Magmatism of the Weddell Sea rift system in Antarctica: Implications for the age and mechanism of rifting and early stage Gondwana breakup

• Published in: Gondwana research 2020-03, Vol.79, p.185-196
• Main Authors: Riley, Teal R., Jordan, Tom A., Leat, Philip T., Curtis, Mike L., Millar, Ian L.
• Format: Article
• Language: English
• Subjects: Back-arc extension; Basalts; Ferrar; Gondwana; Large igneous province
• ISSN: 1342-937X; 1878-0571
• DOI: 10.1016/j.gr.2019.09.014

Thick (∼800 m) basaltic successions from the eastern Antarctic Peninsula have been dated in the interval 180–177 Ma and preserve a transition from a continental margin arc to a back-arc extensional setting. Amygdaloidal basalts from the Black Coast region of the eastern margin of the Antarctic Peninsula represent a rare onshore example of magmatism associated with back-arc extension that defines the early phase of Weddell Sea rifting and magmatism, and Gondwana breakup. The early phase of extension in the Weddell Sea rift system has previously been interpreted to be related to back-arc basin development with associated magnetic anomalies attributed to mafic-intermediate magmatism, but with no clearly defined evidence of back-arc magmatism. The analysis provided here identifies the first geochemical evidence of a transition from arc-like basalts to the development of depleted back-arc basin basalts in the interval 180–177 Ma. The exposed Black Coast basaltic successions are interpreted to form a minor component of magmatism that is also defined by onshore sub-ice magnetic anomalies, as well as the extensive magnetic anomalies of the southern Weddell Sea. Back-arc magmatism is also preserved on the Falkland Plateau where intrusions postdating 180 Ma are associated with early phase rifting in the Weddell Sea rift system. Back-arc extension was probably short-lived and had ceased by the time the northern Weddell Sea magmatism was emplaced (