One of the most interesting developments in geosciences over the last decade has been a new understanding of the complex interaction of surface processes and tectonics in active mountain belts. Much of the initial work was based on the Southern Alps of New Zealand. Evidence suggests that focused erosion strongly influences the position of deformational fronts, localization of faults, and deeper seated flow of the lithosphere. Mechanical modelling has played an important role in the development of these ideas and Dr Phaedra Upton at the University of Otago, in conjunction with her colleagues at the University of Maine, is actively involved in this research.
This is an NSF funded project through the University of Maine, in collaboration with Associate Professors Karl Mueller and Greg Tucker and their students at the University of Colorado, Boulder. The aim of the project is to investigate the nature of coupling between tectonics and erosion in west-central Taiwan. We plan to document along-strike variations in late Quaternary compressive strain in western Taiwan, where regional topographic gradients, probably related to more rapid late Quaternary erosion, appear to correlate with modern strain gradients and patterns of crustal thickening, including hindward reactivation of thrust sheets. The Puli embayment in the west-central Taiwan fold-thrust belt lies approximately 1500 meters lower than the neighbouring mountains along strike to the north and south. Preliminary geologic and geodetic evidence suggests that thrusting occurs over the width of the topographic depression; instead of being concentrated at the front of the thrust belt, as is the case in the adjacent part of the thrust belt where the topography maintains a classic wedge shape.
My contribution to the project is three-dimensional thermo-mechanical modelling. I use these models to test and refine our ideas of a feedback mechanism between topography, erosion and wedge deformation. Initial results suggests that there are two features of the region which contribute to the topographic signal we observe
- Weaker, less dense sediments have been incorporated into the orogen in the Puli region as a result of the presence of a depocentre along this portion of the orogen. Being weaker, these sediments deform more readily than the slates and shales that surround them. This focuses uplift and deformation into this region.
- The weaker sediments are more easily eroded, thus material is removed more rapidly from this part of the orogen. This also affects the form of the resultant mountain range.
Upton, P., Mueller, K. and Chen Y-G.,* *Influence of lateral variations in material properties and erosion rate on the mechanics/kinematics/form of a three-dimensional wedge: results from numerical models. /Submitted to Journal of Geophysical Research – Solid Earth/
This is an NSF (Continental Dynamics) funded project through the University of Maine with 9 other institutions. This project focuses on an area in southern Alaska with possibly the highest signal for erosion-tectonic interaction on earth. The orogen contains the highest coastal mountain range on earth being attacked by glacial erosion at possibly the highest rates on earth, and deformation is occurring at some of the highest rates within continental crust anywhere. Also, because the St. Elias Mountains sit at the end of the Pacific storm track, the growth of the orogen substantially influences the climate of the whole region. Our modelling component of the study will concentrate on the controls on deformation, including far-field boundary conditions, erosion and material properties.
Berger, A.L., Gulick, S.P.S., Spotila, J.A., Upton, P., Jaeger, J.M., Chapman, B., Worthington, L.A., Pavlis, T.L., Ridgway, K.D., Willems, B., and McAleer, R.J., Quaternary tectonic response to intensified glacial erosion in an orogenic wedge. /Accepted pending revision Nature Geoscience/
I am working with Rasmus Theide (University of Minnesota) and Manfred Strecker (University of Potsdam) to quantify the temporal and spatial scales at which coupling between focused erosion and tectonics is occurring in the Sutlej region of the Himalaya, NW India.