Numerical modeling and analysis of neotectonics in New Zealand: An integrated study of faults, lithosphere dynamics, continental collision and orogeny, and coupling of surface erosion with mantle processes.

摘要

I applied thin-shell, 2-D, and 3-D finite element modeling techniques, combined with available geophysical and geological observations, to investigate major tectonic issues of New Zealand neotectonics that are not clear or less thoroughly studied.; I constructed “realistic” thin-shell models that include faults and variations in elevation, heat flow, and thickness of the crust and mantle lithosphere. I did numerous calculations to systematically test the primary unknown parameters. Fault slip rates, stress direction, and geodetic velocities were used to determine the best-fitting neotectonic model of New Zealand. I have found that the faults in New Zealand have effective fault friction ∼0.17. Tectonic deformation has different styles across the country. The long-term average slip rate of the Alpine fault is varying along its strike, generally increasing northeastward until slip is partitioned among the strands of the Marlborough system. There is a very complicated slip partitioning in the transition zone from the southern Alpine fault to the Puysegur trench. Tectonic deformation in North Island is jointly controlled by a balance between gravitational potential energy difference and traction from the Hikurangi subduction thrust. Hikurangi forarc is an independent plate sliver moving relative to the Pacific and Australia plates. An active thrust fault may exist offshore SE coast of South Island.; To resolve the controversy about how mantle lithosphere deforms under oblique convergence beneath the central South Island, I developed 2-D and 3-D models that fit gravity anomalies, travel time delays, and published crust and mantle structures. I presented theory and techniques for numerical methods. I also developed coupled erosion-tectonic models to study the effects of erosion and sedimentation. I considered three proposed mantle processes. The surface topography, uplift rate, isostatic gravity anomaly, deep seismicity, and magnetotulleric results were used to determine the preferred model. Both 2-D and 3-D models prefer the Australia plate wedge model. Preexisting fault structures have a significant influence on tectonic deformation in central South Island. Tectonic transpression plays a major role in determining surface topography distribution while surface erosion influences the landscape evolution only as a 2 nd-order effect. Strong erosion indirectly influences stress state in the lithosphere by thermal perturbation. In the presence of preexisting fault structures I show that the strike-slip weakening is not a major cause of the viscosity variation in the central Southern Alps, contrary to the suggestion of some other studies.