Crustal flow beneath Iceland

Abstract

[1] Theoretical and experimental studies indicate that when oceanic crust is hotter than about 800°C, variations in crustal thickness drive lower crustal flow. We investigate the nature of crustal flow beneath Iceland, where zero-age crust varies in thickness from under 20 km to over 40 km over a distance of 100 km and temperatures exceed 1000°C below depths of a few kilometers. We model the regional characteristics of crustal flow using the two-dimensional channel flow equation with depth-dependent viscosity. The model predicts the observed decay in crustal thickness contrasts between zero-age and off-axis crust on shore Iceland and development of a sharp Moho step as the plate moves away from the rift axis. These features become locked in place as plate cooling increases the viscosity. Observations are best matched by model predictions when the solidus viscosity is of order 10 18 Pa s, in agreement with viscosity estimates from deformation rates associated with deglaciation and plate boundary processes. Crustal flow acts to erase the crustal thickness memory of ridge-plume interaction, so that maps of Icelandic crustal thickness can be used neither to derive a detailed plume flux history nor to test in detail whether the Iceland Plume center is fixed relative to other hot spots. Crustal flow beneath Iceland is an unusually clear example of the kind of flow postulated to explain continental phenomena including exhumation of metamorphic core complexes and associated development of low-angle detachments within extensional terrains and sharp-edged plateau topography in major collisional belts.

Crustal accretion of thick mafic crust in Iceland: implications for volcanic rifted margins

“…This is consistent with the absence of seismicity in the LC of Iceland (Stefánsson et al 1993), with the exception of active magmatic areas of the NVZ and the major transform fault zones (Jacobsdóttir 2008;Soosalu et al 2010). Jones and Maclennan (2005) argue that initially hot weak LC near the hotspot flows along-strike beneath the NVZ thereby decreasing the LC thickness. The LC thins to the north and south away from the hotspot for >100 km creating the broad Iceland platform.…”

“…2). Modification of original crustal thicknesses by LC flow would be superimposed on regional changes in the thermal structure and crustal thickness along the Mid-Atlantic Ridge (Hooft et al 2006;Jones and Maclennan 2005;White and McKenzie 1989). Similarly, Bell and Buck (1992) interpreted the lack of segmentation in along-axis bathymetry and mantle Bouguer gravity anomaly of the Reykjanes Ridge as a result of lateral flow of hot, weak crustal material.…”

Crustal accretion at high temperature spreading centres: Rheological control of crustal thickness

“…This is in contrast to studies like Jones and MacLennan (2005) who assumed a central maximum crust thickness as initial condition of their crust flow model motivated by observations (Darbyshire et al, 2000). In their dynamical crust formation Given these conflicting results it is important to discuss how robust is the result of a missing fifth mode with a thickest crust near the axis.…”

Subvolcanic subsidence and caldera formation during subaerial seafloor spreading in Iceland

“…Coupled with the densifi cation that occurs when magma chambers cool (e.g., Dzurisin et al, 1991Dzurisin et al, , 2002, magmatic processes create signifi cant volumes of relatively dense material in the subsurface beneath volcanic centers. The mobility and weakness of the Icelandic crust down to midcrustal levels (Bell and Buck, 1992;Jones and Maclennan, 2005) indicate that if intrusive loading is indeed responsible for subsidence of the Vatnsdalur structural basin, and sub vol canic subsidence in Iceland in general, then this subsidence may be accommodated on July 26, 2012 gsabulletin.gsapubs.org Downloaded from by ductile fl ow in the upper to middle crust (Brandsdóttir et al, 1997;Maclennan et al, 2001;Menke, 1999). This deformation would have therefore occurred at a lower strain rate and therefore was more likely to be accommodated without large-scale faulting.…”