Parental magma of the Skaergaard intrusion: constraints from melt inclusions in primitive troctolite blocks and FG-1 dykes

AbstractThe discrepancy between Na-rich compositions of modern carbonatitic lavas (Oldoinyo Lengai volcano) and alkali-poor ancient carbonatites remains a topical problem in petrology. Although both are supposedly considered to originate via fractional crystallization of a “common parent” alkali-bearing Ca-carbonatitic magma, there is a significant compositional gap between the Oldoinyo Lengai carbonatites and all other natural compositions reported (including melt inclusions in carbonatitic minerals). In an attempt to resolve this, we investigate the petrogenesis of Ca-carbonatites from two occurrences (Guli, Northern Siberia and Tagna, Southern Siberia), focusing on mineral textures and alkali-rich multiphase primary inclusions hosted within apatite and magnetite. Apatite-hosted inclusions are interpreted as trapped melts at an early magmatic stage, whereas inclusions in magnetite represent proxies for the intercumulus environment. Melts obtained by heating and quenching the inclusions, show a progressive increase in alkali concentrations transitioning from moderately alkaline Ca-carbonatites through to the “calcite CaCO3 + melt = nyerereite (Na,K)2Ca2(CO3)3” peritectic, and finally towards Oldoinyo Lengai lava compositions. These results give novel empirical evidence supporting the view that Na-carbonatitic melts, similar to those of the Oldoinyo Lengai, may form via fractionation of a moderately alkaline Ca-carbonatitic melt, and therefore provide the “missing piece” in the puzzle of the Na-carbonatite’s origin. In addition, we conclude that the compositions of the Guli and Tagna carbonatites had alkali-rich primary magmatic compositions, but were subsequently altered by replacement of alkaline assemblages by calcite and dolomite.

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The Kraemer Island macrodyke, East Greenland: solidification of a flood basalt conduit

Geological Magazine ◽

10.1017/s0016756801006070 ◽

2002 ◽

Vol 139 (2) ◽

pp. 171-190 ◽

Cited By ~ 8

Author(s):

PETER MOMME ◽

J. RICHARD WILSON

Keyword(s):

Partition Coefficients ◽

Parental Magma ◽

Flood Basalt ◽

Wall Rock ◽

Dyke Swarm ◽

Flood Basalts ◽

Skaergaard Intrusion ◽

Continuous Feeding ◽

Late Stages ◽

Light Rare Earth Elements

The Kraemer Island macrodyke that is exclusively exposed on Kraemer Island about 7 km west of the Skaergaard Intrusion belongs to a regional dyke swarm termed the ‘Skaergaard-like dykes’ (or FG-1 dykes). Weakly modally layered olivine gabbros dominate the exposed parts of the intrusion that has a width of 650 m to 1000 m. Plagioclase (core An68±2) and Ca-rich pyroxene (core Mg no. 79±1) grains are normally zoned, whereas olivine grains (Fo50–65) are homogeneous. Calculated mineral–magma equilibria, based on experimentally determined Mg–Fe magma–olivine and magma–clinopyroxene partition coefficients, suggest that the observed olivine and clinopyroxene compositions in the gabbros cannot have formed from a common parental magma. The unzoned nature of olivine grains and their iron-rich com-positions relative to clinopyroxene suggest post-cumulus Mg–Fe exchange between olivine and interstitial melt. A gabbroic pegmatite is developed in the centre of the intrusion along its entire exposed 5 km strike length. Here, mineral zonation is limited and compositions are similar to rims of cumulus minerals in the enveloping olivine gabbros. The pegmatite could therefore represent interstitial melt mobilized from gabbroic cumulates that later accumulated and crystallized at its present stratigraphic location. Cumulus olivines in the gabbros are close to equilibrium with Ca-rich pyroxene in the pegmatite. This is interpreted as reflecting interstitial melt mobility during the late stages of solidification of the macrodyke. Chilled margins are well preserved at the intrusion margins and are rich in Fe (14–15.3% FeOTOT), Ti (3–3.3% TiO2) and light rare-earth elements ([La/Sm]N = 1.2–1.3), similar to magmas well represented in the overlying sequence of contemporaneous High-Ti Series flood basalts. It is therefore likely that extensive wall-rock melting adjacent to the macrodyke reflects continuous feeding of the overlying flood basalts through the Kraemer Island macrodyke.

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Melt Inclusions in Plagioclase Macrocrysts at Mount Jourdanne, Southwest Indian Ridge (~64° E): Implications for an Enriched Mantle Source and Shallow Magmatic Processes

Minerals ◽

10.3390/min9080493 ◽

2019 ◽

Vol 9 (8) ◽

pp. 493 ◽

Cited By ~ 2

Author(s):

Wei Li ◽

Chunhui Tao ◽

Wen Zhang ◽

Jia Liu ◽

Jin Liang ◽

...

Keyword(s):

Mantle Source ◽

Melt Inclusions ◽

Parental Magma ◽

Southwest Indian Ridge ◽

Host Magma ◽

Enriched Mantle ◽

Magma Supply ◽

General Chemical ◽

Indian Ridge ◽

Ocean Ridge

Plagioclase ultraphyric basalts (PUBs) with up to 40% millimeter-sized plagioclase crystals, were sampled from the Mount Jourdanne volcanic massif (~64° E) in the Southwest Indian Ridge. The geochemistry of the host glass, the glassy melt inclusions and their host plagioclase macrocrysts (An60-69) are used to reveal the mantle heterogeneity and to discuss the origin of Mount Jourdanne PUBs. The melt inclusions trapped in plagioclase display low MgO and high SiO2 contents and show rare earth element (REE) patterns resembling enriched mid-ocean ridge basalts (E-MORB). Together with their positive Sr and Eu anomalies, these features indicate that they were derived from an enriched mantle source, likely a refertilized peridotite or a pyroxenite. In contrast to some 61–67° E basalts, there is a lack of negative Eu anomalies in the PUB host glasses, precluding large amounts of plagioclase crystallization from their parental magma. Petrographic observations and the general chemical similarity between melt inclusions and melts equilibrated with the clinopyroxene cores in regional gabbros and/or troctolites suggest that these plagioclase macrocrysts originate from gabbroic mush within the lower crust. The density contrasts allow the effective segregation of plagioclase prior to their incorporation into the host magma. We propose that these plagioclase macrocrysts were entrained when a new batch of magma passed through the crustal mush zone, and resulted in the formation of the PUB. Eruption of Mount Jourdanne PUBs requires a minimum ascending velocity of 5 m d−1 for the host magma, which is not as high as the eruption rate for typical MORB samples. It is likely that the PUB host magma erupts during a period with reduced magma supply, whereas eruption of aphyric lavas correspond to the fast volcanic formation of the Mount Jourdanne massif.

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The water content and parental magma of the second chassignite NWA 2737: Clues from trapped melt inclusions in olivine

Meteoritics and Planetary Science ◽

10.1111/maps.12073 ◽

2013 ◽

Vol 48 (3) ◽

pp. 474-492 ◽

Cited By ~ 13

Author(s):

Qi He ◽

Long Xiao ◽

Weibiao Hsu ◽

J. Brian BALTA ◽

Harry Y. McSween ◽

...

Keyword(s):

Water Content ◽

Melt Inclusions ◽

Parental Magma

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The Lower Silurian Osmundsberg K-bentonite. Part II: mineralogy, geochemistry, chemostratigraphy and tectonomagmatic significance

Geological Magazine ◽

10.1017/s001675689700811x ◽

1998 ◽

Vol 135 (1) ◽

pp. 15-26 ◽

Cited By ~ 47

Author(s):

WARREN D. HUFF ◽

STIG M. BERGSTRÖM ◽

DENNIS R. KOLATA ◽

HEPING SUN

Keyword(s):

Melt Inclusions ◽

Tectonic Setting ◽

Analytical Data ◽

Clay Fraction ◽

Parental Magma ◽

Margin Setting ◽

Lower Silurian ◽

Regional Correlation ◽

Tectonically Active ◽

Chemical Fingerprinting

The Lower Silurian Osmundsberg K-bentonite is a widespread ash bed that occurs throughout Baltoscandia and parts of northern Europe. This paper describes its characteristics at its type locality in the Province of Dalarna, Sweden. It contains mineralogical and chemical characteristics that permit its regional correlation in sections elsewhere in Sweden as well as Norway, Estonia, Denmark and Great Britain. The <2 μm clay fraction of the Osmundsberg bed contains abundant kaolinite in addition to randomly ordered (RO) illite/smectite (I/S). Modelling of the X-ray diffraction tracings showed the I/S consists of 18% illite and 82% smectite. The high smectite and kaolinite content is indicative of a history with minimal burial temperatures. Analytical data from both pristine melt inclusions in primary quartz grains as well as whole rock samples can be used to constrain both the parental magma composition and the probable tectonic setting of the source volcanoes. The parental ash was dacitic to rhyolitic in composition and originated in a tectonically active collision margin setting.Whole rock chemical fingerprinting of coeval beds elsewhere in Baltoscandia produced a pronounced clustering of these samples in the Osmundsberg field of the discriminant analysis diagram. This, together with well-constrained biostratigraphic and lithostratigraphic data, provides the basis for regional correlation and supports the conclusion that the Osmundsberg K-bentonite is one of the most extensive fallout ash beds in the early Phanerozoic. The source volcano probably lay to the west of Baltica as part of the subduction complex associated with the closure of Iapetus.

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Sulphide melt and aqueous fluid saturation in the PGE–Au mineralisation of the Skaergaard intrusion: evidence from melt inclusions

Contributions to Mineralogy and Petrology ◽

10.1007/s00410-020-1656-5 ◽

2020 ◽

Vol 175 (2) ◽

Author(s):

Jonas M. Pedersen ◽

Thomas Ulrich ◽

Thorsten Nagel ◽

Christian Tegner

Keyword(s):

Melt Inclusions ◽

Aqueous Fluid ◽

Skaergaard Intrusion ◽

Fluid Saturation

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Refractory megacrysts and magnesium-rich melt inclusions within spinel in oceanic tholeiites: Indicators of magma mixing and parental magma composition

Earth and Planetary Science Letters ◽

10.1016/0012-821x(77)90148-0 ◽

1977 ◽

Vol 37 (1) ◽

pp. 81-89 ◽

Cited By ~ 81

Author(s):

Colin H. Donaldson ◽

Roy W. Brown

Keyword(s):

Melt Inclusions ◽

Magma Mixing ◽

Parental Magma ◽

Magma Composition

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Compositions and formation conditions of primitive magmas of the Karymsky volcanic center, Kamchatka: evidence from melt inclusions and trace-element thermobarometry

Петрология ◽

10.31857/s0869-5903273258-281 ◽

2019 ◽

Vol 27 (3) ◽

pp. 258-281

Author(s):

D. P. Tobelko ◽

M. V. Portnyagin ◽

S. P. Krasheninnikov ◽

E. N. Grib ◽

P. Yu. Plechov

Keyword(s):

Trace Element ◽

Subduction Zones ◽

Melt Inclusions ◽

Parental Magma ◽

Reliable Data ◽

Volcanic Center ◽

Volcanic Front ◽

Formation Conditions ◽

Morb Source ◽

Karymsky Volcanic Center

This paper reports the results of a study of naturally and experimentally quenched melt inclusions in magnesian olivine (Fo77–89) from a basalt sample from the Karymsky volcanic center, which is located in the middle segment of the Eastern Volcanic Front of Kamchatka. The conditions of parental magma formation were estimated using modern methods of trace-element thermometry. Based on direct H2O measurements in inclusions and thermometry of coexisting olivine and spinel, it was shown that the parent melts contained at least 4.5 wt % H2O and crystallized at a temperature of 1114 ± 27°C and an oxygen fugacity of DQFM = 1.5 ± 0.4. The obtained estimates of H2O content and crystallization temperature are among the first and currently most reliable data for the Eastern Volcanic Front of Kamchatka. The primary melt of the Karymsky volcanic center was derived from peridotitic material and could be produced by ~12–17% melting of an enriched MORB source (E-DMM) at ~1230–1250°C and ~1.5 GPa. Our estimates of mantle melting temperature beneath Kamchatka are slightly lower than values reported previously and up to 50°C lower than the dry peridotite solidus, which indicates the influence of a slab-derived hydrous melt. The combined approach to the estimation of the initial H2O content of melt employed in this study can provide a more reliable data in future investigations, and its application will probably to decrease the existing temperature estimates for the mantle wedge above subduction zones.

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