Variation of effective elastic thickness and melt production along the Deccan–Reunion hotspot track

Abstract

We estimate the effective elastic thickness (Te) along the Deccan–Reunion hotspot track using admittance analysis of seafloor topography and the free-air gravity field, both corrected for the thermal effects of a cooling lithosphere. Our results reveal that the volcanic edifices (Saya de Malha Bank, Chagos–Maldives–Laccadives Ridge) formed in the first 30 Myr after the Deccan volcanism [∼ 65 Myr], on lithosphere with Te values of 4 ± 2 km, while the younger volcanic edifices on the African plate (Reunion, Mauritius, Nazareth Bank) were emplaced on lithosphere with Te values of 17 ± 9 km. These estimates suggest that the hotspot volcanism occurred on juvenile lithosphere in the first 30 Myr, implying that the mid-ocean ridge remained near the hotspot for ∼ 30 Myr. In contrast, in the last 30 Myr volcanism occurred on aged lithosphere in an intraplate setting, which might indicate that the mid-ocean ridge migrated rapidly to the north after the African plate moved over the hotspot. This conclusion of a rapid shift from plume-influenced mid-ocean ridge (MOR) volcanism to intraplate plume volcanism is supported by geochemical (major and trace element) interpretations of data from Ocean Drilling Program (ODP) Leg 115. An estimate of the melt-production rate shows a striking increase in the small Te region relative to the large Te region of the hotspot track, which suggest a strong interrelation between Te and melt production. However, there is also variation of melt emplacement rates within the region of low Te that may be due to unknown changes in the rates of plate motions or somewhat episodic melt production.