Filling the Bushveld Complex magma chamber: lateral expansion, roof and floor interaction, magmatic unconformities, and the formation of giant chromitite, PGE and Ti-V-magnetitite deposits

Kruger, F. J.

doi:10.1007/s00126-005-0016-8

Cited by 169 publications

(95 citation statements)

References 80 publications

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“…9.3): the western limb, eastern limb, the far western limb, the northern limb. A fifth limb (referred to as "the Bethal limb", in the south crops out as a small inlier of granophyre and comprises only Upper Zone stratigraphy that is covered by Karoo sediments (Buchanan 1979;Kruger 2005). Seismic and gravity data suggested that the Eastern and Western Limbs originally formed a continuous intrusion (Cawthorn and Webb 2001;Cole et al 2014;Webb et al 2004).…”

Section: Bushveld Complexmentioning

confidence: 95%

“…The Merensky Reef lies at the base of a specific and very laterally persistent cyclic unit that contains thin basal chromitite layers (Vermaak 1976). The base of the Merensky Reef was used by some workers to define the boundary between the Upper Critical Zone and the Main Zone (Kruger 2005). The PGE-mineralization and the vertical succession are variable depending on the localities considered but are consistent across the entire intrusion in comprising a package of thin chromite stringers and locally pegmatoidal orthocumulate orthopyroxenite overlain by norite (Cawthorn 2002;Naldrett et al 2009b;Viljoen 1999).…”

Section: Merensky Reef Of the Bushveld Complexmentioning

confidence: 99%

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Platinum-Group Element Deposits in Layered Intrusions: Recent Advances in the Understanding of the Ore Forming Processes

Godel

2015

Springer Geology

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Section: Bushveld Complexmentioning

confidence: 95%

Section: Merensky Reef Of the Bushveld Complexmentioning

confidence: 99%

Platinum-Group Element Deposits in Layered Intrusions: Recent Advances in the Understanding of the Ore Forming Processes

Godel

2015

Springer Geology

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“…In the RLS, the initial 87 Sr/ 86 Sr ratio of the LZ ranges from 0.7045 to 0.7070 (Kruger 2005). If this range is that of the mantle source at 2058 Ma, this source would evolve to a 87 Sr/ 86 Sr ratio of 0.7069-0.7093 between 2058 and 180 Ma, assuming the Rb/Sr ratio over that time interval was equal to that of primitive mantle (0.030, Sun and McDonough 1989).…”

Section: A Long-lived 18 O-enriched Mantle Component?mentioning

confidence: 97%

The oxygen isotope composition of Karoo and Etendeka picrites: High δ18O mantle or crustal contamination?

Harris

Roux

Cochrane

et al. 2015

Contrib Mineral Petrol

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Explanations for the high δ 18 O values in Tuli/Mwenezi picrites are limited to (1) alteration, (2) crustal contamination, and (3) derivation from mantle with an abnormally high δ 18 O. Previously, a variety of models that range from crustal contamination to derivation from the 'enriched' mantle lithosphere have been suggested to explain high concentrations of incompatible elements such as K, and average εNd and εSr values of −8 and +16 in Mwenezi (Nuanetsi) picrites. However, the primitive character of the magmas (Mg# 73), combined with the lack of correlation between δ 18 O values and radiogenic isotopic compositions, MgO content, or Mg# is inconsistent with crustal contamination. Thus, an 18 O-enriched mantle source having high incompatible trace element concentration and enriched radiogenic isotope composition is indicated. High δ 18 O values are accompanied by negative Nb and Ta anomalies, consistent with the involvement of the mantle lithosphere, whereas the high δ 18 O themselves are consistent with an eclogitic source. Magma δ 18 O values about 1 ‰ higher than expected for mantle-derived magma are also a feature of the Bushveld mafic and ultramafic magmas, and the possibility exists that a long-lived 18 O-enriched mantle source has existed beneath southern Africa. A mixed eclogite peridotite source could have developed by emplacement of oceanic lithosphere into the cratonic keel during Archaean subduction.

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“…The Bushveld Complex consists of an 400 km-wide, 7-to 9-km-thick sequence of layered mafic-ultramafic rocks (referred to as the Rustenburg Layered Suite), which may be a shallowly dipping, interconnected sheet (Webb et al 2004), that is associated with pre-and syn-layered suite marginal sills and intrusions (e.g., Eales and Cawthorn 1996;Kruger 2005) (Fig. 1.8a).…”

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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Filling the Bushveld Complex magma chamber: lateral expansion, roof and floor interaction, magmatic unconformities, and the formation of giant chromitite, PGE and Ti-V-magnetitite deposits

Cited by 169 publications

References 80 publications

Platinum-Group Element Deposits in Layered Intrusions: Recent Advances in the Understanding of the Ore Forming Processes

Platinum-Group Element Deposits in Layered Intrusions: Recent Advances in the Understanding of the Ore Forming Processes

The oxygen isotope composition of Karoo and Etendeka picrites: High δ18O mantle or crustal contamination?

Geochronology of Layered Intrusions

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