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| Titel |
Subaqueous Archean continental flood basalts were emplaced on hot continental crust |
| VerfasserIn |
Nicolas Flament, Patrice Rey, Nicolas Coltice, Gilles Dromart, Nicolas Olivier |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050201
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| Zusammenfassung |
| Large basaltic provinces up to 15 km thick are common in Archean cratons. Despite
significantly contributing to the thickening of the continental crust, many Archean flood
basalts that show continental contamination remained below sea level during their eruption.
In this contribution, we suggest that one possible way of maintaining basaltic piles several
kilometers thick below sea level is via gravity-driven lower crustal flow of hot continental
crust. Using numerical experiments, we show that the characteristic time to remove the
anomaly in crustal thickness associated with a continental flood basalt (CFB) decreases
exponentially with Moho temperature (TM) from 2.5 Gyr for TM - 300 °C to 5 Myr for TM
- 1050 °C. Therefore, the removal of the thickness anomaly associated with CFBs erupted
on cold continents occurs by a combination of brittle deformation and erosion,
two processes of time scale of a few tens of million years. This is consistent with
observations for Phanerozoic CFBs that are subject to important erosion and would not be
preserved in the geological record over billions of years, contrary to subaqueous
Archean CFBs. We show, based on sedimentary and structural observations, that
the subsidence of the -¤ 1.4-km-thick basalts of the Kylena Formation and lower
600-m-thick basalts of the Maddina Formation in the Meentheena Centrocline (Pilbara
Craton, Western Australia) occurred without any significant tectonic extension in -¤
15 Myr and -¤ 11 Myr, respectively. We interpret our observations as the surface
expression of the removal of thickness anomaly by the flow of lower continental
crust. From our modeling results, the subsidence of these basalts over such time
scales requires Moho temperatures -¥ 900 ºC. The example of the Fortescue Group
illustrates that thick subaqueous Archean CFBs are the result of the accumulation of
several basaltic packages, each erupted over -¼ 30 Myr. Moho temperatures -½ 800 °C
are required to maintain such basaltic packages below sea level by lower crustal
flow. Thus, the prevalence of subaqueous CFBs in the Archean record suggests that
they were dominantly emplaced on hot, weak continental crust and that Archean
continental geotherms were significantly warmer than their modern counterparts. |
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