Tectonomagmatic controls on Gondwana break‐up models: Evidence from the Proto‐Pacific Margin of Antarctica

Geochemical and isotopic data are presented that suggest the existence of a large, Middle Jurassic subduction‐related magmatic province common to both the Antarctic Peninsula and southern South America. We argue that during the initial stages of Gondwana breakup, Pacific margin magmas were derived from an enriched lithospheric mantle source similar to that for the contemporaneous within‐plate Ferrar‐Tasman suite. Enriched lithospheric initial‐rifting magmas were succeeded, in at least part of the Rocas Verdes basin, by transitional early drift magmas and then by entirely asthenospheric mid‐ocean ridge basalt (MORB) magmas representing lithospheric rupture and seafloor spreading. We propose a plate interaction model for the initial stages of Gondwana breakup relating the broad zone of lithospheric mantle melting to a reduction in plate boundary forces. The change from Gondwanide compression to lithospheric extension in the Jurassic is linked to a change from shallow to steeply dipping subduction and to a slowing of subduction rates caused possibly by a decreasing age of the subducting plate. Ridge‐trench interaction may have followed subduction of young, hot oceanic lithosphere, possibly causing a temporary cessation of subduction and a further reduction in plate boundary forces, thus facilitating breakup.