Tectonic Reconstruction of the Ellice Basin

A geophysical survey of the Ellice Basin, located in the south equatorial Pacific between the Ontong Java and Manihiki plateaus, revealed evidence for an extinct seafloor spreading system between the Pacific Plate and the Manihiki Plate. The spreading occurred during the Cretaceous Normal Superchron, the longest normal period of magnetic polarity from 121 to 83 Ma, and therefore lacks magnetic-isochron-derived age and plate motion constraints. Utilizing high-resolution bathymetric data acquired on survey KM1609 during December 2016-January 2017, morphological and directional analyses were performed on the seafloor spreading fabric. Plate motion between the Pacific Plate and the Manihiki Plate during the Cretaceous Normal Superchron is described by three main stages of spreading. Stage 1 spreading was generally E-W until a clockwise rotation of the spreading direction rotated transform faults by similar to 15 degrees and lengthened spreading ridges to form Stage 2 zed pattern rhomboids. An offset between Stage 2 fracture zones evidences the presence of a complex and short-lived Stage 3. Reconstructions, with respect to the Pacific Plate, are created for each of the three stages. Our reconstructions show that there was an earlier opening history prior to Stage 1 that ultimately reconstructs the Ontong Java and Manihiki plateaus; its quantification will await high-resolution multibeam bathymetry data closer to the two plateaus.