Hot spot activity and tectonic settings near Amsterdam–St. Paul plateau (Indian Ocean)

Abstract

[1] The Amsterdam-St. Paul (ASP) plateau is located in the central part of the Indian Ocean and results from the interaction between the ASP hot spot and the Southeast Indian Ridge (SEIR). It is located near the diffuse boundary between the Capricorn and Australian plates. The seamount chain of the Dead Poets (CDP) is northeast of the ASP plateau and may represent older volcanism related to the ASP hot spot; this chain consists of two groups of seamounts: (1) large flat-topped seamounts formed 8-10 Ma and (2) smaller conical seamounts formed during the last 2 Myr. The ASP hot spot has produced two pulses of magmatism that have been ponded under the ASP plateau and erupted along the divergent boundary between the Capricorn and Australian plates. The N65°orientation of the CDP as well as the seamount's elongated shapes support an opening motion between the Capricorn and Australian plates along a suture oriented in the N155°direction. This motion compared to the Antarctic plate amounts to an apparent velocity of 7.7 cm/yr northeastward for the Capricorn-Australian block. This motion does not fit with a fixed plume model. We suggest, therefore, that the ASP plume experienced a motion of about 1-2 cm/yr to the SW, which is opposite to the asthenospheric flow in this region and suggests a deep-seated plume.

Building of the Amsterdam-Saint Paul plateau: A 10 Myr history of a ridge-hot spot interaction and variations in the strength of the hot spot source

“…Geophysical data presented in this paper and in the companion paper by E. Courrèges et al (submitted manuscript, 2011) and published geochemical and age data [ Graham et al , 1999; Doucet et al , 2004; Nicolaysen et al , 2007; Janin et al , 2009, 2010, 2011] are consistent with the formation of the ASP plateau as resulting from the interaction between the ASP hot spot and the SEIR that provided excess melt resulting in anomalous depths and in excess crust. However, the absence of a long wavelength depth anomaly, expected from a strong and broad thermal effect, as well as the limit of the magmatic activity to a narrow lithospheric compartment, points to a weak hot spot source.…”

“…For the purpose of our discussion, we consider that the hot spot track represented in Figure 1 is a plausible averaged model, which, for any given time, provides the possible location of the hot spot within a 100 to 120 km diameter. The motion of the ASP hot spot inferred by Janin et al [2011] remains below this uncertainty. The SEIR past positions were derived from the magnetic anomaly crossings of E. Courrèges et al (submitted manuscript, 2011) (Figure 2).…”

“…The plate model [ Anderson , 2002] suggests that the locations of melting anomalies are controlled by plate wide stresses and that the presence of fertile, not necessarily hotter, patches in the mantle allow the genesis of large volcanic features, such as Hawaii‐Emperor, Louisville or Iceland. Plate stress field and deformation in the presence of fertile/hotter mantle is a good explanation for the more recent magmatic phase of the Dead Poets chain [ Janin et al , 2011] but not for the temporal variations in the axial magmatic budget discussed in this paper. It is difficult to explain an increase in the melting rates at the ridge axis by intraplate deformation.…”

“…Crustal and depth values were sampled on this age interval from the available grids and averaged to obtain the displayed points. Areas close to the volcanoes of the central line, linked to the off‐axis activity of the hot spot [ Janin et al , 2011] were removed from the data set to avoid introducing biases, since we are interested on the average values of the crust formed at the ridge axis. These values are plotted as a function of time in Figure 7.…”

“…Here we focus on the analysis of the bathymetry and gravity data to show that the building of the ASP volcanic plateau is a complex process, involving ridge jumps and variations in the strength of the hot spot source. Detailed analysis of the kinematic evolution of the SEIR through 10 Myr from the interpretation of the magnetic anomalies and of the geochronology of the volcanic edifices are presented in two companion papers [ Janin et al , 2011; E. Courrèges et al, Evolution of ridge segmentation on the St‐Paul‐Amsterdam plateau from 10 Ma, in the context of ridge‐hot spot interaction, submitted to Journal of Geophysical Research, 2011].…”