Pervasive fluid

A pervasive fluid moves independently of structural and lithologic control through a rock and leads to a homogenization of whatever differences in isotopic composition may have existed prior to metamorphism. 

Pervasive fluid flow through a porous, permeable medium is described by Darcy s law, written here for three dimensions (cf. Bear, 1972) ... 

In this chapter the case of the oxygen isotopic composition of the Dales Gorge Member of the Brockman iron formation will be considered (Figure 3). This formation is underlain by shales of the Marra Mamba Formation that contain extractable hydrocarbon biomarkers generated before or during a peak regional metamorphic event 2,450-2,000 Ma (Brocks et al., 1999). It is unlikely that such labile material could have survived the pervasive fluid migration that would... 

It is also important to note that these factors influence permeability on different scales as described by Brace (1984), permeabilities measured on the scale of a drill hole (30-300 m) can be much higher, due to widely spaced fractures, than those measured on a laboratory sample (5-15 cm). Thus drill hole permeabilities may be appropriate for estimating the flux of channeled fluids through the crust, but laboratory scale permeability, if properly measured, affords a better estimate of truly pervasive fluid flow. 

The aqueous fluids formed by melting of ices in asteroids reacted with minerals to produce a host of secondary phases. Laboratory studies provide information on the identities of these phases. They include hydrated minerals such as serpentines and clays, as well as a variety of carbonates, sulfates, oxides, sulfides, halides, and oxy-hydroxides, some of which are pictured in Figure 12.15. The alteration minerals in carbonaceous chondrites have been discussed extensively in the literature (Zolensky and McSween, 1988 Buseck and Hua, 1993 Brearley, 2004) and were most recently reviewed by Brearley (2006). In the case of Cl chondrites, the alteration is pervasive and almost no unaltered minerals remain. CM chondrites contain mixtures of heavily altered and partially altered materials. In CR2 and CV3oxb chondrites, matrix minerals have been moderately altered and chondrules show some effects of aqueous alteration. For other chondrite groups such as CO and LL3.0-3.1, the alteration is subtle and secondary minerals are uncommon. In some CV chondrites, a later thermal metamorphic overprint has dehydrated serpentine to form olivine. 

Convection in Melt Growth. Convection in the melt is pervasive in all terrestrial melt growth systems. Sources for flows include buoyancy-driven convection caused by the solute and temperature dependence of the density surface tension gradients along melt-fluid menisci forced convection introduced by the motion of solid surfaces, such as crucible and crystal rotation in the CZ and FZ systems and the motion of the melt induced by the solidification of material. These flows are important causes of the convection of heat and species and can have a dominant influence on the temperature field in the system and on solute incorporation into the crystal. Moreover, flow transitions from steady laminar, to time-periodic, chaotic, and turbulent motions cause temporal nonuniformities at the growth interface. These fluctuations in temperature and concentration can cause the melt-crystal interface to melt and resolidify and can lead to solute striations (25) and to the formation of microdefects, which will be described later. 

Figure 14 Selection of time-integrated fluid fluxes from the literature. The average regional, pervasive flow-dominated flux of ni(fluid) m(7ock) (2(r) denoted with diagonal ruled bar (computed using geometric mean ...

Hoisch T. D. (1991) The thermal effects of pervasive and channelized fluid flow in the deep crust. J. Geol. 99, 69-80. 

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