The Role of Fluids in Crustal Processes (1990) / Chapter Skim
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10. Fluid Pressure History in Subduction Zones: Evidence from Fluid Inclusions in the Kodiak Accretionary Complex, Alaska
10. Fluid Pressure History in Subduction Zones: Evidence from Fluid Inclusions in the Kodiak Accretionary Complex, Alaska
Pages 148-157
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From page 148... ...
One reason fluid inclusions are valuable is that fluids reach thermodynamic equilibrium with each other far faster than solid phases. If fluid pressures in a deforming rock mass fluctuate, fluid inclusions trapped in continuously growing crystals may preserve some record of the fluid pressure history and thermochemical evolution.
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From page 149... ...
characteristics of methane in conjunction with independent determinations of the quartz crystallization temperature, resolved by analysis of coeval water-rich fluid inclusions. Moreover, considering each fluid inclusion analysis as a single paleofluid pressure measurement, justified on the basis that fluid temperatures remained constant during crystal growth, suggests that during the growth of veins fluid pressures fluctuated widely, and fluid pressures close to initial, fracture-forming, near-lithostatic values appeared repeatedly.
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From page 150... ...
used methanerich and water-rich fluid inclusions in syntectonic veins from three units of the Kodiak accretionary complex, Alaska, to investigate the fluid temperature history of veinforming fluids. The veins chosen for this study were interpreted to have formed during deformation of sediments within the decollement zone between the subducting oceanic and overriding North American plate.
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From page 151... ...
pioneered the use of methane plus water fluid inclusions in tectonic studies. Large-quartz crystals growing into cavities during Alpine tectonism trapped fluid inclusions; these inclusions, like the Kodiak samples, similarly record fluctuating fluid pressures.
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From page 152... ...
Future Prospects for Fluid Inclusion Research Methane and water are increasingly being recognized as the most important fluid constituents in subduction zones (Ernst, 1972; Magantz and Taylor, 1976; Cloos, 1984; Moore et al., 1987; Vrolijk, 1987~. In reconnaissance examinations of syntectonic veins from accretionary complexes in Japan, Washington, and Papua New Guinea, methane-r~ch and water-r~ch fluid inclusions have been recognized, suggesting that analysis of fluid inclusions may prove useful in accretionary complexes around the world.
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From page 153... ...
More information regarding the physical properties of sediments is required to better understand fluid flow and its effect on how sediments deform. Research into the source, path, and migration history of fluids is required to better understand the gross hydrogeology of subduction zones and to determine how the fluid pressure history is intertwined with hydrogeology.
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From page 154... ...
(1988~. Rapid subsidence and upthrusting in the Northern Appenines deduced by fluid inclusions studies in quartz crystals from Poretta Terme, Schweiz, Mineral.
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From page 155... ...
(1986~. Channelized fluid flow along melanges of the Ghost Rocks Fm., Kodiak accretionary complex, Alaska (abs.)
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From page 156... ...
S Geological Survey, Menlo Park Increased pore pressures, especially pore pressures approaching lithostatic loads, change the state of effective stress and greatly reduce the work necessary for tectonic deformation (Hubbert and Rubey, 1959; Rubey and Hubbert, 1959~.
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From page 157... ...
have also commented that the current rate is sufficient to generate the total carbon reservoir. There are obvious complications, for example, differing rates of degassing in the geologic past and recycling of carbonate rocks in subduction zones.
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