Episodic silicic volcanism in Patagonia and the Antarctic Peninsula: Chronology of magmatism associated with the break-up of Gondwana

New SHRIMP U-Pb zircon, Rb-Sr whole-rock, and Ar-40-Ar-39 data are presente d for the Jurassic silicic volcanic rocks and related granitoids of Patagon ia and the Antarctic Peninsula. U-Pb is the only reliable method for dating crystallization in these rocks; Rb-Sr is prone to hydrothermal resetting a nd Ar-Ar is additionally affected by initial excess Ar-40. Volcanism spanne d more than 30 My, but three episodes are defined on the basis of peak acti vity: V1 (188-178 Ma), V2 (172-162 Ma) and V3 (157-153 Ma). The first essen tially coincides with the Karoo-Ferrar magmatism of South Africa, Antarctic a and Tasmania. nle silicic products of V1 are lower-crustal melts that hav e incorporated upper-crustal material. The geochemistry of V2 and V3 ignimb rites is more characteristic of destructive plate margins, bur the presence of inherited Zircon still points to a crustal source. The pattern of volca nism corresponds in space and in time to migration away from the Karoo mant le plume towards the proto-Pacific margin of Gondwana during rifling and Br eak-up. The heat required to initiate bulk crustal fusion may have been sup plied by the spreading plume-head, but thinning of the crust during contine ntal dispersion would also have facilitated anatexis.