Bryan C. Storey
Gateway Antarctica
University of Canterbury
October 22, 2004
The initial breakup of the Gondwana supercontinent in Early Jurassic times was heralded by emplacement of three large igneous provinces that have distinctive geochemical characteristics:
The links between these provinces and the processes involved in their generation has been uncertain for many years with the Karoo province being most closely linked to a mantle plume based partly on the presence of iron rich basalts within the province. However, the opportunities provided by high precision SHRIMP and Ar-Ar dating have shown that at least part of the Chon Aike province, and the Karoo and Ferrar provinces were emplaced within a short duration and close to 182 Ma (see Riley and Knight, 2001, for a review, and Riley et al. 2004 for new data on the age of rhyolites associated with basalts within the Karoo Province). This has lead to speculation about similar processes being responsible for the three provinces and the location, shape and extent of thermal anomalies beneath the different provinces. The discovery of ultramafic lamprophyres within the Ferrar Province (Riley et al. 2003) has perhaps provided the most conclusive evidence to date of a mantle plume beneath the Ferrar province although this raises serious questions about the size and shape of a thermal anomaly beneath what is essentially a long linear shaped igneous province.
There is a widely held view that the centre of thermal activity responsible for the three igneous provinces laid in the Weddell Sea sector between South America, southern Africa and Antarctica (Elliott and Fleming 2000, 2004; Ferris et al. 2000, 2003; Storey et al. 2001). If this was true magmas would have, in the case of the Ferrar province, been transported through dyke or sill complexes for distances in excess of two thousand kilometers away from the Weddell Sea sector towards present day Australia. Although this provides a neat explanation for the linear province that parallels the continental margin, the role that subduction processes played in producing the magmas and/or controlling their location remains speculative also (Hathway 2000). In any case, the three provinces continue to provoke more questions that answers although new data continue to point towards one single very large province that has at least some common causal relationships rather than three smaller provinces with separate origins.
References
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Elliot, D.H., Fleming, T.H., 2004. Occurrence and Dispersal of Magmas in the Jurassic Ferrar Large Igneous Province, Antarctica. Gondwana Research, Vol 7, No. 1, 223 – 237.
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Ferris, J.K., Storey, B.C., Vaughan, A. P.M., Kyle, P.R., Jones, P.C., 2003. The Dufek and Forrestal intrusions, Antarctica: a centre for Ferrar Large Igneous Province dike emplacement? Geophysical Research Letters Vol. 30, NO. 6, 81-3 – 81-4.
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