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Plume and plate controlled hotspot trails in the South Atlantic

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O'Connor, J. , Jokat, W. , Le Roex, A. , Class, C. , Wijbrans, J. R. , Kessling, S. , Kuiper, K. and Nebel, O. (2012): Plume and plate controlled hotspot trails in the South Atlantic , AGU Fall Meeting 2012, San Francisco, CA, USA, 3 December 2012 - 7 December 2012 .
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Discovering if hotspots observed on the Earth’s surface are explained by underlying plumes rising from the deep mantle or by a shallow plate-cracking mechanism continues to be an essential goal in Earth Science. Key evidence underpinning the mantle plume concept is the existence of narrow, age-progressive volcanic trails recording past plate motion relative to surface hotspots and their deep causal plumes. Using the icebreaker RV Polarstern we sampled scattered hotspot trails on the 2,000 km-wide southeast Atlantic hotspot swell, which projects down to one of the Earth’s two largest and deepest regions of slower-than-average seismic wave speed – the Africa Low Shear Wave Velocity Province – caused by a massive thermo-chemical ‘pile’ on the core-mantle boundary. We showed recently using 40Ar/39Ar isotopic ages – and crustal structure and seafloor ages – that these hotspot trails are age progressive and formed synchronously across the swell, consistent with African plate motion over plumes rising from the stable edge of a Low Shear Wave Velocity Province (LLSVP) (O’Connor et al., 2012). We showed furthermore that hotspot trails formed initially only at spreading boundaries at the outer edges of the swell until roughly 44 million years ago, when they started forming across the swell, far from spreading boundaries in lithosphere that was sufficiently weak (young) for plume melts to reach the surface. We concluded that if plume melts formed synchronous age progressive hotspot trails whenever they could penetrate the lithosphere, then hotspot trails in the South Atlantic are controlled by the interplay between deep plumes and the shallow motion and structure of the African plate. Our observations reveal a plate tectonic-controlled cycle from the creation of deep thermo-chemical piles (LLSVP) and initiation of deep mantle plumes at the CMB to the shallow formation of the resulting hotspot trails. Moreover, suppression of plume melts from venting to the plate surface for tens of millions of years implies that the plumes responsible for the southeast Atlantic hotspot swell and hotspot trails transported more material and heat from the core mantle boundary than measured by hotspot volcanism.

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