were reported (e.g., Wilkinson & Hensel, ) supporting the high modal amounts of analcime in our thermodynamic model.…”

Section: Discussionsupporting

confidence: 86%

“…Mugearites are relatively rare on Earth, and we do not have a good analogue for its low-grade metamorphic phases. However, analcime-rich mugearites were reported (e.g., Wilkinson & Hensel, 1991) supporting the high modal amounts of analcime in our thermodynamic model. Ehlmann et al (2009) noted that locations where they detected hydrated silica and/or analcime correspond to areas that were characterized as quartzofeldspathic using thermal infrared spectroscopy (Bandfield, 2006).…”

Section: Zeolitessupporting

confidence: 84%

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Phase Equilibria Modeling of Low‐Grade Metamorphic Martian Rocks

et al. 2019

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Hydrous phases have been identified to be a significant component of Martian mineralogy. Particularly, prehnite, zeolites, and serpentine are evidence for low‐grade metamorphic reactions at elevated temperatures in mafic and ultramafic protoliths. Their presence suggests that at least part of the Martian crust is sufficiently hydrated for low‐grade metamorphic reactions to occur. A detailed analysis of changes in mineralogy with variations in fluid content and composition along possible Martian geotherms can contribute to determine the conditions required for subsurface hydrous alteration, fluid availability, and rock properties in the Martian crust. In this study, we use phase equilibria models to explore low‐grade metamorphic reactions covering a pressure‐temperature range of 0–0.5 GPa and 150–450 °C for several Martian protolith compositions and varying fluid content. Our models replicate the detected low‐grade metamorphic/hydrothermal mineral phases like prehnite, chlorite, analcime, unspecified zeolites, and serpentine. Our results also suggest that actinolite should be a part of lower‐grade metamorphic assemblages, but actinolite may not be detected in reflectance spectra for several reasons. By gradually increasing the water content in the modeled whole‐rock composition, we can estimate the amount of water required to precipitate low‐grade metamorphic phases. Mineralogical constraints do not necessarily require an elevated geothermal gradient for the formation of prehnite. However, restricted crater excavation depths even for large impact craters are not likely sampling prehnite along colder gradients, suggesting either a geotherm of ~20 °C/km in the Noachian or an additional heat source such as hydrothermal or magmatic activity.

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Section: Discussionsupporting

confidence: 86%

Section: Zeolitessupporting

confidence: 84%

Phase Equilibria Modeling of Low‐Grade Metamorphic Martian Rocks

et al. 2019

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“…The former group incudes volcanics from New South Wales (Southern Highlands and Barrington provinces; Menzies and Wass 1983;O'Reilly and Zhang 1995;Central Province;Wilkinson and Hensel 1991) and the latter includes St Helena lavas (White and Hofmann 1982). Except for its higher TiO 2 , the Mindora host basalt illustrates the compositional prerequisites of one parental melt in terms of M-value w $ 74, level of CIPW normative undersaturation, LREE concentrations and MORB-like Nd and Sr isotopic characteristics, with the proviso, of course, that the extensive megacrystal unmixing and the metamorphic textures of the pyroxenites preclude a cognate relationship between them and the host basalt.…”

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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“…However, a coarse aggregate of anorthoclase and corundum in basanite from Mt Leura near Rubyvale, central Queensland (Robertson & Sutherland 1992), supports the presence of such highly evolved vein assemblages. So too does evidence for isotopic homogeneity within megacryst suites of east Australian basaltic magmas (Wilkinson & Hensel 1991).…”

Section: Discussionmentioning

confidence: 98%

“…These are typically angular cleavage fragments that are not resorbed. They plot close to the compositional boundary with albite, a feature characteristic of some east Australian anorthoclase megacrysts in alkali basalts (Wilkinson & Hensel 1991). Unlike the pegmatoidal sanidine this anorthoclase is not barian.…”

Section: Xenocrystsmentioning

confidence: 98%