Plate tectonics of New Zealand: insights from 3D thermomechanical modelling
More Info
expand_more
Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.
Abstract
New Zealand sits on an oblique convergent plate boundary between the Australian plate in the east, and the Pacific plate in the west. The tectonic setting comprises two opposing subduction zones, Hikurangi (ca. 25 Ma) in the north and Puysegur (ca. 20-6 Ma) in the south, and a transpressional continental transform fault, the Alpine Fault (ca. 23-22 Ma), linking the two subduction zones. Despite New Zealand being well-studied through several geological and geophysical methods, the dynamic evolution of the processes involved in the subduction zones and the continental transform are still not clear. An exploratory investigation, which employs 3D thermomechanical numerical modelling, is conducted in order to gain insights into the dynamic tectonic evolution of New Zealand. The finite-differences code (‘I3ELVIS’) iteratively solves the conservation laws (mass, momentum, and energy) in a staggered grid. The study focuses on three aspects of the dynamic evolution: (i) the 3D geometric and structural development; (ii) the topographic development; and (iii) the faults/stress development. Four sets of models are constructed to study the influence of prescribed weak-zones’ geometry on New Zealand’s tectonic evolution. The modelling results indicate that the continental transform system does not appear to be attaining a steady state. The results exhibit key tectonic features such as an oblique continental transform and the migration of subduction zones into the transform, all of which are consistent with natural observations. The interpretations of modelling results reflect (3D) structural development of the transform which are comparable to the interpretation of seismic survey transects. The observed key structural features are the steeply-dipping Alpine Fault, the thickening of the lower continental crust, and the presence of thrusting fault-blocks in the upper continental crust. An observed set of splay faults in the modelling results reflect the similarities, in faults and stress development, to the the Marlborough Fault System.