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1 Borehole Research Group, Department of Geology, University of Leicester, Leicester, LE1 7RH, UK
2 Department of Earth Sciences, The University, Leeds, LS9 9JT, UK
3 Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
In Antarctica, Mesozoic tholeiitic magmatic rocks have been divided previously into the Ferrar and Dronning Maud Land magmatic provinces. In both provinces, K-Ar geochronology has established a spectrum of Jurassic ages, which supported relatively long-lived coeval magmatic episodes within each province. However, recent Ar-Ar geochronology has indicated that the Ferrar magmatism occurred over a short interval (176.6 ± 1.8 Ma).
To further constrain the age relationships within the two provinces, new Ar-Ar geochronology has yielded the following ages from three different regions: NE Heimefrontfjella (Dronning Maud Land), basaltic lava 172.4 ± 2.1 Ma, dolerite still 182.1 ± 1.9 Ma; 10 dolerites from the Theron Mountains (Coats Land), 172.6 ± 1.7 to 181.9 ± 2.5 Ma, although two dolerites with low K plagioclase gave ages of c. 190 Ma; Dufek Intrusion (Transantarctic Mountains) 182.5 ± 2.4 Ma.
The Dufek intrusion is an extremely large layered gabbroic complex, which is an integral part of the Ferrar Magmatic Province, but is slightly older than the basalts in this province; suggesting an early intrusive episode followed by somewhat later volcanic episodes. A similar age distribution has also been demonstrated in NE Heimefrontfjella.
The new Ar-Ar ages confirm a short-lived but widespread Mid-Jurassic magmatic episode within Antarctica. This magmatic episode is c. 25 Ma older than the earliest evidence for the separation of Africa and Antarctica, suggesting that the plume responsible for the magmatism in Dronning Maud Land and the Karoo province in southern Africa was not the driving force for continental separation. However, the magmatism in Dronning Maud Land and Coats Land in Antarctica and the postulated position of the plume correlate with the position of the failed Weddell Sea Rift System. The plume may have provided the driving force for this rift system, but, it did not possess sufficient energy to drive continental separation.
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