This study investigates the relationship between the hotspot-ridge interaction and the formation of oceanic plateaus and seamounts in the Southwest Indian Ocean. We first calculated the relative distance between the Southwest Indian Ridge (SWIR) and relevant hotspots on the basis of models of plate reconstruction, and then calculated the corresponding excess magmatic anomalies of the hotspots on the basis of residual bathymetry and Airy isostasy. The results reveal that the activities of the Marion hotspot can be divided into three main phases: interaction with the paleo-Rodrigues triple junction (73.6-68.5 Ma), interaction with the SWIR (68.5-42.7 Ma), and intra-plate volcanism (42.7-0 Ma). These three phases correspond to the formation of the eastern, central, and western parts of the Del Cano Rise, respectively. The magnitude and apparent periodicity of the magmatic volume flux of the Marion hotspot appear to be dominated by the hotspot-ridge distance. The periodicity of the Marion hotspot is about 25 Ma, which is much longer than that of the Hawaii and Iceland hotspots (about 15 Ma).
Southwest Indian Ocean, hotspot-ridge interaction, magmatic volume flux, oceanic plateaus, seamounts
Citation:Zhang T, Lin J, Gao J Y. Interactions between hotspots and the Southwest Indian Ridge during the last 90 Ma: Implications on the formation of oceanic plateaus and intra-plate seamounts.Numerous seamounts are generated at plate boundaries by the volcanic and tectonic activities of mid-ocean ridges and transform faults [1]. Correspondingly, hotspots are mainly observed as intra-plate volcanism [2]. With the interaction of mid-ocean ridges and hotspots, the intensity of hotspot activity is amplified, resulting in the formation of broad plateaus [3]. These plateaus and seamounts (or seamount chains) substantially reflect the intensity of magmatism and the tracks of hotspots [2,[4][5][6][7], and record the ages, locations and magmatic volume of seamounts created by hotspots. It would be useful to study the time variation and periodicity of the intensity of hotspot activity and the interaction of hotspots, mid-ocean ridges and transform faults [4,5,8,9]. Radioactive dating of rocks can be adopted to determine directly the ages of seamounts, and the thickness of the oceanic crust (layer 2A to layer 3) can be regarded as a first-order measure of the mantle magmatic volume [10]. However, very few rock samples have been taken and there has been little determination of the crustal thickness from seismic velocity profiles of ocean bottom experiments. In many areas that have been little studied, the mentioned methods cannot be used to calculate hotspot tracks and