Landscape Response to Oblique Convergence: Insights from Numerical Modeling and from the Marlborough Fault System, New Zealand

Abstract

Strike-slip and oblique faults are prominent tectonic features that can dramatically influence the landscape at all scales. In this dissertation, I explore the effects of strike-slip and oblique faults on the landscape, from the scale of orogenies to individual river channels. I focus on the Marlborough Fault System, a multi-strand strike-slip fault system in New Zealand, at the transition between the Hikurangi Subduction Zone and the oblique Alpine fault. In Chapters 2 and 3 I use low-temperature thermochronology to investigate tectonic histories by interpreting timing and relative rates of exhumation across the landscape. Chapter 2 reveals the 10-13 Ma development of the Wairau fault, the resultant formation of a restraining bend at the Alpine-Wairau fault junction, and the onset of exhumation in a broad region caused by this restraining bend. In Chapter 3, using the same method, I identify the earliest manifestation of the Early Kaikōura Orogeny, with exhumation focused on the (present-day) north side of the Awatere fault beginning in the early Eocene. In the western MFS, the modern MFS faults do not exert a strong control on exhumation. I invert thermochronology data from Chapters 2 and 3, with other published data, for recent exhumation rates across the MFS. Exhumation rates are ~3-3.6 mm/yr adjacent to the Alpine fault, and ~0.9-1.4 mm/yr in the Seaward Kaikōura range. In Chapter 4, I use a landscape evolution model to determine the effects of preexisting topography on the landscape expression of a strike-slip fault. Modeled channels crossing a strike-slip fault were subject to a regular and effective cycle of channel offset by fault slip and shortening by stream capture. Relief of shutter ridges makes stream capture more difficult, especially when the fault slip rate is slow relative to channel and hillslope erosion. Comparison to the MFS shows that real-world complexities – such as lithological variations – can disrupt these expected patterns, allowing long, fault-parallel channel offsets to form. Videos 1-5 show example models from Ch.4: 1 shows the initial condition; 2, a faster-slipping fault; 3, a slower-slipping fault; 4 and 5, a stream channel “evading” capture. Attached dataset contains model input files.