Collaborative Research: Super-Plateau Breakup and Cretaceous Quiet Zone Tectonics

Oregon State University, Corvallis OR

Investigators

Abstract

Almost 30% of the Pacific plate south of the equator formed in a period where Earth's magnetic field was exceptionally stable. During this Cretaceous period, the Ontong-Java-Nui (OJN) volcanic outpouring also occurred, creating a large plateau (1/100 of Earth's area) that eventually split apart. With no reversals of the magnetic field to generate the characteristic crustal anomalies that allow scientists to track tectonic plate motions, it has not been possible to understand the cause-effect relation between this deep magmatic generation and the change in plate motion at the surface. While satellite measurements provide broad indication of seafloor structure, it is not possible to discern the narrow abyssal hills that would have formed at the fast spreading centers that controlled the plateau breakup. More detailed seafloor mapping and sampling are required. Undergraduate and graduate students will receive training in marine geological data acquisition during this study and some will participate in post-cruise analysis via class projects. Podcasts of a research seminar will extend the reach of the new knowledge. The OJN breakup is hypothesized to have occurred via spreading at the Osbourn Trough, along unmapped spreading centers in the Ellice Basin. Like other early Cretaceous oceanic plateaus, the OJN seems to have formed near a triple junction. Better understanding of Pacific tectonics during the Cretaceous normal superchron should shed light on the connections between oceanic plateau formation, breakup, plate reorganizations and associations with mantle plumes. In addition, paleolatitude data from the super-plateau remnants can to be tied to a common Pacific reference frame to refine the Pacific apparent polar wander path, which will then be compared with the Indo-Atlantic reference frame to determine the relative contributions from hotspot drift and true polar wander. Understanding evolution of OJN-linked processes is a long-term undertaking. This study takes the first step in this process with a multibeam survey of the Ellice Basin that will combine mapping of the central parts of this large basin where extinct spreading centers are likely to be located and remnants of fracture zones can be easily discerned. Coupled with selective dredging and Ar dating of basaltic rocks, as well as existing samples from IODP Site U1365 near Osbourn Trough, it will be possible to determine the timing of the inferred change in spreading direction, termination of Ellice Basin spreading, and the end of rifting along the Osbourn Trough.