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Vrolijk, P.J., 1987

Paleohydrogeology and fluid evolution of the Kodiak accretionary complex, Alaska

Bibliographic Reference

Vrolijk, P.J., 1987, Paleohydrogeology and fluid evolution of the Kodiak accretionary complex, Alaska: University of California, Santa Cruz, Ph.D. dissertation, 232 p., illust., maps.


Deformation and metamorphism of water-rich sediments and hydrothermally altered ocean crust contribute to high pore pressures and consequently fluid migration patterns in subduction zones. Understanding the migration of fluids and fluid-rock interactions is critical to unraveling the complicated history of subduction complexes. My work in the Kodiak accretionary complex, Alaska, suggests that the following processes were important during subduction and accretion of the units preserved in the accretionary complex: (1) At intermediate levels in the subduction zone (8-15 km), progressive deformation causes large fluctuations in fluid pressure, with fluid pressures varying from near-lithostatic values to pressures 20-45% less. Moreover, high fluid pressures apparently help drive deformation in fault zones. (2) Fluid flow along faults and fractures is rapid and extensive enough to perturb the thermal structure of the subduction zone. (3) Fluids migrating in fault zones are isotopically distinct from fluids in less deformed sequences. Additionally, fluids in coherent units may be derived from local sources whereas fluids in fault zones must be derived from some exotic source, probably at deeper levels. (4) Textural and stable isotope studies document the nature of fluid migration during continued consolidation of the sediment. At early stages fluid flow is pervasive through intergranular pore spaces. As faults and fractures develop throughout the rock, however, they provide barriers to flow normal to fracture planes yet form high conductivity conduits for fluid flow along the plane of fractures. Throughout the subduction zone fluid flow appears to have been concentrated mostly along fault zones.

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