Timing and distribution of Early Cretaceous syn-rift volcanism on the southwestern Australian rifted continental margin

2D seismic reflection data and results from the Deep Sea Drilling Project and International Ocean Discovery Program (IODP) constrain the final stages of breakup between Greater India and Australia during opening of the eastern Indian Ocean. Breakup occurred between 136-134 Ma on the Perth Abyssal Plain (PAP) adjacent to the central part of the western Australian margin and ca. 126-124 Ma adjacent to the Naturaliste Plateau (NP) on the southern part of the margin. Extension between the NP and continental shelf formed the deepwater Mentelle Basin (MB) during the interim. Breakup on the southwestern Australian margin was accompanied by eruption of the Bunbury Basalt in the Perth Basin beneath the continental shelf from 137-130 Ma. Similar age basalts were encountered in dredges from the NP (132-129 Ma) and at IODP Site U1513 (135-128 Ma), where the eastern NP is onlapped by syn-rift strata of the western MB. Volcaniclastic strata age 134-126 Ma overlaying the basalts at Site U1513 indicate that the NP remained above wavebase until final breakup from India. Seismic data show the volcaniclastic strata extend into the eastern MB, where it interfingers with a westward thickening wedge of clastic strata shed from the continental shelf. High amplitude reflectors within the volcaniclastic unit in the eastern MB are similar to (but stratigraphically above) reflectors from the basalt flows at Site U1513, and are interpreted to be caused by laterally extensive (up to 20 km) flows interbedded within the volcaniclastic unit. High amplitude 1 3 km wide conical features near the top of the volcaniclastic unit in the central and eastern MB are interpreted as small volcanic vents. We thus infer that volcanism in the eastern MB continued until the time of breakup west of the NP and that the NP, MB, and southern PB hosted a broad eruptive complex during the final stages of breakup. The flows in the eastern MB are concentrated above a series of conical reflectors spanning 15 km breadth that lie immediately below the volcanic/volcaniclastic strata. This feature aligns with the edge of oceanic crust in the PAP, and is interpreted to be a failed southern extension of the PAP spreading center that became inactive as the PAP spreading center migrated westward along the northern edge of the NP prior to final breakup between Australia and India at 126 Ma.