Abstract
A fluid density in an inclusion is commonly observed to be too low for the P-T estimates for the postulated time of trapping, and is generally attributed to a fluid loss during the uplift process. It is more difficult to explain a fluid density which is too high. In the 1700 m.y. Front Range migmatites, such high densities occur in some of CO2 inclusions which were deduced to have formed during the migmatization episode. The peak P-T estimates for migmatization in the Front Range are 4–6 kb and 650°–700° C (in sillimanite field) but pressures required to form the most dense inclusions are >7.6 kb (in kyanite field). The high density is not likely to be a relic of a higher pressure condition earlier than the main migmatization episode for the following reasons: (a) no kyanite (or any other relic high pressure phase) has been found in the Precambrian Front Range; (b) the high density inclusions are rare in zones with least signs of deformation and melting (paleosomes and quartz inclusions within feldspar grains) which instead contain relatively undisturbed early inclusions; (c) high density inclusions with Th <−30° C are associated with heavily altered plagioclase caused by hydrothermal activity which was a late event in leucosome formation. Further, there is evidence for post-entrapment change(s) in density: an intragranular trail in quartz contains CO2 inclusions that exhibit almost the whole range in Th (−40 to +24° C) as displayed by the entire population of the early CO2 inclusions (−66 to +30° C). The density of an inclusion in the trail is not related to inclusion size but to the position of the inclusion relative to apparent micro-shear zones crossing the CO2 trail. A change to a higher density (=a smaller volume) could have resulted from an initially isobaric cooling path which intersects CO2 isochores with increasingly higher densities. Additional excess pressure may have resulted from overthrusting. However, because high density inclusions occur selectively in the zones in which plagioclase shows alteration indicating a high \(a_{H_2 O}\) and because there is a correlation between shear zones and high density inclusions, it is postulated that local hydrolytic weakening of quartz was necessary for the decrease of inclusion volume which occurred during deformation. The localized deformation may also result in an excess pressure. However, the introduction of a small amount of H2O into these inclusions as a possible cause of high density inclusions cannot be ruled out.
Similar content being viewed by others
References
Birch JR (1966) Compressibility; elastic constants. In: Clark SP (ed) Geol Soc Am Mem 97:107–173
Blacic JD, Christie JM (1984) Plasticity and hydrolytic weakening of quartz single crystals. J Geophys Res 89:4223–4239
Brown PE, Lamb WM (1986) Mixing of H2O-CO2 in fluid inclusions; geobarometry and Archean gold deposits. Geochim Cosmochem Acta 50:847–852
Burruss RC, Hollister LS (1979) Evidence from fluid inclusions for a paleogeothermal gradient at the geothermal test well site, Los Alamos, New Mexico. J Volcanol Geothermal Res 5:163–177
Burton B (1987) Recalculation of the Fe2O3-Fe TiO3 phase diagram. EOS 68:296
Crawford ML, Hollister LS (1986) Metamorphic fluids: The evidence from fluid inclusions. In: Walther JV, Wood BJ (eds) Fluid-rock interactions during metamorphism. Springer, Berlin Heidelberg New York Tokyo, pp 1–35
Crawford ML, Kraus DW, Hollister LS (1979) Petrologic and fluid inclusion study of calc-silicate rocks, Prince Rupert, British Columbia. Am J Sci 279:1135–1159
Dietrich RV, Mehnert KR (1960) Proposal for the nomenclature of migmatites and associated rocks. Intern Geol Congr, 21st, Copenhagen, 1960, Rept Session, Norden, (Suppl) Vol Sect 1–21:56–67
Duebendorfer EM, Houston RS (1987) Proterozoic accretionary tectonics at the southern margin of the Archean Wyoming craton. Bull Geol Soc Amer 98:554–568
Elliott D (1973) Diffusion flow laws in metamorphic rocks. Geol Soc Amer Bull 83:2621–2638
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
Ferry JM (1984) A biotite isograd in south-central Maine: Mineral reactions, fluid transfer, and heat transfer. J Petrol 25:871–893
Ferry JM, Burt DM (1982) Characterization of metamorphic fluid composition through mineral equilibria. In: Ferry JM (ed) Characterization of metamorphism through mineral equilibria. Reviews in Mineralogy, 10, Mineral. Soc Amer Washington, DC, pp 207–262
Grant JA, Olsen SN (1987) Isocon analysis of migmatites, Front Range, Colorado. 1987 GSA Abstracts with Programs 19:681
Gratier JP, Jenatton L (1984) Deformation by solution-deposition, and re-equilibration of fluid inclusions in crystals depending on temperature, internal pressure and stress. J Struct Geol 6:189–200
Holdaway MJ (1971) Stability of andalusite and the aluminum silicate phase diagram. Am J Sci 271:97–131
Hollister LS (1981) Information intrinsically available from fluid inclusions. In: Hollister LS, Crawford ML (eds) Short course in fluid inclusions: Applications to petrology. Min. Assoc. of Canada, Calgary, pp 1–9
Hollister LS, Crawford ML, Roedder E, Burruss RC, Spooner ETC, Touret J (1981) Practical aspects of microthermometry. In: Hollister LS, Crawford ML (eds) Short course in fluid inclusions: Applications to petrology. Min Assoc of Canada, Calgary, pp 278–301
Holloway JR (1981) Compositions and volumes of super-critical fluids in the earth's crust. In: Hollister LS, Crawford ML (eds) Short course in fluid inclusions: Applications to petrology. Min Assoc of Canada, Calgary, pp 13–38
Jacobs GK, Kerrick DM (1981) APL and FORTRAN programs for a new equation of state for H2O, CO2, and their mixtures at supercritical conditions. Computers Geosci 7:131–143
Kreulen R, Schuiling RD (1982) N2-CH4-CO2 fluids during formation of the Dome de L'Agout, France. Geochim Cosmochim Acta 46:193–203
Leroy J (1979) Contribution à l'étallonage de la pression interne des inclusions fluides lors de leur décrepitation. Bull Mineral 120:584–593
Lovering TS, Goddard EN (1950) Geology and ore deposits of the Front Range, Colorado, US Geol Surv Prof Paper 223, 319 p
Olsen SN (1982) Open- and closed-system migmatites in the Front Range, Colorado. Am J Sci 282:1596–1622
Olsen SN (1984) Mass-balance and mass-transfer in migmatites from the Colorado Front Range. Contrib Mineral Petrol 85:30–44
Olsen SN (1987) The composition and role of the fluid in migmatites: a fluid inclusion study of the Front Range rocks. Contrib Mineral Petrol 96:104–120
Pecher A, Boullier AM (1984) Evolution á pression et temperature élevées d'inclusions fluides dans un quartz synthétique. Bull Mineral 107:139–143
Peterman ZE, Hedge CE, Braddock WA (1968) Age of Precambrian events in the northeastern Front Range, Colorado. J Geophys Res 73:2277–2296
Pichavant M, Ramboz C, Weisbrod A (1982) Fluid immiscibility in natural processes: use and misuse of fluid inclusion data. 1. Phase equilibria analysis — A theoretical and geometrical approach. Chem Geol 37:1–27
Roedder E (1984) Fluid inclusions: Reviews in mineralogy 12. Mineral Soc Am, Washington, DC, 644 p
Skinner BJ (1966) Thermal expansion. In: Clark SP (ed) Handbook of physical constants. Geol Soc Am Mem 97:75–96
Sterner JM, Bodnar RJ (1984) Synthetic fluid inclusions in natural quartz. I. Compositional types synthesized and applications to experimental geochemistry. Geochim Cosmochim Acta 48:2659–2668
Sterner JM, Bodnar RJ (1986) Re-equilibration of fluid inclusion in quartz at elevated temperatures and pressures: The role of H2O diffusion. EOS 67:407
Swanenberg HEC (1980) Fluid inclusions in high-grade metamorphic rocks from SW Norway. Geologica Ultraiectina, Utrecht, no 25, 146 p
Taylor HP (1977) Water/rock interactions and the origin of H2O in granitic batholiths. J Geol Soc Lond 133:509–558
Touret J (1982) An empirical phase diagram for part of the N2-CO2 system at low temperature. Chem Geol 37:49–59
Touret J (1985) Fluid regime in southern Norway: The record of fluid inclusions. In: Tobi AC, Touret JLR (eds) The deep Proterozoic crust in the north atlantic provinces, D Reidel, Dordrecht, pp 517–549
Walther JV, Wood BJ (1986) Fluid-rock interactions during metamorphism. Springer, Berlin Heidelberg New York Tokyo, 218 p
Wanamaker BJ, Kohlstedt DL, Evans B (1987) Reequilibration of fluid inclusions in San Carlos olivine by point defect diffusion. EOS 68:417
Winkler HGF (1979) Petrogenesis of metamorphic rocks. 5th ed, Springer, Berlin Heidelberg New York, 348 p
Yoder HS (1950) High-low quartz inversion up to 10,000 bars. Am Geophys Union Trans 31:827–835
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Olsen, S.N. High-density CO2 inclusions in the Colorado Front Range. Contrib Mineral Petrol 100, 226–235 (1988). https://doi.org/10.1007/BF00373589
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00373589