Backarc Basins pp 281-314 | Cite as

Tectonic Framework of the East Scotia Sea

  • Peter F. Barker


This chapter reviews the tectonic evolution of the East Scotia Sea, testing and extending previously published conclusions in light of the additional and expanded data sets now available. The East Scotia Sea floor was generated behind the east-migrating South Sandwich Trench, at a spreading center now lying along 30°W. On its western flank, lineated magnetic anomalies are identified out to at least anomaly 5 (10–11 Ma) and probably out to anomaly 5B (ca. 15 Ma). Spreading was essentially symmetric at about 27 mm/year from 15 Ma to about 5–7 Ma, then slowly accelerated. From 4 Ma to 1.7 Ma, spreading was at 50 mm/year and slightly asymmetric. Since 1.7 Ma, spreading has been up to 15% asymmetric, favoring accretion to the arc flank, within an overall rate of 65 mm/year. Asymmetry is confined within segments bounded by fracture zones that in some cases were created only at 1.7 Ma. A relation between asymmetric spreading, segmentation, and ridge migration seems likely. The median valley is between 6 and 20 km wide and exceptionally is up to 1200 m deep, but usually is smaller and the ridge flanks smooth, as is typical of faster spreading. The ridge crest depth is 500 m or more deeper than the global MOR average. Before 3–4 Ma the ridge was rougher and probably the ridge crest shallower.

In the south, the extensional zone is narrower, and the present spreading probably started only about 3 Ma, after an eastward ridge jump associated with ridge crest-trench collision in the South Sandwich forearc. The ridge jump caused fragments of the previous South Sandwich arc and forearc to be transferred to the Scotia and Antarctic plates, as part of the inevitable adjustment of plate boundaries following ridge crest collision. The detailed history of collision along the South Scotia Ridge is poorly known, but previous collisions involved similar transfers of arc and forearc fragments and may have influenced previous episodes of backarc extension.

On the eastern flank, volcanoes of the South Sandwich island arc lie on ocean floor aged from about 10 Ma to as young as 3 Ma, formed during the present spreading episode. Both island-arc and backarc extensional volcanic geochemistry seems to reflect varying degrees of contamination of the mantle, by fluids from the subducting South American lithosphere, and of partial melting. The rocks appear similar to but simpler than those from other intraoceanic backarc environments, showing only minor prior source depletion. However, the arc chemistry is geographically heterogeneous and does not reflect systematic north-south variation in the age and sediment cover of the subducted slab, as might have been expected.

The distribution of older magnetic anomalies on the western flank suggests that congruent ocean floor of the eastern flank should occupy most of the present forearc. If so, there has been significant tectonic erosion of the northeast corner of the forearc, where also serpentinized ultrabasic rocks have been dredged. This corner lies directly above the locus of tearing of the subducting slab at its northern end. In the southern forearc off Montagu Island, dredge hauls have identified an abnormally elevated block as a fragment of a 31 Ma calc-alkaline arc volcano, presumably associated with the early stages of Scotia Sea evolution.

There is no correlation between the level of development of the accretionary prism in the lower forearc and the sediment cover of the subducting slab. Variations along strike in the elevation of the forearc mid-slope high have controlled the transport of arc volcaniclastic sediment to the trench, and hence influenced accretionary prism development to some extent, but the main control appears to have been tectonic.


Magnetic Anomaly Sandwich Plate Ocean Floor Backarc Basin Accretionary Prism 
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.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Allen, A. 1966. Seismic refraction investigations in the Scotia Sea, Br. Antarct. Surv. Sci. Rep. 55: 44 ppGoogle Scholar
  2. Alvarez, W. 1982. Geological evidence for the geographical pattern of mantle return flow and the driving mechanism of plate tectonics, J. Geophys. Res. 87:6697–6710CrossRefGoogle Scholar
  3. Atwater, T. 1989. Plate tectonic history of the northeast Pacific and western North America, in The Eastern Pacific Ocean and Hawaii (E. L. Winterer, D. M. Hussong, and R. W. Decker, eds.), pp. 21–72, Geol. Soc. America, BoulderGoogle Scholar
  4. Baker, P. E. 1968. Comparative volcanology and petrology of the Atlantic island arcs, Bull. Volcanol. 32:189–206CrossRefGoogle Scholar
  5. Baker, P. E. 1978. The South Sandwich Islands: iii. petrology of the volcanic rocks, Br. Antarct. Surv. Sci. Rept. 93: 34 ppGoogle Scholar
  6. Baker, P. E. 1990. E. South Sandwich Islands, in Volcanoes of the Antarctic Plate and Southern Oceans (W. E. LeMasurier and J. W. Thomson, eds.), Vol. 48, pp. 361–395, Antarctic Res. Ser., American Geophysical Union, Washington, DCGoogle Scholar
  7. Barker, P. F. 1970. Plate tectonics of the Scotia Sea region, Nature 228:1293–1296CrossRefGoogle Scholar
  8. Barker, P. F. 1972. A spreading centre in the East Scotia Sea, Earth Planet. Sci. Lett. 15:123–132CrossRefGoogle Scholar
  9. Barker, P. F. 1979. The history of ridge-crest offset at the Falkland-Agulhas fracture zone from a small-circle geophysical profile, Geophys. J. R. Astron. Soc. 59:131–145CrossRefGoogle Scholar
  10. Barker, P. F. 1982. The Cenozoic subduction history of the Pacific margin of the Antarctic Peninsula: ridge crest-trench interactions, J. Geol. Soc. London 139:787–801CrossRefGoogle Scholar
  11. Barker, P. F., Barber, P. L., and King, E. C. 1984. An early Miocene ridge crest-trench collision on the South Scotia Ridge near 36W, Tectonophysics 102:315–332CrossRefGoogle Scholar
  12. Barker, P. F., and Burrell, J. 1977. The opening of Drake Passage, Mar. Geol. 25:15–34CrossRefGoogle Scholar
  13. Barker, P. F., Dalziel, I. W. D., and Storey, B. C. 1991. Tectonic development of the Scotia Arc region, in Geology of Antarctica (R. J. Tingey, ed.), pp. 215–248, Oxford University Press, OxfordGoogle Scholar
  14. Barker, P. F., and Hill, I. A. 1980. Asymmetric spreading in back-arc basins, Nature 285:562–564CrossRefGoogle Scholar
  15. Barker, P. F., and Hill, I. A. 1981. Back-arc extension in the Scotia Sea, Phil. Trans. R. Soc. Lond. A 300:249–262CrossRefGoogle Scholar
  16. Barker, P. F., Hill, I. A., Weaver, S. D., and Pankhurst, R. J. 1982. The origin of the eastern South Scotia Ridge as an intra-oceanic island arc, in Antarctic Geoscience (C. Craddock, ed.), pp. 203–211, Univ. Wisconsin Press, MadisonGoogle Scholar
  17. Barker, P. F., and Lawver, L. A. 1988. South American-Antarctic plate motion over the past 50 Myr, and the evolution of the South American-Antarctic Ridge, Geophys. J. R. Astron. Soc. 94:377–386CrossRefGoogle Scholar
  18. Barrow, J. Sir. 1830. Account of the island of Deception, one of the New Shetland Isles, J. R. Geogr. Soc. 1:62–66Google Scholar
  19. Brett, C. P. 1977. Seismicity of the South Sandwich Islands region, Geophys. J. R. Astron. Soc. 51:453–464CrossRefGoogle Scholar
  20. Brett, C. P., and Griffiths, D. H. 1975. Seismic wave attenuation and velocity anomalies in the eastern Scotia Sea, Nature 253:613–614CrossRefGoogle Scholar
  21. Cande, S. C., and Kent, D. V. 1992. A new geomagnetic polarity time scale for the Late Cretaceous and Cenozoic, J. Geophys. Res. 97:13,917–13,951Google Scholar
  22. Cande, S. C., Leslie, R. B., Parra, J. C., and Hobart, M. 1987. Interaction between the Chile Ridge and Chile Trench: geophysical and geothermal evidence, J. Geophys. Res. 92:495–520CrossRefGoogle Scholar
  23. Chase, C. G. 1978. Extension behind island arcs and motions relative to hotspots, J. Geophys. Res. 83:5385–5388CrossRefGoogle Scholar
  24. Cohen, R. S., and O’Nions, R. K. 1982. Identification of recycled continental material in the mantle from Sr, Nd and Pb isotope investigation, Earth Planet. Sci. Lett. 61:73–84CrossRefGoogle Scholar
  25. Cook, J. 1777. A voyage towards the South Pole and around the World Performed in His Majesty’s Ships the “Resolution” and “Adventure” in the Years 1772–75, Shanan and Cadell, LondonGoogle Scholar
  26. Debenham, F. 1945. The Voyage of Captain Bellingshausen to the Antarctic Seas, 1819–1821 (translated from the Russian), Vols. 1, 2, Hakluyt Society, LondonGoogle Scholar
  27. DeMets, C., Gordon, R. G., Argus, D. F., and Stein, S. 1990. Current plate motions, Geophys. J. Int. 101:425–478CrossRefGoogle Scholar
  28. Elsasser, W. M. 1971. Sea floor spreading as thermal convection, J. Geophys. Res. 76:1101–1112CrossRefGoogle Scholar
  29. Ewing, J. I., Ludwig, W. J., Ewing, M., and Eittreim, S. L. 1971. Structure of the Scotia Sea and Falkland Plateau, J. Geophys. Res. 76:7118–7137CrossRefGoogle Scholar
  30. Forsyth, D. W. 1975. Fault plane solutions and tectonics of the South Atlantic and Scotia Sea, J. Geophys. Res. 80:1429–1443CrossRefGoogle Scholar
  31. Fryer, P. 1992. A synthesis of Leg 125 drilling of serpentine seamounts on the Mariana and Izu-Bonin fore-arcs, in Proc. ODP, Sci Results, 125 (P. Fryer, J. A. Pearce, et al., eds.), pp. 593–614, Ocean Drilling Program, College Station, TXCrossRefGoogle Scholar
  32. Gass, I. G., Harris, P. G., and Holdgate, M. W. 1963. Pumice eruption in the area of the South Sandwich Islands, Geol Mag. 100:321–330CrossRefGoogle Scholar
  33. Griffiths, D. H. 1963. Geophysical investigations in the Scotia Arc and Graham Land, Br. Antarct. Surv. Bull. 1: 27–32Google Scholar
  34. Griffiths, D. H., Riddihough, R. P., Cameron, H. A. D., and Kennet, P. 1964. Geophysical investigations of the Scotia Arc, Br. Antarct. Surv. Sci. Rep. 46: 43 ppGoogle Scholar
  35. Gripp, A. E., and Gordon, R. J. 1990. Current plate velocities relative to the hotspots incorporating the NUVEL-1 global plate motion model, Geophys. Res. Lett. 17:1109–1112CrossRefGoogle Scholar
  36. Hamilton, I. W. 1989. Geophysical investigations of subduction-related processes in the Scotia Sea, unpublished Ph.D. thesis, Birmingham University, U.KGoogle Scholar
  37. Harland, W. B., Cox, A. V., Llewellyn, P. G., Pickton, C. A. G., Smith, A. G., and Walters, R. 1982. A Geologic Time Scale, Cambridge University Press, CambridgeGoogle Scholar
  38. Harrington, P. K., Barker, P. F., and Griffiths, D. H. 1972. Crustal structure of the South Orkney Islands area from seismic refraction and magnetic measurements, in Antarctic Geology and Geophysics (R. J. Adie, ed.), pp. 27–32, Universitetsforlaget, OsloGoogle Scholar
  39. Hawkes, D. D. 1962. The structure of the Scotia Arc, Geol. Mag. 99:85–91CrossRefGoogle Scholar
  40. Hawkesworth, C. J., O’Nions, R. K., Pankhurst, R. J., and Evensen, N. M. 1977. A geochemical study of island-arc and back-arc tholeiites from the Scotia Sea, Earth Planet. Sci. Lett. 36:253–262CrossRefGoogle Scholar
  41. Heezen, B. C., and Johnson, G. L. 1965. The South Sandwich Trench, Deep-Sea Res. 12:185–197Google Scholar
  42. Herdman, H. F P. 1948. Soundings taken during Discovery investigations 1932–1939, Discovery Reports 25: 39–106Google Scholar
  43. Hill, I. A., and Barker, P. F. 1980. Evidence for Miocene back-arc spreading in the central Scotia Sea, Geophys. J. R. Astron. Soc. 63:427–440CrossRefGoogle Scholar
  44. Holdgate, M. W., and Baker, P. E. 1979. The South Sandwich Islands. I: General description, Br. Antarct. Surv. Sci. Rept. 91: 76 ppGoogle Scholar
  45. Isacks, B., and Molnar, P. 1971. Distribution of stresses in the descending lithosphere from a global survey of focal mechanism solutions of mantle earthquakes, Rev. Geophys. Space Phys. 9:103–174CrossRefGoogle Scholar
  46. Jarrard, R. D. 1986. Relations among subduction parameters, Rev. Geophys. 24:217–284CrossRefGoogle Scholar
  47. Kemp, S., and Nelson, A. L. 1931. The South Sandwich Islands, Discovery Reports 3:133–198Google Scholar
  48. LaBrecque, J. L., Kent, D. V., and Cande, S. C. 1977. Revised magnetic polarity time scale for late Cretaceous and Cenozoic time, Geology 5:330–335CrossRefGoogle Scholar
  49. Langel, R. A. 1992. International geomagnetic reference field: The sixth generation, J. Geomagn. Geoelectr. 44:679–707CrossRefGoogle Scholar
  50. Lawver, L. A., and Dick, H. J. B. 1983. The American-Antarctic Ridge. J. Geophys. Res. 88:8193–8202CrossRefGoogle Scholar
  51. Livermore, R. A., and Woollett, R. W. 1993. Seafloor spreading in the Weddell Sea and southwest Atlantic since the late Cretaceous, Earth Planet. Sci. Lett. 117:475–495CrossRefGoogle Scholar
  52. Ludwig, W. J., and Rabinowitz, P. D. 1982. The collision complex of the North Scotia Ridge, J. Geophys. Res. 87:3731–40CrossRefGoogle Scholar
  53. Luff, I. W., 1982. Petrogenesis of the island arc tholeiite series of the South Sandwich Islands, unpublished Ph.D. thesis, University of Leeds, U.KGoogle Scholar
  54. Macdonald, D. I. M., Storey, B. C., and Thomson, J. W. 1987. South Georgia, p. 63, BAS GEOMAP Series, Sheet 1, 1:250,000, Geological map and supplementary text, British Antarctic Survey, CambridgeGoogle Scholar
  55. Mattey, D. P., Carr, R. H., Wright, I. P., and Pillinger, C. P. 1984. Carbon isotopes in submarine basalts, Earth Planet. Sci. Lett. 70:196–206CrossRefGoogle Scholar
  56. Matthews, D. H. 1959. Aspects of the geology of the Scotia Arc, Geol. Mag. 95:425–441CrossRefGoogle Scholar
  57. Maurer, H., and Stocks, T. 1933. Die echolotungen des Meteor. Wiss. Ergebn. Deut. Atlantic Expedition Meteor, 1925–27, pp. 1–309Google Scholar
  58. McAdoo, D. C., and Marks, K. M. 1992. Gravity fields of the Southern Ocean from Geosat data, J. Geophys. Res. 97:3247–3260CrossRefGoogle Scholar
  59. Menard, H. W. 1978. Fragmentation of the Farallon plate by pivoting subduction, J. Geol. 86:99–110CrossRefGoogle Scholar
  60. Minster, J. B., and Jordan, T. H. 1978. Present-day plate motions, J. Geophys Res. 83:5331–5354CrossRefGoogle Scholar
  61. Muenow, D. W., Liu, N. W. K., Garcia, M. O., and Saunders, A. D. 1980. Volatiles in submarine volcanic rocks from the spreading axis of the East Scotia Sea back-arc basin, Earth Planet. Sci. Lett. 47:272–278CrossRefGoogle Scholar
  62. NGDC-NOAA. 1993. Global Relief CD-ROM Data Set, National Geophysical Data Center, BoulderGoogle Scholar
  63. Parsons, B. L., and Sclater, J. G. 1977. An analysis of the variation of ocean floor bathymetry and heat flow with age, J. Geophys. Res. 82:803–827CrossRefGoogle Scholar
  64. Pearce, J. A. 1982. Trace element characteristics of lavas from destructive plate boundaries, in Andesites: Orogenic Andesites and Related Rocks (R. S. Thorpe, ed.), pp. 525–548, Wiley, ChichesterGoogle Scholar
  65. Pearce, J. A., Baker, P. E., Harvey, P. E., and Luff, I. W. in press. Geochemical evidence for subduction fluxes, mantle melting and fractional crystallization beneath the South Sandwich island arc, J. Petrol. Google Scholar
  66. Pelayo, A. M., and Wiens D. A. 1989. Seismotectonics and relative plate motions in the Scotia Sea region, J. Geophys. Res. 94:7293–7320CrossRefGoogle Scholar
  67. Saunders, A. D., and Tarney, J. 1979. The geochemistry of basalt from a back-arc spreading centre in the East Scotia Sea, Geochim. Cosmochim. Acta 43:555–572CrossRefGoogle Scholar
  68. Saunders, A. D., and Tarney, J. 1991. Back-arc basins, in Oceanic Basalts (P. A. Floyd, ed.), pp. 219–263, Blackie, Van Nostrand, Reinhold, GlasgowCrossRefGoogle Scholar
  69. Simpson, P., and Griffiths, D. H. 1982. The structure of the South Georgia continental block, in Antarctic Geoscience (C. Craddock, ed.), pp. 185–192, University of Wisconsin Press, MadisonGoogle Scholar
  70. Steiger, R. H., and Jaeger, E. 1977. Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmochronology, Earth Planet. Sci. Lett. 36:359–362CrossRefGoogle Scholar
  71. Suess, E. 1909. Das Antlitz der Erde, III Band, Freytag, LeipzigGoogle Scholar
  72. Taylor, B. 1987. A geophysical survey of the Woodlark-Solomons region, in Marine Geology, Geophysics, and Geochemistry of the Woodlark Basin-Solomon Islands (B. Taylor and N. F. Exon, eds.), Earth Science Ser., Vol. 7, pp. 25–48, Circum-Pacific Council for Energy and Mineral Resources, Earth Science Ser., Houston, TXGoogle Scholar
  73. Tectonic Map of the Scotia Arc. 1985. 1:3000000. BAS (Misc) 3, British Antarctic Survey, CambridgeGoogle Scholar
  74. Tomblin, J. F. 1979. The South Sandwich Islands. II: The geology of Candlemas Island, Br. Antarct. Surv. Sci. Rept. 92: 33 ppGoogle Scholar
  75. Tyrrell, G. W. 1945. Report on rocks from West Antarctica and the Scotia Arc, Disc. Rep. 23:37–102Google Scholar
  76. Vlaar, N. J., and Wortel, M. J. R. 1976. Lithospheric ageing, instability and subduction, Tectonophysics 32: 331–351CrossRefGoogle Scholar
  77. Von Huene, R., Kulm, L. D., and Miller, J. 1985. Structure of the frontal part of the Andean convergent margin, J. Geophys. Res. 90:5429–5442CrossRefGoogle Scholar
  78. Wilson, D. S. 1993. Confirmation of the astronomical calibration of the magnetic polarity timescale from sea-floor spreading rates, Nature 364:788–790CrossRefGoogle Scholar
  79. Woodhead, J., Eggins, S., and Gamble, J. 1993. High field strength and transition element systematics in island arc and back-arc basin basalts: evidence for multi-phase melt extraction and a depleted mantle wedge, Earth Planet. Sci. Lett. 114:491–504CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 1995

Authors and Affiliations

  • Peter F. Barker
    • 1
  1. 1.British Antarctic SurveyNatural Environment Research CouncilCambridgeEngland

Personalised recommendations