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DTSTART;TZID=Europe/Paris:20191105T093000
DTEND;TZID=Europe/Paris:20191105T120000
DTSTAMP:20260504T202220
CREATED:20190401T093601Z
LAST-MODIFIED:20190401T093601Z
UID:17598-1572946200-1572955200@lmv.uca.fr
SUMMARY:Comité de direction
DESCRIPTION:
URL:https://lmv.uca.fr/agenda/comite-de-direction-19/
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DTSTART;TZID=Europe/Paris:20191105T133000
DTEND;TZID=Europe/Paris:20191105T170000
DTSTAMP:20260504T202220
CREATED:20190827T130719Z
LAST-MODIFIED:20191009T135741Z
UID:20034-1572960600-1572973200@lmv.uca.fr
SUMMARY:Séminaire Bruno Dhuime
DESCRIPTION:Continental growth\, onset of plate tectonics and rise of the continents \n  \nUnderstanding when and how the continental crust was generated is an important step in unraveling the evolution of the Earth system\, yet these questions remain a matter of great debate. Hf isotopes in zircon and Nd isotopes in sediments suggest that new continental crust was generated continuously\, but with a marked decrease in the growth rate at ~3 Ga\, which can be related to the onset of plate tectonics. By 3 Ga at least ~65–75% of the present volume of the continental crust had been generated. There is increasing evidence that ~3 Ga also marked the transition between two different types of continental crust. Pre-3 Ga crust was on average mafic\, dense and relatively thin (<20 km). In contrast\, continental crust that formed after 3 Ga gradually became more intermediate in composition and thicker. The increase in crustal thickness is accompanied by increasing rates of crustal reworking and increasing input of sediment to the ocean. These changes may have been accommodated by a change in the lithosphere strength at around 3 Ga\, as the latter became strong enough to support high relief crust. A box model is used to evaluate the timing of crust generation and destruction from 4–0 Ga. Relatively large volumes of crust were destroyed in the late Archaean and Early Proterozoic and over 100% of the present volume of continental crust has been recycled back into the mantle since 3 Ga.
URL:https://lmv.uca.fr/agenda/seminaire-bruno-dhuime/
CATEGORIES:Séminaire
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