Metamorphism
The role of fluids
Bjørn Jamtveit and Haakon Austrheim
Physics of Geological Processes,University of Oslo, P.O.Box 1048 Blindern,
N-0316 Oslo, Norway
2
The evolution of the Earth’s lithosphere is, in a major way, affected by
metamorphic processes. This applies to its chemical and mineralogical
composition as well as its physical properties on all scales from the
nanometer scale to the size of the tectonic plates. Studies of metamorphism
during the last couple of decades indicate that fluids may be as important
in a changing lithosphere, as water is in the biosphere. History dependent
observables of metamorphic rocks, such as their microstructures,
compositional variations, deformation features etc, directly reflect the
dynamics of fluid-rock interactions. The migration of the fluids produced
during
prograde
metamorphic
processes
or
consumed
during
retrogression, links metamorphism at depth to the evolution of the other
Earth systems: The hydrosphere, the atmosphere, and the biosphere.
THE EVOLVING LITHOSPHERE
Most of the Earth’s lithosphere evolves under conditions where metamorphic
processes are the dominant transformation mechanisms. From the early 80’s
until quite recently, the metamorphic evolution of the Earth’s crust was to a large
extent regarded as a more or less passive recorder of it’s pressure and
temperature history as dictated by plate tectonic processes (cf. England and
Thompson, 1984). Today, however, metamorphism is recognized to be almost as
dependent on the presence of fluids, as biological systems are on the presence of
water (Yardley, 2009). Fluid-rock interactions during metamorphism may, in a
major way, control large-scale geodynamic processes by controlling: the
mechanical strength and thus the support of mountain belts (Jackson et al.,
2004); the density of the lithosphere and thus the subsidence of sedimentary
basins (Kaus et al., 2005); and the volatile content of the mantle wedge during
subduction processes, thereby affecting arc magmatism (Kerrick and Connolly,
2001). Even our ability to interpret the larger scale features of the lithospheric
mantle through seismic waves may be affected by metamorphic volatilization
processes (Boudier et al., 2009).
3
The release or consumption of fluids by metamorphism are two fundamentally
different processes in the lithosphere. When magmatic or metamorphic rocks
formed at elevated temperatures are exposed to water or other fluids at
temperatures below the temperature of their formation, they usually react to
form rocks with a higher content of volatile components. Retrograde
metamorphism therefore depends critically on the nature and abundance of
external fluids (Jamtveit et al., 2000; 2008). More than any other factor, including
pressure and temperature variations, the timing of retrogressive metamorphism
is controlled by the supply of external fluids. Near or at the Earth’s surface,
similar reactions of rocks with fluids play an important role in weathering
(Røyne et al., 2008), which may involve natural CO2-sequestration by carbonate
precipitation (Kelemen and Matter, 2008; Oelkers et al., 2008).
A fundamentally different situation arises when relatively volatile-rich
sedimentary or metamorphic rocks experience prograde metamorphism. A key
process in this case is the expulsion of fluid from the site of fluid generation
(Connolly, 2010).
Migration of fluids to and from the sites of retrograde and prograde
metamorphism plays a key role in the global H2O and carbon cycles and
ultimately in the coupling between metamorphism and the near-surface
hydrosphere, atmosphere and biosphere realms (cf. Connolly and Kerrick, 2001;
Svensen et al., 2004; Rupke et al., 2004; Kelemen and Matter, 2008; Bach and
Frueh-Green, 2010).
METAMORPHIC RATE CONTROLS
Interpretations of metamorphic mineral assemblages and microstructures
within the conceptual framework of equilibrium thermodynamics has provided
valuable insights to the conditions of formation of metamorphic rocks (e.g.
Spear, 1995). The equilibrium assumption is based on the idea that metamorphic
reactions are fast compared to the rate of change in externally controlled
variables, such as temperature and pressure. Although this may be a good
approximation in some situations, the equilibrium approach has the very
4
unfortunate aspect that all history-dependent features of the rocks are ignored,
thereby also excluding the most important sources of direct information about
the underlying metamorphic processes that generated the rock of interest
(figure 1). The central role of kinetics in controlling both microstructures and
mineral assemblages in metamorphic rocks has been illustrated by numerous
experimental, theoretical, and petrographic studies over the last two decades
(see for example Rubie, 1998; Lüttge et al., 2004; Pattison and Tinkham, 2009,
and references therein). Several of these studies point to slow nucleation as a
key factor affecting overstepping of metamorphic reactions. Moreover, the
realization that most metamorphic phase transformations take place by
dissolution-reprecipitation reactions (Putnis and John, 2010) emphasizes the
role of fluids as a central ingredient in metamorphism, even when their role is
merely catalytic. Limited, or transient, availability of intergranular fluids have
been put forward as the most plausible explanation for slow kinetics during
regional metamorphism (Baxter, 2003).
A generic rate law for metamorphic reactions may be expressed by three main
terms:
R ≈ k(T) Gn As
Where R is the rate of reaction (for example in mol/m3s), k(T)is a temperature
dependent kinetic rate constant, G is the ‘overstepping’ of the equilibrium
condition (or chemical affinity), n is a constant, and As is the specific surface area.
In most models of metamorphic kinetics, the reaction rate, R, falls with time
because the reactions tends to push the system towards equilibrium and thus
reduces the affinity of the reaction. In addition, as the reaction progresses, the
area of reactive mineral surface will normally be reduced as the amounts of
reactants diminish, and the reactant grain may be shielded from the fluid by
product phases (cf. Martin and Fyfe, 1970). Such models do however, largely
ignore, the complexity of reactive fluid-mineral interfaces.
Recent studies have demonstrated that the processes taking place at the
interface across which fluids and minerals interact may be far more complex
than hitherto thought. The interface itself may evolve in a highly dynamic way
5
leading to a wide range of structures, including complex pore structures and
fracture patterns (cf. Putnis, 2009; Renard et al, 2009; Raufaste et al., 2010).
Most importantly, these surface processes may generate reactive surface areas
much larger than those predicted by existing reactive-transport models, and
keep generating new surface area by fracturing and porosity generation as the
reactions proceed. As discussed below, this is absolutely essential for the rate of
volatilization processes in the Earth crust. Mechanical effects in particular, may
cause an increase in reactive surface area by reaction driven fracturing
processes, so that the reaction rate may, for a while, accelerate with time rather
than slowing down continuously after the onset of reaction (Røyne et al., 2008;
Jamtveit et al., 2009).
For small systems, such as mineral inclusions, mechanical effects may have the
opposite effect and slow down or even halt metamorphic reactions by
preventing the system from expanding – a phenomenon known as mechanical
closure (Schmid et al., 2008).
FLUID PRODUCTION
Prograde metamorphism will in most
cases produce fluids through
devolatilization reactions. These fluids will have a tendency to move upwards
due to the effect of gravity acting on the difference between their density and the
density of the surrounding rock. Thus, it has long been recognized that rocks
undergoing prograde metamorphism may only have a discrete fluid phase when
devolatilization reactions actually take place (Walther and Orville, 1982). If the
rate of fluid production is high relative to the rate at which fluid can escape
through preexisting permeability, fluid escape will be associated with local
hydrofracturing (Flekkoy et al., 2001). Evidence for this is seen in abundant
veining during regional metamorphism of volatile-rich rocks (e.g. Fisher and
Brantley, 1992; Cesare, 1994; Widmer and Thompson, 2001).
The intimate coupling between devolatilization reactions and fluid migration is
emphasized by numerical modeling (Connolly and Podladchikov, 1998; Connolly,
2010). These models suggest that fluid loss, even on a crustal scale, may be
6
focused by the generation of porosity waves (focused pulses of fluids). The
existence of such ‘waves’ is supported by observations of pipe-like fluid release
structures associated with sill intrusions in sedimentary basins where the heat
from the sills drives fluid production and fluid pressure increase (figure 2;
Jamtveit, et al. 2004).
Recent studies have provided strong evidence that
metamorphic fluid release of greenhouse gasses from carbon-rich sedimentary
rock have triggered some of the largest climate changes, and associated
extinctions, in the history of the Earth (Svensen et al., 2004; Svensen and
Jamtveit, 2010).
FLUID CONSUMPTION
When metamorphic rocks experience a period of cooling, they will often not
back-react with fluids to form a lower temperature mineral assemblage. The
main reason is that fluids produced during prograde metamorphism escape, and
are no longer available for retrograde reactions. Supply of external fluids is
therefore critical for the progress of retrograde metamorphic reactions.
Furthermore, if such external fluids are supplied, they are likely to be strongly
out of equilibrium with the rock in which they infiltrate. Consequently,
retrograde volatilization reactions are often fast and they may produce a variety
of complex patterns and features typical of far-from-equilibrium systems.
In a system that is essentially closed to all major components, except the
externally supplied volatile components (usually H2O or CO2), volatilization
reactions will normally result in a significant increase in the total solid volume.
Under ‘far-from-equilibrium’ conditions, this may produce local overpressures
far beyond what is required to fracture the rock (cf. Ostapenko, 1976; Wheeler,
1987). Since the fracturing generates new surface area where volatilization
reactions may start, this tends to speed up the overall rate of volatilization and
allows pervasive fluid-rock interaction at considerably larger scales than would
otherwise be possible. In the following, we examine important examples of such
fracturing assisted volatilization processes.
7
Serpentinization
Serpentinization is probably the most important metamorphic hydration
processes. The reaction of olivine-rich mantle derived peridotites to form
serpentinites is associated with a reduction in rock density from ca. 3.3 g/cm3 to
less than 2.7 g/cm3. Hydration of end-member forsterite (Mg-olivine) can be
described by the reaction:
(1) 2Mg2SiO4 + 3 H2O = Mg3Si2O5(OH) 4 + Mg(OH) 2
forsterite
+ water = serpentine
+ brucite
In a natural system the Fe-component of the original olivine will be at least
partly absorbed by a corresponding Fe-component in the brucite. This
component may subsequently be involved in a very important redox reaction
that oxidizes ferrous Fe to form magnetite (Fe3O4) and hydrogen in the water is
reduced to form H2 (Peretti et al., 1992; Bach et al., 2006) which may sustain
hydrogen-based microbial communities (Takai et al., 2004). In the presence of
carbon, serpentinization may be responsible for the production of CH 4 that’s
seeps out at midoceanic ridges (Charlou et al., 1998). This environment with
possible production of abiotic metane and other hydrocarbons is regarded as
the most likely location for the origin of life (Konn et al., 2009).
Complete serpentinization results in a solid volume increase of nearly 50%, and
causes a pronounced change in rheology, magnetic properties, and porosity.
Reaction (1) furthermore produces considerable heat (≈290 kJ/kg forsterite
consumed), and serpentinization has been suggested as an explanation of
observed heat flow anomalies in oceanic basins (Delescluse and Chamot-Rooke,
2008).
The rate of serpentinization is at a maximum at a temperature close to 300C
(Martin and Fyfe, 1985; Wegner and Ernst, 1983). At lower temperatures, the
kinetic constant for the serpentinization reaction (k(T)) limits the overall rate. At
higher temperatures, the approach to equilibrium reduces the affinity of the
hydration reactions (G) and thus its rate. The higher the reaction rate (and the
concomitant rate of rock volume increase), relative to the rates of ductile
8
deformation mechanisms, the more probable it is that serpentinization will
cause fracturing, because there is insufficient time for the rock to accommodate
the extra volume generated. Figure 3 shows fracture patterns developed in
serpentinized peridotes. The characteristic length-scales of the fractures vary
over more than 4 orders of magnitude from a few meters to less than 100
microns.
Natural CO2-sequestration
In the presence of C-bearing fluids, carbonation of peridotites (figure 4) is
produces even more heat than hydration reactions, and these reactions are
expected to be even faster than hydration at temperatures below 200C (cf.
Kelemen and Matter, 2008). Carbonation is a natural CO2-sequestration process,
and although the maximum rate of carbonation occurs at temperatures below
the ‘metamorphic regime’ (150-200C, depending on pressure), the physical and
chemical processes involved (as well as their coupling) are very similar.
Petrographic studies indicate that infiltration of C-bearing fluids into peridoties
often utilizes pre-existing fractures associated with sea-floor serpentinization.
However, it is also evident that the carbonate growth itself produces sufficient
‘swelling pressure’ (cf. MacDonal and Fyfe, 1985) to generate additional
fractures. There is little doubt that both serpentinization and carbonation of
peridotites it to a major extent influenced by mechanical processes, in particular
generation of reactive surface area by fracturing over a large range of scales.
Mechanical effects
Most experimental studies on the rates of metamorphic reactions have been
carried out using fine-grained rock powders, no fracturing is observed. However,
this does limit the relevance of such experiments, and kinetic theories based on
these, to fluid-rock reactions in natural systems. Peridotites, in particular, are
often coarse grained and almost invariably undergo extensive fracturing during
reaction with fluids (cf. MacDonald and Fyfe, 1985; O’Hanley, 1992; Iyer et al.,
9
2008). Some of this fracturing may occur as a response to far field (tectonic-)
stresses, however, there is ample evidence that the volume change associated
with the serpentinization process itself may generate stresses sufficient to
fracture rocks and mineral grains under a range of conditions (cf. Iyer et al.,
2008; Jamtveit et al., 2008).
To our knowledge, no experimental studies have so far examined the effect of
fracturing on metamorphic reactions rates. However, numerical models (cf.
Jamtveit et al., 2008; Røyne et al., 2008) have produced micro- and outcrop-scale
structures very similar to those observed in natural systems (figure 5). A key
feature of such models is that the reaction-driven fracturing accelerates the rate
of reaction by increasing the reactive surface area (Ar) at an early stage of the
reaction. Furthermore, because the length of the fractures may easily exceed the
typical diffusion distances, the overall volume of rocks affected by reaction with
fluid will be much larger than predicted by a pure reaction diffusion model. This
argument is further strengthened by the fact that reactions that consume fluids
normally produce an increase in the solid volume, and in the absence of
fracturing, pre-existing porosity would rapidly be clogged by the reaction and
the reaction would stop due to lack of fluids.
METASOMATISM: OPEN VERSUS CLOSED SYSTEMS
The issue of how to deal with thermodynamic equilibrium in open systems
relevant to metamorphic rocks was the subject of heated debate in the 1950s
and 1960s (cf. Weill and Fyfe, 1964, and references therein). In the context of the
preceding discussions on metamorphic kinetics, the question of how to deal with
open systems reappears as a central issue in petrology. The main challenge is the
coupling between mass transfer and stress generation. In a reacting rock volume,
where open system behavior is possible, two limiting scenarios are possible. The
system may change its volume and thus cause perturbations to the local stress
field, or it may maintain a constant volume by exchanging mass with its
environment. In practice, a combination of these scenarios will occur, but one or
the other is often dominant.
10
The limited amounts of fluids available during metamorphism often put severe
constraints on ‘open system behavior’. The early stages of sea-floor
serpentinization usually lead to very modest changes in rock composition (Bach
et al., 2006). This stage is invariably associated with extensive fracturing and
formation of characteristic mesh textures (cf. figure 5c). Later alteration under
more open-system conditions appears to be more of a volume for volume
replacement process. Volume for volume replacement also seems to be common
in other metamorphic processes characterized by high fluid fluxes, such as
albitization, rodingitization, scapolization etc. The settings in which these
processes occur are usually connected to regions with high thermal gradients,
such as around cooling intrusives, or localized zones of deformation that act as
fluid channels. Pervasive retrogressive metamorphism outside such zones is
almost invariably associated with reaction-driven fracturing, highlighting the
general importance of mechanical processes for fluid-rock reactions in the
lithosphere.
FUTURE PERSPECTIVES
Earth science is no longer a narrative about the past. Increasing the relevance of our
science for resolving challenges connected to energy, environment, water, and other
natural resources etc., demands more focus on the future of our planet. This requires
more focus on the processes that shape our planet, than on its equilibrium states. The
future of metamorphic petrology as a relevant field of research requires that we
increase the focus on those features of metamorphic rocks that act as a memory of the
underlying processes. Such features are not the equilibrium features. It is the opinion
of the authors of this article that more focus on the complex patterns of metamorphic
rocks, and in particular the microstructures and their coupling to both chemical and
physical processes, may save metamorphic petrology from ending up as a largely
anachronistic branch of geology. We furthermore believe that the role of fluids is
essential in controlling the evolution of the lithosphere, and also firmly connects
metamorphic processes to the evolution of the hydrosphere, biosphere and
atmosphere. This is hopefully demonstrated through the accompanying articles in this
volume of Elements.
11
ACKNOWLEDGEMENTS
Reviews by Paul Meakin and Jamie Connolly are gratefully acknowledged. This
study was supported by a Center of Excellence grant to the PGP (Physics of
Geological Processes Center) from the Norwegian Research Council
REFERENCES
Agrinier P, and Cannat, M, (1997) Oxygen isotope constraints on serpentinization
processes in ultramafic rocks from the Mid-Atlantic Ridge (23°N). Proc. ODP Sci.
Results 153, pp. 381–388.
Austrheim H (1987) Eclogitization of lower crustal granulites by fluid migration
through shear zones. Earth and Planetary Science Letters, 81: 221-232
Bach W, Paulick, H., Garrido, C.J., Ildefonse, B., Meurer, W.P., and Humphris, S.E.,
2006, Unraveling the sequence of serpentinization reactions: petrography, mineral
chemistry, and petrophysics of serpentine from MAR 15N (ODP Leg 209, Site 1274).
Geophysical Research Letters, 33, L13306
Bach W, and Früh-Green, G, 2010, Hydration of the oceanic lithosphere and its
implications for sea-floor processes. Elements, 6, x-y
Baxter E. F. (2003) Natural constraints on metamorphic reaction rates. Geological
Society, London, Special Publications, 220: 183 - 202.
Boudier, F., Baronnet, A., and Mainprice D., Serpentine mineral replacements of
natural olivine and their seismic implications: Oceanic lizardite versus subductionreleated antigorite. Journal of Petrology, (in press).
Cesare, B. (1994) Synmetamrophic veining – origin of andalusite-bearing veins in the
Vendrette di Ries contact aureole, Easter Alps, Italy, Journal of Metamorphic
geology, 12, 643-653
Charlou, J.L., Fouquet, Y., Bougault, H., Donval, J.P., Etoubleau, J., Jean-Baptiste,
12
P., Dapoigny, A., Appriou, P. and Rona, P.A. 1998. Intense CH4 plumes generated by
serpentinization of ultramafic rocks at the intersection of the 15 Deg 20’N fracture
zone and the Mid-Atlantic Ridge. Geochimica et Cosmochimica Acta, 62(13): 23232333.
Connolly, JAD (2010) Metamorphic devolatilization and fluid flow: Time and spatial
scales. Elements, 6, x-y
Connolly JAD, Kerrick DM (2002) Metamorphic controls on seismic velocity of
subducted oceanic crust at 100-250 km depth. Earth and Planetary Science Letters,
204: 61-74
Connolly JAD, Kerrick DM (2001) Metamorphic devolatilization of subducted
marine sediments and the transport of volatiles into the Earth's mantle, Nature, 411,
293-296
Connolly JAD, Podladchikov YY
(1998) Compaction-driven fluid flow in
viscoelastic rock. Geodinamica Acta, 11: 55-84
England and Thompson (1984) Pressure-temperature-time paths of regional
matemorphism. 1. Heat-transfer during the evolution of thickened continental crust.
Journal of Petrology, 25, 894-928
Fisher, DM and Brantley SL (1992) Models of quartz overgrowth and vein formation:
Deformation and episodic fluid flow in an ancient subduction zone. Journal of
Geophysical Research, 97, 20043-20061
Flekkøy, E.G., Malthe-Sørensen, A., Jamtveit, B. (2002) Modelling hydrofracture
Journal of Geophys Res. 107, 101029/20005B0.0.132
Iyer, K., Jamtveit, B., Mathiesen, J., Malthe-Sørenssen, A., and Feder, J (2008)
Reaction-assisted hierarchical fracturing during serpentinization. Earth and Planetary
Science Letters, 267, 503-516
13
Jackson JA, Austrheim H, McKenzie D, and Priestley, K. (2004) Metastability.
Mechanical strength, and the support of mountain belts. Geology, 32: 625-628
Jamtveit, B, Austrheim, H., and Malthe-Sørensen, A. (2000) Accelerated hydration of
the Earth’s deep crust induced by stress perturbations. Nature, 408, 75-79
Jamtveit, B, Svensen, H, Podladchikov, Y, and Planke, S (2004) Hydrothermal vent
complexes associated with sill intrusions in sedimentary basins. Geological Society of
London, spec. publ., 234, 233-241
Jamtveit, B., Malthe-Sørenssen, A., and Kostenko, O. (2008) Reaction enhanced
permeability during retrogressive metamorphism. Earth and Planetary Science
Letters, 267, 620-627
Jamtveit, B., Putnis, C., Malthe-Sørenssen, A. (2009) Reaction induced fracturing
during replacement processes, Contributions to Mineralogy and Petrology, 157, 127133
Kaus BJP, Connolly JAD, Podladchikov YY, Schmalholz SM (2005) Effect of
mineral phase transitions on sedimentary basin subsidence and uplift Earth and
Planetary Science Letters, 267, 213-228
Kelemen PB, Matter J (2008) In situ carbonation of peridotite for CO2 storage.
PNAS, 105: 17295-17300
Kerrick DM, and Connolly JAD (2001) Metamorphic devolatilization of subducted
oceanic metabasalts: implications for seismicity, arc magmatism and volatile
recycling. Earth and Planetary Science Letters, 189: 19-29
Konn, C., Charlou, J.L. Donval, J.P., Holm, N.G., Deharis, F. and Bouillon, S. 2009.
Hydrocarbons and oxidized organic compounds in hydrothermal fluids from Rainbow
and Lost City ultramafic-hosted vents. Chemical Geology 258, 299-314.
Lüttge A, Bolton EW, and Rye DM (2004) A kinetic model of metamorphism: an
application to siliceous dolomites. Contributions to Mineralogy and Petrology, 146,
546-565
MacDonald AH and Fyfe WS (1985) Rate of serpentinization in seafloor
environments. Tectonophysics, 116, 123-135
14
Martin B and Fyfe WS (1970) Some experimental and theoretical observations on the
kinetics of hydration reactions with particular reference to serpentinization. Chemical
Geology, 6, 185-202
Oelkers, EH, Gislason SR and Matter J, 2008, Mineral carbonation of CO2. Elements,
4, 333-337
O’Hanley, DS, 1992, Solution to the volume problem in serpentinization. Geology,
20: 705-708
Ostapenko, G.T., 1976, Excess pressure on the solid phases generated by hydration
(according to experimental data on the hydration of periclase). Traslated from
Geokhimikiya, 6, 824-844.
Peretti A, Dubessy J, Mullis J, Frost BR, and Trommsdorff V (1992) Highly reducing
conditions during Alpine metamorphism of the Malenco peridotite (Sondrio, Northern
Italy) indicated by mineral paragenesis and H2 in fluid inclusions. Contributions to
Mineralogy and Petrology, 112: 329-340
Plümper O, Putnis A (2009) The Complex Hydrothermal History of Granitic Rocks:
Multiple Feldspar Replacement Reactions under Subsolidus Conditions. Journal of
Petrology, 50: 967-987
Putnis A (2002) Mineral replacement reactions: from macroscopic observations to
microscopic mechanisms. Mineralogical Magazine, 66: 689-708
Putnis A (2009) Mineral replacement reactions, MSA Reviews in mineralogy, 70, 87124
Putnis A and John T (2010) Replacement processes in the Earth's crust. Elements, 6,
Renard, F, Dysthe, DK, Meakin, P, Feder, J, Morris, S, and Jamtveit, B, 2009, Pattern
formation during healing of fluid-filled fractures. Geofluids, 9, 365-372
Rupke LH, Morgan JP, Hort M, Connolly JAD (2004) Serpentine and the subduction
zone water cycle. Earth and Planetary Science Letters Volume, 223: 17-34
15
Røyne, A., Jamtveit, B., Mathiesen, J., Malthe-Sørenssen, A. (2008) Controls on
weathering rates by reaction induced hierarchical fracturing. Earth and Planetary
Science Letters, 275, 364-369
Schmid, D.W., Abart, R., Podladchikov, Y.Y., Milke, R. 2009. Matrix rheology
effects on reaction rim growth II: coupled diffusion and creep model. Journal of
Metamorphic Geology, 27, 83-91.
Spear, FS (1995) Metamorphic phase equilibria and pressure-temperature-time paths.
Min Soc Am Monogr Wash, p. 799
Svensen, H, Planke, S, Malthe-Sørenssen, A, Jamtveit, B, Myklebust, R, Rasmussen,
T, and Rey, S (2004) Explosive release of methane from volcanic basins. A triggering
mechanism for global climate change. Nature, 429, 542-545
Svensen H and Jamtveit B (2010) Global climate change driven by metamorphic
devolatilization. Elements, 6, x-y
Takai, K.,Gamo, T., Tsunogai, U., Nakayama, N., Hirayama, H., Nealson, K.H,. and
Horikoshi, K. 2004. Geochemical and microbiological evidence for a hydrogen-based,
hyperthermophilic subsurface lithautotrophic microboial ecosystem (HyperSLiME)
beneath an active deep-sea hydrothermal field. Extremophiles, 8(4):269-82.
Walther JV and Orville PM (1982) Volatile production and transort in regional
metamorphism. Contribution to Mineralogy and Petrology, 79, 252-257
Wegner WW and Ernst WS, 1983, Experimentally determined hydration and
dehydration reaction rates in the system MgO-SiO2-H2O. American Journal of
Science, 283-A, 151-180
Wheeler, J. (1987) The significance of grain-scale stresses in the kinetics of
metamorphism, Cont.Min.Petrology, 97, 397-404
Weill, DF and Fyfe WS, 1964, A discussion of the Korzhinskii and Thompson
treatment of thermodynamic equilibrium in open systems. Geochimica et
Cosmochimica Acta, 28, 565-576.
16
Widmer, T., and Thompson, A.B. (2001) Local origin of high pressure vein material
in eclogite facies rocks of the Zermatt-Saas zone, Switzerland. American Journal of
Science. 301: 627-656
Yardley BWD (2009) The role of water in the evolution of the continental crust.
Journal of the Geological Society of London, 166, 585-600.
Yardley BWD, Valley JW (1997) The petrologic case for a dry lower crust.
Journal of Geophysical Research – solid earth, 102: 12173-12185
17
FIGURES AND FIGURE CAPTIONS
Figure 1. Example of a microstructure with a memory of the underlying processes.
Reaction induced fracturing of scapolite (Sca) around bent aggregates of prehnite
(Pre), albite (Ab) and titanite (bright inclusions). The fracturing and bending occur as
prehnite, albite and titanite replace phlogopite (not seen) and causes a volume
expansion generating compressive stresses. It is these stresses that crack the brittle
scapolite and bend the more ductile prehnite. The fractures allow more fluid into the
system, allowing the replacement process to proceed. Example from the Bamble
sector, SE-Norway.
18
Figure 2. Satellite images from the Loriesfontein area in the western part of the Karoo
Basin, South Africa. The dry landscape is dominated by a relatively flat topography
with numerous circular hills. These hills, seen as bright "blobs" in the images, are
hydrothermal pipes filled with brecciated and metamorphosed shale. The pipes
formed as a result of methane degassing during contact metamorphism of black shale
some 182.5 Ma. The dolerite intrusions responsible for the contact metamorphism are
now located about 100 meters below the surface. The carbon gas made it to the
paleosurface and contributed to global warming in the Jurassic (cf. Svensen and
Jamtveit, 2010). The pipes are typically 100-150 meters in diameter (note the road in
the upper left area of the image).
19
Figure 3. Serpentinization across scales. The field of view ranges over ca. 4 orders of
magnitude, from ca. 10 meters (a) to 1 mm (c). a) Serpentinized peridotites from the
Norwegian Caledonides at Røragen, near Røros (6233N, 1148’E). b) Tortoiseshell
texture in serpentinized peridotite from the Mid-Atlantic ridge, Ocean Drilling
Program Hole 670A, Sample 109-670A-5R-1 (Agrinier and Cannat, 1997). c)
photomicrograph of mesh texture in partly serpentinized olivine crystal form the Leka
ophiolite complex, Norway.
20
Figure 4. Examples of natural CO2 sequestration. a) Ophicarbonate from Røragen, SE
Norway. Fractured clasts of serpentinite (green) in a calcite-dominated matrix. The
fractures through the clasts are also filled with carbonate. Coin is 2 cm across. b)
Back scattered electron (BSE-) image showing fractured olivine (light grey) partly
replaced by calcite (Cc) surrounded by serpentine (dark grey). The fracturing is
related to stresses set up by the serpentinization reaction. It is these fractures that
allow carbon-bearing fluids to penetrate into fresh olivine grains. Sample from the
Oman ophiolite.
21
Figure 5. Microstrutcures and mechanical models of fragmentation. a) Fracturing
around partly serpentinized olivine crystals in a plagioclase matrix from a troctolite
(Duluth gabbro). b) Discrete element model of fracturing around expanding polygons
in elastic matrix (2 phase system) (see Jamtveit et al., 2008 for details). Blue ‘grains’
are completely unreacted, white are completely reacted. White lines are broken bonds.
Fractures connect unreacted grains to regions in contact with a fluid and thus help
propagating the hydration process. c) Mesh texture generated during serpentinization
of olivine grain in partly serpentinized peridotites from the Leka ophiolite complex,
Norway (see Iyer et al., 2008 for details). d) Discrete element model of fragmentation
of rectangular domain (1 phase system) driven by reaction-induced swelling during
reactions with a fluid that gets access to domain boundaries and fracture walls (Røyne
et al., 2008). Color code as in b (numbers along the colored bar represents reaction
progress 1.0=100% reacted).