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Early Stages of Gondwana Break-Up |
Department of Geological Sciences and Byrd Polar Research Center, The Ohio State University, Columbus, Ohio 43210, USA
Magmatic and tectonic activity in Antarctica associated with the early stages of continental rifting and break-up of Gondwanaland culminated with tholeiitic magmatism at about 175–180 Ma. In the Ross Sea sector of the Transantarctic Mountains, Jurassic igneous rocks, comprising pyroclastic rocks and Ferrar Group tholeiitic basalts, overlie fluvial strata of the Permian-Upper Triassic Gondwana sequence. Petrological, structural and volcanological data suggest that the Jurassic pyroclastic rocks and overlying flood basalts were erupted into a volcano-tectonic rift system associated with lithospheric extension and decompression melting. Geochemically the Ferrar tholeiites form part of the Gondwana low-Ti province, but they exhibit marked differences in initial 87Sr/86Sr ratios and in high field strength element abundances in comparison with other parts of the province.
Three Early to Middle Jurassic tectono-magmatic terrains were present in this part of Gondwanaland: a plate margin magmatic arc; a belt of silicic within-plate igneous rocks inboard of the arc; and a continental flood basalt province (the Gondwana low-Ti province). Silicic volcanism mainly preceeded emplacement of Ferrar tholeiites, whereas major silicic activity elsewhere either accompanied basaltic magmatism or, though spatially separated preceded it. Younger magmatic episodes have obscured much of the plate margin record. Lack of reliable age determinations makes details of relations between tectonism and magmatism difficult to assess.
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