Coupling of South American and African Plate motion and plate deformation

Science

Volumn 279, Issue 5347, 1998, Pages 60-63

  Silver, Paul G ^a   Russo, Raymond M ^b   Lithgow Bertelloni, Carolina ^a,c  

^a GEOPHYSICAL LABORATORY   (United States)

^b NORTHWESTERN UNIVERSITY   (United States)

^c UNIVERSITY OF MICHIGAN   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

MANTLE CIRCULATION; PLATE DEFORMATION; PLATE MOTION; PLATE TECTONICS;

AFRICA; ARTICLE; GEOLOGY; MOTION; PRIORITY JOURNAL; SEA; SOUTH AMERICA; VELOCITY;

EID: 0032472219     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.279.5347.60     Document Type: Article

References (45)

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13. There are several lines of evidence supporting the notion that SA is coupled to general mantle circulation. First, the only other potentially significant driving force, ridge-push, does not change on sufficiently short time scales to cause such a rapid change in plate motion. The change must be caused by changes in the tractions at the plate boundary or basal tractions. There is no evidence for a decrease in boundary resistance forces or increase in boundary driving forces, so the only alternative is a change in the basal traction (that could take the form of basal shear tractions or possibly horizontal normal tractions applied to the sides of deep continental roots). Other lines of evidence include: the apparent absence of an asthenospheric decoupling zone beneath continental plates in general [P. G. Silver, Annu Rev. Earth Planet. Sci. 24, 385 (1996)] and South America in particular [D. E. James and M. Assumpçao, Geophys. J. Int. 126, 1 (1996)], as inferred from seismic anisotropy, and the suggestion, from seismic tomography of coherent translation of the SA plate and upper mantle over the last 130 My [J. C. Van-Decar, D. E. James, M. Assumpção, Nature 378, 25 (1995)]. If SA is coupled to mantle circulation, it is reasonable to suppose that the other plates of the Atlantic basin, particularly Africa, are similarly coupled (2). For a general discussion of coupling of plate motions to mantle circulation, see C. Lithgow-Bertelloni and M. A. Richards, Rev. Geophys., in press.
14. There are several lines of evidence supporting the notion that SA is coupled to general mantle circulation. First, the only other potentially significant driving force, ridge-push, does not change on sufficiently short time scales to cause such a rapid change in plate motion. The change must be caused by changes in the tractions at the plate boundary or basal tractions. There is no evidence for a decrease in boundary resistance forces or increase in boundary driving forces, so the only alternative is a change in the basal traction (that could take the form of basal shear tractions or possibly horizontal normal tractions applied to the sides of deep continental roots). Other lines of evidence include: the apparent absence of an asthenospheric decoupling zone beneath continental plates in general [P. G. Silver, Annu Rev. Earth Planet. Sci. 24, 385 (1996)] and South America in particular [D. E. James and M. Assumpçao, Geophys. J. Int. 126, 1 (1996)], as inferred from seismic anisotropy, and the suggestion, from seismic tomography of coherent translation of the SA plate and upper mantle over the last 130 My [J. C. Van-Decar, D. E. James, M. Assumpção, Nature 378, 25 (1995)]. If SA is coupled to mantle circulation, it is reasonable to suppose that the other plates of the Atlantic basin, particularly Africa, are similarly coupled (2). For a general discussion of coupling of plate motions to mantle circulation, see C. Lithgow-Bertelloni and M. A. Richards, Rev. Geophys., in press.
15. There are several lines of evidence supporting the notion that SA is coupled to general mantle circulation. First, the only other potentially significant driving force, ridge-push, does not change on sufficiently short time scales to cause such a rapid change in plate motion. The change must be caused by changes in the tractions at the plate boundary or basal tractions. There is no evidence for a decrease in boundary resistance forces or increase in boundary driving forces, so the only alternative is a change in the basal traction (that could take the form of basal shear tractions or possibly horizontal normal tractions applied to the sides of deep continental roots). Other lines of evidence include: the apparent absence of an asthenospheric decoupling zone beneath continental plates in general [P. G. Silver, Annu Rev. Earth Planet. Sci. 24, 385 (1996)] and South America in particular [D. E. James and M. Assumpçao, Geophys. J. Int. 126, 1 (1996)], as inferred from seismic anisotropy, and the suggestion, from seismic tomography of coherent translation of the SA plate and upper mantle over the last 130 My [J. C. Van-Decar, D. E. James, M. Assumpção, Nature 378, 25 (1995)]. If SA is coupled to mantle circulation, it is reasonable to suppose that the other plates of the Atlantic basin, particularly Africa, are similarly coupled (2). For a general discussion of coupling of plate motions to mantle circulation, see C. Lithgow-Bertelloni and M. A. Richards, Rev. Geophys., in press.
16. There are several lines of evidence supporting the notion that SA is coupled to general mantle circulation. First, the only other potentially significant driving force, ridge-push, does not change on sufficiently short time scales to cause such a rapid change in plate motion. The change must be caused by changes in the tractions at the plate boundary or basal tractions. There is no evidence for a decrease in boundary resistance forces or increase in boundary driving forces, so the only alternative is a change in the basal traction (that could take the form of basal shear tractions or possibly horizontal normal tractions applied to the sides of deep continental roots). Other lines of evidence include: the apparent absence of an asthenospheric decoupling zone beneath continental plates in general [P. G. Silver, Annu Rev. Earth Planet. Sci. 24, 385 (1996)] and South America in particular [D. E. James and M. Assumpçao, Geophys. J. Int. 126, 1 (1996)], as inferred from seismic anisotropy, and the suggestion, from seismic tomography of coherent translation of the SA plate and upper mantle over the last 130 My [J. C. Van-Decar, D. E. James, M. Assumpção, Nature 378, 25 (1995)]. If SA is coupled to mantle circulation, it is reasonable to suppose that the other plates of the Atlantic basin, particularly Africa, are similarly coupled (2). For a general discussion of coupling of plate motions to mantle circulation, see C. Lithgow-Bertelloni and M. A. Richards, Rev. Geophys., in press.
17. It is unlikely for there to be any other way for stress to be transmitted from Af to SA. If transmitted through the plates themselves (acting as a stress guide), the stress would have to cross the ridge, where plates are thinnest, leading to a severe disruption in the spreading process, which is not observed.
18. 21 Pa-s, a value compatible with inferences from post-glacial rebound.
19. By allowing Af and Eu to act as one plate, we are implicitly allowing infinite compressional stresses to develop at the plate boundary between them, maximizing the effect of the collision. The size of the colliding plates is crucial for the collision to have any effect on the general mantle circulation. This approach was attempted previously (17) as a way of testing the influence of the India/Eurasia collision on the Pacific Plate, although no change in plate motion was found.
20. M. Richards and C. Lithgow-Bertelloni, Earth Planet. Sci. Lett. 137, 19 (1996).
21. These are estimated from balanced cross sections, which range from 100 to 200 km: F. Mégard, J. Geol. Soc. London 129, 893 (1984); B. M. Sheffels, Geology 18, 812 (1990); R. W. Allmendingerer et al., Tectonics 2, 1 (1983); R. W. Allmendinger et al., ibid. 9, 789 (1990); P. Baby et al., ibid. 11, 523 (1992).
22. These are estimated from balanced cross sections, which range from 100 to 200 km: F. Mégard, J. Geol. Soc. London 129, 893 (1984); B. M. Sheffels, Geology 18, 812 (1990); R. W. Allmendingerer et al., Tectonics 2, 1 (1983); R. W. Allmendinger et al., ibid. 9, 789 (1990); P. Baby et al., ibid. 11, 523 (1992).
23. These are estimated from balanced cross sections, which range from 100 to 200 km: F. Mégard, J. Geol. Soc. London 129, 893 (1984); B. M. Sheffels, Geology 18, 812 (1990); R. W. Allmendingerer et al., Tectonics 2, 1 (1983); R. W. Allmendinger et al., ibid. 9, 789 (1990); P. Baby et al., ibid. 11, 523 (1992).
24. These are estimated from balanced cross sections, which range from 100 to 200 km: F. Mégard, J. Geol. Soc. London 129, 893 (1984); B. M. Sheffels, Geology 18, 812 (1990); R. W. Allmendingerer et al., Tectonics 2, 1 (1983); R. W. Allmendinger et al., ibid. 9, 789 (1990); P. Baby et al., ibid. 11, 523 (1992).
25. These are estimated from balanced cross sections, which range from 100 to 200 km: F. Mégard, J. Geol. Soc. London 129, 893 (1984); B. M. Sheffels, Geology 18, 812 (1990); R. W. Allmendingerer et al., Tectonics 2, 1 (1983); R. W. Allmendinger et al., ibid. 9, 789 (1990); P. Baby et al., ibid. 11, 523 (1992).
26. L. Leffler et al., Geophys. Res. Lett., 24, 1031 (1997); E. Norabuena et al., Science, in press.
27. L. Leffler et al., Geophys. Res. Lett., 24, 1031 (1997); E. Norabuena et al., Science, in press.
28. Described by M. A. Richards and D. C. Engebretson [Eos Trans. Am. Geophys. Union 75, 63 (1994)] for Pacific-Farallon motions at the time of the formation of the bend in the Hawaii-Emperor sea mount chain. S. Zhong and M. Gurnis [Nature 383, 245 (1996)] showed that transforms guide plate motions in mantle convection models with realistic faults and plates.
29. Described by M. A. Richards and D. C. Engebretson [Eos Trans. Am. Geophys. Union 75, 63 (1994)] for Pacific-Farallon motions at the time of the formation of the bend in the Hawaii-Emperor sea mount chain. S. Zhong and M. Gurnis [Nature 383, 245 (1996)] showed that transforms guide plate motions in mantle convection models with realistic faults and plates.
30. J. Mammerickx and D. Sandwell, J. Geophys. Res. 91, 1975 (1986).
31. This estimate is based on the assumption that SA's northward motion is primarily driven by basal shear and that the ridge-transform offsets have become the dominant resistive force once SA's northward motion has ceased.
32. T. H. Dixon and A. Mao, Geophys. Res. Lett. 24, 535 (1997).
33. S. Stein, H. J. Melosh, J. B. Minster, Earth Planet. Sci. Lett. 36, 51 (1977).
34. J. G. Schilling, Nature 352, 397 (1991).
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38. E. Widom, R. W. Carlson, J. B. Gill, H. U. Schmincke, Chem. Geol., in preparation.
39. The New England hot spot in the Great Meteor-Atlantis seamounts [R. A. Duncan, J. Geophys. Res. 89, 9980 (1984); B. E. Tucholke and N. C. Smoot, ibid. 95, 17555 (1990)], which also lie a few hundred kilometers east of the adjacent MAR. Further south, isotopically distinct Sierra Leone, Circe, Shona, and Discovery mantle plumes have been observed in a similar eastward-displaced position relative to the local MAR (C. J. H. Hartnady and A. P. LeRoex, Earth Planet. Sci. Lett. 75 (1985); J. G. Schilling et al., J. Geophys. Res. 99, 12005 (1994); J. Douglass, J. G. Schilling, R. H. Kingsley, C. Small, Geophys. Res. Lett. 22, 2893 (1995)]. Although the motion histories of these hot spots are poorly known compared to that of Iceland or Tristan da Cunha, the regular distribution of near-MAR hot spots on the east side of the ridge is compatible with westward drift of the MAR relative to Atlantic basin hot spots since at least 30 Ma.
40. The New England hot spot in the Great Meteor-Atlantis seamounts [R. A. Duncan, J. Geophys. Res. 89, 9980 (1984); B. E. Tucholke and N. C. Smoot, ibid. 95, 17555 (1990)], which also lie a few hundred kilometers east of the adjacent MAR. Further south, isotopically distinct Sierra Leone, Circe, Shona, and Discovery mantle plumes have been observed in a similar eastward-displaced position relative to the local MAR (C. J. H. Hartnady and A. P. LeRoex, Earth Planet. Sci. Lett. 75 (1985); J. G. Schilling et al., J. Geophys. Res. 99, 12005 (1994); J. Douglass, J. G. Schilling, R. H. Kingsley, C. Small, Geophys. Res. Lett. 22, 2893 (1995)]. Although the motion histories of these hot spots are poorly known compared to that of Iceland or Tristan da Cunha, the regular distribution of near-MAR hot spots on the east side of the ridge is compatible with westward drift of the MAR relative to Atlantic basin hot spots since at least 30 Ma.
41. The New England hot spot in the Great Meteor-Atlantis seamounts [R. A. Duncan, J. Geophys. Res. 89, 9980 (1984); B. E. Tucholke and N. C. Smoot, ibid. 95, 17555 (1990)], which also lie a few hundred kilometers east of the adjacent MAR. Further south, isotopically distinct Sierra Leone, Circe, Shona, and Discovery mantle plumes have been observed in a similar eastward-displaced position relative to the local MAR (C. J. H. Hartnady and A. P. LeRoex, Earth Planet. Sci. Lett. 75 (1985); J. G. Schilling et al., J. Geophys. Res. 99, 12005 (1994); J. Douglass, J. G. Schilling, R. H. Kingsley, C. Small, Geophys. Res. Lett. 22, 2893 (1995)]. Although the motion histories of these hot spots are poorly known compared to that of Iceland or Tristan da Cunha, the regular distribution of near-MAR hot spots on the east side of the ridge is compatible with westward drift of the MAR relative to Atlantic basin hot spots since at least 30 Ma.
42. The New England hot spot in the Great Meteor-Atlantis seamounts [R. A. Duncan, J. Geophys. Res. 89, 9980 (1984); B. E. Tucholke and N. C. Smoot, ibid. 95, 17555 (1990)], which also lie a few hundred kilometers east of the adjacent MAR. Further south, isotopically distinct Sierra Leone, Circe, Shona, and Discovery mantle plumes have been observed in a similar eastward-displaced position relative to the local MAR (C. J. H. Hartnady and A. P. LeRoex, Earth Planet. Sci. Lett. 75 (1985); J. G. Schilling et al., J. Geophys. Res. 99, 12005 (1994); J. Douglass, J. G. Schilling, R. H. Kingsley, C. Small, Geophys. Res. Lett. 22, 2893 (1995)]. Although the motion histories of these hot spots are poorly known compared to that of Iceland or Tristan da Cunha, the regular distribution of near-MAR hot spots on the east side of the ridge is compatible with westward drift of the MAR relative to Atlantic basin hot spots since at least 30 Ma.
43. The New England hot spot in the Great Meteor-Atlantis seamounts [R. A. Duncan, J. Geophys. Res. 89, 9980 (1984); B. E. Tucholke and N. C. Smoot, ibid. 95, 17555 (1990)], which also lie a few hundred kilometers east of the adjacent MAR. Further south, isotopically distinct Sierra Leone, Circe, Shona, and Discovery mantle plumes have been observed in a similar eastward-displaced position relative to the local MAR (C. J. H. Hartnady and A. P. LeRoex, Earth Planet. Sci. Lett. 75 (1985); J. G. Schilling et al., J. Geophys. Res. 99, 12005 (1994); J. Douglass, J. G. Schilling, R. H. Kingsley, C. Small, Geophys. Res. Lett. 22, 2893 (1995)]. Although the motion histories of these hot spots are poorly known compared to that of Iceland or Tristan da Cunha, the regular distribution of near-MAR hot spots on the east side of the ridge is compatible with westward drift of the MAR relative to Atlantic basin hot spots since at least 30 Ma.
44. D. T. Sandwell and W. H. F. Smith, J. Geophys. Res., in press.
45. We thank W. Smith for providing us with a custom version of Atlantic basin gravity anomalies; S. Solomon, C. DeLima, S. Stein, P. Lundgren, C. Bina, A. Nicolas, and A. le Roex for stimulating discussions; S. Sacks for South American GPS data before publication; J. Dunlap for manuscript preparation; and M. Acierno and S. Keiser for computer support. We used GMT (P. Wessel and W. Smith) to make many figures in this report. Supported by NSF grant EAR 93-16457 (P.G.S. and R.R.), by an NSF-NATO Fellowship (R.R.), by an NSF postdoctoral fellowship (C.L.-B.) and by the Carnegie Institution of Washington (P.G.S. and C.L-B.).