Zircon U–Pb chronology and Hf isotopes of the Lebowa Granite Suite and petrogenesis of the Bushveld Complex, South Africa.

Autor: Skursch, Ole, Corfu, Fernando, Tegner, Christian, Lesher, Charles E., Andreasen, Rasmus, Hagen-Peter, Graham. A., Vervoort, Jeff D.
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Zdroj: Contributions to Mineralogy & Petrology; Feb2022, Vol. 177 Issue 2, p1-17, 17p
Abstrakt: The Bushveld Large Igneous Province (BLIP) was emplaced in three stages (I, II, and III) over some 19 m.y. (c. 2061–2042 Ma). The Bushveld Complex is the main constituent of the BLIP and hosts the world's largest ferroan granite (Lebowa Granite Suite) and several granophyres (Rashoop Granophyre Suite) directly overlying the world's largest layered mafic intrusion (Rustenburg Layered Suite). New zircon U–Pb ages (measured by ID-TIMS) for the Lebowa Granite Suite and a textural variant termed Zwartbank Pseudogranophyre yield identical crystallization ages ranging from 2054.3 ± 0.7 to 2056.5 ± 0.9 Ma. Zircons from the uppermost Rustenburg Layered Suite (Upper Zone) yield an indistinguishable age of 2055.1 ± 2.1 Ma. These ages demonstrate that the Bushveld granitoids, together with the Rustenburg Layered Suite belong to BLIP Stage II. Additionally, most Lebowa Granite Suite samples contain zircons with primary growth zonation that yield ages up to 2064 Ma. We interpret these as antecrysts originating from BLIP Stage I. Isotope compositions of Hf in zircon (measured by LA-MC-ICPMS in situ and on solutions) are essentially uniform at εHf (2055 Ma) = − 7.2 to − 5.6, and indistinguishable from published data for the uppermost Rustenburg Layered Suite. We interpret the indistinguishable ages and similar isotopic compositions of the Lebowa Granite Suite and the Rustenburg Layered Suite as support for direct petrogenetic linkages. The Hf isotopic composition of the Rustenburg Layered Suite has been attributed to enriched mantle sources, but we show that crustal assimilation by mantle-derived magmas can also explain these compositions for both the Lebowa Granite Suite and Rustenburg Layered Suite. We propose that the Lebowa Granite Suite formed during Stage II, but zircon antecrysts indicate that some remobilization of granitic material formed during Stage I was also involved. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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