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A steady-state plate-tectonic kinematic model of crustal accretion in Iceland is presented. It describes quantitatively the overall time-averaged movements of solid crustal elements during the accretion process, and correlates accretion parameters in the axial zone (width of lava deposition zone, total lava production rate, width of horizontal strain zone, spreading velocity, normal faulting) with structural properties in the Tertiary lava pile (lava dips, lava deposition rate, dyke fraction). The model is used, firstly, to predict the accretion parameters of the Tertiary volcanic zone on the basis of observed structural properties in the Tertiary lava pile; secondly, to predict possible structures of the lower crust in terms of a lava/intrusion ratio; thirdly, the model may be used to calculate the crustal temperature field caused by intrusions, but this application is outside the scope of the present paper. The model is essentially a further development of a previous one presented earlier by the author. The analysis, in terms of the model, of various published structural observations indicates that the width of lava deposition and the spreading rate in the Tertiary volcanic zone were consistent with the corresponding properties in the present-day volcanic zone. This may suggest a certain uniformity in the volcanic processes during the last 10-15 Ma. The visible Tertiary lava pile was, according to the model, deposited outside the innermost 50-km-wide central part of the volcanic zone, which may explain the difference in appearance between the two main volcanic regions of Iceland, i.e., the active volcanic zone and the Tertiary flood basalts. Furthermore, an analysis of possible structures of the lower crust, consistent with various surface observations, indicates a gradual rather than a sharp transition from an upper lava-dominated crust to a lower intrusion-dominated crust.
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