Magmas trapped at the continental lithosphere–asthenosphere boundary

C. Crépisson (1) , Guillaume Morard (2) , H. Bureau (2) , Gaëlle Prouteau (3) , Yann Morizet (4, 3) , S. Petitgirard (4) , C. Sanloup (5)

1 iSTeP - Institut des Sciences de la Terre de Paris
2 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
3 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
4 LPG - Laboratoire de Planétologie et Géodynamique [UMR 6112]
5 PGM2 - Pétrologie, géochimie, minéralogie magmatiques

The lithosphere-asthenosphere boundary (LAB) beneath the continents is a key interface in plate tectonics, yet its nature remains elusive. A partial melt layer has been advocated to explain its geophysical characteristics. However, the main counter-argument is that such a layer can not be stable as melts should rise through the lithosphere. Density measurements of volatile-containing alkali basalts taken as a proxy for LAB melts show that they are neutrally buoyant at the pressure (P)- temperature (T) conditions of the LAB under continents. Complementary X-ray diffraction and Raman data provide structural insights on melt compaction mecha- nisms. Basalts generated below the lithosphere may thus be gravitationally trapped and accumulate over time. Their presence provide answers to key questions on continental lithosphere geodynamics, and in particular on cratonic keels stability. This buoyancy trap would cease to exist at higher mantle T such as those relevant of the Archean, and as such, could be linked to the onset of plate tectonics.

Domaines: Sciences de la Terre

C. Crépisson, Guillaume Morard, H. Bureau, Gaëlle Prouteau, Yann Morizet, et al.. Magmas trapped at the continental lithosphere–asthenosphere boundary. Earth and Planetary Science Letters, 2014, 393, pp.105 - 112. ⟨10.1016/j.epsl.2014.02.048⟩. ⟨hal-00959932⟩