A new paper from Dr. Barry Hanan and others using numerical models of plume–ridge interaction to study the cause of variations in the influence of the Iceland hotspot along the Mid-Atlantic Ridge and determine the origin of the NE–SW asymmetry evident in the residual topography and crustal thickness.
The origin of the asymmetry in the Iceland hotspot along the Mid-Atlantic Ridge from continental breakup to present-day
Samuel M. Howella, Garrett Itoa, Asbjørn J. Breivikb, Abhishek Raib, Rolf Mjeldec, Barry Hanand, Kaan Sayitd, Peter Vogte
a Dept. of Geology and Geophysics, SOEST, University of Hawai‘i at Mānoa, 1680 East–West Rd., Honolulu, HI 96822, USA
b Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern, 0316 Oslo, Norway
c Department of Earth Sciences, University of Bergen, Allegt. 41, NO-5007 Bergen, Norway
d Department of Geological Sciences, San Diego State University, San Diego, CA 92182-1020, USA
e Marine Science Institute, University of Santa Barbara, Santa Barbara, CA 93106-6150, USA
The Iceland hotspot has profoundly influenced the creation of oceanic crust throughout the North Atlantic basin. Enigmatically, the geographic extent of the hotspot influence along the Mid-Atlantic Ridge has been asymmetric for most of the spreading history. This asymmetry is evident in crustal thickness along the present-day ridge system and anomalously shallow seafloor of ages ∼49–25 Ma∼49–25 Ma created at the Reykjanes Ridge (RR), SSW of the hotspot center, compared to deeper seafloor created by the now-extinct Aegir Ridge (AR) the same distance NE of the hotspot center. The cause of this asymmetry is explored with 3-D numerical models that simulate a mantle plume interacting with the ridge system using realistic ridge geometries and spreading rates that evolve from continental breakup to present-day. The models predict plume-influence to be symmetric at continental breakup, then to rapidly contract along the ridges, resulting in widely influenced margins next to uninfluenced oceanic crust. After this initial stage, varying degrees of asymmetry along the mature ridge segments are predicted. Models in which the lithosphere is created by the stiffening of the mantle due to the extraction of water near the base of the melting zone predict a moderate amount of asymmetry; the plume expands NE along the AR ∼70–80%∼70–80% as far as it expands SSW along the RR. Without dehydration stiffening, the lithosphere corresponds to the near-surface, cool, thermal boundary layer; in these cases, the plume is predicted to be even more asymmetric, expanding only 40–50% as far along the AR as it does along the RR. Estimates of asymmetry and seismically measured crustal thicknesses are best explained by model predictions of an Iceland plume volume flux of ∼100–200 m3/s∼100–200 m3/s, and a lithosphere controlled by a rheology in which dehydration stiffens the mantle, but to a lesser degree than simulated here. The asymmetry of influence along the present-day ridge system is predicted to be a transient configuration in which plume influence along the Reykjanes Ridge is steady, but is still widening along the Kolbeinsey Ridge, as it has been since this ridge formed at ∼25 Ma∼25 Ma.
S.M. Howell, G. Ito, A.J. Breivik, A. Raib, R. Mjelde, B. Hanan, K. Sayit, P. Vogt, The origin of the asymmetry in the Iceland hotspot along the Mid-Atlantic Ridge from continental breakup to present-day, Earth and Planetary Science Letters,Volume 392, 15 April 2014, Pages 143–153, http://dx.doi.org/10.1016/j.epsl.2014.02.020