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Project Results Cont.
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| Contraction is a measure of whether an area is expanding or contracting. It is useful for recognizing regions of extension and compression in the orogen. Contraction is calculaetd using the folowing formula:
s = 0.5(dDx/dx + dDy/dy) Below are contour maps of contraction during each epoch of terrane accretion. Positive values indicate regions of contraction whereas negative values indicate regions of expansion. |
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Epoch 1: Time step between photos 1 and 2. Note that there is no real pattern to the areas of expansion and contraction. Although it is noteworthy that there are areas within the wedge and the terrane that are expanding during orogenesis. Velocity displacement vectors are indicated by the arrows. | ||||||||||||||
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Epoch 2: Time step between photos 2 and 3. This is just prior to the collision between the terrane and the wedge. There is still no overall pattern of expansion or contraction, although there are areas of expansion in both the wedge and the terrane. | ||||||||||||||
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Epoch 3: Time step between photos 3 and 4. This is just after the collision between the terrane and the wedge. There are still regions of contraction and expansion in the wedge and the terrane, although there is no overall pattern. | ||||||||||||||
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Epoch 4: Time step between photos 4 and 5. This is during the initial collision between the terrane and the wedge. Note the increase in the area of compression within the wedge relative to the earlier epochs. | ||||||||||||||
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Epoch 5: Time step between photos 5 and 6. This covers the time when thrusts develop within the wedge, which is indicated by the wide band of contraction at the suture between the terrane and the wedge. Also note the large area of contraction within the wedge at this time. | ||||||||||||||
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Epoch 6: Time step between photos 6 and 7. This covers the time period when the deformation begins to step out from the suture zone to the toe of the accreting terrane. | ||||||||||||||
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Epoch 7: Time step between photos 7 and 8. This is when the basal fault at the base of the accreted terrane beins to take up the strain in the orogen. Note that there is no overall pattern. | ||||||||||||||
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Epoch 8: The final state of contraction. This is when all of the active faulting is localized at the toe of the accreted terrane. Note that within the new wedge there are large areas that are not undergoing contraction or expansion. | ||||||||||||||
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