Abstract
The 3,622±72 m.y. Uivak gneisses of northern Labrador consist of two major rock suites: regionally developed layered granodioritic gneisses (Uivak I suite) interpreted as derived from earlier tonalitic igneous parents by the massive introduction of potassium and rubidium, and a less extensive group of iron-rich porphyritic granodiorites and ferro-diorites (Uivak II suite) emplaced after at least one major period of deformation and migmatisation had affected the Uivak I gneisses. Samples from both suites fall on the 3,622 m.y. Rb/Sr whole-rock isochron.
The age is provisionally interpreted as that of Rb metasomatism and homogenisation affecting both suites. It is suggested that the low initial ratio of 0.7014±0.0008 obtained from both suites need not be diagnostic of a short crustal residence if the evidence for massive addition of Rb to this level of the crust at 3,622 m.y. is accepted.
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Bridgwater, D., Collerson, K.D., Hurst, R.W., Jesseau, C.W.: Field characters of the early Precambrian rocks from Saglek, Coast of Labrador. Pap. Geol. Surv. Canada 74-1a, 287–296 (1975)
Hurst, R.W., Bridgwater, D., Collerson, K.D., Wetherill, G.W.: 3,600 m.y. Rb-Sr ages in very early Archean gneisses from Saglek Bay, Labrador. Earth Planet. Sci. Lett. 27, 393–403 (1975)
Collerson, K.D., Jesseau, C.W., Bridgwater, D.: Crustal development of the Archean gneiss complex: Eastern Labrador. MS submitted to Nato Advanced Study Institute on the early history of the Earth, Leicester (1975). New York: J. Wiley (in prep.)
McGregor, V.R.: The early Precambrian geology of the Godthaab district, West Greenland. Phil. Trans. Roy. Soc. London, Ser. A 273, 343–358 (1973)
Moorbath, S., O'Nions, R.K., Pankhurst, R.J., Gale, N.H., McGregor, V.R.: Further rubidiumstrontium age determinations on the very early Precambrian rocks of the Godthaab district, West Greenland. Nature Phys. Sci. 240, 78–82 (1972)
Bridgwater, D., Keto, L., McGregor, V.R., Myers, J.S.: Archean gneiss complex of Greenland. In: Escher, A., Watt, W.S., Geology of Greenland. Geological Survey of Greenland publications (in press)
Collerson, K.D., Bridgwater, D.: The Upernavik supracrustals, a metamorphosed Archaean cover sequence in the Nain Province, Labrador. Geol. Soc. Am. Abstracts with programs, NE section meeting Syracuse (1975)
Taylor, F.C., in Wanless, R.K., Stevens, R.D., Lachance, G.R., Delabio, R.N.D.: Age determinations and geological studies. K-Ar Isotopic ages, Report 12, Pap. Geol. Surv. Canada 74-2, 56 (1974)
Bridgwater, D., Watson, J., Windley, B.F.: The Archaean craton of the North Atlantic region. Phil. Trans. Roy Soc. London, Ser. A 273, 493–512 (1973)
Bridgwater, D., McGregor, V.R.: Field work on the very early Precambrian rocks of the Isua area, southern West Greenland, Rapp. Grønlands Geol. Unders. 65, 49–54 (1974)
McGregor, V.R.: The earliest granites: Evidence from the Godthaab district, West Greenland. Abstract submitted to Nato Advanced Study Institute on the early history of the Earth, Leicester (1975)
Windley, B.F., Bridgwater, D.: The evolution of Archean low- and high-grade terrains. Spec, publ. Geol. Soc. Aust. 3, 33–46 (1971)
Arth, J.G., Hanson, G.N.: Geochemistry and origin of the early Precambrian crust of northeastern Minnesota. Geochim. Cosmochim. Acta 39, 325–361 (1975)
Taylor, S.R.: Trace element abundances and the chondritic Earth model. Geochim. Cosmochim. Acta 28, 1989–1998 (1964)
Anhaeusser, C.R., Mason, R., Viljoen, M.J., Viljoen, R.P.: A reappraisal of some aspects of Precambrian shield geology. Bull Geol. Soc. Am. 80, 2175–2200 (1969)
Viljoen, M.J., Viljoen, R.P.: A proposed new classification of the granitic rocks of the Barberton region. Spec. publ. Geol. Soc. S. Africa 2, 153–180 (1969)
Engel, A.E.J.: The Barberton mountain land: clues to the differentiation of the Earth. Trans. Geol. Soc. S. Africa 71 (annex) 255–270 (1969)
Heier, K.S.: Geochemistry of granulite facies rocks and problems of their origin. Phil. Trans. Roy. Soc. London, Ser. A 273, 429–442 (1973)
Glikson, A.Y., Sheraton, J.W.: Early Precambrian trondhjemitic suites in Western Australia and northwestern Scotland and the geochemical evolution of shields. Earth Planet. Sci. Lett. 17, 227–242 (1972)
Tarney, J., Skinner, A.C., Sheraton, J.W.: A geochemical comparison of major Archaean gneiss units from northwest Scotland and East Greenland. Int. Geol. Congr. 24th, Montreal 1, 162–173 (1972)
Simonen, A., Vorma, A.: Amphibole and biotite from rapakivi. Bull. Comm. Geol. Finland 238 (1969)
Bridgwater, D., Sutton, J., Watterson, J.: Crustal downfolding associated with igneous activity. Tectonophysics 21, 57–77 (1974)
De Waard, D., Wheeler, E.P., II: Chemical and petrologic trends in anorthositic and associated rocks of the Nain massif, Labrador. Lithos 4, 367–380 (1971)
Bridgwater, D., Windley, B.F.: Anorthosites, post orogenic granites, acid volcanic rocks and crustal development in the North Atlantic shield during the mid-Proterozoic. Spec. publ. Geol. Soc. S. Africa 3, 307–318 (1974)
Engel, A.E.J., Itson, S.P., Engel, C.G., Stickney, D.M., Cray, E.J., Jr.: Crustal evolution and global tectonics: a petrogenic view. Bull. Geol. Soc. Am. 85, 843–858 (1974)
Goldich, S.S., Hedge, C.E., Stern, T.W.: Age of the Morton and Montevideo gneisses and related rocks, Southwestern Minnesota. Bull. Geol. Soc. Am. 81, 3671–3696 (1970)
Bridgwater, D., Fyfe, W.S.: The pre-3 b.y. crust: Fact fiction-fantasy. Geoscience Canada 1, 3, 7–11 (1974)
Moorbath, S.: Evolution of Precambrian crust from strontium isotopic evidence. Nature 254, 395–398 (1975)
Riley, G.H., Compston, W.: Theoretical and technical aspects of Rb-Sr geochronology. Geochim. Cosmochim. Acta 26, 1255–1281 (1962)
Alsopp, H.L., Davies, R.D., Kramers, J., Nicolaysen, L.O., Stacey, J.S.: Isotopic evidence for a new model for the formation of the early crust. (Abs.) European Geophysical Soc. meeting Trieste (1974)
Hart, R.J., Nicolaysen, L.O., Slawson, W.F., Stacey, J.S., Welke, H.J.: The variation of isotopic tracers with depth in the South African crust and its bearing on early crustal differentiation and cooling (Abs.) European Geophysical Soc. meeting Trieste (1974)
Armstrong, R.L.: A model for Sr and Pb isotope evolution in a dynamic Earth. Rev. Geophys. 6, 175–199 (1968)
O'Nions, R.K., Pankhurst, R.K.: Rare-earth element distribution in Archaean gneisses and anorthosites, Godthaab area, West Greenland. Earth Planet. Sci. Lett. 22, 328–338 (1974)
Taylor, F.C.: Reconnaissance geology of part of the Precambrian Shield, northeastern Quebec and northern Labrador. Pap. Geol. Surv. Canada 70-24 (1970)
Morgan, W.C.: Geology of the Precambrian Ramah Group and basement rocks in the Nachvak Fiord —Saglek Fiord area, north Labrador. Pap. Geol. Surv. Canada 74-54 (in press)
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Bridgwater, D., Collerson, K.D. The major petrological and geochemical characters of the 3,600 m.y. Uivak gneisses from Labrador. Contr. Mineral. and Petrol. 54, 43–59 (1976). https://doi.org/10.1007/BF00370871
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DOI: https://doi.org/10.1007/BF00370871