Abstract
Models for regional metamorphism have been constructed to determine the thermal effects of reaction enthalpy and the amount of fluid generated by dehydration metamorphism. The model continental crust contains an average of 2.9 wt % water and dehydrates by a series of reactions between temperatures of 300 and 750° C. Large scale metamorphism is induced by instantaneous collision belt thickening events which double the crustal thickness to 70 km. After a 20 Ma time lag, erosion due to isostatic rebound restores the crust to its original thickness in 100 Ma. At crustal depths greater than 10 km, where most metamorphism takes place, fluid pressure is unlikely to deviate significantly from lithostatic pressure. This implies that lower crustal porosity can only be maintained if rock pores are filled by fluid. Therefore, porosities are primarily dependent on the rate of metamorphic fluid production or consumption and the crustal permeability. In the models, permeability is taken as a function of porosity; this permits estimation of both fluid fluxes and porosities during metamorphism. Metamorphic activity, as measured by net reaction enthalpy, can be categorized as endothermic or exothermic depending on whether prograde dehydration or retrograde hydration reactions predominate. The endothermic stage begins almost immediately after thickening, peaks at about 20 Ma, and ends after 40 to 55 Ma. During this period the maximum and average heat consumption by reactions are on the order 11.2·10−14 W/cm3 and 5.9·10−14 W/ cm3, respectively. The maximum rates of prograde isograd advance decrease from 2.4·10−8 cm/s, for low grade reactions at 7 Ma, to 7·10−10 cm/s, for the highest grade reaction between 45 and 58 Ma. Endothermic cooling reduces the temperature variation in the metamorphic models by less than 7% (40 K); in comparison, the retrograde exothermic heating effect is negligible. Dehydration reactions are generally poor thermal buffers, but under certain conditions reactions may control temperature over depth and time intervals on the order of 1 km and 3 Ma. The model metamorphic events reduce the hydrate water content of the crust to values between 1.0 and 0.4 wt % and produce anhydrous lower crustal granulites up to 15 km in thickness. In the first 60 Ma of metamorphism, steady state fluid fluxes in the rocks overlying prograde reaction fronts are on the order of 5·10−11 g/cm2-s. These fluid fluxes can be accommodated by low porosities (<0.6%) and are thus essentially determined by the rate of devolitalization. The quantity of fluid which passes through the metamorphic column varies from 25000 g/cm2, within 10 km of the base of the crust, to amounts as large as 240000 g/cm2, in rocks initially at a depth of 30 km. Measured petrologic volumetric fluid-rock ratios generated by this fluid could be as high as 500 in a 1 m thick horizontal layer, but would decrease in inverse proportion of the thickness of the rock layer. Fluid advection causes local heating at rates of about 5.9·10−14 W/cm3 during prograde metamorphism and does not result in significant heating. The amount of silica which can be transported by the fluids is very sensitive to both the absolute temperature and the change in the geothermal gradient with depth. However, even under optimal conditions, the amount of silica precipitated by metamorphic fluids is small (<0.1 vol %) and inadequate to explain the quartz veining observed in nature. These results are based on equilibrium models for fluid and heat transport that exclude the possibility of convective fluid recirculation. Such a model is likely to apply at depths greater than 10 km; therefore, it is concluded that large scale heat and silica transport by fluids is not extensive in the lower crust, despite large time-integrated fluid fluxes.
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References
Bear J (1972) Dynamics of fluids in porous media. American Elsevier, New York, 763 pp
Bickle MJ, McKenzie D (1987) The transport of heat and matter by fluids during metamorphism. Contrib Mineral Petrol 95:384–392
Brace WF (1984) Permeability of crystalline rocks: new in situ measurements. J Geophys Res 89:4327–4330
Connolly JAD, Thompson AB (1989) Crustal anatexis in orogenic belts. Terra Nova (in press)
Chamberlain CP, Rumble D (1989a) Thermal anomalies in a regional metamorphic terrain: an isotopic study of the role of fluids. J Petrol (in press)
Chamberlain CP, Rumble D (1989b) The influence of fluids on the thermal history of a metamorphic terrain. J Geol Soc London (in press)
Dullien FAL (1979) Porous media: fluid transport and pore structure. Academic Press, New York
England PC, Richardson SW (1977) The influence of erosion upon the mineral facies of rocks from different metamorphic environments. J Geol Soc London 134:201–213
England PC, Thompson AB (1984) Pressure-temperature-time paths of regional metamorphism I. Heat transfer during the evolution of regions of thickened continental crust. J Petrol 25:894–928
England PC, Thompson AB (1986) Some thermal and tectonic models for crustal melting in collision zones. In: Coward MP, Rice AC (eds) Collision tectonics. Geol Soc London 19:83–94
Etheridge MA, Wall VA, Vernon RH (1983) The role of the fluid phase during regional metamorphism and deformation. J Metamorph Petrol 83:205–226
Etheridge MA, Wall VA, Cox SF, Vernon RH (1984) High fluid pressures during regional metamorphism and deformation. J Geophys Res 89:4344–4358
Ferry JM (1979) Reaction mechanisms, physical conditions, and mass transfer during hydrothermal alteration of mica and feldspar in granitic rocks from south-central Maine, USA. Contrib Mineral Petrol 68:125–139
Ferry JM (1983) On the control of temperature, fluid composition, and reaction progress during metamorphism. Am J Sci 83A:201–232
Ferry JM (1986) Reaction progress: a monitor of fluid-rock interaction during metamorphism and hydrothermal events. In: Walther JV, Wood BJ (eds) Fluid-rock interactions during metamorphism. Springer, New York Berlin Heidelberg Tokyo, pp 60–88
Ferry JM (1987) Metamorphic hydrology at 13 km depth and 400–550° C. Am Mineral 72:39–58
Fisher GW (1978) Rate laws in metamorphism. Geochim Cosmochim Acta 42:1035–1050
Fournier RO, Potter RW (1982) An equation correlating the solubility of quartz in water from 25° to 900° C at pressures up to 10 000 bars. Geochim Cosmochim Acta 46:1969–1973
Fournier RO, Rosenbauer RJ, Bischoff JL (1982) The solubility of quartz in aqueous sodium chloride solution at 350° C and 180 to 500 bars. Geochim Cosmochim Acta 46:1975–1978
Fyfe WS, Price NJ, Thompson AB (1978) Fluids in the earth's crust. Elsevier, Amsterdam
Graham CM, Greis KM, Sheppard SMF, Turi B (1983) Genesis and mobility of the H2O-CO2 fluid phase during regional greenschist and epidote amphibolite facies metamorphism. J Geol Sox London 140:577–600
Hall J (1986) The physical properties of layered rocks in deep continental crust. In: Dawson JB, Carswell DA, Hall J, Wedepohl KH (eds) The nature of the lower continental crust. Geol Soc Spec Pub 24:51–62
Hyndman RD (1988) Dipping seismic reflectors, electrically conductive zones, and trapped water in the crust over a subducting plate. J Geophys Res 93:13391–13405
Hemley JJ, Montoya JW, Marienko JW, Luce RW (1980) Equilibria in the system Al2O3-SiO2-H2O and some general implications for alteration/mineralization processes. Econ Geol 75:210–228
Kirby SH (1984) Introduction and digest to the special issue on chemical effects of water on the deformation and strength of rocks. J Geophys Res 89:3991–3995
Kirby SH (1985) Rock mechanics observations pertinent to the rheology of the continental Lithosphere and the localization of shear zones. Tectonophysics 119:1–27
Lasaga AC (1986) Metamorphic reaction rate laws and development of isograds. Mineral Mag 50:359–373
McKenzie D (1985) The extraction of magma from the crust and mantle. Earth Planet Sci Lett 74:81–91
Murrell SAF (1985) Aspects of relationships between deformation and prograde metamorphism that causes the evolution of water. In: Thompson AB, Rubie DC (eds) Metamorphic reactions: kinetics, textures, and deformation. Springer, New York Berlin Heidelberg Tokyo, pp 211–241
Nehlig P, Juteau T (1988) Flow porosities, permeabilities and preliminary data on fluid inclusions and fossil thermal gradients in the crustal sequence in the central sequence of the Sumail Ophiolite (Oman). Tectonophysics 151:199–221
Peacock SM (1987) Thermal effects of metamorphic fluids in subduction zones. Geology 15:1057–1060
Peacock SM (1989) Numerical constraints on rates of metamorphism, fluid production, and fluid flux during regional metamorphism. Geol Soc Am Bull (in press)
Ridley J (1985) The effect of reaction enthalpy on the progress of a metamorphic reaction. In: Thompson AB, Rubie DC (eds) Metamorphic reactions. Springer, New York Berlin Heidelberg Tokyo, pp 80–97
Ridley J (1986) Modelling of the relations between enthalpy and the buffering of reaction progress in metamorphism. Mineral Mag 50:375–384
Ridley J, Thompson AB (1986) The role of mineral kinetics in the development of metamorphism. In: Walther JV, Wood BJ (eds) Fluid-rock interactions during metamorphism. Springer, New York, pp 154–193
Rubie DC (1986) The catalysis of mineral reactions by water and restrictions on the presence of aqueous fluid during metamorphism. Mineral Mag 50:399–415
Rumble D (1988) Fluid flow during regional metamorphism. EOS 69:465
Rutter EH, Brodie KH (1985) The permeation of water into hydrating shear zones. In: Thompson AB, Rubie DC (eds) Metamorphic reactions: kinetics, textures, and deformation. Springer, New York Berlin Heidelberg Tokyo, pp 242–250
Sibson RH (1983) Continental fault structure and the shallow earthquake source. J Geol Soc 140:741–767
Shi Y, Wang C-H (1987) Two-dimensional modeling of the P-T-t paths of regional metamorphism in simple overthrust terrains. Geology 15:1048–1051
Thompson AB (1987) Some aspects of fluid motion during metamorphism. J Geol Soc 144:309–312
Thompson AB (1988a) Dehydration melting of crustal rocks. Rend Soc Ital Min Petr 43:41–60
Thompson AB (1988b) Fluids and rock deformation. Rend Soc Ital Mineral Petrol 43:61–64
Thompson AB, Connolly JAD (1989) Metamorphic fluids and anomalous porosities in the lower crust. Tectonophysics (in press)
Thompson AB, England PC (1984) Pressure-temperature-time paths of regional metamorphism II. Their inference and interpretation using mineral assemblages in metamorphic rocks. J Petrol 25:929–955
Trimmer D (1982) Laboratory measurements of ultralow permeability of geologic materials. Rev Sci Instrum 53:1246–1254
Ungerer P, Doligez B, Chenet PY, Burrus J, Bessis F, Lafargue E, Giroir G, Heum O, Egger S (1987) A 2-D model of basin scale petroleum by two-phase flow. Application to some case studies. In: Migration of hydrocarbons in sedimentary basins. IFP Collection 45. Editions Technip, Paris, pp 415–446
Valley JW (1986) Stable isotope geochemistry of metamorphic rocks. In: Valley JW, Taylor HP Jr, O'Niel JR (eds) Stable isotopes in high temperature geological processes. Rev Mineral 16, Mineral Soc Am 445–490
Veblen DR, Ferry JM (1983) A TEM study of the biotite-chlorite reaction and comparison with petrologic observations. Am Mineral 68:1160–1168
Wall VJ, Etheridge MA (1988) Regional metamorphic fluid migration: single pass or circulation. EOS 69:464
Walther JV, Orville PM (1982) Volatile production and transport in regional metamorphism. Contrib Mineral Petrol 79:252–257
Walther JV, Wood BJ (1984) Rate and mechanism in prograde metamorphism. Contrib Mineral Petrol 88:246–259
Wood BJ, Graham CM (1986) Infiltration of aqueous fluid and high fluid: rock ratios during greenschist facies metamorphism: a discussion. J Petrol 27:751–761
Wood BJ, Walther JV (1986) Fluid flow during metamorphism and its implications for fluid-rock ratios. In: Walther JV, Wood BJ (eds) Fluid-rock interactions during metamorphism. Springer, New York Berlin Heidelberg Tokyo, pp 89–108
Yardley BWD (1986) Fluid migration and veining in the Connemara Schists, Ireland. In: Walther JV, Wood BJ (eds) Fluidrock interactions during metamorphism. Springer, New York Berlin Heidelberg Tokyo, pp 89–108
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Connolly, J.A.D., Thompson, A.B. Fluid and enthalpy production during regional metamorphism. Contrib Mineral Petrol 102, 347–366 (1989). https://doi.org/10.1007/BF00373728
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DOI: https://doi.org/10.1007/BF00373728