New Bathymetry Reveals Detailed History of Transform Fault Segmentation at the Clarion Fracture Zone

Between 150°W and 135°W, the Clarion Fracture Zone (FZ) coalesces from six discrete FZ traces to a single FZ over a period of 30 million years, coinciding with a change in plate motion that placed the associated transform fault (TF) in compression. Although FZ observations suggest segmented TFs may unify to a single TF as a response to tectonic compression, little is known about the timing of this process, as well as how it may alter lithosphere structure. Using new bathymetry and gravity data from the Clarion FZ, we investigate this process through interpreted structural maps of the seafloor, numerical simulations of a segmented FZ, and modeling of gravitational anomalies. From 3154 mapped volcanic ridges and faults, we observe temporally correlated changes in intra-transform spreading center (ITSC) fabrics and plate motions that suggest that ITSC fabrics further from the center of the FZ responded to compressional changes in plate motion sooner (up to 5 million years) than ITSC fabrics located near the center of the FZ. Using the 2D finite-difference, visco-elastic-plastic code SiStER, we simulate the tectonic evolution of a differentially cooling lithosphere broken by several FZs and subject to compression or extension. We vary parameters such as the number of initial ITSC segments (0-4) and the rate of compression or extension (0-4.5 mm/year). In some model cases, we also vary the strength of the initial FZ offset by introducing small, low-viscosity weaknesses in the modeled lithosphere at the FZ. Gravity anomalies are calculated from the simulated lithospheric structure by using Talwani's 2D polygon algorithm. We then compare model predicted and existing satellite-derived gravity anomalies over the segmented Clarion FZ to constrain the relative timing of compressional changes along individual transform segment traces and structural changes within the FZ. Our observations suggest that compression and extension are not uniformly distributed across a segmented FZ and that ITSCs may impede stress transmission across a segmented TF.