Episodic Silicic Volcanism in Patagonia and the Antarctic Peninsula: Chronology of Magmatism Associated with the Break-up of Gondwana

Abstract

data are presented for the Jurassic silicic volcanic rocks and related Jurassic magmatism in western Gondwana constituted granitoids of Patagonia and the Antarctic Peninsula. U-Pb is the the most voluminous episode of continental volcanism in only reliable method for dating crystallization in these rocks; Rb-Sr the Phanerozoic era. During Early-Middle Jurassic time, is prone to hydrothermal resetting and Ar-Ar is additionally affected some (25-3) 10 6 km 3 of basalt and, to a lesser extent, by initial excess 40 Ar. Volcanism spanned more than 30 My, but rhyolite were erupted onto the supercontinent in its early three episodes are defined on the basis of peak activity: V1 (188-178 stages of break-up. Recent high-precision geochronology Ma), . The first (U-Pb and Ar-Ar) has shown that much of the basalt essentially coincides with the Karoo-Ferrar mafic magmatism of volcanism occurred during a very short period around South Africa, Antarctica and Tasmania. The silicic products of 183-184 My ago The geochemistry of V2 and V3 ignimbrites is more of the silicic volcanism have so far been lacking. This characteristic of destructive plate margins, but the presence of inherited paper is concerned with the chronology of the largest of zircon still points to a crustal source. The pattern of volcanism these silicic outbursts, the Jurassic volcanic province of corresponds in space and in time to migration away from the Karoo Patagonia and the Antarctic Peninsula. Although the mantle plume towards the proto-Pacific margin of Gondwana during emphasis here is on the geochronology and its significance rifting and break-up. The heat required to initiate bulk crustal for the history of volcanism, full geochemical and isotopic fusion may have been supplied by the spreading plume-head, but data will be presented in a companion paper (Riley et thinning of the crust during continental dispersion would also have al., 2000), which will also deal more completely with the facilitated anatexis.