309 Precambrian Geology (Posters)

Wednesday, 4 November 2015
9:00 AM - 6:30 PM
Exhibit Hall

NEW U-PB BADDELEYITE AGE AND PALEOMAGNETIC CONSTRAINTS FOR THE UITKOMST COMPLEX IN SOUTH AFRICA: CLUES TO THE TIMING OF INTRUSION

Paper number: 309-1
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The exact chronology of the Uitkomst Complex (UC), a member of the Bushveld LIP in South Africa, remains unkown. Here, we report geochronological, paleomagnetic and geochemical results from the UC and a crosscutting dyke at the Nkomati Mine, and provide new clues on the timing of emplacement. U-Pb baddeleyite dating, performed at the Museum of Natural History in Stockholm (Sweden), reveals a 207Pb/206Pb date of 2054.5 ± 6.9 Ma, which provides a minimum age constraint for the UC intrusion. Our age is nominally older than the previous age of 2044 ± 8 Ma (De Waal et al. 2001) reported for UC, and near identical to the U-Pb zircon ages of 2054.4 ± 1.8 Ma (Scoates and Friedman, 2008) and 2054.89 ± 0.37 Ma (Zeh et al., 2015) from the Critical Zone of the Rustenburg Layered Suite (RLS) in the Bushevld LIP. Paleomagnetic tests, achieved at the University of Johannesburg (South Africa), together with geochemical results indicate that the studied dyke is much older than previously thought. The calculated pole of the UC (Long. 28.7°N; Lat. 58.5°E; dp = 6.2; dm = 9.4; N = 3) is similar to established poles for the RLS. We suggest that the UC is older than previously considered, and was emplaced at the same time as, if not before the Critical Zone. Our data questions the location of the UC in the time model for the Bushveld LIP (Rajesh et al., 2013).

References

De Waal SA, Maier WD, Armstrong RA, Gauert CDK (2001) Parental magma and emplacement of the stratiform UItkomst Complex, South Africa. The Canadian Mineralogist 39: 557-571.

Rajesh HM, Chisonga BC, Shindo K, Beukes NJ, Armstrong RA (2013) Petrographic, geochemical and SHRIMP U-Pb titanite age characterization of the Thabazimbi mafic sills: Extended time frame and a unifying petrogenetic model for the Bushveld Large Igneous Province. Precambrian Research, (2010), doi:10.1016/j.precamres. 2013.02.002.

Scoates JS, Friedman RM (2008) Precise age of the Planiniferous Merensky reef, Bushveld Complex, South Africa, by the U-Pb zircon chemical abrasion ID-TIMS technique. Bulletin of the Society of Economic Geologists, 103: 465-473.

Zeh A, Ovtcharova M, Wilson AH, Schaltegger U (2015) The Bushveld Complex was emplaced and cooled in less than one million years – results of zirconology, and geotectonic implications. Earth Planet. Sci. Lett. (2015), http:// dx.doi.org/10.1016.j.epsl.2015.02.035