Seismic structure of the lithosphere and upper mantle beneath the ocean islands near mid-oceanic ridges

摘要

Deciphering the seismic character of the younglithosphere near mid-oceanic ridges (MORs) is a challenging endeavor. Inthis study, we determine the seismic structure of the oceanic plate near theMORs using the P-to-S conversions isolated from quality data recordedat five broadband seismological stations situated on ocean islands in theirvicinity. Estimates of the crustal and lithospheric thickness values from waveform inversion of the P-receiver function stacks at individual stationsreveal that the Moho depth varies between ~ 10 ± 1 km and~ 20 ± 1 km with the depths of thelithosphere–asthenosphere boundary (LAB) varying between ~ 40 ± 4 and ~ 65 ± 7 km. We found evidence for anadditional low-velocity layer below the expected LAB depths at stations onAscension, S?o Jorge and Easter islands. The layer probably relates to thepresence of a hot spot corresponding to a magma chamber. Further, thinning ofthe upper mantle transition zone suggests a hotter mantle transition zonedue to the possible presence of plumes in the mantle beneath the stations.