LIP emplacement during Rodinia assembly identified through integrated high-precision geochronology and paleomagnetism
Michael TD Wingate
Tectonics Special Research Centre
University of Western Australia
September 15, 2004
Recent research provides evidence that LIPs were emplaced during assembly of the Rodinia supercontinent, in contrast to Phanerozoic LIPs, which are more commonly associated with continental breakup.
Hanson et al., 2004 (August LIP of the month) presented new U-Pb and paleomagnetic data for mafic rocks of the Umkondo LIP, which occurs over two million square kilometres of the Kalahari craton of southern Africa and Antarctica. They showed that the Umkondo LIP was emplaced between 1112 and 1105 Ma, and was precisely coeval with mafic magmatism in the Midcontinent Rift and SW US diabase province in the cratonic core of North America. The precision of the geochronology permits relative magnetic polarity of the two cratons to be constrained, and led the authors propose a novel alternative to previous reconstructions of Kalahari and Laurentia. They placed Kalahari to the east of Laurentia (present coordinates) and argued that the Umkondo and Keweenawan LIPs are parts of a single, very large intraplate igneous province. Although paleomagnetic data require substantial separation of the two cratons at 1.1 Ga, Hanson et al. suggested that the intervening space was occupied either by another continental block or by a large oceanic plateau. In addition to providing valuable new constraints on Rodinia reconstructions, this study implies that mantle upwelling required to generate LIPs may occur independently of the supercontinent cycle.
Combined geochronological, geochemical, and paleomagnetic studies of mafic igneous rocks in Australia led to discovery of the Warakurna LIP (January 2004 LIP of the month) by Wingate et al. (2004). The Warakurna LIP covers at least 1.5 million square kilometres in central and Western Australia, and includes layered mafic-ultramafic intrusions and mafic to felsic volcanic rocks and dikes in central Australia, a 1000-km-long mafic sill province in Western Australia, and several swarms of mafic dikes. SHRIMP U-Pb zircon and baddeleyite geochronology indicates that most of the mafic magmatism occurred between 1078 and 1070 Ma. Although at least 25 Ma younger than the Umkondo and Laurentian provinces, the Warakurna LIP provides a second example of LIP emplacement during assembly of the Rodinia supercontinent.
References
Hanson, R.E., Bowring, S.A., Ramezani, J., Dalziel, I.W.D., Crowley, J.L., Gose, W.A., Pancake, J.A., Seidel, E.K., Blenkinsop, T.G., Mukwakwami, J., 2004. 1.1-Billion-Year-Old Large-Scale Magmatism in the Kalahari and Laurentian Cratons During Rodinia Supercontinent Assembly. Science, 304, 1126-1129.
Wingate, M.T.D., Pirajno, F., Morris, P.A.. The Warakurna large igneous province: a new Mesoproterozoic large igneous province in west-central Australia. Geology, 32, 105-108.