Geodynamic process as advection-convection of the Mid-Atlantic Ocean Ridge (MAR), that is exposed on land in Iceland is investigated. Advection is considered for the plate spreading velocity. Geodetic GPS data during 2000-2010 is used to estimate plate spreading velocity along a profile in the Eastern Volcanic Zone (EVZ), Iceland striking N102˚E, approximately parallel to the NUVEL-1A spreading direction between the Eurasian and North American plates. To predict subsurface mass flow patterns, temperature-dependent Newtonian rheology is considered in the finite-element models (FEM). All models are considered 2-D with steady-state, incompressible rheology whose viscosity depends on the subsurface temperature distribution. The thickness of lithosphere along the profile in the EVZ is identified by 700˚C isotherm and 10 22 Pa s iso-viscosity, those reach 50 ± 3 km depth at distance of 100 km from rift axis. Geodetic observation and model prediction results show the ~90% of spreading is accommodated within ~45 km of the rift axis in each direction. Model predicts ~8.5 mm•yr −1 subsidence at the surface of rift center when magmatic plumbing is inactive. The rift center (the highest magmatic influx is ~11 mm•yr −1) in model shifts ~10-20 km west to generate observed style surface deformation. The spreading velocity, isotherm and depth of isotherm are the driving forces resulting in the surface deformation. These three parameters have more or less equal weight. However, as the center of deformation in the EVZ shifts and most of the subsidence takes place in the volcanic system that is currently the active which is the located of plate axis.
North America‐Eurasia relative plate motion across the Mid‐Atlantic Ridge in south Iceland is partitioned between overlapping ridge segments, the Western Volcanic Zone (WVZ) and the Eastern Volcanic Zone. The Thingvellir graben, a 4.7 km wide graben, lies along the central axis of the WVZ and has subsided >35 m during the Holocene. An ~8 km long leveling profile across the graben indicates a subsidence rate of ~1 mm yr−1 from 1990 to 2007, relative to the first (westernmost) benchmark. Modeled GPS velocities from 1994 to 2003 estimate a spreading rate of 6.7 ± 0.5 mm yr−1 or 35% of the full plate motion rate and up to 6.0 mm yr−1 subsidence. The combined geodetic observations show that the deformation zone is 10 times wider than the graben width. We utilize these geodetic observations to test the effects of ridge thermal structure on the kinematics across divergent boundaries. We apply a nonlinear rheology, thermomechanical model implemented in a finite element model. A 700°C isotherm is applied for the brittle to ductile transition in the crust, representing a dry olivine rheology. We adjust the depth of this isotherm to solve for the best fit model. The best fit model indicates that the 700°C isotherm is at 8 km depth below the ridge axis, which results in an average thermal gradient of 87.5°C km−1 in the upper crust. The thermomechanical model predicts a subsidence rate of 4 mm yr−1, comparable to our geodetic observations.
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