Tectonic reconstructions in magnetic quiet zones: Insights from the greater Ontong Java Plateau

A substantial portion of the Pacifi c basin is composed of seafl oor formed during the Cretaceous Normal Superchron (CNS). Because this region lacks the magnetic lineations typically required to constrain tectonic reconstructions, we employ additional methods for interpreting CNS Pacifi c history, involving seafl oor fabric, basement paleolatitudes, and age data. We utilize seafl oor fabric, including fracture zones and the rift margins of large igneous provinces, to derive quantitative rotations. The timing of such rotations is constrained using rock ages, bounding magnetic isochrons, and estimates of interactions with surrounding terrains. The method relies on highresolution shipboard bathymetry and rock ages, as much fi ne-scale seafl oor fabric useful for reconstructions is not visible in satellite altimetry data. We show that the Ontong Java, Manihiki, and Hikurangi oceanic plateaus likely originated as one large superplateau, the Ontong Java Nui (OJN). Reconstructions of OJN at 123 Ma reveal large offsets between observed and predicted paleolatitudes. Observed paleolatitudes exhibit a systematic bias, which may be attributed to large-scale rotation of the entire plateau. Such a rotation would imply either that OJN was initially decoupled from the Pacifi c plate and able to rotate independently or that the orientation of the Pacifi c plate at 123 Ma differed from conventional model predictions. However, large uncertainties in absolute plate motion models prior to ca. 80 Ma preempt a conclusive interpretation for OJN formation. Given an ~10 km resolution limit for satellite altimetry, continued investments in seagoing research will be needed to investigate tectonic events in magnetic quiet zones.