Rapid Formation of the Ellice and Osbourn Basins and Ontong Java Nui Breakup Kinematics

Breakup of the proposed greater Ontong Java Nui large igneous province during the Cretaceous Normal Superchron can be constrained by the opening of the Ellice Basin (EB) separating the Ontong Java and Manihiki Plateaus and the Osbourn Basin separating the Manihiki and Hikurangi Plateaus. Dating of recovered dredged samples using plagioclase Ar-40/Ar-39 and zircon U/Pb geochronology methods indicates that spreading was well underway in the EB by 118 Ma with full spreading rates up to 3X faster than any observed today of 30-45 cm/yr and spreading likely continued until 112-108 Ma. Ellice Basin samples show diverse geochemical affinities ranging from mid-ocean ridge basalt (MORB) or Ontong Java-like to more enriched OIB-like. Pb and Nd isotopes from six samples contain varying influences from Pacific MORB and possibly Ontong Java. The geochemistry shows a lack of a clear mantle plume influence despite EB's close temporal and spatial relationship to Ontong Java, while some data resemble the Louisville Seamounts. This compositional diversity complements morphological differences among dredge sites and shows that both in situ MORB and younger overprinted features related to the nearby Tuvalu Seamounts were sampled. Ar-40/Ar-39 geochronology confirms the age of International Ocean Discovery Program Site U1365 near the Osbourn Trough (OT) to be 102.60 +/- 0.26 Ma (2 sigma, n = 18). This age constrains the timing of a spreading reorientation event observed in the OB to coincide with a global plate reorganization event around 105 Ma and estimates the cessation of spreading at the OT to 96 Ma. Plain Language Summary Ontong Java Nui is proposed to have been the largest volcanic system on Earth when it erupted about 120 million years ago on the sea floor in the Pacific Ocean. Shortly after it erupted, plate tectonics supposedly split this massive volcanic feature into five fragments that drifted away from each other. We present new age and geochemistry results from samples collected in two ocean basins that separate the three main fragments of this feature still located in the western Pacific Ocean. We suggest that all three fragments separated extremely rapidly, possibly as much as 3X faster than any plate tectonics today and stopped in roughly their current configuration only 20 million years after they began to spread. We also show that the source of magma in one of the basins, the Ellice Basin (EB), differed slightly from the initial volcanism that made up Ontong Java Nui as a whole. These are the first ages and geochemistry data for the EB, and they, along with our new ages from the Osbourn Basin, are critical to further understanding the eruption and breakup history of Ontong Java Nui.

Automated summary

About 120 million years ago, a large amount of lava erupted on the Pacific Ocean floor, forming the proposed largest volcanic system on Earth called Ontong Java Nui. Plate tectonics then caused this system to break up into five fragments, which drifted away from each other in the western Pacific Ocean. By analyzing dated samples and conducting geochemical analysis, it has been found that these three main fragments separated extremely rapidly, possibly 3 times faster than current plate tectonics, and stopped spreading in their current configuration about 20 million years after the initial eruption. Additionally, the magma source in the Ellice Basin and Osbourn Basin differed slightly from the initial volcanism of Ontong Java Nui as a whole. These new age and geochemical data are crucial for further understanding the eruption and breakup history of Ontong Java Nui.