Nature and preservation of Late Jurassic breakup-related volcanism in the carnarvon basin, North West shelf, Australia

The North West Australian Margin, which formed as Greater India rifted from Australia during the Jurassic to Early Cretaceous, is recognised as an archetypal magma-rich rifted margin, with records of extensive igneous activity in the Exmouth Plateau and Exmouth Sub-Basin (ESB) of the Northern Carnarvon Basin (NCB). Pre-breakup magmatism is manifested by a large ∼400 × 150 km intrusive sill complex, emplaced into Triassic and Jurassic strata in the Late Jurassic and Early Cretaceous. An apparent lack of extrusive igneous rocks has caused previous works to describe the region as a large intrusive igneous province. Here, we describe two recently identified Upper Jurassic volcanic centres: the Pyrenees Volcano in the eastern ESB (first reported here), and the Toro Volcanic Complex (TVC), in the western ESB. Although offset by Early Cretaceous normal faulting, the edifice of the Pyrenees Volcano and associated lava flows are well preserved beneath a protective carapace of Upper Jurassic strata below the angular Intra-Hauterivian Unconformity on the Novara Arch. In contrast, a significant proportion of the TVC was peneplaned beneath an intra-Valanginian (Early Cretaceous) unconformity following breakup-related uplift. As Upper Triassic to Lower Cretaceous strata appear to have been eroded over the Ningaloo Arch in the southern ESB, we postulate that Late Jurassic extrusive volcanism may have been more spatially extensive, prior to erosion associated with Early Cretaceous exhumation in the southern NCB. Hence our findings suggest that the NCB was potentially host to significantly more extrusive volcanism than has been preserved within basin fill. Our findings also have broader implications for the conditions required to preserve extrusive igneous material in sedimentary basins within large igneous provinces that have undergone complex histories of rift-related vertical motion.