Abstract
Schists from two mylonitic localities in the footwall of a low-angle normal fault in the eastern Alps record different degrees of embrittlement during exhumation, depending on the extent to which fluid–rock reactions proceeded. At one site, graphitic schists preserve textural evidence for two metamorphic reactions that modified \( {\rm X}_{\mathop {\rm CO}\nolimits_2 } \) and/or fluid volume: (1) reaction between graphite and aqueous fluid that increased \( {\rm X}_{\mathop {\rm CO}\nolimits_2 } \) without changing the molar amount of fluid, and (2) replacement of titanite by rutile, calcite, and quartz. The latter reaction involved net consumption of increasingly CO2-rich fluid. Areas where the first reaction proceeded are associated with abundant Mode I microcracks. Fluid inclusion arrays within the microcracks show that \( {\rm X}_{\mathop {\rm CO}\nolimits_2 } \) increased from ∼0.1 to 0.6 during decompression from 4.75 to 2 kbar at a reference temperature of 500°C. Titanite consumption is most pronounced within transgranular Mode I microcracks, but microcracks do not crosscut products of this reaction; fluid consumption during reaction was coeval with the end of microcracking, at least on a local scale. At the other site, graphitic schists lack small-scale Mode I cracks as well as evidence for graphite consumption during decompression. SEM imaging shows that graphite is anhedral and pitted at the first site, but occurs in clusters of euhedral grains at the second site. Mass balance calculations demonstrate that rocks with partially consumed graphite were infiltrated by an externally derived, H2O-rich fluid that drove subsequent graphite-fluid reaction. Evidence for similar fluid infiltration is absent at the second site. Variations in the degree of reaction progress indicate that fluid pathways and deformation style were heterogeneous on the scale of millimeters to kilometers during exhumation from mid-crustal depths.
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References
Axen GJ, Bartley JM, Selverstone J (1995) Structural expression of a rolling hinge in the footwall of the Brenner Line normal fault, eastern Alps. Tectonics 14:1380–1392
Axen GJ, Selverstone J, Wawrzyniec T (2001) High-temperature embrittlement of extensional Alpine mylonite zones in the midcrustal ductile–brittle transition. J Geophys Res 106:4337–4348
Behrmann J (1988) Crustal scale extension in a convergent orogen: the Sterzing-Steinach mylonite zone in the Eastern Alps. Geodin Acta 2:63–73
Bigalke J, Junge A, Zulauf G (2004) Electronically conducting brittle–ductile shear zones in the crystalline basement of Rittsteig (Bohemian Massif, Germany): evidence from self potential and hole-to-surface electrical measurements. Int J Earth Sci 93:44–51
Binu-Lal SS, Kehelpannala KV, Satish-Kumar M, Wada H (2003) Multistage graphite precipitation through protracted fluid flow in sheared metagranitoid, Digana, Sri Lanka: evidence from stable isotopes. Chem Geol 197:253
Bowers TS, Helgeson HC (1983) Calculation of the thermodynamic and geochemical consequences of nonideal mixing in the system H2O–CO2–NaCl on phase relations in geologic systems: equation of state for H2O–CO2–NaCl fluids at high pressures and temperatures. Geochim Cosmochim Acta 47:1247–1275
Brown PE, Hagemann SG (1994) MacFlinCor: a computer program for fluid inclusion data reduction and manipulation. In: De Vivo BD, Frezzotti ML (eds) Fluid inclusions in minerals: methods and applications. Virginia Polytechnic Institute, Blacksburg, pp 231–250
Chiodini G, Cardellini C, Amato A, Boschi E, Caliro S, Frondini F, Ventura G (2004) Carbon dioxide Earth degassing and seismogenesis in central and southern Italy. Geophys Res Lett 31:16
Colletini C, Barchi MR (2002) A low-angle normal fault in the Umbria region (Central Italy): a mechanical model for the related microseismicity. Tectonophysics 359:97–115
Collettini C, Barchi M, Pauselli C, Federico C, Pialli G (2000) Seismic expression of active extensional faults in northern Umbria (Central Italy). J Geodyn 29:309–321
Connolly JAD, Trommsdorff V (1991) Petrogenetic grids for metacarbonate rocks: pressure–temperature phase-diagram projection for mixed-volatile systems. Contrib Mineral Petrol 108:93–105
Connolly JAD, Cesare B (1993) C-O-H-S fluid composition and oxygen fugacity in graphitic metapelites. J Metamorph Geol 11:379–388
Duan ZH, Zhang ZG (2006) Equation of state of the H2O–CO2 system up to 10 GPa and 2,573 K: molecular dynamics simulations with ab initio potential surface. Geochim Cosmochim Acta 70:2311–2324
French BM (1966) Some geological implications of equilibrium between graphite and C–H–O gas phase at high temperatures and pressures. Rev Geophys 4:223–253
Fügenschuh B, Mancktelow NS, Seward D (2000) Cretaceous to Neogene cooling and exhumation history of the Oetztal-Stubai basement complex, eastern Alps: a structural and fission track study. Tectonics 19:905–918
Holland TJB, Powell R (1998) An internally-consistent thermodynamic data set for phases of petrological interest. J Metamorph Geol 16:309–343
Kerrick DM, Caldeira K (1993a) Metamorphic CO2 degassing and early Cenozoic paleoclimate. GSA Today 4:57–63
Kerrick DM, Caldeira K (1993b) Paleoatmospheric consequences of CO2 released during early Cenozoic regional metamorphism in the Tethyan orogen. Chem Geol 108:201–230
Kerrick DM, Jacobs GK (1981) A modified Redlich–Kwong equation for H2O, CO2, and H2O–CO2 mixtures at elevated pressures and temperatures. Am J Sci 281:735–767
Kretz R (1996) Graphite deformation in marble and mylonitic marble, Grenville Province, Canadian Shield. J Metamorph Geol 14:399–412
Lammerer B (1988) Thrust-regime and transpression-regime tectonics in the Tauern Window (eastern Alps). Geol Rundsch 143–156
López Sánchez-Viscaíno V, Connolly JAD, Gómez-Pugnaire MT (1997) Metamorphism and phase relations in carbonate rocks from the Nevado-Filábride Complex (Cordilleras Béticas, Spain): application of the Ttn + Rt + Cal + Qtz + Gr buffer. Contrib Mineral Petrol 126:292–302
Mancktelow NS, Stöckli DF, Grollimund B, Müller W, Fügenschuh B, Viola G, Seward D, Villa IM (2001) The DAV and Periadriatic fault systems in the Eastern Alps south of the Tauern Window. Int J Earth Sci 90:593–622
Miller SA, Colletini C, Chiaraluce L, Cocco M, Barchi M, Kaus BJP (2004) Aftershocks driven by a high-pressure CO2 source at depth. Nature 427:724–727
Morteani G (1974) Petrology of the Tauern Window, Austrian Alps. Fortschr Geol 52:195–220
Nesbitt BE, Mendoza CA, Kerrick DM (1995) Surface fluid convection during Cordilleran extension and the generation of metamorphic CO2 contributions to Cenozoic atmospheres. Geology 23:99–101
Newton RC, Manning CE (2000) Quartz solubility in H2O–NaCl and H2O–CO2 solutions at deep crust-upper mantle pressures and temperatures: 2–15 kbar and 500–900°C. 64:2993–3005
Ohmoto H, Kerrick D (1977) Devolatilization equillibria in graphitic systems. Am J Sci 277:1013–1044
Pattison DRM (2005) The fate of graphite in prograde metamorphism of pelites: an example from the Ballachulish aureole, Scotland. Lithos 88:85–99
Post A, Tullis J, Yund R (1996) Effects of chemical environment on dislocation creep of quartzite. J Geophys Res 101:22143–122155
Radhika UP, Santosh M (1996) Shear-zone hosted graphite in southern Kerala, India: implications for CO2 infiltration. J Southeast Asian Earth Sci 14:265–273
Selverstone J (1988) Evidence for east-west crustal extension in the Eastern Alps: implications for the unroofing history of the Tauern Window. Tectonics 7:87–105
Selverstone J (2005) Preferential embrittlement of graphitic schists during extensional unroofing in the Alps: the effect of fluid composition on rheology in low-permeability rocks. J Metamorph Geol 23:461–470
Selverstone J, Spear FS, Franz G, Morteani G (1984) High-pressure metamorphism in the SW Tauern Window, Austria: P–T paths from hornblende-kyanite-staurolite schists. J Petrol 25:501–531
Selverstone J, Gutzler DS (1993) Post-125 Ma carbon storage associated with continent-continent collision. Geology 21:885–888
Selverstone J, Spear FS (1985) Metamorphic P–T paths from pelitic schists and greenstones in the southwest Tauern Window, Eastern Alps. J Metamorph Geol 3:439–465
Selverstone J, Axen GJ, Bartley JM (1995) Fluid inclusion constraints on the kinematics of footwall uplift beneath the Brenner Line normal fault, eastern Alps. Tectonics 14:264–278
Stampfli GM, Borel GD, Marchant R, Mosar J (2002) Western Alps geological constrains on western Tethyan reconstructions. J Virt Expl 7:75–104
Stöckli DF (1995) Tectonics SW of the Tauern Window (Mauls area, Südtirol). Diploma Thesis, ETH-Zürich, 272 pp
Wawrzyniec T, Selverstone J, Axen GJ (1999) Correlations between fluid composition and deep-seated structural style in the footwall of the Simplon low-angle normal fault, Switzerland. Geology 27:715–718
Wopenka B, Pasteris JD (1993) Structural characterization of kerogens to granulite-facies graphite: applicability of Raman microprobe spectroscopy. Am Min 78:533–557
Zhang ZG, Duan ZH (2005) Prediction of the PVT properties of water over a wide range of temperatures and pressures from molecular dynamics simulation. Phys Earth Planet Int 149:335–354
Acknowledgments
Funding for this research was provided by NSF grant EAR-0509937 to JS, and a NSF Graduate Research Fellowship, a GSA Research Grant, and a UNM Wengerd Fund travel grant to AA. Helpful discussions and insight from T. Wawrzyniec, A. Brearley, M. Roy, and J. Tullis, and written comments from Brian Evans and an anonymous reviewer, are greatly appreciated. Thanks to A. Hawkins for field assistance. J. Berlin and M. Spilde are gratefully acknowledged for their support with electron microprobe and scanning electron microprobe analyses.
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Communicated by T.L. Grove.
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Ault, A.K., Selverstone, J. Microtextural constraints on the interplay between fluid–rock reactions and deformation. Contrib Mineral Petrol 156, 501–515 (2008). https://doi.org/10.1007/s00410-008-0298-9
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DOI: https://doi.org/10.1007/s00410-008-0298-9