Mantle processes during Gondwana break-up and dispersal

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 lit hosphere, and possible causes for lithospheric extension. The number of CFB provinces within Gondwana is much less than the number of mantle plumes th at are likely to have been emplaced beneath it in the 300 Ma prior to its i nitial break-up. Also, the difference between the age of the peak of CFB vo lcanism 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 Parana-Etendeka a nd Deccan CFBs that there are igneous rocks with major, trace element and r adiogenic isotope ratios indicative of melting within a mantle plume. These younger CFBs are also clearly associated with hot spot traces on the adjac ent ocean floor. The widespread 180 Ma magmatic event is attributed to part ial melting within the lithosphere in response to thermal incubation over 3 00 Ma. In the case of the Ferrar (Antarctica) this was focussed by regional plate margin forces. The implication is that supercontinents effectively s elf-destruct in response to the build up of heat and resultant magmatism, s ince these effects significantly weaken the lithosphere and make it more su sceptible to break-up in response to regional tectonics. The younger CFB of Parana-Etendeka was generated, at least in part, because the continental l ithosphere had been thinned in response to regional tectonics. While magmat ism in the Deccan was triggered by the emplacement of the plume, that too m ay have been beneath slightly thinned lithosphere. (C) 1999 Elsevier Scienc e Limited. All rights reserved.