Plate Tectonics Versus Earth Crust Displacement???

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    * Problems:
          o No adequate explanation for what caused geosynclines to develop and then deform. Airy isostasy (observed topography due to crustal root) was mechanism invoked.
                + Airy Isostasy -
                      # Layer below crust acts as fluid in the long term.
                      # Where crust is thick (mountains), it sinks into the fluid layer until bouyancy provides support. Where crust is thin (oceans), fluid wells up underneath.
                      # Why? - Stress Balance (fig. 2.29 in K&V):
                      # Thinning of crust by erosion or thickening by deposition, leads to adjustment in the form of uplift or subsidence due to removal or addition of loads, respectively.
          o No explanation for ophiolites in mountain belts (allow geosyncline formation in deep water? not just on continental shelves?)
          o No explanation of large amounts of shortening observed in Alps (down-sucking of European platform beneath Alpine geosyncline?)

Isostasy is undoubtedly an important driving mechanism for deformation on the Earth today, but it is not the only one.