Gerbault Muriel, Fontaine F. J., Rabinowicz M., Bystricky M. (2017). Elastic flexure controls magma trajectories and explains the offset of primary volcanic activity upstream of mantle plume axis at la Reunion and Hawaii hotspot islands. Earth and Planetary Science Letters, 462, p. 142-156. ISSN 0012-821X.
Titre du document
Elastic flexure controls magma trajectories and explains the offset of primary volcanic activity upstream of mantle plume axis at la Reunion and Hawaii hotspot islands
Gerbault Muriel, Fontaine F. J., Rabinowicz M., Bystricky M.
Source
Earth and Planetary Science Letters, 2017,
462, p. 142-156 ISSN 0012-821X
Surface volcanism at la Reunion and Hawaii occurs with an offset of 150-180 km upstream to the plume axis with respect to the plate motion. This striking observation raises questions about the forcing of plume-lithosphere thermo-mechanical interactions on melt trajectories beneath these islands. Based on visco-elasto-plastic numerical models handled at kilometric resolution, we propose to explain this offset by the development of compressional stresses at the base of the lithosphere, that result from elastic plate bending above the upward load exerted by the plume head. This horizontal compression adopts a disc shape centered around the plume axis: (i) it is 20 km thick, (ii) it has a 150 km radius, (iii) it lays at the base of the elastic part of the lithosphere, i.e., around, similar to 50-70 km depth where the temperature varies from similar to 600 degrees C to similar to 750 degrees C, (iv) it lasts for 5 to 10 My in an oceanic plate of age greater than 70 My, and (vi) it is controlled by the visco-elastic relaxation time at 50-70 km depth. This period of time exceeds the time during which both the Somalian/East-African and Pacific plates drift over the Reunion and Hawaii plumes, respectively. This indicates that this basal compression is actually a persistent feature. It is inferred that the buoyant melts percolating in the plume head pond below this zone of compression and eventually spread laterally until the most compressive principal elastic stresses reverse to the vertical, i.e., similar to 150 km away from the plume head. There, melts propagate through dikes upwards to similar to 35 km depth, where the plate curvature reverses and ambient compression diminishes. This 30-35 km depth may thus host a magmatic reservoir where melts transported by dykes pond. Only after further magmatic differentiation can dykes resume their ascension up to the surface and begin forming a volcanic edifice. As the volcano grows because of melt accumulation at the top of the plate, the lithosphere is flexed downwards, inducing extra tensile stress at 30-35 km depth and compression at 15 km depth (induced by the edifice load). It implies that now the melts pond at similar to 15 km and form another magmatic reservoir lying just underneath the crust. These processes explain the ponding of primary (shield) melts at similar to 35 km and similar to 15 km depths as recorded below La Reunion, Mauritius or Hawaii volcanoes, all shifted by similar to 150 km with respect to the plume axis.
Plan de classement
Sciences fondamentales / Techniques d'analyse et de recherche [020]
;
Géophysique interne [066]
