Mantle sources and magma evolution of the Rooiberg lavas, Bushveld Large Igneous Province, South Africa

Günther, T.; Haase, Karsten M.; Klemd, Reiner; Teschner, Claudia

doi:10.1007/s00410-018-1477-y

Cited by 20 publications

(16 citation statements)

References 122 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…8a-b), with slightly more pronounced enrichment in LILE, Th and U compared to other Finnish~2.45 Ga layered intrusions and dykes. Similar levels of enrichment are found in the komatiitic basalts of the Vetreny belt and in the Bushveld B1 magma, both of which show signs of contamination by up to 15-20 wt% of crustal or sub-continental lithospheric mantle (SCLM) material (Puchtel et al 1997;Barnes et al 2010;Kulikov et al 2010;Günther et al 2018). The Näränkävaara parental magma also displays a notable positive Sr anomaly with 200-600 ppm Sr (Fig.…”

Section: Geochemical Characteristics Of the Parental Magmamentioning

confidence: 55%

Parental magma, magmatic stratigraphy, and reef-type PGE enrichment of the 2.44-Ga mafic-ultramafic Näränkävaara layered intrusion, Northern Finland

et al. 2019

View full text Add to dashboard Cite

About 20 mafic-ultramafic layered intrusions in the northern Fennoscandian shield were emplaced during a widespread magmatic event at 2.5-2.4 Ga. The intrusions host orthomagmatic Ni-Cu-PGE and Cr-V-Ti-Fe deposits. We update the magmatic stratigraphy of the 2.44-Ga Näränkävaara mafic-ultramafic body, northeastern Finland, on the basis of new drill core and outcrop observations. The Näränkävaara body consists of an extensive basal dunite (1700 m thick), and a layered series comprising a peridotitic-pyroxenitic ultramafic zone (600 m thick) and a gabbronoritic-dioritic mafic zone (700 m thick). Two reversals are found in the layered series. The composition of the layered series parental magma was approximated using a previously unidentified marginal series gabbronorite. The parental magma was siliceous high-Mg basalt with high MgO, Ni, and Cr, but also high SiO 2 and Zr, which suggests primary magma contamination by felsic crust. Cu/Pd ratio below that of primitive mantle implies PGE-fertility. The structural position of the marginal series indicates that the thick basal dunite represents an older wallrock for the layered intrusion. A subeconomic reef-type PGE-enriched zone is found in the border zone between the ultramafic and mafic zones and has an average thickness of 25 m with 150-250 ppb of Pt + Pd + Au. Offset-type metal distribution and high sulfide tenor (50-300 ppm Pd) and R-factor (10 5) suggest reef formation by sulfide saturation induced by fractional crystallization. The reef-forming process was probably interrupted by influx of magma related to the first reversal. Metal ratios suggest that this replenishing magma was PGE-depleted before emplacement.

show abstract

Section: Geochemical Characteristics Of the Parental Magmamentioning

confidence: 55%

Parental magma, magmatic stratigraphy, and reef-type PGE enrichment of the 2.44-Ga mafic-ultramafic Näränkävaara layered intrusion, Northern Finland

et al. 2019

View full text Add to dashboard Cite

show abstract

“…An ideal example against the generation of the Rooiberg Group rhyolites by fractionation of basaltic magma is perhaps their very high 87 Sr/ 86 Sr i of 0.7321 ± 0.0029 (Walraven, 1985). We have also recalculated initial Sr (2.05 Ga) isotopic values of the available Rb-Sr isotopic analyses of the Rooiberg Group felsic volcanics in more recent literature (Buchanan et al, 2004;Günther et al, 2018;Harmer & Farrow, 1995). After data filtration [because some of the initial values are lower than the accepted initial Sr isotopic composition of Solar System, i.e., 0.69897 ± 3, Paspanastassiou & Wasserburg, 1968], 41 individual values are considered for interpretation, giving an average of 0.70693 ± 0.00272 from a range of 0.69903-0.71433 (Table S2).…”

Section: Genetic Type and Igneous Process Of Formation Of Lgsmentioning

confidence: 99%

Geochemical evolution of the Lebowa Granite Pluton in western Bushveld Igneous Complex, South Africa: More insight into the evolution of bimodal A‐type granitoid

Mutele

Misra

2021

Geological Journal

View full text Add to dashboard Cite

The 2.05 Ga Bushveld Igneous Complex (BIC) in the Kaapvaal Craton, South Africa, with an areal extent of 65,000 km 2 , represents one of the largest bimodal A-type granitoid suites in the world. The igneous activity of this complex begun with the Rooiberg Group of basalt-rhyolite bimodal volcanism, followed by the emplacement of the ultramafic-mafic Rustenburg Layered Suite (RLS), and finally the granitoid rocks of the Rashoop Granophyre (RG) and Lebowa Granite Suite (LGS). In this study, we present our new borehole description and whole-rock chemical data on the LGS from the relatively unknown western BIC to constrain the origin of the LGS and try to evaluate their geochemical relationship to the Rooiberg Group felsic volcanics. In the western BIC, the LGS is locally represented by the hydrothermally altered Paalkraal Granite and the Kenkelbos Granite that together form a central dome-like feature. The Veekraal Granite forms the peripheral part of the dome. These granitoids are, in general, coarse-grained, porphyritic, or equigranular, showing granophyric intergrowth, and consist of quartz, perthitic microcline, and albitic plagioclase with minor opaque and interstitial hornblende/biotite. Our whole-rock chemical data on western LGS, along with those from the Groblersdal area, eastern BIC (taken as reference), form a cluster in the 'granite' field in the normative Ab-An-Or diagram with mean Or/(Ab+Or) 0.5 (0.11), and are peralkaline to weakly peraluminous in composition. These A-type granitoids are strictly 'ferroan' and calc-alkalic to alkali-calcic in nature, and evolved through partial melting as evident mainly in process identification plots. In bulk chemical composition, the LGS and high-SiO 2 Rooiberg Group rhyolites overlap with the experimental melts generated during dehydration melting of tonalite-granodiorite, indicating the Archaean Kaapvaal TTG as their possible source.Constraints from experimental petrology further suggest the pressure and temperature of this relatively anhydrous (≤1 wt% H 2 O) melting were 2-1 kbar (i.e., ≤7.5 km crustal depth) and 920 C, respectively. As suggested before, the parent magma of the voluminous mafic-ultramafic body (RLS) of the BIC, forming a voluminous magma chamber in shallow crustal depth, provided the heat for this partial melting event.The following igneous event as evident from field description in the literature, our new borehole description and whole-rock chemical data, were a limited chemical

show abstract

“…Errors on the initial Nd isotope ratios in Table 4 are calculated by propagating errors on both 143 Nd/ 144 Nd and 147 Sm/ 144 Nd through the age correction. For more analytical details see [63]. 59 Co, 60 Ni, 61 Ni, and 63 Cu in BMS were determined by in situ spot analyses on sulphides in three polished thin sections and five polished ore sections.…”

Section: Sample Idmentioning

confidence: 99%

“…For more analytical details see [63]. 59 Co, 60 Ni, 61 Ni, and 63 Cu in BMS were determined by in situ spot analyses on sulphides in three polished thin sections and five polished ore sections. He and Ar functioned as carrier gas with a flux of 0.9 l/min.…”

Section: Sample Idmentioning

confidence: 99%

See 1 more Smart Citation

Magmatic PGE Sulphide Mineralization in Clinopyroxenite from the Platreef, Bushveld Complex, South Africa

et al. 2020

View full text Add to dashboard Cite

The Platreef, at the base of the northern limb of the Bushveld Complex in South Africa, hosts platinum-group element (PGE) mineralization in association with base-metal sulphides (BMS) and platinum-group minerals (PGM). However, whilst a magmatic origin of the stratiform mineralization of the upper Platreef has been widely confirmed, the processes responsible for the PGE and BMS mineralization and metasomatism of the host rocks in the Platreef are still under discussion. In order to contribute to the present discussion, we present an integrated petrographical, mineral-chemical, whole-rock trace- and major-element, sulphur- and neodymium-isotope, study of Platreef footwall clinopyroxenite drill core samples from Overysel, which is located in the northern sector of the northern Bushveld limb. A metasomatic transformation of magmatic pyroxenite units to non-magmatic clinopyroxenite is in accordance with the petrography and whole-rock chemical analysis. The whole-rock data display lower SiO2, FeO, Na2O and Cr (<1700 ppm), and higher CaO, concentrations in the here-studied footwall Platreef clinopyroxenite samples than primary magmatic Platreef pyroxenite and norite. The presence of capped globular sulphides in some samples, which display differentiation into pyrrhotite and pentlandite in the lower, and chalcopyrite in the upper part, is attributed to the fractional crystallization of a sulphide liquid, and a downward transport of the blebs. In situ sulphur (V-CDT) isotope BMS data show isotopic signatures (δ34S = 0.9 to 3.1 ‰; Δ33S = 0.09 to 0.32‰) close to or within the pristine magmatic range. Elevated (non-zero) Δ33S values are common for Bushveld magmas, indicating contamination by older, presumably crustal sulphur in an early stage chamber, whereas magmatic δ34S values suggest the absence of local crustal contamination during emplacement. This is in accordance with the εNd (2.06 Ga) (chondritic uniform reservoir (CHUR)) values, of −6.16 to −6.94, which are similar to those of the magmatic pyroxenite and norite of the Main Zone and the Platreef in the northern sector of the northern Bushveld limb. Base-metal sulphide textures and S–Se-ratios give evidence for a secondary S-loss during late- to post-magmatic hydrothermal alteration. The textural evidence, as well as the bulk S/Se ratios and sulphide S isotopes studies, suggest that the mineralization in both the less and the pervasively hydrothermally altered clinopyroxenite samples of Overysel are of magmatic origin. This is further supported by the PPGE (Rh, Pt, Pd) concentrations in the BMS and mass-balance calculations, in both of which large proportions of the whole-rock Pd and Rh are hosted by pentlandite, whereas Pt and the IPGE (Os, Ir, Ru) were interpreted to mainly occur in discrete PGM. However, the presence of pentlandite with variable PGE concentrations on the thin section scale may be related to variations in the S content, already at S-saturation during magmatic formation, and/or post-solidification mobilization and redistribution.

show abstract

Mantle sources and magma evolution of the Rooiberg lavas, Bushveld Large Igneous Province, South Africa

Cited by 20 publications

References 122 publications

Parental magma, magmatic stratigraphy, and reef-type PGE enrichment of the 2.44-Ga mafic-ultramafic Näränkävaara layered intrusion, Northern Finland

Parental magma, magmatic stratigraphy, and reef-type PGE enrichment of the 2.44-Ga mafic-ultramafic Näränkävaara layered intrusion, Northern Finland

Geochemical evolution of the Lebowa Granite Pluton in western Bushveld Igneous Complex, South Africa: More insight into the evolution of bimodal A‐type granitoid

Magmatic PGE Sulphide Mineralization in Clinopyroxenite from the Platreef, Bushveld Complex, South Africa

Contact Info

Product

Resources

About