View from the North American plate (west) side across the axial rift valley at Thingvellir, Iceland. This valley is part of the western volcanic zone, one of two parallel segments making up the ridge in Iceland. Geological and GPS data indicate that the total spreading between the North American and Eurasian plates, about 2 cm/yr, is divided about evenly between the two segments.
Bathymetry and heat flow for the Iceland region. Heat flow shown as heat flow
fraction (measured values normalized by the global average values for that
lithospheric age). Lithosphere younger than about 35 Myr indicated by the
positions of magnetic anmaly 13 (solid line) after Mueller et al. (1997) or
approximated by dashed line.
Previous work [Stein and Stein, 1993] showed that the heat flow anomalies near hot spots on old crust are small compared to reference models for the evolution of oceanic lithosphere. Hence, these features cannot be due to large scale, relatively shallow lithospheric reheating. However, heat flow in young lithosphere (less than about 65 Million years old) is, on average, less than predicted by conduction-only cooling reference models due to wide-spread hydrothermal circulation. Thus, for Iceland on young oceanic crust, heat flow is compared to the measured average heat flow with lithospheric age rather than conductive reference models which do not account for the lower heat flow due to hydrothermal circulation.
Heat flow data grouped in five million year age bins for the Eurasian and North American plates,
compared to the predictions of the GDH1 thermal model [Stein and Stein, 1992]
which does not include
the effect of hydrothermal circulation, and a linear fit to the observed global
average values [Stein, 2003].
Seafloor heat flow near Iceland on the North American side of the Mid-Atlantic Ridge is comparable to that for oceanic lithosphere elsewhere, and thus shows no evidence of reheating. Heat flow on the Eurasian side of the Mid-Atlantic Ridge is somewhat higher than both the observed global average and on corresponding western side for ages less than about 35 million year old crust [Stein and Stein, 2003]. The mechanism for this asymetry is unclear, since thermal affects due to the hotspot formation are expected to be greater on the North American plate [see discussion in Stein and Stein, 2003; DeLaughter, Stein, and Stein, 2005].
Also, I have showed that the heat flow anomalies associated with other hot spots on young oceanic lithosphere, such as the Pacific superswell [Stein and Abbott, 1991; DeLaughter, Stein, and Stein, 2005], may be compared to the measured average heat flow with lithospheric age rather than conductive reference models which do not account for the lower heat flow due to hydrothermal circulation.
DeLaughter, J., C. A. Stein, and S. Stein, Hotspots: a view from the swells, in Foulger, G. R., J. Natland, D. C. Presnall, and D. L. Anderson (eds.), Plates, plumes, and paradigms, Geol. Soc. Am. Sp. Paper 388, 257-278, doi: 10.1130/2005.2388(16), 2005. For pdf click here
Stein, C. A., Heat flow and flexure at subduction zones, Geophys. Res. Lett., 30, No. 23, 2197 doi 10.1029/2003GL018478, (05 December) 2003. For pdf click here
Stein, C. A., and D. H. Abbott, Heat flow constraints on the South Pacific superswell, J. Geophys. Res., 96, 16,083-16,100, 1991. For pdf click here
Stein, C. and S. Stein, A model for the global variation in oceanic depth and heat flow with lithospheric age, Nature, 359, 123-128, 1992. For pdf click here
Stein, C. and S. Stein, Constraints on Pacific midplate swells from global depth-age and heat flow-age models, in Pringle, M., W. Sager, W. Sliter, and S. Stein (eds), The Mesozoic Pacific, Geophysical Monograph 76, 53-76, American Geophysical Union, 1993. For pdf click here
Stein, C. and S. Stein, Mantle plumes: heat flow near Iceland, Astronomy and Geophysics, 44, 8-10, 2003. For pdf click here