Trace-element study and age dating of zircon from chromitites of the Bushveld Complex (South Africa)

Yudovskaya, Marina A.; Kinnaird, Judith A.; Naldrett, A. J.; Родионов, Н. В.; Антонов, А. В.; Симакин, С. Г.; Kuzmin, D. V.

doi:10.1007/s00710-013-0269-3

Cited by 30 publications

(11 citation statements)

References 74 publications

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“…Its Cr and platinum-group element (PGE) deposits constitute a major portion of the world's economic reserves9. Recent U–Pb geochronology suggested that the RLS was emplaced into the Transvaal Supergroup within a period of <1 Myr10, which confirmed the earlier data1112131415 and improved age precision to better than ∼0.1% (refs 10, 12). Simple thermal models indicate that the entire thickness of the complex could have been emplaced and reached its solidus temperature within 0.1 Myr1016.…”

supporting

confidence: 54%

U–Pb geochronology documents out-of-sequence emplacement of ultramafic layers in the Bushveld Igneous Complex of South Africa

Mungall

Kamo

McQuade³

2016

Nat Commun

146

124

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Layered intrusions represent part of the plumbing systems that deliver vast quantities of magma through the Earth's crust during the formation of large igneous provinces, which disrupt global ecosystems and host most of the Earth's endowment of Pt, Ni and Cr deposits. The Rustenburg Layered Suite of the enormous Bushveld Igneous Complex of South Africa has been presumed to have formed by deposition of crystals at the floor of a subterranean sea of magma several km deep and hundreds of km wide called a magma chamber. Here we show, using U–Pb isotopic dating of zircon and baddeleyite, that individual chromitite layers of the Rustenburg Layered Suite formed within a stack of discrete sheet-like intrusions emplaced and solidified as separate bodies beneath older layers. Our U–Pb ages and modelling necessitate reassessment of the genesis of layered intrusions and their ore deposits, and challenge even the venerable concept of the magma chamber itself.

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supporting

confidence: 54%

U–Pb geochronology documents out-of-sequence emplacement of ultramafic layers in the Bushveld Igneous Complex of South Africa

Mungall

Kamo

McQuade³

2016

Nat Commun

146

124

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“…Trend 1 is characterised by a common decrease in U, Ti and Th/U, trend 2 by a significant increase in Th/U (0.5 up to 10), with decreasing or constant Ti and U, and trend 3 by a significant increase in U, at decreasing and/or constant Th/U and Ti. The systematic changes of the U, Th and Ti contents likely resulted from magmatic fractionation of accessory minerals together with zircon, such as rutile, apatite and even thorite that are observed in thin section (also see Yudovskaya et al, 2013).…”

Section: Zircon Textures Zoning Composition Inclusions and Crystalmentioning

confidence: 96%

“…The latter comprise whole-rock isochron and mineral data which scatter between 2044 ± 3 Ma and 1995 ± 50 Ma (Schoenberg et al, 1999;Nomade et al, 2004;Reisberg et al, 2011;Coggon et al, 2012). Some U-Pb zircon ages obtained by SHRIMP (Sensitive High Resolution Ion Microprobe) also reveal a high degree of scatter and overlap with the CA-ID-TIMS and Ar-Ar data (Yudovskaya et al, 2013). The most precise U-Pb ages to date suggest a crystallisation time interval for BC rocks of 3-5 million yr.…”

Section: Introductionmentioning

confidence: 93%

The Bushveld Complex was emplaced and cooled in less than one million years – results of zirconology, and geotectonic implications

Zeh

Ovtcharova

Wilson

et al. 2015

Earth and Planetary Science Letters

249

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“…Whether the duration is 1, 5, or 10 Ma or longer, directly impacts estimates for rates of mantle melting, melt extraction, magma transport, magma flux, and cooling, and even potential environmental impacts (i.e., degassing associated with eruptive equivalents). Recent compilations of available geochronological data, combining in some cases published (analytical technique and data tables available) and unpublished (ages reported in abstracts with no associated data), suggest that most of the products of Bushveld-related magmatism may have crystallized in the interval of 2054-2061 Ma (Mapeo et al 2004;Scoates and Friedman 2008;Yudovskaya et al 2013;Rajesh et al 2013 Ar plateau or inverse isochron ages). Few studies involve common reference materials, reference values, and data reduction techniques.…”

Section: Crystallization and Cooling Of The Merensky Reef And Bushvelmentioning

confidence: 97%

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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Trace-element study and age dating of zircon from chromitites of the Bushveld Complex (South Africa)

Cited by 30 publications

References 74 publications

U–Pb geochronology documents out-of-sequence emplacement of ultramafic layers in the Bushveld Igneous Complex of South Africa

U–Pb geochronology documents out-of-sequence emplacement of ultramafic layers in the Bushveld Igneous Complex of South Africa

The Bushveld Complex was emplaced and cooled in less than one million years – results of zirconology, and geotectonic implications

Geochronology of Layered Intrusions

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