Fractional crystallization of Si-undersaturated alkaline magmas leading to unmixing of carbonatites on Brava Island (Cape Verde) and a general model of carbonatite genesis in alkaline magma suites

Weidendorfer, Daniel; Schmidt, Max W.; Mattsson, Hannes B.

doi:10.1007/s00410-016-1249-5

Cited by 61 publications

(33 citation statements)

References 64 publications

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“…AI, ASI and CaO contents of the silicate melts in the range of composition exposed in 4.2.1). We assume that immiscible carbonate melts can be produced at any stage along the differentiation course, though, it is unclear whether such immiscible processes can occur for primitive magma (Weidendorfer et al, 2016). The grey line in Fig.…”

Section: Carbonatite Ree Enrichments Across the Differentiation Coursmentioning

confidence: 99%

A window in the course of alkaline magma differentiation conducive to immiscible REE-rich carbonatites

Nabyl

Massuyeau

Gaillard

et al. 2020

Geochimica et Cosmochimica Acta

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This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Section: Carbonatite Ree Enrichments Across the Differentiation Coursmentioning

confidence: 99%

A window in the course of alkaline magma differentiation conducive to immiscible REE-rich carbonatites

Nabyl

Massuyeau

Gaillard

et al. 2020

Geochimica et Cosmochimica Acta

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“…In equation 4, D0* and E* for trivalent cations (M2 site) are obtained by using equation 5and (6) (Wood and Blundy 1997;Mollo et al 2016): Fig 3b). Furthermore, Cpx with low Al content and moderate aegirine content are often related to alkaline igneous complexes associated with carbonatites (Marks et al 2004, Weidendorfer et al 2016, Vuorinen et al 2005. Finally the parametrization of REE partition coefficients between alkaline melt and Cpx that is proposed herein allows one to obtain DREE from major element composition of Cpx only, T should also be estimate (spreadsheet available in supplementary table).…”

Section: Prediction Of Ree Element Partitioningmentioning

confidence: 99%

“…Such HREE enrichments of Cpx have been tentatively attributed to the preferential incorporation of HREE in the VI-coordinated M1 site, whereas light and middle REE (LREE and MREE, respectively) are preferentially incorporated in the VIII-coordinated M2 site (Bottazi et al 1999;Fedele et al 2009;Olin and Wolff 2010;Reguir et al 2012, Beard et al 2019. Cpx enriched in HREE relative to MREE also display uncommon positive Zr and Hf anomalies (e.g., Bakti et al 2018;Baudouin et al 2016;Marks et al 2004;Weidendorfer et al 2016).…”

Section: Introductionmentioning

confidence: 99%

“…These substitutional variations seem to occur for specific compositions (e.g., high Mn or Na contents, usually in alkaline rocks), though HREE enrichments have been observed in both aegirine (NaFe 3+ Si2O6) and diopside (CaMgSi2O6) (Marks et al 2004;Möller and Williams-Jones 2016;Reguir et al 2012;Weidendorfer et al 2016;Beard et al 2019). Subtle HREE enrichments are also occasionally observed in basanite (Woodland and Jugo 2007) and in silica-saturated rocks such as diorites (e.g., Zhang et al 2017).…”

Section: Introductionmentioning

confidence: 99%

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Trace element partitioning between clinopyroxene and alkaline magmas: parametrization and role of M1 site on HREE enrichment in clinopyroxenes

Baudouin

France

Boulanger

et al. 2020

Contrib Mineral Petrol

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Trace element partitioning between minerals and liquids provides crucial constraints on igneous processes. We quantified trace element concentrations in clinopyroxene (Cpx) phenocrysts and their phonolite melt inclusions from the 2007-08 eruption of Oldoinyo Lengai (Tanzania), and report Cpx-melt partition coefficients (D) and corresponding partitioning equations for rare earth elements (REE) and high field strength elements (HFSE) in alkaline magmas. Heavy REE (HREE: Er, Tm, Yb, Lu) are enriched relative to middle REE in alkaline Cpx and display a specific partitioning behavior that is characteristic of alkaline systems. HFSE (Ti, Zr, Hf) and HREE have similar D values (DHf = 0.25; DLu = 0.4) that are significantly higher than MREE (DSm = 0.06). High DHREE/DMREE are strongly correlated with the high values of DZr and DHf relative to the low DMREE values. In this study, REE partitioning between phonolite melt and Cpx is not consistent with standard models assuming incorporation of all REE in the Cpx M2 site, but rather highlights HREE substitution in both the M1 and M2 sites. Here we highlight the preferential incorporation of HREE in the VI-coordinated M1 site, whereas light REE and MREE remain mostly distributed in the VIII-coordinated M2 site. REE partitioning is strongly dependant on Cpx chemistry: the ideal ionic radius and HREE incorporation in the M1 site increase with increasing Fe 3+ content and decrease with increasing Mg 2+ and Al VI content. In our study, we focus on alkaline evolved magmas, and update existing models to obtain adequate DHREE for alkaline evolved melts. We provide equations to quantify REE and HFSE partitioning, and HREE enrichment in Cpx, those are based on Cpx major element composition and temperature. We propose a new model based on the lattice strain approach that predicts HREE partitioning between Cpx and alkaline magmas. The knowledge of the melt composition or of the trace element contents is not required to obtain DREE from the new model. An improved parameterization of HFSE partitioning between Cpx and phonolite and trachy-phonolite melts is also provided herein. We eventually discuss the potential implications of those new data on our understanding of REE deposits that are commonly associated with igneous alkaline complexes.

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“…Not all of the islands exhibit the entire compositional range of the archipelago; for example, São Vicente is limited to mafic rocks, whereas Brava is dominated by peralkaline phonolites. Cape Verde also exhibits carbonatitic rocks, which are found in both the basement complexes and the mature stages of at least 5 of the 10 islands (Jørgensen and Holm, 2002;Mourão et al, 2010Mourão et al, , 2012Weidenorfer et al, 2016;Mata et al, 2017).…”

Section: Cape Verdementioning

confidence: 99%

Peralkaline Felsic Magmatism of the Atlantic Islands

Jeffery

Gertisser

2018

Front. Earth Sci.

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The oceanic-island magmatic systems of the Atlantic Ocean exhibit significant diversity in their respective sizes, ages, and the compositional ranges of their eruptive products. Nevertheless, almost all of the Atlantic islands and island groups have produced peralkaline felsic magmas, implying that similar petrogenetic regimes may be operating throughout the Atlantic Ocean, and arguably elsewhere. The origins of peralkaline magmas are frequently linked to low-degree partial melting of enriched mantle, followed by protracted differentiation in the shallow crust. However, additional petrogenetic processes such as magma mixing, crustal melting, and contamination have been identified at numerous peralkaline centers. The onset of peralkalinity leads to magma viscosities lower than those typical for metaluminous felsic magmas, which has profound implications for processes such as crystal settling. This study represents a compilation of published and original data which demonstrates trends that suggest that the peralkaline magmas of the Atlantic Ocean islands are generated primarily via extended (up to ∼ 95%), open system fractional crystallization of mantle-derived mafic magmas. Crustal assimilation is likely to become more significant as the system matures and fusible material accumulates in the crust. Magma mixing may occur between various compositional end-members and may be recognized via hybridized intermediate magmas. The peralkaline magmas are hydrous, and frequently zoned in composition, temperature, and/or water content. They are typically stored in shallow crustal magma reservoirs (∼ 2-5 km), maintained by mafic replenishment. Low melt viscosities (1 × 10 1.77 to 1 × 10 4.77 Pa s) facilitate two-phase flow, promoting the formation of alkali-feldspar crystal mush. This mush may then contribute melt to an overlying melt lens via filter pressing or partial melting. We utilize a three-stage model to account for the establishment, development, and termination of peralkaline magmatism in the ocean island magmatic systems of the Atlantic. We suggest that the overall control on peralkaline magmatism in the Atlantic is magma flux rate, which controls the stability of upper crustal magma reservoirs. The abundance of peralkaline magmas in the Atlantic suggests that their development must be a common, but not inevitable, stage in the evolution of ocean islands.

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Fractional crystallization of Si-undersaturated alkaline magmas leading to unmixing of carbonatites on Brava Island (Cape Verde) and a general model of carbonatite genesis in alkaline magma suites

Abstract: This page was generated automatically upon download from the ETH Zurich Research Collection. For more information, please consult the Terms of use.

Cited by 61 publications

References 64 publications

A window in the course of alkaline magma differentiation conducive to immiscible REE-rich carbonatites

A window in the course of alkaline magma differentiation conducive to immiscible REE-rich carbonatites

Trace element partitioning between clinopyroxene and alkaline magmas: parametrization and role of M1 site on HREE enrichment in clinopyroxenes

Peralkaline Felsic Magmatism of the Atlantic Islands

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