The Role of Crustal Strength in Controlling Magmatism and Melt Chemistry During Rifting and Breakup

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  • John J. Armitage, Institut de Physique du Globe de Paris
  • ,
  • Kenni D. Petersen
  • ,
  • Marta Pérez-Gussinyé, Universitat Bremen

The strength of the crust has a strong impact on the evolution of continental extension and breakup. Strong crust may promote focused narrow rifting, while wide rifting might be due to a weaker crustal architecture. The strength of the crust also influences deeper processes within the asthenosphere. To quantitatively test the implications of crustal strength on the evolution of continental rift zones, we developed a 2-D numerical model of lithosphere extension that can predict the rare Earth element (REE) chemistry of erupted lava. We find that a difference in crustal strength leads to a different rate of depletion in light elements relative to heavy elements. By comparing the model predictions to rock samples from the Basin and Range, USA, we can demonstrate that slow extension of a weak continental crust can explain the observed depletion in melt chemistry. The same comparison for the Main Ethiopian Rift suggests that magmatism within this narrow rift zone can be explained by the localization of strain caused by a strong lower crust. We demonstrate that the slow extension of a strong lower crust above a mantle of potential temperature of 1,350 °C can fit the observed REE trends and the upper mantle seismic velocity for the Main Ethiopian Rift. The thermo-mechanical model implies that melt composition could provide quantitative information on the style of breakup and the initial strength of the continental crust.

OriginalsprogEngelsk
TidsskriftGeochemistry, Geophysics, Geosystems
Vol/bind19
Nummer2
Sider (fra-til)534-550
Antal sider17
ISSN1525-2027
DOI
StatusUdgivet - feb. 2018

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