Mesozoic Break-up of Gondwanaland: Geochronology of Antarctic Tholeiites

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Elliot and Foland OPP 9527816 Abstract This award supports a project to investigate igneous rocks associated with the break-up of the Gondwanaland supercontinent. The initial break-up of Gondwanaland during the Mesozoic was associated with a major magmatic event during which voluminous extrusive lava flows and intrusive sills and dikes were formed. Study of these igneous products which are related to large-scale processes of continental disruption is important in constraining the temporal and spatial nature of break-up. This magmatism is expressed by the Karoo tholeiites of southern Africa and related rocks in Dronning Maud Land, Antarctica, and by Ferrar tholeiites of the Transantarctic Mountains. The geochronology of mafic igneous intrusive and extrusive events will be examined in Antarctica in two distinct areas: in Dronning Maud Land and in the Ross Sea sector of the Transantarctic Mountains. The former is directly associated with the initial rifting which separated Africa from Antarctica while the latter, the Ferrar, has a less direct relationship but nevertheless is part of the initial phase of igneous activity. The objectives of the research are to: (1) establish the time of emplacement and duration of the Mesozoic magmatism in Dronning Maud Land; (2) refine the geochronology of the Ferrar Group with the application of U/Pb zircon dating as well as 40Ar/39Ar dating; (3) establish the timing of alteration of the Vestfjella lavas and other post-crystallization events recorded by secondary minerals in Dronning Maud Land; and (4) evaluate possible relationships of Dronning Maud Land magmatism and alteration to the Lebombo Monocline in southern Africa and to the Ferrar Group and other magmatism associated with Gondwanaland break-up. Mineral samples will be used to date the events using the 40Ar/39Ar, U-Pb, and Rb-Sr methods. The minerals include: primary igneous phases (feldspar, biotite, zircon) that will be the focus for establishing timing of ma gmatic events; and, secondary phases (apophyllite, phyllosilicate) to address timing of alteration events. Based upon recent experience and success in related studies, the results are expected to have broad implications not only for specific questions dealing with the region but also for tectonic models and geochronologic methods. The results will address: Gondwanaland break-up; spatial and temporal relations of magmatism in Antarctica; tectonic models for the generation of flood basalt provinces; and, application of geochronologic methods, especially to altered basic igneous rocks.