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| Titel |
Testing Predictions of Continental Insulation using Oceanic Crustal Thicknesses |
| VerfasserIn |
Mark Hoggard, Oliver Shorttle, Nicky White |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250135712
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| Publikation (Nr.) |
 EGU/EGU2016-16611.pdf |
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| Zusammenfassung |
| The thermal blanketing effect of continental crust has been predicted to lead to elevated
temperatures within the upper mantle beneath supercontinents. Initial break-up is associated
with increased magmatism and the generation of flood basalts. Continued rifting and sea-floor
spreading lead to a steady reduction of this thermal anomaly. Recently, evidence in support of
this behaviour has come from the major element geochemistry of mid-ocean ridge
basalts, which suggest excess rifting temperatures of ∼ 150 ∘C that decay over
∼ 100 Ma.
We have collated a global inventory of ∼ 1000 seismic reflection profiles and ∼ 500
wide-angle refraction experiments from the oceanic realm. Data are predominantly located
along passive margins, but there are also multiple surveys in the centres of the major
oceanic basins. Oceanic crustal thickness has been mapped, taking care to avoid
areas of secondary magmatic thickening near seamounts or later thinning such as
across transform faults. These crustal thicknesses are a proxy for mantle potential
temperature at the time of melt formation beneath a mid-ocean ridge system, allowing us
to quantify the amplitude and duration of thermal anomalies generated beneath
supercontinents.
The Jurassic break-up of the Central Atlantic and the Cretaceous rifting that
formed the South Atlantic Ocean are both associated with excess temperatures of
∼ 50 ∘C that have e-folding times of ∼ 50 Ma. In addition to this background
trend, excess temperatures reach > 150 ∘C around the region of the Rio Grande
Rise, associated with the present-day Tristan hotspot. The e-folding time of this
more local event is ∼ 10 Ma, which mirrors results obtained for the North Atlantic
Ocean south of Iceland. In contrast, crustal thicknesses from the Pacific Ocean reveal
approximately constant potential temperature through time. This observation is in
agreement with predictions, as the western Pacific was formed by rifting of an oceanic
plate.
In summary, variations in oceanic crustal thickness support the existence of continental
insulation effects. Characteristic e-folding times are ∼ 50 Ma, but excess break-up
temperatures are significantly lower than previously expected at around ∼ 50 ∘C. We
tentatively suggest that higher excess temperatures of > 150 ∘C occur in the vicinity of
upwelling mantle plumes, which are associated with shorter e-folding times of ∼ 10 Ma. |
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