Systematic variations in morphological characteristics of global transform faults

We quantify systematic variations in morphological characteristics of global transform faults and investigate their dependence on spreading rate, local magma supply, and other tectonic variables. Detailed analyses were conducted on 78 transform faults where high-resolution multibeam bathymetry and other geophysical data are available. The investigated transform systems span a wide range of spreading rate and local magma supply, including examples from the East Pacific Rise, Juan de Fuca Ridge, Chile Rise, Pacific-Antarctic Ridge, Southeast Indian Ridge, Central Indian Ridge, Mid-Atlantic Ridge, American-Antarctic Ridge, Southwest Indian Ridge, and other systems. The analyses revealed systematic global and local variations in transform morphological characteristics: (1) The average lengths of the investigated systems show a moderate increase in transform age offset with decreasing spreading rate. The average transform lengths for the investigated fast, intermediate fast, slow, and ultra-slow systems are 1.0 Ma (standard deviation σ = 0.9 Ma), 1.5 Ma (σ = 0.9 Ma), 2.2 Ma (σ = 1.7 Ma), and 5.3 Ma (σ = 3.5 Ma), respectively, corresponding to average transform length of 111 km (σ = 75 km), 81 km (σ = 73 km), 71 km (σ = 40 km), and 92 km (σ = 49 km), respectively. (2) Morphological “hooks”, i.e., axial morphological highs that curve around a ridge-transform intersection, appear to be most distinctive in regions of relatively robust magma supply, especially at fast and intermediate fast ridges. (3) In contrast, “nodal basins” usually develop at the ridge-transform intersection of relatively slow spreading systems and low magma supply. The depth of the nodal basin appears to moderately increase with decreasing spreading rate with an average depth of 3.8 km (σ = 0.5 km) for the investigated systems. (4) For a subset of 11 selected transform systems with relatively good geophysical data coverage, the average depth calculated along the length of the transform faults are 3.4 km (σ = 0.5 km), 3.7 km (σ = 0.45), and 4.4 km (σ = 0.48 km) for the fast, intermediate fast, and slow systems, respectively. Thus the calculated values of average transform fault depth, ridge-transform intersection depth, and age-offset of the investigated systems all appear to increase with decreasing spreading rate. However, the observed relatively large values of standard deviations, as well as multiple examples of transform systems with major morphological and geophysical anomalies, appear to suggest the additional influence of local magma supply and other tectonic variables. We are currently conducting geodynamics models to investigate the mechanisms controlling these systematic variations.