The Role of Fluids in Crustal Processes (1990) / Chapter Skim
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9. Smoluchowski's Dilemma Revisited: A Note on the Fluid-Pressure History of the Central Appalachian Fold-Thrust Belt
9. Smoluchowski's Dilemma Revisited: A Note on the Fluid-Pressure History of the Central Appalachian Fold-Thrust Belt
Pages 140-147
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From page 140... ...
The high fluid pressures accompanying this topographically-dnven flow system later facilitated the development of first-order structures in the valley and edge. Later joint sets that do not correlate across the Allegheny Front are more likely to be a consequence of fluid pressure pulses developed during local tectonic compaction and the development of first-order Alleghanian structures.
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From page 141... ...
Are there geological structures that enable the geologist 141 to distinguish topographically driven flow from other mechanisms including tectonic compaction that might have been the source of high fluid pressures in a foreland foldthrust belt? In principle, regional joint sets could serve as such structures.
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From page 142... ...
The curvature of the Central Appalachian Valley and Ridge is accommodated by abrupt changes in the orientation of the first-order folds. Strictly parallel joint sets reflect the kinematics of thrust sheets associated with straight-axis kink folds.
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From page 143... ...
Low strength of the salt changed the character of the Appalachian foreland tectonics from duplex structures of the valley and ridge to layer parallel shortening of the Appalachian Plateau (Davis and Engelder, 1987~.] A correlation may be based on the common occurrence of a clockwise rotation of joint propagation in both the valley and ridge and the Appalachian Plateau.
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From page 144... ...
An understanding of the extent to which joints correlate in both time and space is critical to identifying the mechanisms for generation of high fluid pressures in a mountain belt. Although rapid joint propagation occurs on the scale of outcrops, the timing of joint propagation at different locations across a foreland is less certain.
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From page 145... ...
If fluid pressures were continuously at lithostatic during realignment of the stress field, then joints should have a uniform distribution of orientations rather than appear as isolated joint sets. Multiple joint sets suggest that fluid pressures rise to lithostatic levels during short-lived events before pore fluids leak off to drop the pressure well below that needed for joint propagation.
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From page 146... ...
In syntectonic veins of the Kodiak accretionary complex, Alaska, fluid inclusions record fluctuating fluid pressures. These fluctuations reflect a history of fracture opening, continued fracture growth, and creation of an interconnected fracture network, with inferred fluid flow toward shallower levels within the subduction zone.
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From page 147... ...
The global water and geochemical budgets also depend on the fluid pressure distribution in subduction zones because mass balance calculations suggest that water must return to the ocean through subduction complexes to prevent the world's oceans from being subducted into the mantle (e.g., Fyfe et al., 1978; Ito et al., 1983~. Fluid pressures appear to play a direct role in mineral diagenesis (e.g., Bird, 1984; Koster van Groos and Guggenheim, 1984, 1986, 1987)
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