Computational Modelling of the Continental Collision near South Island, New Zealand

English Abstract:

Among tectonic plate boundary types, the process of continental collision is poorly resolved, especially compared to the evolution of subduction, spreading, and transform plate boundary systems. There is still debate about the first-order response of the mantle lithosphere (sub-crustal lithosphere), such as whether there is distributed pure shear-type thickening, subduction-like consumption of the sub-crustal portions of the plate, or a combination of these two. This work explores in more detail a number of questions regarding the dynamics of the coupled crust and mantle lithosphere at continental collision. It focuses on the active continental convergence occurring at the South Island of New Zealand as a natural prototype for collision. The modest amount of shortening in this collision and relative abundance of observational constraints make this an ideal locale for studying the geodynamic processes of early orogenesis — a key step in understanding continental collisions generically. An important feature of the South Island tectonics is the highly oblique nature of the plate collision meaning high rate of along-strike material transfer. The oppositely verging subduction zones bounding the collision likely have their own influence on the deformation. However, previous studies on modelling the dynamics of the South Island collision have not included these important factors in the direction parallel to the plate boundary; instead considering this as a two-dimensional problem. In the scope of the research, we are conducting 3D geodynamical modelling to explore these tectonic questions for the collision. Here, we present the first results of forward computational modelling of the transpressional lithospheric system demonstrating the influence of rheology and varied rates of strike-slip versus convergent plate motion on the structures formed.