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| Titel |
Upper mantle anisotropy of the Borborema Province, NE Brazil: Implications for intra-plate deformation and sub-cratonic asthenospheric flow |
| VerfasserIn |
Ian Bastow, Jordi Julià, Aderson Nascimento, Reinhardt Fuck, Tania Buckthorp, Jacob McClellan |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250097347
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| Publikation (Nr.) |
 EGU/EGU2014-12918.pdf |
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| Zusammenfassung |
| The geological record of the Borborema province in northeast Brazil documents
tectonic events that characterised the Precambrian formation and Mesozoic breakup of
Gondwana. Large-scale shear zones and associated granitic plutons that developed
during the Neoproterozoic Brasiliano/Pan-African orogeny, and major sedimentary
basins of Mesozoic age, indicate significant deformation across the region. However,
whether or not the shear zones resulted from Precambrian terrane accretion, or
are simply the result of episodes of subsequent intra-plate deformation is debated.
Also poorly understood is the effect of the thick São Francisco mantle keel on
present-day asthenospheric flow. To address these issues we have performed a teleseismic
shear wave splitting study of mantle seismic anisotropy from a new broadband
seismograph network in the Borborema region. Splitting parameters (Ï, δt) in the
heart of the Province are dominated by null measurements (δt = 0), suggesting the
lithosphere beneath the region may not have been deformed to the extent observed at
Precambrian accretionary boundaries elsewhere on Earth. The intra-plate shear zone
hypothesis may thus be more appropriate for the region. The null observations also
indicate that horizontal asthenospheric strain fabrics due, for example, to absolute
plate motion, or the deflection of asthenosphere around the São Fransisco keel,
are poorly developed. Towards the Brazilian coast, splitting observations, with
δt = 1.6 s, display anisotropic fast directions that parallel the extension directions
during the time of formation of the South Atlantic. This implies that the mantle
lithosphere was deformed but not completely destroyed during the breakup of Gondwana. |
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