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

Abstract

[1] The Amsterdam-Saint Paul plateau results from a 10 Myr interaction between the South East Indian Ridge and the Amsterdam-Saint Paul hot spot. During this period of time, the structure of the plateau changed as a consequence of changes in both the ridge-hot spot relative distance and in the strength of the hot spot source. The joint analysis of gravity-derived crust thickness and bathymetry reveals that the plateau started to form at ∼10 Ma by an increase of the crustal production at the ridge axis, due to the nearby hot spot. This phase, which lasted 3-4 Myr, corresponds to a period of a strong hot spot source, maybe due to a high temperature or material flux, and decreasing ridge-hot spot distance. A second phase, between ∼6 and ∼3 Ma, corresponds to a decrease in the ridge crustal production. During this period, the hot spot center was close to the ridge axis and this reduced magmatic activity suggests a weak hot spot source. At ∼3 Ma, the ridge was located approximately above the hot spot center. An increase in the hot spot source strength then resulted in the building of the shallower part of the plateau. The variations of the melt production at the ridge axis through time resulted in variations in crustal thickness but also in changes in the ridge morphology. The two periods of increased melt production correspond to smooth ridge morphology, characterized by axial highs, while the intermediate period corresponds to a rougher, rift-valley morphology. These variations reveal changes in axial thermal structure due to higher melting production rates and temperatures.

The Amsterdam–St. Paul Plateau: A complex hot spot/DUPAL‐flavored MORB interaction

“…Considering those samples as representative of the bulk composition of the seamounts, we can explain this observation as follows: (1) the large old seamounts may result from larger degrees of melting, and therefore exhibit a more dilute enriched signature because of mixing with local depleted mantle melts and (2) the youngest seamounts, which formed above lithospheric cracks [ Janin et al , 2011], would result from lower degrees of melting of more enriched materiel left by the plume under or in the lithosphere. Maia et al [2011] suggested an episodic activity of ASP mantle plume. In the frame of Maia et al models, the youngest seamounts are related to the second pulse which constructed the ASP plateau [ Janin et al , 2011].…”

“…The construction of the ASP plateau began about 10 Myr ago [ Maia et al , 2008, 2011] and resulted in two separate magmatic stages: on‐axis and off‐axis successively. The difference between on‐ and off‐axis magmatism is highlighted by the morphology of the structure with (1) on‐axis magmatism, building a thicker oceanic crust, and (2) off‐axis magmatism, occurring later, and resulting into the construction of seamounts on the oceanic floor.…”

“…The MD157/PLURIEL cruise (N/O Marion Dufresne, September/October 2006, P. I.: M. Maia) was dedicated to the mapping and sampling of the plateau and of a chain of seamounts built on the Australian plate, and named the Chain of “Dead Poets” (CDP; Figure 1). The geochronological study resulting from this sampling and the geophysical data have been presented elsewhere [ Courreges , 2010; Janin et al , 2011; Maia et al , 2011]. These previous studies revealed the complexity of (1) this ridge‐hot spot interaction, resulting in a multistage construction of the plateau, and (2) of the regional geodynamics due to the diffuse boundary within the Indo‐Australian plate.…”

Variable Crustal Production Originating From Mantle Source Heterogeneity Beneath the South East Indian Ridge and Amsterdam‐St. Paul Plateau

“…The ASP Plateau is presently in a period of diminishing plume‐ridge interaction indicated by a decrease in axial crustal thickness since 1.4 Ma. Using high‐resolution bathymetric (gridded at 200 m) and gravity data (gridded at 1 km) as well as magnetic anomalies from the PLURIEL (September/October 2006) and BOOMERANG 06 expeditions (February/April 1996; Maia et al, ; Scheirer et al, ), we present a detailed analysis of the Amsterdam‐St. Paul Plateau and of the morphological evolution of the SEIR axis during the last 3 Myr.…”

“…(a) Bathymetric map of the Amsterdam‐St. Paul Plateau based on multibeam data from Maia et al () and the regional map with depth anomaly (inset). The ASP plume has been approaching (black circles show approximate locations since 9 Ma) the SEIR (thin, black lines) for >10 Ma.…”