Mantle processes during Gondwana break-up and dispersal |
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| Institution: | 1. Faculty of Science, Charles University, Albertov 6, CZ-12843 Prague, Czech Republic;2. Czech Geological Survey, Klárov 3, CZ-11821 Prague, Czech Republic;3. Institute of Geology, The Czech Academy of Sciences, Rozvojová 269, CZ-16500 Prague, Czech Republic;4. Institute of Geological Sciences, University of Wroc?aw, pl. M.Borna 9, PL-50234 Wroc?aw, Poland;5. Institute of Earth Physics, Masaryk University, Tvrdého 12, CZ-60200 Brno, Czech Republic;1. Institute of Geography and Geology, University of Würzburg, Am Hubland, 97074 Würzburg, Germany;2. Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa;1. Department of Geological Sciences, University of Cape Town, Rondebosch 7701, South Africa;2. Geology Department, Rhodes University, Grahamstown 6140, South Africa;3. Department of Geosciences and Geography, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland;4. Earth and Planets Laboratory, Carnegie Institution for Science, 5241 Broad Branch Road, NW, Washington, DC 20015-1305, United States of America;5. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA |
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| Abstract: | This paper reviews the Mesozoic continental flood basalts (CFBs) associated with the break-up and dispersal of Gondwana from 185-60 Ma, the conditions for melt generation in mantle plumes and within the continental mantle lithosphere, and possible causes for lithospheric extension. The number of CFB provinces within Gondwana is much less than the number of mantle plumes that are likely to have been emplaced beneath it in the 300 Ma prior to its initial break-up. Also, the difference between the age of the peak of CFB volcanism and that of the oldest adjacent ocean crust decreases with the age of volcanism during the break-up and dispersal of Gondwana. The older CFBs of Karoo and Ferrar appear to have been derived largely from source regions within the mantle lithosphere. It is only in the younger Paranâ-Etendeka and Deccan CFBs that there are igneous rocks with major, trace element and radiogenic isotope ratios indicative of melting within a mantle plume. These younger CFBs are also clearly associated with hot spot traces on the adjacent ocean floor. The widespread 180 Ma magmatic event is attributed to partial melting within the lithosphere in response to thermal incubation over 300 Ma. In the case of the Ferrar (Antarctica) this was focussed by regional plate margin forces. The implication is that supercontinents effectively self-destruct in response to the build up of heat and resultant magmatism, since these effects significantly weaken the lithosphere and make it more susceptible to break-up in response to regional tectonics. The younger CFB of Paranâ-Etendeka was generated, at least in part, because the continental lithosphere had been thinned in response to regional tectonics. While magmatism in the Deccan was triggered by the emplacement of the plume, that too may have been beneath slightly thinned lithosphere. |
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