East Pacific Rise 15.4°N: A geochemical approach at very small spatial and temporal scale in a hotspot-ridge context.
Berengere Mougel1, Arnaud Agranier2, Morgane Le Saout3, Pascal Gente2, Christophe Hemond2
Contact: mougel@ipgp.fr
1Institut de Physique du Globe de Paris, Sorbonne Paris Cité CNRS, UMR, Paris, France
2Laboratoire Domaines Océaniques, UMR6538, IUEM, Plouzane, France
3Monterey Bay Aquarium Research Institute, Moss Landing, United States
EPR 16°N segment is an atypical ridge segment. The ridge in this area is the shallowest and widest of the entire EPR and connects to the Mathematician seamounts chain. Both geochemical signatures of MORB and geophysical observations strongly support a recent (≤ 1my) hotspot influence on this segment [e.g., Weiland and Macdonald, 1996; Carbotte et al., 2000; Shah and Buck, 2006; Le Saout et al., 2014]. A large set of lava samples has been collected by submersible during PaRiSub cruise (2010) along two ~20km profiles, one covering the axis, the other one crossing it. Together with the acquisition of micro-bathymetric data obtained by AUV, this cruise adopted a sampling and imaging strategy specifically adapted to the scale of volcanic edifices. Therefore, we took advantage of the dense and precise sampling to develop a very high-resolution geochemical study, almost matching the bathymetric resolution. Axial data has already demonstrated the high efficiency of such approach [Mougel et al., 2014, 2015]. Here, we study the transversal sampling profile in order to 1) discuss in conjunction with the new micro-bathymetric data, the geochemical evolution of the lavas over time in this area, and 2) couple the geochemical information with previous geophysical studies, and integrate it into a spatio-temporal reconstruction of the EPR/Mathematician hotspot system. The latest starts 600 kya [Cormier et al., 1998)] with the segment inflation and a global change in the ambient mantle composition, followed by two successive jumps of the ridge axis (250 and 150 kya) towards the seamounts chain [Carbotte et al., 2000]. During this phase as the two systems are getting closer, the ridge starts to sample other mantle signatures. Among them, relics of regional depleted mantle, small enriched local heterogeneities, and two other signatures belonging to the hotspot heterogeneous source. One of them becomes apparent only during the last 100 years [Carlut et al., 2004] and constitutes a previously unknown isotopic signature for MORB.
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