Contents Volume 52, 1991 Magnetic and tectonic history of the Late Proterozoic Upper Little Dal and Coates Lake Groups of northwestern Canada J.K. Park and C.W. Jefferson (Ottawa, Ont., Canada) The petrography and geochemistry of the Clericy Pluton: an ultrapotassic poyroxenite-syenite suite of late Archean age from the Abitibi region, Quebec J.H. Bourne (Montréal, Que., Canada) and M. L’Heureux ( Destor, Que., Canada ) Geochemistry of metasedimentary rocks in the late Archean Hemlo—Heron Bay greenstone belt, Superior Province, Ontario: implications for provenance and tectonic setting Yuanming Pan, M.E. Fleet (London, Ont., Canada) and W.E. Stone (Hamilton, Ont., Canada) Archean orogenic ultrapotassic magmatism: an example from the southern Abitibi greenstone belt M.R. Lafléche, C. Dupuy (Montpellier, France) and J. Dostal (Halifax, N.S., Canada ) Metagabbros in the Modum Complex, southern Norway: an important heat source for Sveconorwegian metamorphism ].A. Munz and R. Morvil (Oslo, Norway ) The conformable emplacement of the Bushveld mafic rocks along a regional unconformity in the Transvaal succession of South Africa E.S. Cheney (Johannesburg, South Africa) and D. Twist (Pretoria, South Africa) Structural history of the southwestern corner of the Kaapvaal Craton and the adjacent Namaqua realm: new observations and a reappraisal W. Altermann and I.W. Halbich (Stellenbosch, South Africa) Origin and order of cyclic growth patterns in mat-ministromatolite bioherms from the Proterozoic Wumishan formation, North China Ruiji Cao (Nanjing, P.R. China) Structural pattern of Pan-African rocks around Moyale, southern Ethiopia S. Tolessa, F.F. Bonavia, M. Solomon, A. Haile-Meskel and E. Teferra (Addis Ababa, Ethiopia) Early Proterozoic continental tholeiites from western Bergslagen, Central Sweden, I. Petrology, geochemical petrogenesis and geotectonic setting P.J. Valbracht, H. Helmers and F.F. Beunk (Amsterdam, The Netherlands) Early Proterozoic continental tholeiites from western Bergslagen, Central Sweden, II. Nd and Sr isotopic variations and implications from Sm-Nd systematics for the Svecofennian sub-continental mantle P.J. Valbracht (Amsterdam, The Netherlands) Early Proterozoic continental tholeiites from western Bergslagen, Central Sweden, III. Geodynamic inferences F.F. Beunk and P.J. Valbracht (Amsterdam, The Netherlands) Relationships between calc-alkaline acidic and basic (mantle-derived )m agmas in Late Archean composite dykes, Kambalda Goldfield, Western Australia C.S. Perring (Nedlands, W.A., Australia) and N.M.S. Rock (Wembley, W.A., Australia ) SHRIMP U-Pb zircon geochronology of the Narryer Gneiss Complex, Western Australia A.P. Nutman, P.D. Kinny, W. Compston and I.S. Williams (Canberra, A.C.T., Australia ) Oxygen and carbon isotope geochemistry of the 3.2 Ga Kaap Valley tonalite, Barberton greenstone belt, South Africa K. Faure and C. Harris (Rondebosch, South Africa) U-Pb zircon geochronology of Precambrian tin-bearing continental-type acid magmatism in central Brazil M.M. Pimentel (Brasilia, Brazil and Oxford, UK), L. Heaman (Toronto, Ont., Canada), R.A. Fuck and O.J. Marini (Brasilia, Brazil ) Decomposition of ocean waters by potassium-40 radiation 3800 Ma ago as a source of oxygen and oxidizing species 1.G. Dragani¢ (Beograd, Yugoslavia) , E. Bjergbakke (Roskilde, Denmark) , Z.D. Dragani¢ (Beograd, Yugoslavia) and K. Sehested (Roskilde, Denmark ) Petrological and stable isotope studies of carbonate and sulfide minerals from the Gunflint Formation, Ontario: evidence for the origin of early Proterozoic iron-formation W.J. Carrigan and E.M. Cameron (Ottawa, Ont., Canada)