Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Marine Geophysics
Document related concepts
Transcript
Marine Geophysics Plate tectonics 何小波 Dept. of Marine Sciences, Ocean College, Zhejiang University Nov. 8, 2016 Ocean College (ZJU) Plate tectonics [email protected] 1/1 Mantle flow and Plate tectonics Two suggested models of plate tectonics show how flow in the mantle might be related to plate movement. Book: Earth’s Dynamic Systems 10th Edition Ocean College (ZJU) Plate tectonics [email protected] 2/1 Convergent plate boundaries Book: Earth’s Dynamic Systems 10th Edition Ocean College (ZJU) Plate tectonics [email protected] 3/1 Convergent plate boundaries Possible modes of behavior of oceanic lithosphere at convergent plate boundaries: Ocean College (ZJU) Plate tectonics [email protected] 4/1 Convergent plate boundaries Possible modes of behavior of oceanic lithosphere at convergent plate boundaries: Ocean College (ZJU) Plate tectonics [email protected] 5/1 Forces active on the plates Include slab-pull, ridge-push, basal drag, and friction along transform faults and in the subduction zone. Book: Earth’s Dynamic Systems 10th Edition Ocean College (ZJU) Plate tectonics [email protected] 6/1 Forces active on the plates Summary of main plate driving forces : Ocean College (ZJU) Plate tectonics [email protected] 7/1 Mantle drag force Ocean College (ZJU) Plate tectonics [email protected] 8/1 Mantle drag force Small-scale convection: mostly associated with mantle plume, subduction and variation in lithospheric thickness Toroidal mantle flow through the western U.S. slab window (Zant and Humphreys, 2008, Geology) Ocean College (ZJU) Plate tectonics [email protected] 9/1 Small scale convection Edge-Driven Convection: (From: http://www.mantleplumes.org/EDGE.html) Ocean College (ZJU) Plate tectonics [email protected] 10 / 1 Ridge push force 1. Ridge push is attributed to the cooling and thickening of the oceanic lithosphere with age. 2. This type of force can be thought of as created by the horizontal pressure gradient attributable to the cooling and thickening of the oceanic lithosphere, 3. and its magnitude can be determined by the regional bathymetry, which is largely a function of plate age. 4. The term “ridge push” is misleading, though, since the force is zero at the ridge, and increases linearly with plate age. Ocean College (ZJU) Plate tectonics [email protected] 11 / 1 Slab pull force Ocean College (ZJU) Plate tectonics [email protected] 12 / 1 Drive or resist: Ocean College (ZJU) Plate tectonics [email protected] 13 / 1 Trench suction force 1. This force acts to draw plates together at a trench. 2. Trench Suction is thought to result from small-scale convection in the mantle wedge, driven by the subducting lithosphere. 3. Related to Trench Suction is Slab Roll-Back. Ocean College (ZJU) Plate tectonics [email protected] 14 / 1 Collisional resistance force 1. For every subducting slab there is an associated resistive force provided by the relatively high viscosity of the warmer, more ductile upper mantle. 2. This force is only significant when young, relatively buoyant, oceanic crust is subducted. 3. Old oceanic crust dips at a steep angle, reducing friction with the overriding plate. 4. This force is velocity independent. 5. Together, the negative buoyancy of the sinking slab and the resistive nature of the slab entering the mantle is called the Net Slab Force. 6. The sum of these two forces is exerted at the colliding margin and contributes to the intra-plate stress field of the surface plates. Ocean College (ZJU) Plate tectonics [email protected] 15 / 1 Transform fault resistance force The resistance at transform faults due to friction. Ocean College (ZJU) Plate tectonics [email protected] 16 / 1 Discussion : Convergence of two continental plates The density of two convergent continental plates are comparable. Why or how one continent can subduct beneath another one ? Book: Earth’s Dynamic Systems 10th Edition Ocean College (ZJU) Plate tectonics [email protected] 17 / 1 Different continental subduction scenarios (Magni, 2013, GRL) Ocean College (ZJU) Plate tectonics [email protected] 18 / 1 Further reading Suggestions for further reading: I Book: Earth’s Dynamic Systems 10th Edition I Geodynamics: Third Edition, Turcotte, D. L. and Schubert, G., Cambridge University Press, 2014. I Mantle Dynamics: Mantle Convection in the Earth and Planets, Schubert, G., Turcotte, D. L. and P. Olson, Cambridge University Press, 2001 Ocean College (ZJU) Plate tectonics [email protected] 19 / 1
