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

Abstract

Abstract. Deciphering the seismic character of the young lithosphere near mid-oceanic ridges (MORs) is a challenging endeavor. In this study, we determine the seismic structure of the oceanic plate near the MORs using the P -to-S conversions isolated from quality data recorded at five broadband seismological stations situated on ocean islands in their vicinity. Estimates of the crustal and lithospheric thickness values from waveform inversion of the P -receiver function stacks at individual stations reveal that the Moho depth varies between ∼ 10 ± 1 km and ∼ 20 ± 1 km with the depths of the lithosphere-asthenosphere boundary (LAB) varying between ∼ 40 ± 4 and ∼ 65 ± 7 km. We found evidence for an additional low-velocity layer below the expected LAB depths at stations on Ascension, São Jorge and Easter islands. The layer probably relates to the presence of a hot spot corresponding to a magma chamber. Further, thinning of the upper mantle transition zone suggests a hotter mantle transition zone due to the possible presence of plumes in the mantle beneath the stations.

Multiscale Seismic Tomography

“…5.4). A recent receiver-function study has also detected a thinner MTZ beneath the Easter hotspot (Haldar et al 2014). Intermediate-depth and deep earthquakes occur actively within the Tonga slab (Fig.…”

Quantifying Periodic Variations in Hotspot Melt Production

“…In our model plume layer, we calculate the total melt fraction F of dry peridotite (Katz et al, 2003) subject to a depth-dependent pressure P(z) and plume temperature determined by summation of a fixed mantle potential temperature and seismically determined plume thermal anomalies (see below (Müller et al, 2008) and κ (=1 × 10 −6 m 2 s −1 ) is thermal diffusivity. Additionally, at Easter, Tristan-Gough, Marquesas, Galápagos, and Réunion, we also calculate values incorporating additional published constraints on seafloor age or lithosphere thickness (Adam et al, 2007;Fischer et al, 1986;Fontaine et al, 2015;Gibson & Geist, 2010;Haldar et al, 2014) to set the top of the melting column (Table A1).…”

Hotspots and Mantle Plumes

“…5.1). A recent receiver-function study also detected a thinner MTZ beneath the Ascension hotspot 5.3 Atlantic Hotspots (Haldar et al 2014). The long-period results of Deuss (2007) show that the MTZ is thinner beneath New England and Discovery, whereas the MTZ is normal beneath Fernando.…”

“…Under the hotspots in the South Pacific superswell, the MTZ is generally thinner than that of the global average (Niu and Inoue 2000;Li et al 2003;Deuss 2007;Suetsugu et al 2009), and the PMPT is generally higher (Courtier et al 2007). A recent receiver-function study has also detected a thinner MTZ beneath the Easter hotspot (Haldar et al 2014). Huang et al (2011) suggested that geochemical zoning is a common feature of mantle plumes beneath the Pacific plate, and the pattern repeats between island chains.…”