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Contributions to Mineralogy and Petrology

, Volume 78, Issue 2, pp 175–188 | Cite as

The Scourie dyke suite: Petrogenesis and geochemical nature of the Proterozoic sub-continental mantle

  • B. L. Weaver
  • J. Tarney
Article

Abstract

The petrogenesis of bronzite-picrite, olivine-gabbro, norite and quartz-tholeiite dykes, which make up the 2.39 b.y. Scourie dyke swarm cutting the Archaean Lewisian gneisses of N.W. Scotland, is interpreted on the basis of their major and trace element geochemistry. Most of the dykes bear primary amphibole and/or phlogopite and, with one exception, are all hypersthene- or quartz-normative. Apart from one tholeiite dyke which shows relative light rare-earth element depletion, all the dykes show enrichment in light rare-earths and large-ion lithophile elements. They do not however show an equivalent enrichment in other incompatible high field strength ions such as Nb and Ta, and in this respect resemble island arc and calc-alkaline basalts. The different dyke types have distinctive rare-earth patterns and other trace element ratios which are maintained over a range of major element compositions.

Petrogenetic modelling of the major and trace element compositions of the various dykes demonstrates that very few can be related by fractional crystallisation. Indeed, even with partial melting mechanisms at least two different mantle sources, with different major and trace element compositons, are required to explain the compositional differences between the major dyke types. The high degrees of mantle melting implied for the generation of the magnesium-rich bronzite-picrites suggests that their rare earth and other trace element patterns closely reflect those of their mantle source. Similar arguments, though less well constrained, can be advanced for the other dyke types. The results suggest that the sub-continental mantle source feeding the dykes was heterogeneous with respect to both major and trace elements, and that their mantle sources must have been enriched in lithophile elements. Enrichment at the time the Lewisian gneisses were generated (i.e. 2.92 b.y. ago) would be compatible with the initial 87Sr/86Sr ratios of the dykes and the inferred Rb/Sr ratios of their mantle sources. The sub-continental mantle sources have thus retained the geochemical signature of the crustgenerating processes some 500 m.y. earlier.

Keywords

Mantle Source Trace Element Pattern Trace Element Geochemistry Trace Element Ratio Melting Mechanism 
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.

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References

  1. Aoki K (1975) Origin of phlogopite and potassic richterite bearing peridotite xenoliths from South Africa. Contrib Mineral Petrol 53:145–156Google Scholar
  2. Allégre CJ, Brevart O, Dupre B, Minster J-F (1980) Isotopic and chemical effects produced in a continuously differentiating converting Earth mantle. Philos Trans R Soc London A297:447–477Google Scholar
  3. Arth JG (1976) Behaviour of trace elements during magmatic processes — a summary of theoretical models and their applications. J Res US Geol Surv 4:41–47Google Scholar
  4. Beach A, Tarney J (1978) Major and trace element patterns established during retrogressive metamorphism of granulite facies gneisses, NW Scotland. Precambrian Res 7:325–348Google Scholar
  5. Best MG (1974) Contrasting types of chromium-spinel peridotite xenoliths in basanitic lavas, western Grand Canyon, Arizona. Earth Planet Sci Lett 23:229–237Google Scholar
  6. Bougault H, Cambon P, Corre O, Treuil M, Joron JL (1979) Evidence for variability of magmatic processes and upper mantle heterogeneity in the axial region of the Mid-Atlantic Ridge near 22° and 36°. Tectonophysics 55:11–34Google Scholar
  7. Chapman HJ (1979) 2,390 M.y. Rb-Sr whole rock age for the Scourie dykes of north-west Scotland. Nature 277:642–643Google Scholar
  8. DePaolo DJ, Wasserburg GJ (1976) Inferences about magma sources and mantle structure from variations of 143Nd/144Nd. Geophys Res Lett 3:743–746Google Scholar
  9. Duncan RA, Green DH (1980) Multistage melting in the formation of ocean crust. Geology 8:22–26Google Scholar
  10. Evans CR, Tarney J (1964) Isotopic ages of Assynt dykes. Nature 204:638–641Google Scholar
  11. Flanagan FJ (1973) 1,972 values for international geochemical reference samples. Geochim Cosmochim Acta 37:1189–1200Google Scholar
  12. Francis DM (1976) The origin of amphibole in lherzolite xenoliths from Nunivak Island, Alaska. J Petrol 17:357–378Google Scholar
  13. Frey FA, Green DH (1974) The mineralogy, geochemistry and origin of lherzolite inclusions in Victorian basanites. Geochim Cosmochim Acta 38:1023–1059Google Scholar
  14. Frey FA, Prinz M (1978) Ultramafic inclusions from San Carlos, Arizona: petrologic and geochemical data bearing on their petrogenesis. Earth Planet Sci Lett 38:129–176Google Scholar
  15. Gill RCO, Bridgwater D (1979) Early Archaean basic magmatism in West Greenland: The geochemistry of the Ameralik dykes. J Petrol 20:695–726Google Scholar
  16. Green DH (1973) Experimental melting studies on a model upper mantle composition at high pressure under water-saturated and water-undersaturated conditions. Earth Planet Sci Lett 19:37–53Google Scholar
  17. Gurney JJ, Hart B (1980) Chemical variations in upper mantle nodules from southern Africa kimberlites. Philos Trans R Soc London A297:273–293Google Scholar
  18. Hamilton PJ, Evensen NM, O'Nions RK, Tarney J (1979) Sm-Nd systematics of Lewisian gneisses: Implications for the origin of granulites. Nature 277:25–28Google Scholar
  19. Hanson GN (1977) Evolution of the suboceanic mantle. J Geol Soc London 134:235–253Google Scholar
  20. Holland JG, Lambert RStJ (1975) The chemistry and origin of the Lewisian gneisses of the Scottish mainland: the Scourie and Inver assemblages and subcrustal accretion. Precambrian Res 2:161–188Google Scholar
  21. Jahn B-M, Sun S-S (1979) Trace element distribution and isotopic composition of Archaean greenstones. Phys Chem Earth 11:597–618Google Scholar
  22. Jahn B-M, Auvray B, Blais S, Capdevila R, Cornichet J, Vical F, Hameurt J (1980) Trace element geochemistry and petrogenesis of Finnish greenstone belts. J Petrol 21:201–244Google Scholar
  23. Jaques AL, Green DH (1980) Anhydrous melting of peridotite at 0–15 kb pressure and the genesis of tholeiitic basalts. Contrib Mineral Petrol 73:287–310Google Scholar
  24. Jordan TH (1978) Composition and development of the continental tectosphere. Nature 274:544–548Google Scholar
  25. Kyle PR (1980) Development of heterogeneities in the sub continental mantle: evidence from the Ferrar Group, Antarctica. Contrib Mineral Petrol 73:89–104Google Scholar
  26. Kushiro I (1972) Effect of water on the composition of magmas formed at high pressures. J Petrol 13:311–334Google Scholar
  27. 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 36:133–156Google Scholar
  28. Langmuir CH, Hanson GN (1980) An evaluation of major element heterogeneity in the mantle sources of basalts. Philos Trans R Soc London A297:383–407Google Scholar
  29. Leake BE, Hendry GL, Kemp A, Plant AG, Harvey PK, Wilson JR, Coats JS, Aucott JW, Lunel T, Howarth RJ (1969) The chemical analysis of rock powders by automatic X-ray fluorescence. Chem Geol 5:7–86Google Scholar
  30. Leeman WP (1976) Petrogenesis of McKinney (Snake River) olivine tholeiite in light of rare-earth element and Cr/Ni distributions. Geol Soc Am Bull 87:1582–1586Google Scholar
  31. Lloyd FE, Bailey DK (1975) Light element metasomatism of the continental mantle: the evidence and the consequences. Phys Chem Earth 9:389–416Google Scholar
  32. Menzies M, Murthy VR (1980) Nd and Sr isotope geochemistry of hydrous mantle nodules and their host alkali basalts: Implications for local heterogenities in metasomatically veined mantle. Earth Planet Sci Lett 46:323–334Google Scholar
  33. Mysen BO (1979) Trace-element partitioning between garnet peridotite minerals and water-rich vapour: experimental data from 5 to 30 kbar. Am Mineral 64:274–287Google Scholar
  34. Nakamura N (1974) Determination of REE, Ba, Fe, Mg, Na and K in carbonaceous and ordinary chondrites. Geochim Cosmochim Acta 38:757–775Google Scholar
  35. Nesbitt RW, Sun S-S (1976) Geochemistry of Archaean spinifex textured peridotites and magnesian and low magnesian tholeiites. Earth Planet Sci Lett 31:433–453Google Scholar
  36. O'Hara MJ (1961) Petrology of the Scourie dyke, Sutherland. Mineral Mag 32:848–865Google Scholar
  37. O'Hara MJ (1962) Some intrusions in the Lewisian complex near Badcall, Sutherland. Trans Edinburgh Geol Soc 19:201–207Google Scholar
  38. O'Hara MJ (1968) The bearing of phase equilibrium studies in synthetic and natural systems on the origin and evolution of basic and ultrabasic rocks. Earth Sci Rev 4:69–133Google Scholar
  39. O'Nions RK, Hamilton PJ, Evensen NM (1977) Variations in 143Nd/144Nd and 87Sr/86Sr ratios in oceanic basalts. Earth Planet Sci Lett 34:13–22Google Scholar
  40. O'Nions RK, Carter SR, Evensen NM, Hamilton PJ (1979) Geochemical and cosmochemical applications of Nd isotope analysis. Ann Rev Earth Planet Sci 7:11–38Google Scholar
  41. Oxburgh RE, Parmentier EM (1978) Thermal processes in the formation of continental lithosphere. Philos Trans R Soc London A288:415–429Google Scholar
  42. Paul DK, Potts PJ, Gibson IL, Harris PG (1975) Rare-earth abundances in Indian kimberlite. Earth Planet Sci Lett 38:211–236Google Scholar
  43. Pearce JA, Norry MJ (1979) Petrologic implications of Ti, Zr, Y and Nb variations in volcanic rocks. Contrib Mineral Petrol 69:33–47Google Scholar
  44. Saunders AD, Tarney J, Weaver SD (1980) Transverse geochemical variations across the Antarctic Peninsula: implications for the genesis of calcalkaline magmas. Earth Planet Sci Lett 46:344–360Google Scholar
  45. Sheraton JW, Skinner AC, Tarney J (1973) The geochemistry of the Scourian gneisses of the Assynt district. In: Park RG, Tarney J (eds) The early Precambrian of Scotland and related rocks of Greenland. Univ Keele, pp 13–30Google Scholar
  46. Shimizu N (1975) Rare-earth elements in garnets and clinopyroxenes from garnet lherzolite nodules in kimberlite. Earth Planet Sci Lett 25:26–32Google Scholar
  47. Stern CR (1980) Geochemistry of Chilean ophiolites: evidence for the compositional evolution of the mantle source of back-arc basin basalts. J Geophys Res 85:955–966Google Scholar
  48. Stosch H-G, Seck HA (1980) Geochemistry and mineralogy of two spinel peridotite suites from Dreiser Weiher, West Germany. Geochim Cosmochim Acta 44:457–470Google Scholar
  49. Stosch H-G, Carlson RW, Lugmair GW (1980) Episodic mantle differentiation: Nd and Sr isotopic evidence. Earth Planet Sci Lett 47:263–271Google Scholar
  50. Sun S-S, Nesbitt RW (1977) Chemical heterogeneity of the Archaean mantle, composition of the Earth and mantle evolution. Earth Planet Sci Lett 35:429–448Google Scholar
  51. Sun S-S, Nesbitt RW (1978) Petrogenesis of Archaean ultrabasic and basic volcanics: evidence from rare-earth elements. Contrib Mineral Petrol 65:301–325Google Scholar
  52. Sun S-S, Nesbitt RW, Sharaskin AYa (1979) Geochemical characteristics of mid-ocean ridge basalts. Earth Planet Sci Lett 44:119–138Google Scholar
  53. Tarney J (1963) Assynt dykes and their metamorphism. Nature 199:672–674Google Scholar
  54. Tarney J (1973) The Scourie dyke suite and the nature of the Inverian event in Assynt. In: Park RG, Tarney J (eds) The early Precambrian of Scotland and related rocks of Greenland. Univ Keele, pp 105–118Google Scholar
  55. Tarney J, Saunders AD, Weaver SD, Donnellan NCB, Hendry GL (1979) Minor element geochemistry of basalts from Leg 49, North Atlantic ocean. In: Initial reports of the Deep Sea Drilling Project Vol 49. US Government Printing Office Washington, pp 657–691Google Scholar
  56. Tarney J, Wood DA, Saunders AD, Cann JR, Varet J (1980) Nature of mantle heterogeneity in the North Atlantic: evidence from deep sea drilling. Philos Trans R Soc London A 297:179–202Google Scholar
  57. Weaver BL, Tarney J (1979) Thermal aspects of komatiite generation and greenstone belt models. Nature 279:689–692Google Scholar
  58. Weaver BL, Tarney J (1980) Rare-earth geochemistry of Lewisian granulite facies gneisses, NW Scotland: implications for the petrogenesis of the Archaean lower continental crust. Earth Planet Sci Lett 51:279–296Google Scholar
  59. Weaver BL, Tarney J (1981a) Chemical changes during dyke metamorphism in high-grade basement terrains. Nature 289:47–49Google Scholar
  60. Weaver BL, Tarney J (1981b) The Scourie dyke suite: Petrography and Mineral chemistry (in preparation)Google Scholar
  61. Whitford DJ, Nicholls IA, Taylor SR (1979) Spatial variations in the geochemistry of Quaternary lavas across the Sunda arc in Java and Bali. Contrib Mineral Petrol 70:341–356Google Scholar
  62. Wilshire HG, Trask NT (1971) Structural and textural relationships of amphibole and phlogopite in peridotite inclusions. Dish Hill, California. Am Mineral 56:240–255Google Scholar
  63. Wood DA (1979) Dynamic partial melting: its application to the petrogeneses of basalt lava series from Iceland, the Faeroe Islands, the Isle of Skye (Scotland) and the Troodos Massif (Cyprus). Geochim Cosmochim Acta 43:1031–1046Google Scholar
  64. Wood DA, Tarney J, Varet J, Saunders AD, Bougault H, Joron J-L, Treuil M, Cann JR (1979a) Geochemistry of basalts drilled in the North Atlantic by IPOD Leg 49: implications for mantle heterogeneity. Earth Planet Sci Lett 42:77–97Google Scholar
  65. Wood DA, Joron J-L, Treuil M, Norry MJ, Tarney J (1979b) Elemental and Sr isotope variations in basic lavas from Iceland and the surrounding ocean floor: the nature of mantle source inhomogeneities. Contrib Mineral Petrol 70:319–339Google Scholar
  66. Wood DA, Tarney J, Weaver BL (1981) Trace element variations in Atlantic Ocean basalts and Proterozoic dykes from northwest Scotland: their bearing upon the nature and geochemical evolution of the upper mantle. Tectonophysics 75:91–112Google Scholar

Copyright information

© Springer-Verlag 1981

Authors and Affiliations

  • B. L. Weaver
    • 1
  • J. Tarney
    • 1
  1. 1.Department of GeologyUniversity of LeicesterLeicesterGreat Britain

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