Influence of the Iceland mantle plume on oceanic crust generation in the North Atlantic

Abstract

When a mantle plume with elevated temperature underlies an oceanic spreading centre it
\naffects the generation of oceanic crust by creating thicker crust. We map the variation in
\ncrustal thickness and seismic velocity along three long-offset seismic profiles acquired over
\noceanic crust generated shortly after continental breakup in the North Atlantic: a 212-kmlong
\nflowline from the Faroes rifted continental margin across crust of 51–42 Ma age, where
\noceanic spreading developed close to the inferred centre of the Iceland mantle plume; a 256 km
\nflowline extending from the Hatton rifted continental margin across crust of 52–40 Ma age,
\nabout 800 km south of the presumed centre of the mantle plume; and a 99 km strike line over
\noceanic crust formed at 43 Ma in the Iceland Basin off the Hatton continental margin. The
\ncrustal velocity structure along each profile is constrained by multichannel seismic reflection
\ndata, which is used primarily to map the sediments, and by densely spaced ocean-bottom
\nseismometers, which recorded wide-angle reflections and refractions to offsets of more than
\n100 km. Over 56 000 crustal diving wave and Moho wide-angle reflection arrivals were used in
\njoint crustal refraction and reflection tomographic inversions. Quantitative error analysis shows
\nthat the seismic velocity of the crust is mostly constrained to within 0.1 km s−1 and the depth
\nof the Moho to within ±250 m. We interpret the crustal thickness and velocity changes along
\nthe profiles as caused primarily by changes in the mantle temperature at the time of crustal
\nformation. If all the oceanic crustal thickness variations are ascribed to mantle temperature
\nchanges, we infer that as mature seafloor spreading developed following continental breakup,
\nthe mantle cooled by ca. 75 ◦C over a 10 Myr period, although it still remained hotter than
\nthe global average of normal oceanic crust. The crust formed close to Iceland is at all times
\nthicker than that formed further away, which we interpret as reflecting higher temperatures
\nclose to the centre of the thermal anomaly created by the mantle plume. Currently at the
\nReykjanes Ridge, south of Iceland, we interpret thicker than normal oceanic crust as being
\ncaused by the presence of hotter mantle, modulated by thickness variations of 1.5–2.0 km
\nwhich are attributed to temporal variations in the mantle plume temperature of about 25 ◦C
\non a 3–6 Myr timescale. A 1.5 km increase in thickness of oceanic crust generated between
\n48 and 45 Ma on the Faroes line is similar in magnitude and duration to those occurring on
\nthe present day Reykjanes Ridge, which we suggest is due to a temperature pulse of ∼25 ◦C.
\nGravity lineations in the northern North Atlantic suggest that the oceanic crust has exhibited
\nsmall thickness fluctuations of similar size throughout its history, interpreted as due to small
\nfluctuations in the temperature of the Iceland mantle plume.