Episodic rifting of a large igneous province concentrated along a microcontinent boundary

Many large igneous provinces (LIPs) comprise once contiguous magmatic products that are now fragmented across multiple tectonic plates. Emplacement of these voluminous magmatic products is commonly coeval with, or shortly followed by, fragmentation into constituent domains. However, the Kerguelen LIP, predominantly within the southern Indian Ocean, rifted after an unusually protracted c. 45 Myr interval post-emplacement. To investigate this protracted post-emplacement rifting, a recent voyage by the RV Investigator sampled the conjugate margins of the Kerguelen Plateau, William's Ridge (WR) and Broken Ridge (BR) for the first time. Dredged volcanic rocks were characterized using petrographic, geochemical (major and trace element, Sr-Nd-Pb-Hf isotopes) and geochronological (⁴⁰Ar/³⁹Ar) techniques. Here, we focus on the sampled 82–67 Ma tholeiitic volcanic rocks. The observed geochemical data in conjunction with rare earth element inversion modeling of these Late Cretaceous volcanic rocks reflect plume–ridge interaction with variable assimilation (≤10%) of continental crust. We propose that the Kerguelen plume transported melt to the WR–BR margin during episodes of extension. Extension and magmatism were localized along the rheologically weak margins of the WR microcontinent. The combination of these mechanically weak boundaries and earlier extensional events facilitated a final ridge jump into the WR–BR margin at c. 44 Ma. We demonstrate a pre-existing history of extension in the Late Cretaceous prior to complete fragmentation in the Eocene, resolving the apparent protracted interval between emplacement and separation of the Kerguelen LIP.