Assimilation and crystallization in basic magma chambers: trace-element and Nd-isotopic variations in the Kerns sill, Nipissing diabase province, Ontario

An investigation has been made of the trace-element and Nd-isotopic effects of assimilation at the roof of the Proterozoic Kerns sill in the 2.2 Ga Nipissing diabase province in Ontario. The ratios Th/Zr, La/Zr, and U/Zr and the concentrations of incompatible elements all tend to increase with decreasing Mg#, Ni, and Cr. These variations have been simulated by computer models in which assimilation and fractionation are coupled (AFC) and the most fractionated magmas (identified by low Mg#, Ni, and Cr and by high incompatible-element concentrations) are also the most contaminated (indicated by higher Th/Zr, La/Zr, and U/Zr and lower 143Nd/144Ndo). The results suggest that the ratio (r) of the change of magma mass due to assimilation relative to the change due to fractionation gradually increased. The latent heat of crystallization may have contributed sufficient heat to melt the roof of the intrusion where ponded crustal melts were separated from the underlying basic magma by a double-diffusive interface. Field relations suggest that this interface was progressively destroyed by convective erosion; thus the degree of contamination increased as the magma became more fractionated. These results are consistent with laboratory investigations designed to simulate assimilation at the roof of basaltic magma chambers.

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Feldspar megacrysts and anorthosite xenolith-bearing dykes in the Narssarssuaq area, South Greenland

Rapport Grønlands Geologiske Undersøgelse ◽

10.34194/rapggu.v154.8168 ◽

1992 ◽

Vol 154 ◽

pp. 49-59

Author(s):

T Winther

Keyword(s):

Open Systems ◽

Early Stage ◽

Rift System ◽

Magma Chambers ◽

Degree Of Contamination ◽

Magma Reservoirs ◽

Incompatible Elements ◽

Low Degree ◽

Alkaline Magmas ◽

Compositional Gradients

Numerous dyke intrusions are found in the Narssarssuaq area of the Gardar province, a Mid-Proterozoic intracontinental rift system. Ten to fifteen percent of these dykes, which range in composition from trachybasalt to phonolite and rhyolite, contain significant proportions of feldspar megacrysts and occasionally anorthosite xenoliths. Two groups of dykes are distinguished; the older group is more alkaline, richer in incompatible elements and contains more anorthosite xenoliths than the younger. It is probable that the main reason for the differences is variation in magma production through time and from one area to another. Chemical zonation in the dykes reflects compositional gradients in the feeding magma reservoirs; the magma reservoirs acting as open systems in which crystal fractionation was an important controlling process. The anorthosite xenoliths are not strictly cognate with their hosts, but were derived from comparable alkaline magmas with a composition roughly corresponding to the most primitive of the dykes. The plagioclase megacrysts were presumably formed at an early stage of the development of the magma chambers. Rb-Sr dating of one of the dykes from the older group of dykes gives an age of 1206 ± 20 Ma and an initial 87Sr/86Sr ratio of 0.7028 ± 0.0001 supporting a low degree of contamination with upper crustal Sr.

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Isotopic and trace element evidence from lavas, bearing on mantle heterogeneity beneath Kenya

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1980.0214 ◽

1980 ◽

Vol 297 (1431) ◽

pp. 259-271 ◽

Cited By ~ 75

Keyword(s):

Trace Element ◽

Incompatible Element ◽

General Trend ◽

Source Region ◽

Mantle Heterogeneity ◽

Pb Isotope ◽

Nd Isotope ◽

Northern Kenya ◽

Incompatible Elements ◽

Light Rare Earth Elements

Nd, Sr and Pb isotope data, together with new major and trace element data are presented for lavas from northern Kenya. A general trend towards silica saturation and decreasing incompatible element contents is observed from the Miocene to the present day. Significantly, the abundances of different incompatible elements decrease The Nd, Sr and Pb isotope compositions of the basic lavas are similar to those observed on the Atlantic ocean islands. Comparison of the Sm/Nd ratios required to produce the Nd isotope ratios with those observed in the rocks indicates that light rare earth elements (r.e.e.) have probably been added to the source region of the lavas comparatively recently. A model involving recent metasomatism of the subcontinental mantle beneath Kenya, which could account for the correlated silica undersaturation and incompatible element content of the lavas, is proposed.

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Trace element and isotopic variations from Mt. Vulture to Campanian volcanoes: constraints for slab detachment and mantle inflow beneath southern Italy

Contributions to Mineralogy and Petrology ◽

10.1007/s00410-006-0062-y ◽

2006 ◽

Vol 151 (3) ◽

pp. 331-351 ◽

Cited By ~ 67

Author(s):

G. De Astis ◽

P. D. Kempton ◽

A. Peccerillo ◽

T. W. Wu

Keyword(s):

Trace Element ◽

Southern Italy ◽

Isotopic Variations

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Episodic trace element and isotopic variations in historical Mauna Loa Lavas: Implications for magma and plume dynamics

Mauna Loa Revealed: Structure, Composition, History, and Hazards - Geophysical Monograph Series ◽

10.1029/gm092p0263 ◽

1995 ◽

pp. 263-288 ◽

Cited By ~ 38

Author(s):

J. M. Rhodes ◽

S. R. Hart

Keyword(s):

Trace Element ◽

Mauna Loa ◽

Plume Dynamics ◽

Isotopic Variations ◽

Episodic Trace

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Parental magma composition of the Main Zone of the Bushveld Complex: Evidence from in-situ LA-ICP-MS trace element analysis of silicate minerals in the cumulate rocks

10.5194/egusphere-egu2020-17903 ◽

2020 ◽

Author(s):

Shenghong Yang ◽

Wolfgang D. Maier ◽

Belinda Godel ◽

Sarah-Jane Barnes ◽

Eero Hanski ◽

...

Keyword(s):

Trace Elements ◽

Trace Element ◽

Bushveld Complex ◽

Trace Element Analysis ◽

Parental Magma ◽

Main Zone ◽

Element Analysis ◽

Silicate Minerals ◽

Incompatible Elements

<p>In-situ trace element analysis of cumulus minerals may provide a clue to the parental magma from which the minerals crystallized. However, this is hampered by effects of the trapped liquid shift (TLS). In the Main Zone (MZ) of the Bushveld Complex, the Ti content in plagioclase grains shows a clear increase from core to rim, whereas most other elements (e.g., rare earth elements (REEs), Zr, Hf, Pb) do not. This is different from the prominent intra-grain variation of all trace elements in silicate minerals in mafic dikes and smaller intrusion, which have a faster cooling rate. We suggest that crystal fractionation of trapped liquid occurred in the MZ of Bushveld and the TLS may have modified the original composition of the cumulus minerals for most trace elements except Ti during slow cooling. Quantitative model calculations suggest that the influence of the TLS depends on the bulk partition coefficient of the element. The effect on highly incompatible elements is clearly more prominent &#173;&#173;than on moderately incompatible and compatible elements because of different concentration gradients between cores and rims of cumulate minerals. This is supported by the following observations in the MZ of Bushveld: 1) positive correlation between Cr, Ni and Mg# of clinopyroxene and orthopyroxene, 2) negative correlation between moderately incompatible elements (e.g., Mn and Sc in clinopyroxene and orthopyroxene, Sr, Ba, Eu in plagioclase), but 3) poor correlation between highly incompatible elements and Mg# of clinopyroxene and orthopyroxene or An# of plagioclase. Modeling suggests that the extent of the TLS for a trace element is also dependent on the initial fraction of the primary trapped liquid, with strong TLS occurring if the primary trapped liquid fraction is high. This is supported by the positive correlation between highly incompatible trace element abundances in cumulus minerals and whole-rock Zr contents.</p><p>We have calculated the composition of the parental magma of the MZ of the Bushveld Complex. The compatible and moderately incompatible element contents of the calculated parental liquid are generally similar to those of the B3 marginal rocks, but different from the B1 and B2 marginal rocks. For the highly incompatible elements, we suggest that the use of the sample with the lowest whole-rock Zr content and the least degree of TLS is the best approach to obtain the parental magma composition. Based on calculation, we propose that a B3 type liquid is the most likely parental magma to the MZ of the Bushveld Complex.</p>

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Combining trace-element compositions, U–Pb geochronology and Hf isotopes in zircons to unravel complex calcalkaline magma chambers in the Upper Cretaceous Srednogorie zone (Bulgaria)

Lithos ◽

10.1016/j.lithos.2008.01.004 ◽

2008 ◽

Vol 104 (1-4) ◽

pp. 405-427 ◽

Cited By ~ 28

Author(s):

I. Peytcheva ◽

A. von Quadt ◽

N. Georgiev ◽

Zh. Ivanov ◽

C.A. Heinrich ◽

...

Keyword(s):

Trace Element ◽

Upper Cretaceous ◽

Hf Isotopes ◽

Magma Chambers

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Igneous Layering in Basaltic Magma Chambers

Springer Geology - Layered Intrusions ◽

10.1007/978-94-017-9652-1_2 ◽

2015 ◽

pp. 75-152 ◽

Cited By ~ 24

Author(s):

O. Namur ◽

Bénédicte Abily ◽

Alan E. Boudreau ◽

Francois Blanchette ◽

John W. M. Bush ◽

...

Keyword(s):

Basaltic Magma ◽

Magma Chambers ◽

Igneous Layering

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Origin of non-cotectic cumulates: A novel approach

Geology ◽

10.1130/g47082.1 ◽

2020 ◽

Vol 48 (6) ◽

pp. 604-608 ◽

Cited By ~ 2

Author(s):

R.M. Latypov ◽

S.Yu. Chistyakova

Keyword(s):

Phase Equilibria ◽

Basaltic Magma ◽

Parental Magma ◽

Magma Chambers ◽

Mechanical Mixing ◽

Novel Approach ◽

In Situ Crystallization ◽

Mechanical Separation ◽

Novel Concept

Abstract Plutonic mafic complexes are composed of cumulates in which minerals mostly occur in cotectic proportions. This is consistent with a concept that basaltic magma chambers predominantly crystallize in situ from margins inward. However, cumulates with two (or more) minerals in proportions that are at odds with those expected from liquidus phase equilibria also locally occur in these complexes. Such non-cotectic cumulates are commonly attributed to either mechanical separation of minerals crystallizing from the same parental magma or mechanical mixing of minerals originating from different parental magmas. Here we introduce a novel concept that does not require any of these processes to produce non-cotectic cumulates. The model involves melts that start crystallizing upon their cooling, while ascending along feeder conduits from deep staging reservoirs toward the Earth’s surface. Depending on the degree of cooling, the melts become successively saturated in one, two, and more liquidus phases. Given that most crystals are kept in suspension, the resulting magmas would contain a cargo of equilibrium phenocrysts in notably non-cotectic proportions. The replenishment of basaltic chambers developing through in situ crystallization by such magmas is likely responsible for the occasional formation of non-cotectic cumulates in plutonic mafic complexes.

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