On the relationships between the Bushveld Complex and its felsic roof rocks, part 1: petrogenesis of Rooiberg and related felsites

Mathez, E. A.; VanTongeren, J. A.; Schweitzer, J. K.

doi:10.1007/s00410-013-0884-3

Cited by 38 publications

(26 citation statements)

References 60 publications

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“…Abundant studies have been conducted on the felsic rocks in the Bushveld Complex (e.g. Hatton and Schweitzer, 1995;Mathez et al, 2013). Using previous studies, we prepared two rhyolitic glasses representative of the felsic end-members ( Fig.…”

Section: Initial Hypothesis and Methodologymentioning

confidence: 99%

“…These host rocks belong to the Rooiberg Group rhyolite (Hatton and Schweitzer, 1995;Buchanan et al, 2004). The Rooiberg Group is divided into four formations comprising the lower Dullstroom and Damwal Formations and the upper Kwaggasnek and Schrikkloof Formations Mathez et al, 2013) with a total thickness of 3-5 km (Twist and French, 1983;. The Dullstroom Formation (61-78 wt.% SiO 2 ) includes interbedded basaltic, andesitic, dacitic and rhyolitic flows and becomes richer in silica with increasing stratigraphic height.…”

Section: Geology Of the Vergenoeg Depositmentioning

confidence: 99%

“…1; Fourie, 2000). Borrok et al (1998) suggested that the basal felsites might also represent a certain facies of the Rooiberg Group rhyolites (Mathez et al, 2013). The basal felsites are overlain by a 40 m thick volcanic breccia (Fig.…”

Section: The Vergenoeg Pyroclastic Rock Suite (Vps)mentioning

confidence: 99%

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Experimental study of liquid immiscibility in the Kiruna-type Vergenoeg iron–fluorine deposit, South Africa

Hou

Charlier

Namur

et al. 2017

Geochimica et Cosmochimica Acta

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In this study we experimentally assess whether the bulk composition of the Kiruna-type iron-fluorine Vergenoeg deposit, South Africa (17 wt.% SiO 2 and 55 wt.% FeO tot) could correspond to an immiscible Fe-rich melt paired with its host rhyolite. Synthetic powder of the host rhyolite was mixed with mafic end-members (ore rocks) in variable proportions. Experimental conditions were 1-2 kbar and 1010°C, with a range of H 2 O and F contents in the starting compositions. Pairs of distinct immiscible liquids occur in experiments saturated with fluorite, under relatively dry conditions, and at oxygen fugacity conditions corresponding to FMQÀ1.4 to FMQ+1.8 (FMQ = fayalite-magnetite-quartz solid buffer). The Si-rich immiscible liquids contain 60.9-73.0 wt.% SiO 2 , 9.1-12.5 wt.% FeO tot , 2.4-4.2 wt.% F, and are enriched in Na 2 O, K 2 O and Al 2 O 3. The paired Fe-rich immiscible melts have 41.0-49.5 wt.% SiO 2 , 20.6-36.1 wt.% FeO tot and 4.5-6.0 wt.% F, and are enriched in MgO, CaO and TiO 2. Immiscibility does not develop in experiments performed under water-rich (aH 2 O > 0.2; a = activity) and/or oxidized (>FMQ+1.8) conditions. In all experiments, solid phases are magnetite, ±fayalite, fluorite and tridymite. Our results indicate that the rocks from the Vergenoeg pipe crystallized in a magma chamber hosting two immiscible silicate melts. Crystallization of the pipe from the Fe-rich melt explains its extreme enrichment in Ca, F and Fe compared to the host rhyolitic rocks. However, its low bulk silica content compared to experimental Fe-rich melts indicates that the pipe formed by remobilization of a mafic crystal mush dominated by magnetite and fayalite. Segregation of evolved residual liquids as well as the conjugate immiscible Si-rich melt produced the host rhyolite. The huge amount of fluorine in Vergenoeg ores ($12 wt.% F) can hardly be explained by simple crystallization of fluorite from the Fe-rich silicate melt (up to 6 wt.% F at fluorite saturation). Instead, we confirm a previous hypothesis that the fluorite enrichment is, in part, due to the migration of hydrothermal fluids.

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Section: Initial Hypothesis and Methodologymentioning

confidence: 99%

Section: Geology Of the Vergenoeg Depositmentioning

confidence: 99%

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Experimental study of liquid immiscibility in the Kiruna-type Vergenoeg iron–fluorine deposit, South Africa

Hou

Charlier

Namur

et al. 2017

Geochimica et Cosmochimica Acta

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“…The Bushveld Complex was emplaced at shallow levels in the crust (0.15-0.25 GPa: Pitra and de Waal 2001) into Paleoproterozoic rocks of the Transvaal Supergroup and the ca. 2061 Ma Rooiberg Group (Walraven 1997), a 6-km-thick sequence of precursor basaltic andesites to rhyolites (Buchanan et al 2002;Mathez et al 2013) that defines the upper age limit for the complex. The layered mafic-ultramafic rocks themselves are overlain and locally cut by a 2.5-km-thick sequence of ca.…”

Section: Geologic Setting Of the Merensky Reef In The Bushveld Complexmentioning

confidence: 99%

Geochronology of Layered Intrusions

Scoates

Wall

2015

Springer Geology

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Layered intrusions crystallize mainly from basaltic magma to form large bodies of igneous rocks that exhibit prominent layering and they preserve stunning rock records of the processes by which magma evolves in crustal magma chambers. These intrusions contain world-class deposits of chromium, platinum group elements (PGE), and vanadium, metals that are vital to industry and society in general. Despite their scientific and practical importance, precise age constraints are lacking for many layered intrusions, and geochronological frameworks linking crystallization and cooling ages for the most part do not exist. This has resulted in critical knowledge gaps related to their origin and formation. This chapter provides an overview of dating methods (U-Th-Pb, 40 Ar/ 39 Ar) and mineral chronometers (e.g., zircon, baddeleyite, rutile, apatite, titanite) potentially present in layered intrusions that is coupled with field, textural, and petrographic criteria for targeting sample selection to allow for the successful implementation of geochronologic studies of layered mafic-ultramafic rocks of any age. As an application, we demonstrate how the thermal history of the Bushveld Complex is documented by mineral ages from samples of the PGE-rich Merensky Reef. High-precision U-Pb zircon ages, involving pretreatment of zircon by the chemical abrasion (annealing and leaching) or CA-TIMS technique, for two samples separated by > 300 km are indistinguishable from each other (2056.88 ± 0.41 Ma, Eastern Limb; 2057.04 ± 0.55 Ma, Western Limb; uncertainty reported as 2s) confirming synchronous crystallization of this horizon at near-solidus conditions across the intrusion. Rapid cooling (~ 125 °C/Ma) down to temperatures of ~ 400-450 °C is defined by U-Pb rutile ages from the same samples (2052( .96 ± 0.61 Ma, 2053.0 ± 2.7 Ma) and a regional hydrothermal event is signaled in 40 Ar/ 39 Ar biotite ages (1999 ± 10 Ma, 2002 ± 10 Ma). The geochronology of layered intrusions, where magma differentiation processes are captured in a wide range of rock textures and structures, represents an essential tool for assessing the evolution of mafic magmatism in the Earth's crust.

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“…The youngest member of the complex is volcanic: the Rooiberg felsic lavas. Controversies exist about the genetic relationship between the felsic and mafic magmas (VanTongeren et al, 2010), as well as about the links of intrusive vs. extrusive magmatic units (Buchanan et al, 2004;Mathez et al, 2013). For example, Walraven (1997) determined an age for the Rooiberg volcanics at 2061±2 Ma (million years ago), which is statistically indistinguishable from U-Pb zircon ages of 2055-2060 Ma obtained from various parts of the Rustenburg Layered Series (Buick et al, 2001;Scoates and Friedman, 2008).…”

Section: Scientific Background and Controversiesmentioning

confidence: 99%

Drilling through the largest magma chamber on Earth: Bushveld Igneous Complex Drilling Project (BICDP)

et al. 2015

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Abstract.A scientific drilling project in the Bushveld Igneous Complex in South Africa has been proposed to contribute to the following scientific topics of the International Continental Drilling Program (ICDP): large igneous provinces and mantle plumes, natural resources, volcanic systems and thermal regimes, and deep life. An interdisciplinary team of researchers from eight countries met in Johannesburg to exchange ideas about the scientific objectives and a drilling strategy to achieve them. The workshop identified drilling targets in each of the three main lobes of the Bushveld Complex, which will integrate existing drill cores with new boreholes to establish permanently curated and accessible reference profiles of the Bushveld Complex. Coordinated studies of this material will address fundamental questions related to the origin and evolution of parental Bushveld magma(s), the magma chamber processes that caused layering and ore formation, and the role of crust vs. mantle in the genesis of Bushveld granites and felsic volcanic units. Other objectives are to study geophysical and geodynamic aspects of the Bushveld intrusion, including crustal stresses and thermal gradient, and to determine the nature of deep groundwater systems and the biology of subsurface microbial communities.

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On the relationships between the Bushveld Complex and its felsic roof rocks, part 1: petrogenesis of Rooiberg and related felsites

Cited by 38 publications

References 60 publications

Experimental study of liquid immiscibility in the Kiruna-type Vergenoeg iron–fluorine deposit, South Africa

Experimental study of liquid immiscibility in the Kiruna-type Vergenoeg iron–fluorine deposit, South Africa

Geochronology of Layered Intrusions

Drilling through the largest magma chamber on Earth: Bushveld Igneous Complex Drilling Project (BICDP)

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