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| Titel |
Timing, rates and geodynamical conditions of continental crust generation, destruction and reworking |
| VerfasserIn |
B. Dhuime, C. J. Hawkesworth, P. A. Cawood |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063297
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| Zusammenfassung |
| The timing, rates and the geodynamical conditions of continental crust generation,
destruction and reworking remain a topic of considerable debate. Around 7% of the
present-day exposed crust consists of rocks of Archaean age, yet models of continental
growth suggest that 20-100% of the present-day volume of the continental crust had formed
by the end of the Archaean. Continental growth models rely on understanding the
balance between the generation of new crust and the reworking of old crust, and
how these have changed with time throughout Earth’s history. For that purpose,
the variations in radiogenic isotope ratios in detrital rocks and minerals are a key
archive.
Two different approaches are considered to model the growth of continents: (1) the
variation of Nd isotopes in continental shales with various deposition ages, which requires a
correction of the bias induced by preferential erosion of younger rocks through an erosion
parameter ’K’; and (2) the variations in U-Pb, Hf and O isotopes in detrital zircons sampled
worldwide. These two approaches independently suggest that the continental crust was
generated continuously, with a marked decrease in the continental growth rate at ca. 3
Ga. The >4 Ga to ~3 Ga period is characterised by relatively high net rates of
continental growth (~3.0 km3.a-1), which are similar to the rates at which new crust is
generated, and destroyed, at the present time. Since 3 Ga the net growth rates are much
lower (~0.8 km3.a-1), and this may be attributed to higher rates of destruction of
continental crust. The inflexion in the continental growth curve at ~3 Ga indicates a
fundamental change in the way the crust was generated and preserved. This change may be
linked to onset of subduction-driven plate tectonics and discrete subduction zones. |
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