Early seafloor spreading and variations in crustal accretion in the Lau Basin

Abstract

Recent geophysical mapping of the western Lau Basin in combination with previously interpreted data has provided a more detailed picture of the basin's early opening history. This thesis focuses on updated compilations of bathymetric, magnetic field and acoustic imagery data in combination with petrologic and seismic data. Expanding on previous magnetic inversions [Taylor et al., 1996; Zellmer and Taylor, 2001] which account for the influence of field skewness and bathymetric relief on the magnetic field, inversion of additional data has led to a new seafloor magnetization map of the basin. This, in conjunction with bathymetric data, resolves distinct terrains throughout the basin, including abyssal hill fabric in the western basin. These N-S oriented ridges and their affiliated magnetic anomalies indicate that organized seafloor spreading initiated earlier in the basin's history than previously interpreted, along now extinct spreading centers in the western basin. Other variations in the fabric of the western basin can be attributed to a broad array of processes beyond rifting and organized spreading, including hummocky terrain indicative of diffuse magmatism and seamounts that may once have been a proto-arc for the nascent basin. A variety of morphologies is not only found within the western basin, but throughout the Lau Basin. This range is evidence that the opening history involved a diversity of crustal production mechanisms due to abrupt variations in the underlying mantle wedge from which crust formed.