The Role of Fluids in Crustal Processes (1990) / Chapter Skim
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4. Fluid Dynamics During Progressive Regional Metamorphism
4. Fluid Dynamics During Progressive Regional Metamorphism
Pages 64-71
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From page 64... ...
Perhaps more surprising is the evidence for large amounts of fluid flow occurring in deeply buried rocks. Essentially this evidence consists of documenting chemical changes in mineral assemblages during metamorphism and calculating the minimum fluid volume necessary to account for the observed changes, as shown in Figure 4.1.
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From page 65... ...
Additionally, there is no guarantee that the fluid has reached complete chemical equilibrium with the mineral assemblage, an assumption inherent in the calculation. However, given the high temperatures involved and the large surface area to fluid volume in metamorphic rocks, the equilibrium assumption is probably reasonable (Walther and Wood, 1986~.
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From page 66... ...
This difference between fluid pressure and rock pressure is maintained by the effective crushing strength of the rock. At some depth the closure of pores and the resultant decrease in permeability causes the fluid pressure gradient to increase dramatically, so that fluid pressure equals lithostatic pressure.
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From page 67... ...
As mentioned above, this observa lion is consistent with the evidence from fluid inclusion studies that indicates that fluid pressure equals rock pres . _ ._ sure during metamorphism.
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From page 68... ...
Noting that the fluid flux, q, is equal Pf>Priz+ / Pf=Pr Ny I Pf |
From page 69... ...
Because quartz is present in most of the mineral assemblages in the Bundnerschiefer, it is anticipated that fluids responsible for the deposition of quartz along the segregation/vein are at quartz saturation. Let us calculate the fluid necessary to precipitate a quartz vein 50 cm in diameter, much like the one shown in FIGURE 4.5 Quartz segregation thought to represent the cross section of quartz precipitated during the lifetime of a major fluid conduit during metamorphism.
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From page 70... ...
On the mainte nance of anomalous fluid pressures: I Thick sedimentary sequences, Geological Society of America Bulletin 79, 10971106.
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From page 71... ...
(1985~. Stable isotopic evidence for large-scale seawater infiltration in a regional metamorphic terrane; The Trois Seigneurs Massif, Pyrenees, France, Contributions to Mineralogy and Petrology 91, 122137.
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