Velocity of vertical fluid ascent within vein-forming fractures

Abstract

Quartz-albite-calcite veins in metamorphic rocks of the Sanbagawa belt, Japan, contain sugary mosaics of equant quartz grains <0.01-1.6 mm in size (blocky texture). The quartz crystals show euhed ral to subhedral double-terminated crystal shape, and concentric growth zoning, indicating suspension in aqueous fl uid during crystal growth until formation of a framework within the crack. Such a crystallization process is only possible when downward crystal settling is balanced by upward fl uid fl ow. Application of crystal settling theory to the crystal size distributions within the veins reveals an extremely high rate of fl uid ascent during blocky vein formation (10 -2 to 10 -1 m/s) due to the low viscosity of the hydrothermal fl uid (~10 -4 Pa⋅s). Such a high rate of ascent suggests the injection of fl uids from mobile hydrofractures within deeper levels of the subduction zone.

Mineralogical and textural variation of silica minerals in hydrothermal flow-through experiments: Implications for quartz vein formation

“…6a and d. It is difficult to know which mechanism operates in natural blocky quartz veins: direct nucleation of quartz from solution or recrystallization from opaline silica. However, some blocky veins consist of euhedral quartz crystals that show concentric growth zoning, coexisting with fine-grained albite (Okamoto et al, 2008;Okamoto and Tsuchiya, 2009), similar to that seen in the M-gr run in the present study.…”

“…In the crustal conditions, the high degree of supersaturation at the sites of vein formation is realized by fluid ascent with sufficiently high flow rate relative to the precipitation rate of silica (Rimstidt and Barnes, 1980), or by a pressure drop related to seismicity (Fournier, 1985). Some studies on blocky veins estimated the extremely high ascent rates in the order of 0.1-1 m s À1 during the vein formation (Bons, 2001;Okamoto and Tsuchiya, 2009). Therefore, the fractures to produce blocky veins could act as the dominant fluid pathways in the Earth's crust.…”

A Hydromechanical Model for Lower Crustal Fluid Flow

“…An essential feature of such a mechanism is that, irrespective of the mean-stress gradient, hydraulic connectivity must be maintained over a vertical interval that is large enough to generate the effective pressures necessary to drive the deformation. Both self-propagating domains of fluid-filled fractures (Gold and Soter 1985) and individual hydrofractures (Rubin 1995;Nakashima 1995;Okamoto and Tsuchiya 2009) have been proposed as the mechanism for such flow. These models suppose that the fractures are closed at depth, i.e., compacted, by the elastic response of the matrix.…”

Silicon isotope fractionation during the precipitation of quartz and the adsorption of H4SiO4(aq) on Fe(III)-oxyhydroxide surfaces

“…In the above KIE Experimental data are from Hazen et al (1989) and Rastsvetaeva et al (2009) However, a special kind of quartz, the so-called Herkimer ''diamond,'' which is extremely pure, is thought to be precipitated under an equilibrium condition. Okamoto and Tsuchiya (2009) suggested that this kind of quartz must be slowly grown in an upward fluid flow to form such a special double-terminated crystal. This also implies a huge solution reservoir for it (e.g., ruling out isotope reservoir effect).…”