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0 0.2 0.4 0.6 0.8 1.0 0 0.2 0.4 0.6 0.8 1.0 0.05 0.90 1.0 Figure 8.15. The amplitude of the horizontally varying part of the temperature, the amplitude of the horizontally varying vertical velocity, and the horizontally averaged part of the temperature as a function of y from a solution ofthe single-mode mean field equations Quareni and Yuen, 1984 for isothermal, impermeable, and stress-free boundaries at Ra 104, 105, and 106.
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Figure 2.8. Pattern of global heat flux variations complete to spherical harmonic degree 12. After Pollack et al. 1993 . For a color version of this figure, see plate section. 0 30' 60' 90' 120' 150' 160 -150' -120' -B0 -60' -30' 0' 0 30' 60' 90' 120' 150' 160 -150' -120' -B0 -60' -30' 0' 0' 30' 60 90' 120' 150 ISO' -150' -120 -90' -60' -30 0 Figure 2.9. Global distribution of volcanoes active in the Quaternary. 0' 30' 60 90' 120' 150 ISO' -150' -120 -90' -60' -30 0 Figure 2.9. Global...
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where HT cp ag is the adiabatic temperature scale height. In a steady state, the shape of the spreading plume is entirely governed by the magnitude of I. For large values of I, corresponding to a large conduit discharge, low plume viscosity or slow plate motion, buoyant spreading dominates over plate advection, and the spreading plume and its topographic rise are nearly circular in planform. For small values of I, corresponding to either a weak plume, fast plate motion or high asthenosphere...
Why Are Island Arcs Arcs
Question 2.6 Why do subduction zones have arcuate structures One of the striking features of subduction zones is their arcuate structure in map view or planform. Subduction zones are made up of a sequence of arc structures with a clear planform curvature this is the origin of the term island arc. A good example is the Aleutian arc, shown in Figures 2.1 and 2.5. Just as accretionary margins are characterized by their orthogonal ridge-transform geometry, subduction zones are characterized by...
Info Csd
Figure 2.13. Segments of an ocean ridge offset by a transform fault. The fracture zones are extensions of the transform faults into the adjacent plates. Figure 2.14. Sketch of a ridge-ridge transform fault showing exaggerated differential vertical subsidence across the fault. Figure 2.14. Sketch of a ridge-ridge transform fault showing exaggerated differential vertical subsidence across the fault. direction, whereas the transform faults lie parallel to the spreading direction. This structure is...
P 1
Figure 2.28. Illustration of Euler's theorem. Plate B is moving counterclockwise relative to plate A. The motion is defined by the angular velocity m about the pole of rotation P. Double lines are ridge segments, and arrows denote direction of motion on transform faults. data include 277 spreading rate determinations based on magnetic anomalies. An example of the magnetic profiles for the spreading boundary between the Cocos and Pacific plates is given in Figure 2.30. The NUVEL-1 model also...
Dip of Subduction Zones
Question 2.3 What determines the subduction dip angle Since the gravitational body force on the subducted lithosphere is downward, it would be expected that the subduction dip angle would tend toward 90 . In fact, as shown in Figure 2.19, the typical dip angle for a subduction zone is near 45 . One explanation is that the oceanic lithosphere is foundering and the trench is migrating oceanward. In this case the dip angle is determined by the flow kinematics Hager and O'Connell, 1981 . While this...