Geodynamics Climatic, geomorphic and geodynamic processes Lecture 13.3 - Orogenic wedges Lecturer: David Whipp david.whipp@helsinki.fi Geodynamics www.helsinki.fi/yliopisto 1
Goals of this lecture Introduce orogenic wedges and how they used to study mountain systems 2
Orogenic wedges Processes Plate convergence, detachment of the mantle lithosphere and crustal thickening build the orogen Orogenic wedges form at the sides of the orogen, facilitating upward and outward growth with a stable geometry Convergence adds mass to the orogen, modifying the stress state in the wedges and leading to growth Beaumont et al., 2000 3
Orogenic wedges Processes Plate convergence, detachment of the mantle lithosphere and crustal thickening build the orogen Orogenic wedges form at the sides of the orogen, facilitating upward and outward growth with a stable geometry Convergence adds mass to the orogen, modifying the stress state in the wedges and leading to growth Beaumont et al., 2000 4
Example orogenic wedge: Taiwan Orogenesis in Taiwan is driven by collision between the Philippine plate and the Eurasian plate To the north, the Philippine plate is subducted beneath Eurasia, but things are more complicated in central Taiwan The tectonics here are complex, but the main structures in the orogen are a series of parallel thrust faults running the length of the island Malavielle and Trullenque, 2009 5
Example orogenic wedge: Taiwan Malavielle and Trullenque, 2009 Plate convergence produces significant internal deformation and uplift Bounding the central section of the orogen are two orogenic wedges, where new material is incorporated in this active orogen 6
Example orogenic wedge: Taiwan Malavielle and Trullenque, 2009 Plate convergence produces significant internal deformation and uplift Bounding the central section of the orogen are two orogenic wedges, where new material is incorporated in this active orogen 7
Orogenic wedges Processes The key here is that the stress state in the wedges is at or near plastic failure when the orogen is growing Any modification to the topography, such as by erosion, will change the geometry of the wedge, which will alter the location of deformation in the orogen in order to restore the stable wedge geometry Beaumont et al., 2000 8
Orogenic wedges Processes The key here is that the stress state in the wedges is at or near plastic failure when the orogen is growing Observations Any modification to the topography, such as by erosion, will change the geometry of the wedge, which will alter the location of deformation in the orogen in order to restore the stable wedge geometry Beaumont et al., 2000 9
Let s see what you ve learned If you re watching this lecture in Moodle, you will now be automatically directed to the quiz! Reference(s): Beaumont, C., Kooi, H., & Willett, S. D. (2000). Coupled tectonic-surface process models with applications to rifted margins and collisional orogens. In M. A. Summerfield (Ed.), Geomorphology and Global Tectonics (p. 367). West Sussex, U.K.: John Wiley & Sons, Ltd. Malavieille, J., & Trullenque, G. (2009). Consequences of continental subduction on forearc basin and accretionary wedge deformation in SE Taiwan: Insights from analogue modeling. Tectonophysics, 466(3 4), 377 394. 10