Two different pyroxene crystallisation trends in the trough bands of the Skaergaard Intrusion, East Greenland

Nwe, Yin Yin

doi:10.1007/bf00376181

Cited by 19 publications

(8 citation statements)

References 9 publications

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“…The LTi samples are two-pyroxene (augite and pigeonite) basalts, while pigeonite is very rare or absent in the HTi ones. In general, all the pyroxenes follow the Skaergaard crystallization trend (Nwe, 1975) with the exception of a few Gramado augites showing lower Ca contents. All the early (E = core of the crystals larger than 1 mm grain size) and late (L = microliths or crystal rims) pyroxenes in HTi rocks are augites (QI core: Wo 34-37 ; rim: Wo 29-37 ; BJ core: Wo 34-39 ; rim: Wo 33-38 ), while the LTi basalts show both augites (FC core: Wo 25-33 ; rim: Wo 29-36 ; BJ core: Wo 30-35 ; rim: Wo 29-41 ) and pigeonites (FC core: Wo 9 ; rim: Wo 8-11 ; BJ core: Wo 8 ; rim: Wo 7-13 ).…”

Section: Pyroxenesmentioning

confidence: 72%

Insights into the petrogenesis of low- and high-Ti basalts: Stratigraphy and geochemistry of four lava sequences from the central Paraná basin

Min

Callegaro

Marzoli

et al. 2018

Journal of Volcanology and Geothermal Research

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Lava flow sequences were sampled in the central part of the Paraná basin aiming to verify the time-related evolution of the Paraná basaltic magmatism. It is shown that low- and high-Ti basalts were erupted synchronously. In particular, Esmeralda and Pitanga flows are interlayered, with the former prevailing in the upper part of the sequence. Evidence for synchronously active magma plumbing systems is also supported by mineralogical data, showing signs of mixing between the two groups. \ud Geochemical data, including Sr-Nd-Pb isotopic compositions are furthermore used to define the mantle source of various low- (Esmeralda and Gramado) and high-Ti (Pitanga and Urubici) magma types. Involvement of a carbonatitic component is proposed for the genesis of the basalts (particularly for the Urubici ones) as suggested by trace element enrichments unrelated to significant isotopic variations. This carbonatitic signature of the mantle source may be conveyed by CO2-rich metasomatic fluids or melts percolating upwards within the sub-continental lithospheric mantle (SCLM) leading to rapid and selective enrichment of incompatible trace elements. Metasomatism was probably localized at the outskirts of the basin, were Urubici tholeiites and contemporaneous carbonatites were erupted. Geochemical data also suggest the occurrence of significant amounts of crustal contamination in the LTi magmas (mainly in the Gramado and in the late Esmeralda lavas) while crustal assimilation seems negligible in the HTi samples. Globally, a very complex picture arises for the genesis of the Paraná tholeiites, with near-synchronous and geographically coincident flows undergoing significantly different extents of interaction with the crust and tapping different mantle sources

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Section: Pyroxenesmentioning

confidence: 72%

Insights into the petrogenesis of low- and high-Ti basalts: Stratigraphy and geochemistry of four lava sequences from the central Paraná basin

Min

Callegaro

Marzoli

et al. 2018

Journal of Volcanology and Geothermal Research

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“…The compositions of pyroxene separates from the LS, UBS, and MBS of the Skaergaard intrusion determined in this study can be used to estimate liquidus temperatures using the method of Lindsley (). Because of the extensive subsolidus reaction in pyroxene (Nwe , ; Nobugai et al . ), these estimates probably represent minimum liquidus temperatures.…”

Section: Discussionmentioning

confidence: 99%

Major element variation of the Skaergaard pyroxene and its petrologic implications

Jang

Naslund

2013

Island Arc

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Pyroxenes from the Layered Series (LS), Upper Border Series (UBS), and Marginal Border Series (MBS) of the Skaergaard intrusion were analyzed using electron microprobe and mineral separation techniques to examine geochemical variations. In general, pyroxenes from all three series show similar trends in major elements vs % crystallization: SiO2, MgO, Al2O3, and TiO2 progressively decrease, FeO and MnO progressively increase, and CaO, Fe2O3, and P2O5 do not change systematically with differentiation. Pyroxenes in the LS and MBS follow a trend similar to that reported by Wager and Brown. The estimated crystallization temperatures closely follow the general trends of published temperature estimates. Major element variation in Skaergaard pyroxenes shows smooth variations with increasing differentiation, indicating that there was no volumetrically significant injection of new magma into the chamber after the initial emplacement. These results strongly support the idea that the Skaergaard intrusion represents in situ crystallization under a closed system magma chamber.

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“…It seems more likely that complex sequences of pyroxene precipitation in the case of hypabyssal terrestrial rocks are due to the internal differentiation of liquid cells trapped within a framework of earlier formed, growing plagioclase feldspars (cf. Nwe, 1975). The compositional complexity of the pyroxenes within each cell and from one cell to another is probably due both to differences in composition of the trapped liquid in each cell and to variable nucleation behaviour and ionic diffusion gradients across the cells as they cooled (Gibb, 1974;Dowry, 1980;Lofgren, 1980).…”

Section: Discussionmentioning

confidence: 99%

“…5a, 5b, 6) contains three areas of orthopyroxene, mainly zoned bronzite (c.Enso), 1 which grade into thin hypersthene margins. The calcic pyroxene component varies (Wager and Brown, 1968;Nwe, 1976). The pyroxene compositional field boundaries are taken from Poldervaart and Hess (1951).…”

Section: Md2 Dyke Ggu 120432mentioning

confidence: 99%

Complex sequential pyroxene growth in tholeiitic hypabyssal rocks from southern West Greenland

1986

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Chemically complex pyroxenes which occur in early Proterozoic tholeiitic dolerite dykes in southern West Greenland have been investigated using back-scattered electron (BSE) imagery, X-ray mapping and electron microprobe analysis. A wide variety of compositions occur within individual pyroxene grains in these rocks. They can be explained by simultaneous nucleation of different pyroxenes, the evolution of domains around these nucleii as a response to differential chemical gradients and the sequential precipitation of different pyroxenes at progressively lower temperatures. As an example, the individual grains in one dyke sample contain domains of bronzite, hypersthene, magnesium pigeonite, augite, and subcalcic augite. Olivine in this sample varies in composition from Fo70to Fo33, although individual grains are only weakly zoned. The wide variation in pyroxene and olivine compositions suggests ranges of crystallization temperatures fromc.1250° to as low as 825°C. Such compositionally variable pyroxenes are possibly characteristic of hypabyssal tholeiitic rocks.

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Two different pyroxene crystallisation trends in the trough bands of the Skaergaard Intrusion, East Greenland

Cited by 19 publications

References 9 publications

Insights into the petrogenesis of low- and high-Ti basalts: Stratigraphy and geochemistry of four lava sequences from the central Paraná basin

Insights into the petrogenesis of low- and high-Ti basalts: Stratigraphy and geochemistry of four lava sequences from the central Paraná basin

Major element variation of the Skaergaard pyroxene and its petrologic implications

Complex sequential pyroxene growth in tholeiitic hypabyssal rocks from southern West Greenland

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