Stabilization and reactivation of cratonic lithosphere from the lower crustal record in the western Canadian shield

  • Rebecca M. Flowers
  • Samuel A. Bowring
  • Kevin H. Mahan
  • Michael L. Williams
  • Ian S. Williams
Original Paper


New U–Pb geochronology for an extensive exposure of high-pressure granulites in the East Lake Athabasca region of the western Canadian shield is consistent with a history characterized by 2.55 Ga stabilization of cratonic lithosphere, 650 million years of lower crustal residence and cratonic stability, and 1.9 Ga reactivation of the craton during lithospheric attenuation and asthenospheric upwelling. High precision single-grain and fragment zircon data define distinctive discordia arrays between 2.55 and 1.9 Ga. U–Pb ion microprobe spot analyses yield a similar range of U–Pb dates with no obvious correlation between date and cathodoluminescence zonation. We attribute the complex U–Pb zircon systematics to growth of the primary populations during a 2.55 Ga high-pressure granulite facies event (~1.3 GPa, 850°C) recorded by the dominant mineral assemblage of the mafic granulite gneisses, with subsequent zircon recrystallization and minor secondary zircon growth during a second high-pressure granulite facies event (1.0 GPa, ~800°C) at 1.9 Ga. The occurrence of two discrete granulite facies metamorphic events in the lower crust, separated by an interval of 650 million years that included isobaric cooling for at least some of this time, suggests that the rocks resided at lower crustal depths until 1.9 Ga. We infer that this phase of lower crustal residence and little tectonic activity is coincident with an extended period of cratonic stability. Detailed structural and thermochronological datasets indicate that multistage unroofing of the lower crustal rocks occurred in the following 200 million years. Extended lower crustal residence would logically be the history inferred for lower crust in most cratonic regions, but the unusual aspect of the history in the East Lake Athabasca region is the subsequent lithospheric reactivation that initiated transport of the lower crust to the surface. We suggest that a weakened strength profile related to the 1.9 Ga heating left the lithosphere susceptible to far-field tectonic stresses from bounding orogens that drove the lower crustal exhumation. An ultimate return to cratonic stability is responsible for the preservation of this extensive lower crustal exposure since 1.7 Ga.


Zircon Zircon Crystal Mafic Granulite Metamorphic Zircon Felsic Granulite 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



This research was supported in part by National Science Foundation (NSF) grant EAR-0310215 to S. A. Bowring and M. L. Williams, and a NSF graduate fellowship and Geological Society of America student research grant to R. M. Flowers. We thank Alexis Ault for assistance during two field seasons. Helpful tectonic and petrologic discussions with Philippe Goncalves and Greg Dumond are greatly appreciated. We thank Urs Schaltegger and an anonymous reviewer for comments that helped clarify the manuscript.


  1. Armstrong RL (1981) Radiogenic isotopes: the case for crustal recycling on a near steady-state no-continental-growth Earth Philos. Trans R Lond A301:443–472CrossRefGoogle Scholar
  2. Baldwin JA, Bowring SA, Williams ML (2003) Petrological and geochronological constraints on high pressure, high temperature metamorphism in the Snowbird tectonic zone, Canada. J Metamorph Geol 21:81–98CrossRefGoogle Scholar
  3. Baldwin JA, Bowring SA, Williams ML, Williams IS (2004) Eclogites of the Snowbird tectonic zone: petrological and U–Pb geochronological evidence for Paleoproterozoic high-pressure metamorphism in the western Canadian Shield. Contrib Mineral Petrol 147:528–548CrossRefGoogle Scholar
  4. Baldwin JA, Bowring SA, Williams ML, Mahan KH (2006) Geochronological constraints on the crustal evolution of felsic high-pressure granulites, Snowbird tectonic zone, Canada. Lithos 88:173–200CrossRefGoogle Scholar
  5. Bell DR, Schmitz MD, Janney PE (2003) Mesozoic thermal evolution of the southern African lithosphere. Lithos 71:273–287CrossRefGoogle Scholar
  6. Berman RG, Davis WJ, Aspler LB, Chiarenzelli JR (2002) SHRIMP U–Pb ages of multiple metamorphic events in the Angikuni Lake area, western Churchill Province, Nunavut. Geological Survey of Canada Current Research. 2002-F3, 9 ppGoogle Scholar
  7. Berman RG, Davis WJ, Pehrsson S (2007) The collisional Snowbird tectonic zone resurrected: growth of Laurentia during the 1.9 Ga accretionary phase of the Hudsonian orogeny. Geology 35:911–914CrossRefGoogle Scholar
  8. Bowring SA, Housh T (1995) The earth’s early evolution. Science 269:1535–1540CrossRefGoogle Scholar
  9. Carson CJ, Ague JJ, Grove M, Coath CD, Harrison TM (2002) U–Pb isotopic behavior of zircon during upper-amphibolite facies fluid infiltration in the Napier Complex, east Antarctica. Earth Planet Sci Lett 199:287–310CrossRefGoogle Scholar
  10. Celerier J, Sandiford M, Hansen D, Quigley M (2005) Modes of active intraplate deformation, Flinders Ranges, Australia. Tectonics 24:TC6006 doi: 10.1029/2004TC001679 CrossRefGoogle Scholar
  11. Cherniak DJ (1993) Lead diffusion in titanite and preliminary results on the effects of radiation damage on Pb transport. Chem Geol 110:177–194CrossRefGoogle Scholar
  12. Cherniak DJ, Watson EB (2000) Pb diffusion in zircon. Chem Geol 172:5–24CrossRefGoogle Scholar
  13. Cherniak DJ, Lanford WA, Ryerson FJ (1991) Lead diffusion in apatite and zircon using ion implantation and Rutherford Backscattering techniques. Geochim Cosmochim Acta 55:1663–1673CrossRefGoogle Scholar
  14. Claoué-Long JC, Compston W, Roberts J. Fanning CM (1995) Two carboniferous ages: a comparison of SHRIMP zircon dating with conventional zircon ages and 40Ar/39Ar analysis. In:Berggren WA, Kent DV, Aubrey M-P, Hardenbol J (eds) Geochronology, time scales and global stratigraphic correlation. SEPM (Society for Sedimentary Geology), Special Publication, Tulsa, pp 3–21, 54Google Scholar
  15. Corfu F, Hanchar JM, Hoskin, PWO, Kinny P (2003) Atlas of zircon textures. In: Hanchar JM, Hoskin PWO (eds) Zircon, reviews in mineralogy and geochemistry, vol 53, pp 468–500Google Scholar
  16. Corrigan D, Hajnal Z, Nemeth B, Lucas SB (2005) Tectonic framework of a Paleoproterozoic arc-continent to continent-continent collisional zone, Trans-Hudson Orogen, from geological and seismic reflection studies. Can J Earth Sci 42:421–434CrossRefGoogle Scholar
  17. Cumming GL, Richards JR (1975) Ore lead isotope ratios in a continuously changing earth. Earth Planet Sci Lett 28:155–171CrossRefGoogle Scholar
  18. Fahrig WF, Christie KW, Eade KE, Tella S (1984) Paleomagnetism of the Tulemalu dykes, Northwest Territories, Canada. Can J Earth Sci 21:544–553Google Scholar
  19. Farmer GL, Bowring SA, Williams ML, Christensen NI, Matzel JP, Stevens LP (2005) Contrasting lower crustal evolution across an Archean-Proterozoic suture: physical, chemical and geochronologic studies of lower crustal xenoliths in southern Wyoming and northern Colorado. In: Karlstrom KE, Keller GR (eds) The Rocky Mountain region: an evolving lithosphere. Geophysical Monograph Series, vol 154, pp 139–162Google Scholar
  20. Flowers RM, Bowring SA, Reiners PW (2006a) Low long term erosion rates and extreme continental stability documented by ancient (U–Th)/He dates in the western Canadian shield. Geology 34:925–928CrossRefGoogle Scholar
  21. Flowers RM, Bowring SA, Williams ML (2006b) Timescales and significance of high-pressure, high-temperature metamorphism and mafic dike anatexis, Snowbird tectonic zone, Canada. Contrib Mineral Petrol 151:558–581CrossRefGoogle Scholar
  22. Flowers RM, Mahan, KH, Bowring SA, Williams ML, Pringle MS, Hodges KV (2006c) Multistage exhumation and juxtaposition of lower continental crust in the western Canadian shield: linking high-resolution U–Pb and 40Ar/39Ar thermochronometry with P–T–D paths. Tectonics 25:TC4003. doi: 10.1029/2005TC001912 CrossRefGoogle Scholar
  23. Goodacre AK, Grieve RAF, Halpenny JF, Sharpton VL, (1987) Horizontal gradient of the Bouguer gravity anomaly map of Canada, Canadian Geophysical Atlas, Map 5Google Scholar
  24. Hanmer S (1994) Geology, East Athabasca mylonite triangle, Saskatchewan. Geol Surv Can Map, 1859AGoogle Scholar
  25. Hanmer S (1997) Geology of the Striding-Athabasca mylonite zone, northern Saskatchewan and southeastern District of Mackenzie, Northwest Territories. Geol Surv Can Bull 501:1–92Google Scholar
  26. Hanmer S, Williams M, Kopf C (1995) Striding-Athabasca mylonite zone: implications for the Archean and Early Proterozoic tectonics of the western Canadian Shield. Can J Earth Sci 332:178–196Google Scholar
  27. Hanmer S, Williams M (2001) Targeted fieldwork in the Daly Bay Complex, Hudson Bay, Nunavut. Geol Surv Can Curr Res, 2001-C15Google Scholar
  28. Harrison TM, Blichert-Toft J, Muller W, Albarede F, Holden P, Mojzsis SJ (2005) Heterogeneous Hadean Hafnium: evidence of continental crust at 4.4 to 4.5 Ga. Science 310:1947–1950CrossRefGoogle Scholar
  29. Hanson GN, Catanzaro EJ, Anderson DH (1971) U–Pb ages for sphene in a contact metamorphic zone. Earth Planet Sci Lett 12:231–237CrossRefGoogle Scholar
  30. Hoffman PF (1988) United Plates of America, the birth of a craton: Early Proterozoic assembly and growth of Laurentia. Annu Rev Earth Planet Sci Lett 16:545–603Google Scholar
  31. Hoskin PWO, Black LP (2000) Metamorphic zircon formation by solid-state recrystallization of protolith igneous zircon. J Metamorph Geol 18:423–439CrossRefGoogle Scholar
  32. Jaffey AH, Flynn KF, Glendenin LE, Bentley WC, Essling AM (1971) Precision measurements of half-lives and specific activities of 235U and 238U. Phys Rev C4:1889–1906Google Scholar
  33. Jordan TH (1978) Composition and development of the continental tectosphere. Nature 274:544–548CrossRefGoogle Scholar
  34. Kopf C (1999) Deformation, metamorphism, and magmatism in the East Athabasca mylonite triangle, northern Saskatchewan: implications for the Archean and early Proterozoic crustal structure of the Canadian Shield. PhD dissertation thesis, University of Massachusetts-Amherst, 208 ppGoogle Scholar
  35. Krikorian L (2002) Geology of the Wholdaia Lake segment of the Snowbird Tectonic Zone, Northwest Territories (Nunavut): a view of the deep crust during assembly and stabilization of the Laurentian craton. Msc Thesis, University of Massachusetts-Amherst, 90 ppGoogle Scholar
  36. Kretz R (1983) Symbols for rock-forming minerals. Am Mineral 68:277–279Google Scholar
  37. Krogh TE (1973) A low contamination method for hydrothermal decomposition of zircon and extraction of U and Pb for isotopic age determinations. Geochim Cosmochim Acta 37:485–494CrossRefGoogle Scholar
  38. Krogh TE (1982) Improved accuracy of U–Pb zircon ages by the creation of more concordant systems using an abrasion technique. Geochim Cosmochim Acta 46:637–649CrossRefGoogle Scholar
  39. Lee JKW, Williams IS, Ellis DJ (1997) Pb, U and Th diffusion in natural zircon. Nature 390:159–161CrossRefGoogle Scholar
  40. Lewry JF, Sibbald TII (1980) Thermotectonic evolution of the Churchill Province in northern Saskatchewan. Tectonophysics 68:5–82CrossRefGoogle Scholar
  41. Ludwig KR (1980) Calculation of uncertainties of U–Pb isotope data. Earth Planet Sci Lett 46:212–220CrossRefGoogle Scholar
  42. Mahan KH, Williams ML (2005) Reconstruction of a large deep-crustal exposure: Implications for the Snowbird tectonic zone and early growth of Laurentia. Geology 33:385–388CrossRefGoogle Scholar
  43. Mahan KH, Williams ML, Baldwin JA (2003) Contractional uplift of deep crustal rocks along the Legs Lake shear zone, western Churchill Province, Canadian Shield. Can J Earth Sci 40:1085–1110CrossRefGoogle Scholar
  44. Mahan KH, Goncalves P, Williams ML, Jercinovic MJ (2006a) Dating metamorphic reactions and fluid flow: application to exhumation of high-P granulites in a crustal-scale shear zone, western Canadian Shield. J Metamorph Geol 24:193–217CrossRefGoogle Scholar
  45. Mahan KH, Williams ML, Flowers RM, Jercinovic MJ, Baldwin JA, Bowring SA (2006b) Geochronological constraints on the Legs Lake shear zone with implications for regional exhumation of lower crust, western Churchill Province, Canadian Shield. Contrib Mineral Petrol. doi: 10.1007/s00410-006-0106-3
  46. Mahan KH, Goncalves P, Flowers R, Williams ML, Hoffman-Setka D (2008) The role of heterogeneous strain in development and preservation of a polymetamorphic record in high-pressure granulites. J Metamorph Geol (in review)Google Scholar
  47. Mattinson JM (2005) Zircon U–Pb chemical abrasion (“CA-TIMS”) method: Combined annealing and multi-step partial dissolution analysis for improved precision and accuracy of zircon ages. Chem Geol 220:47–66CrossRefGoogle Scholar
  48. McDonough MR, McNicoll VJ, Schetselaar EM, Grover TW (2000) Geochronological and kinematic constraints on crustal shortening and escape in a two-sided oblique-slip collisional and magmatic orogen, Paleoproterozoic Taltson magmatic zone, northeastern Alberta. Can J Earth Sci 37:1549–1573CrossRefGoogle Scholar
  49. McFarlane CRM, Connelly JN, Carlson WD (2004) Intracrystalline redistribution of Pb in zircon during high-temperature contact metamorphism. Chem Geol 217:1–28CrossRefGoogle Scholar
  50. Mills A, Berman RG, Hanmer SK, Davis W (2000) New insights into the tectonometamorphic history of the Uvauk complex, Nunavut. Geo Canada 2000 CD-ROM, Geol. Assoc. Canada, May-June, Abstract 733Google Scholar
  51. Nasdala L, Lengauer CL, Hanchar JM, Kronz A, Wirth R, Blanc P, Kennedy AK, Seydoux-Guillaume AM (2002) Annealing of radiation damage and the recovery of cathodoluminescence. Chem Geol 191:121–140CrossRefGoogle Scholar
  52. Percival JA, Stern RA, Rayner N (2003) Archean adakites from the Ashuanipi complex, eastern Superior Province, Canada: geochemistry, geochronology and tectonic significance. Contrib Mineral Petrol 145:265–280CrossRefGoogle Scholar
  53. Pidgeon RT (1992) Recrystallization of oscillatory zoned zircon: some geochronological and petrological implications. Contrib Mineral Petrol 110:463–472CrossRefGoogle Scholar
  54. Pidgeon RT, Nemchin AA, Hitchen GJ (1998) Internal structures of zircons from Archean granites from the Darling Range batholith: Implications for zircon stability and the interpretation of zircon U–Pb ages. Contrib Mineral Petrol 132:288–299CrossRefGoogle Scholar
  55. Ross GM, Eaton DW, Boerner DE, Miles W (2000) Tectonic entrapment and its role in the evolution of continental lithosphere: An example from the Precambrian of western Canada. Tectonics 19:116–134CrossRefGoogle Scholar
  56. Ross GM, Milkereit B, Eaton D, White D, Kanasewich ER, Burianyk MJA (1995) Paleoproterozoic collisional orogen beneath the western Canada sedimentary basin imaged by Lithoprobe crustal seismic reflection data. Geology 23:195–199CrossRefGoogle Scholar
  57. Rubatto D, Williams IS, Buick IS (2001) Zircon and monazite response to prograde metamorphism in the Reynolds Range, central Australia. Contrib Mineral Petrol 140:458–468CrossRefGoogle Scholar
  58. Sanborn-Barrie M, Carr SD, Theriault R (2001) Geochronological constraints on metamorphism, magmatism and exhumation of deep-crustal rocks of the Kramanituar Complex, with implications for the Paleoproterozoic evolution of the Archean western Churchill Province, Canada. Contrib Mineral Petrol 141:592–612Google Scholar
  59. Schaltegger U, Fanning CM, Gunther D, Maurin JC, Schulmann K, Gebauer D (1999) Growth, annealing and recrystallization of zircon and preservation of monazite in high-grade metamorphism: conventional and in-situ U–Pb isotope, cathodoluminescence and microchemical evidence. Contrib Mineral Petrol 134:186–201CrossRefGoogle Scholar
  60. Silver LT, Deutsch S (1963) Uranium-lead isotopic variations in zircons–a case study. J Geol 71:721–758CrossRefGoogle Scholar
  61. Snoeyenbos DR, Williams ML, Hanmer S (1995) Archean high-pressure metamorphism in the western Canadian Shield. Eur J Min 7:1251–1272Google Scholar
  62. Stacey JC, Kramers JD (1975) Approximation of terrestrial lead isotope evolution by a two-stage model. Earth Planet Sci Lett 26:207–221CrossRefGoogle Scholar
  63. Stern RA, Berman RG (2000) Monazite U–Pb and Th–Pb geochronology by ion microprobe, with an application to in situ dating of an Archean metasedimentary rock. Chem Geol 172:113–130CrossRefGoogle Scholar
  64. Sun SS, McDonough WF (1989) Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders AD, Norry MJ (eds) Magmatism in oceanic basins. Geological Society Special Publication, London, pp 313–345Google Scholar
  65. Vavra G, Gebauer R, Schmid W, Compston W (1996) Multiple zircon growth and recrystallization during polyphase Late Carboniferous to Triassic metamorphism in granulites of the Ivrea Zone (Southern Alps): an ion microprobe (SHRIMP) study. Contrib Mineral Petrol 122:337–368CrossRefGoogle Scholar
  66. Vavra G, Schmid R, Gebauer D (1999) Internal morphology, habit and U–Th–Pb microanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea Zone (Southern Alps). Contrib Mineral Petrol 134:380–404CrossRefGoogle Scholar
  67. Wiedenbeck M (1995) An example of reverse discordance during ion microprobe zircon dating: an artifact of enhanced ion yield from radiogenic labile Pb. Chem Geol 125:197–218CrossRefGoogle Scholar
  68. Williams ML, Hanmer S (2005) Structural and metamorphic processes in the lower crust: evidence from an isobarically cooled terrane, the East Athabasca mylonite triangle. In: Brown M, Rushmer T (eds) Evolution and differentiation of the continental crust. Cambridge University Press, Cambridge, pp 232–268Google Scholar
  69. Williams IS, Compston W, Black LP, Ireland TR, Foster JJ (1984) Unsupported radiogenic Pb in zircon: a cause of anomalously high Pb–Pb, U–Pb and Th–Pb ages. Contrib Mineral Petrol 88:322–327CrossRefGoogle Scholar
  70. Williams ML, Hanmer S, Kopf C, Darrach M (1995) Syntectonic generation and segregation of tonalitic melts from amphibolite dikes in the lower crust, Striding-Athabasca mylonite zone, northern Saskatchewan. J Geophys Res 100:15717–15734CrossRefGoogle Scholar
  71. Williams ML, Mellis EA, Kopf C, Hanmer S (2000) Microstructural Tectonometamorphic processes and the development of gneissic layering: a mechanism for metamorphic segregation. J Metamorph Geol 18:41–57CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Rebecca M. Flowers
    • 1
  • Samuel A. Bowring
    • 2
  • Kevin H. Mahan
    • 1
  • Michael L. Williams
    • 3
  • Ian S. Williams
    • 4
  1. 1.Department of Geological SciencesUniversity of ColoradoBoulderUSA
  2. 2.Department of Earth, Atmospheric and Planetary SciencesMassachusetts Institute of TechnologyCambridgeUSA
  3. 3.Department of GeosciencesUniversity of MassachusettsAmherstUSA
  4. 4.Research School of Earth SciencesThe Australian National UniversityCanberraAustralia

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