Abstract
There is little concensus on the relative importance of crystal fractionation and differential partial melting to the chemical diversity observed within most types of volcanic suites. A resolution to this controversy is best sought in suites containing high MgO lavas such as the Chukotat volcanics of the Proterozoic Cape Smith foldbelt, Ungava, Quebec. The succession of this volcanic suite consists of repetitive sequences, each beginning with olivine-phyric basalt (19-12 wt% MgO), grading upwards to pyroxene-phyric basalt (12-8 wt% MgO) and then, in later sequences, to plagioclase-phyric basalt (7-4 wt% MgO). Only the olivine-phyric basalts have compositions capable of equilibrating with the upper mantle and are believed to represent parental magmas for the suite. The pyroxene-phyric and plagioclase-phyric basalts represent magmas derived from these parents by the crystal fractionation of olivine, with minor chromite, clinopyroxene and plagioclase. The order of extrusion in each volcanic sequence is interpreted to reflect a density effect in which successively lighter, more evolved magmas are erupted as hydrostatic pressure wanes. The pyroxene-phyric basalts appear to have evolved at high levels in the active part of the conduit system as the eruption of their parents was in progress. The plagioclase-phyric basalts may represent residual liquids expelled from isolated reservoirs along the crust-mantle interface during the late stages of volcanic activity.
A positive correlation between FeO and MgO in the early, most basic olivine-phyric basalts is interpreted to reflect progressive adiabatic partial melting in the upper mantle. Although this complicates the chemistry, it is not a significant factor in the compositional diversification of the volcanic suite. The preservation of such compositional melting effects, however, suggests that the most basic olivine-phyric basalts represent primitive magmas. The trace element characteristics of these magmas, and their derivatives, indicate that the mantle source for the Chukotat volcanics had experienced a previous melting event.
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References
Arndt NT, Nesbitt RW (1981) Trace elements and the origin of komatiites and komatiitic basalts. In: Arndt NR, Nisbet EG (eds) Komatiites. Allen and Unwin, in press
Arndt NT (1977) Ultrabasic magmas and high-degree melting of the mantle. Contrib Mineral Petrol 64:205–221
Arndt NT, Brooks C (1980) Penrose Conference Report: Komatiites. Geology 8:155–156
Arndt NT, Naldrett AJ, Pyke DR (1977) Komatiite and iron-rich tholeiitic lavas of Munro Township, northeast Ontario. J Petrol 21:629–651
Arth JG, Arndt NT, Naldrett AJ (1977) Genesis of Archean komatiites — trace element evidence from Munro Township. Geology 5:590–594
Arth JG (1976) Behaviour of trace elements during magmatic processes — a summary of theoretical models and their application. J Res USGS 4:41–47
Baragar WRA, Scoates RFJ (1981) The Circum-Superior Belt: A Proterozoic plate margin ? In: Kröner A (ed) Precambrian plate tectonics. Elsevier, Amsterdam, pp 297–330
Bottinga Y, Weill DF (1970) Densities of liquid silicate systems calculated from partial molar volumes of oxide components. Am J Sci 169–182
Carter NL (1970) Mineralogy and chemistry of the earth's upper mantle based on the partial fusion — partial crystallization model. Bull Geol Soc Am 81:2021–2034
Clarke DB (1970) Tertiary basalts from Baffin Bay: Possible primary magma from the mantle. Contrib Mineral Petrol 25:203–204
Cox KG (1980) A model for flood basalt volcanism. J Petrol 21:629–650
Dimroth E, Baragar WRA, Bergeron R, Jackson GD (1970) The filling of the Circum-Ungava Geosyncline. Geol Surv Can Paper 74-1A
Ducan RA, Green DH (1980) The role of multi-stage melting in the formation of oceanic crust. Geology 8:22–26
Francis DM, Hynes AJ (1979) Komatiite-derived tholeiites in the Proterozoic of New Quebec. Earth Planet Sci Lett 44:473–481
Gariepy C, Ludden JN Brooks C, Van Schmus R (1981) The petrogenesis of granitic rocks from the Chibougamau district, western Abitibi Belt. Precamb Res (in press)
Green DH, Hibberson WO, Jacques AL (1979) Petrogenesis of midocean ridge basalts. In: McElhinny MW (ed) The earth: its origin, structure and evolution. Academic Press, New York, pp 265–300
Green DH, Ringwood AE (1967) The genesis of basaltic magmas. Contrib Mineral Petrol 15:103–190
Hanson GN, Langmuir CH (1978) Modelling of major elements in mantle-melt systems using trace element approaches. Geochim Cosmochim Acta 42:725–741
Haughton DR, Roeder PL, Skinner BJ (1974) Solubility of sulfur in mafic magmas. Econ Geol 69:451–467
Hynes AJ, Francis DM (1981a) A transect of the early Proterozoic Cape Smith foldbelt, New Quebec. Tectonophysics (in press)
Hynes A, Francis DM (1981 b) Komatiitic basalts of the Cape Smith fold belt, New Quebec, Canada. In: Arndt NT, Nisbet EG (eds) Komatiites. Allen and Unwin (in press)
Jakobsson SP, Jonsson J, Shido F (1978) Petrology of the Western Reykjanes Peninsula. J Petrol 19:669–705
Jensen LS (1976) A new cation plot for classifying sub-alkalic volcanic rocks. Ont Dept Mines Misc Paper 66
Langmuir CH, Bender JF, Bence AE, Hanson GN, Taylor SR (1977) Petrogenesis of basalts from the FAMOUS area: Mid-Atlantic Ridge. Earth Planet Sci Lett 36:133–156
Langmuir CH, Hanson GN (1980) An evaluation of major element heterogeneity in the mantle sources of basalts. Philos Trans R Soc Lond A297:383–408
Ludden JN, Gelinas L (1981) Trace element characteristics of komatiites and komatiitic basalts from the Abitibi metavolcanic belt of Quebec. In: Arndt NT, Nisbet EG (eds) Komatiites. Allen and Unwin (in press)
Maaløe S, Jakobsson SP (1980) The PT phase relations of a primary oceanite from the Reykjanes Peninsula, Iceland. Lithos 13:237–246
Mysen BO, Kushiro I, Nicholls IA, Ringwood AE (1974) A possible mantle origin of andesite magmas: Discussion of a paper by Nicholls and Ringwood. Earth Planet Sci Lett 21:221–229
Nesbitt RW, Sun S-S (1980) Geochemical features of some Archean and post-Archean high-magnesium-low-alkali liquids. Philos Trans R Soc Lond A297:365–381
Nesbittt RW, Sun S-S, Purvis AC (1979) Komatiites: Geochemistry and genesis. Can Mineral 17:165–186
O'Hara MJ (1977) Geochemical evolution during fractional crystallization of a periodically refilled magma chamber. Nature 266:503–507
Pearce JA, Norry MJ (1979) Petrogenetic implications of Ti, Zr, Y, and Nb variations in volcanic rocks. Contrib Mineral Petrol 69:33–47
Presnall DC, Dixon JR, O'Donnel TH, Dixon SA (1979) Generation of mid-ocean ridge tholeiites. J Petrol 20:3–36
Roeder PL, Emslie RF (1970) Olivine-liquid equilibrium. Contrib Mineral Petrol 29:275–289
Schroeder B, Thompson G, Sulanowska M, Ludden JN (1980) Analysis of geological materials using an automated X-ray fluorescence system. X-Ray Spect 9:198–205
Schwarz EJ, Fujiwara Y (1977) Komatiitic basalts from the Proterozoic Cape Smith Range in Northern Quebec, Canada. Geol Assoc Can Spec Pap 16:193–201
Stolper E (1980) A phase diagram for mid-ocean ridge basalts: Preliminary results and implications for petrogenesis. Contrib Mineral Petrol 74:13–27
Sun S-S, Nesbitt RW (1978) Petrogenesis of Archean ultrabasic and basic volcanics: evidence from rare earth elements. Contrib Mineral Petrol 65:301–325
Sun S-S, Nesbitt RW (1977) Chemical heterogeneity of the Archean mantle composition of the earth and mantle evolution. Earth Planet Sci Lett 35:429–448
Wright TL, Doherty PC (1970) A linear programming and least squares computer method for solving petrographic mixing problems. Geol Soc Amer Bull 81:1995–2008
Zindler A (1981) Nd and Sr isotopic studies of komatiites and related rocks. In: Arndt NT, Nisbet EG (eds) Komatiites. Allen and Unwin (in press)
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Francis, D.M., Hynes, A.J., Ludden, J.N. et al. Crystal fractionation and partial melting in the petrogenesis of a Proterozoic high-MgO volcanic suite, Ungava, Québec. Contr. Mineral. and Petrol. 78, 27–36 (1981). https://doi.org/10.1007/BF00371141
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DOI: https://doi.org/10.1007/BF00371141