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  Late-Orogenic Juvenile Magmatism of the Mesoproterozoic Namaqua Metamorphic Province, South Africa, and Relationships to Granulite-Facies REE-Th and Iron Oxide Mineralizations

Ballouard, C., Elburg, M. A., Harlov, D. E., Tappe, S., Knoper, M. W., Eglinger, A., Andreoli, M. A. G. (2021): Late-Orogenic Juvenile Magmatism of the Mesoproterozoic Namaqua Metamorphic Province, South Africa, and Relationships to Granulite-Facies REE-Th and Iron Oxide Mineralizations. - Journal of Petrology, 62, 8, egab059.
https://doi.org/10.1093/petrology/egab059

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Ballouard, Christophe, Autor
Elburg, Marlina A., Autor
Harlov, D. E.1, Autor              
Tappe, Sebastian, Autor
Knoper, Michael W., Autor
Eglinger, Aurélien, Autor
Andreoli, Marco A. G., Autor
Affiliations:
13.6 Chemistry and Physics of Earth Materials, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum, ou_146036              

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Schlagwörter: post-orogenic mafic magmatism, melt-melt immiscibility, A-type granites, Koperberg Suite, Namaqua-Natal orogenic belt, Steenkampskraal REE-Th deposit
 Zusammenfassung: The Bushmanland Subprovince of the Mesoproterozoic Namaqua-Natal orogenic belt in southern Africa hosts numerous occurrences of monazite-magnetite (biotite-apatite-sulfide)-bearing veins and granitoid dykes, including the Steenkampskraal vein system, which is one of the highest-grade REE-Th ore deposits in the world. Here, we provide whole-rock geochemical data along with zircon and monazite U-Pb dates and monazite Sm-Nd isotope analyses of these REE-Th-rich veins and granitoid dykes. The U-Pb geochronology indicates that the monazite-rich veins and granitoid dykes formed between 1050 and 1010 Ma, contemporaneously with late-Namaqua granulite-facies metamorphism. They are also coeval with the Koperberg Suite mafic magmas at 1060—1020 Ma and the late stage of a major event of A-type granitoid magmatism that occurred from 1100 to 1030 Ma (i.e. the Spektakel Suite). Similar to the mafic intrusive rocks from the Koperberg Suite, monazite-rich veins and granitoid dykes, located in the southern part of the Bushmanland Subprovince, have more radiogenic Nd isotopic compositions (ENd(t)~ -1 to zero) than equivalent dykes and veins to the north (ENd(t)~ -12 to -6). Mafic rocks of the Koperberg Suite reach Th and La concentrations of >400 ppm that significantly exceed those of other rock types from the region, except for the monazite-rich veins and granitoid dykes, which suggests a genetic link between these rocks. Within veins and granitoid dykes, monazite, biotite and magnetite are commonly anhedral and occur interstitially between the felsic minerals; they are, thus, late crystallizing phases. The whole-rock REE-Th concentrations of the granitoid dykes increase with Fe-Mg contents. Therefore, their incompatible element enrichment is not linked to assimilation-fractional crystallization processes. The Nd isotopic signature as well as Fe-Mg- and REE-Th-rich character of the Koperberg Suite and monazite-rich granitoid dykes might reflect partial melting of lithospheric mantle domains, metasomatized during previous Namaqua subduction events, and the mixing of mantle-derived melts with REE-Th-rich metamorphic fluids during their ascent through the crust. We propose that the monazite-magnetite vein mineralizations represent Fe-P-rich immiscible liquids that exsolved from mantle-derived magmas with compositions similar to the most mafic and monazite-rich granitoid dykes. Within this petrogenetic model, conjugate silicate-rich immiscible liquids formed the more felsic granitoid dykes characterized by lower modal abundances of biotite, magnetite and monazite. Although they do not reach similarly high REE-Th concentrations, other A-type granitoids from the region, represented by the Spektakel Suite, also share geochemical affinities with mafic igneous rocks from the Koperberg Suite; they may have originated by melting of underplated equivalents of these late-orogenic mafic rocks.

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Sprache(n): eng - Englisch
 Datum: 20212021-07-10
 Publikationsstatus: Final veröffentlicht
 Seiten: -
 Ort, Verlag, Ausgabe: -
 Inhaltsverzeichnis: -
 Art der Begutachtung: -
 Identifikatoren: DOI: 10.1093/petrology/egab059
GFZPOF: p4 T3 Restless Earth
 Art des Abschluß: -

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Titel: Journal of Petrology
Genre der Quelle: Zeitschrift, SCI, Scopus
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Ort, Verlag, Ausgabe: -
Seiten: - Band / Heft: 62 (8) Artikelnummer: egab059 Start- / Endseite: - Identifikator: CoNE: https://gfzpublic.gfz-potsdam.de/cone/journals/resource/journals293
Publisher: Oxford University Press