Quantifying Crustal Growth in Arc‐Backarc Systems: Gravity Inversion Modeling of the Lau Basin

Abstract The formation and evolution of arc‐backarc systems govern crustal production in some of the most volcanically and hydrothermally active environments on Earth. This study presents the first complete three‐dimensional density model of the active arc‐backarc system in the southwest Pacific comprising the Lau Basin and Tofua arc. Seafloor density and crustal thickness maps reveal changes in crustal composition and growth rates throughout the basin and along the volcanic arc. Crustal thickness varies significantly between the different centers of accretion (i.e., assemblages), resulting from seafloor spreading and subsurface melt accumulation below volcanic fields. Volumetric growth rates were calculated for each assemblage, corresponding to their respective contribution to basin expansion. The highest crustal density and growth rates are thought to be related to a mantle‐derived melt source entering the basin from the north around the edge of the subducting Pacific Plate. This study shows that the inverse modeling approach can be applied to global gravity data sets to characterize and quantify the density and thickness of the crust anywhere in the oceans.