Modeling, Visualizing, and Understanding Complex Tectonic Structures on the Surface and in the Sub-Surface

Steven Wild, Old Dominion University

Abstract

Plate tectonics is a relatively new theory with many details of plate dynamics which remain to be worked out. Moving plates can interact by divergence, lateral sliding, convergence, or collision. At a convergent plate boundary, a lithospheric slab of oceanic crust and upper mantle is subducted at a trench and dips down under a magmatic arc — either oceanic or continental. Textbooks show a static view of convergent boundaries but plate dynamics require that subduction zones and magmatic arcs must migrate with time. Therefore I develop animated models to help convey this motion. Also, convergent plate boundaries cannot continue along strike or down dip indefinitely without changing. Subduction zones change orientation and eventually terminate. They may bend and shear or tear and open a window for asthenospheric flow.

Two different convergent plate boundaries are the primary focus of my studies: the Tonga subduction zone where the Pacific plate moving beneath an island arc is torn along the Samoan Island Archipelago, and the Andean subduction zone in central South America where the Nazca plate moves beneath a continental arc. I choose these zones because they exhibit tears or shears, where subduction stops, or changes dip suddenly. To examine these features I use several modeling and visualization techniques. COLLADA (COLLabrative Design Activity) models in Google Earth and Google Earth Application Programming Interface (API) are used for visualizing and teaching of plate boundary systems. The testing of COLLADA models for geoscience concepts showed positive learning gains. Kinematic models are made to study strain rates and possible methods of plate evolution. Dynamic COMSOL numerical models are created to probe temperature and flow fields in the subduction zone. Animated COLLADA models are designed for different models of subduction initiation and development for the Tonga trench for both research and educational purposes. The development of these models led to a new hypothesis of this region's formation. Using these models and Google Earth materials studies in undergraduate classes tested the effectiveness of Google Earth based lab activities for enhancing student understanding of geoscience.

In the central Andean subduction zone, emergent COLLADA models are made from mining GeoMapApp (http://www.geomapapp.org) and published contour data to demonstrate the unique geometry of the Nazca plate having adjacent subduction angles of 10° and 30°. This led to the research question, can the Nazca plate support this geometry by shearing without tearing? A literature review shows efforts to explore this topic by means of hypocenter, teleseismic, and thermal data to have no consensus on the topic. To this end a new approach is taken to examine this region by applying the methods of kinematic and dynamic modeling to further explore this question. These different models of the Andean system lead to the conclusion that no major magmatic window could have opened between the fiat and steep subduction areas given the time and deformation mechanisms available.