A high-resolution model for Eurasia-North America plate kinematics since 20 Ma

Abstract

S U M M A R YWe derive the first chronologically detailed model of Eurasia-North America plate motion since 20 Ma from ship and airplane surveys of the well-expressed magnetic lineations along this slowly spreading plate boundary, including previously unavailable dense Russian magnetic data from the southern Reykjanes Ridge and northern Mid-Atlantic ridge near the Charlie Gibbs fracture zone. From more than 7000 crossings of 21 magnetic anomalies from Anomaly 1n (0.78 Ma) to Anomaly 6n (19.7 Ma), we estimate best-fitting finite rotations and realistic uncertainties. Linear regressions of total opening distances versus their reversal ages at different locations along the plate boundary show that reversal boundaries are shifted systematically outwards from the spreading axis with respect to their idealized locations, with the outward shift ranging from more than 5 km between Iceland and the Charlie Gibbs fracture zone to ∼2 km elsewhere. This outward displacement, which is a consequence of the finite zone of seafloor accretion, degrades estimates of the underlying plate motion and is thus removed for the ensuing kinematic analysis. The corrected plate motion rotations reveal surprising, previously unrecognized features in the relative motions of these two plates. Within the uncertainties, motion was steady from 20 to 8 Ma around a pole that was located ∼600 km north of the present pole, with seafloor spreading rates that changed by no more than 5 per cent (1 mm yr −1 ) along the Reykjanes Ridge during this period. Seafloor spreading rates decreased abruptly by 20 ± 2 per cent at 7.5-6.5 Ma, coinciding with rapid southward migration of the pole of rotation and a 5 • -10 • counter-clockwise change in the plate slip direction. Eurasia-North America plate motion since 6.7 Ma has remained remarkably steady, with an apparently stationary axis of rotation and upper limit of ±2 per cent on any variations in the rate of angular rotation during this period. Based on the good agreement between seismotectonic constraints on present deformation in northeast Asia and directions of motion that are predicted by our 6.7 Ma to present pole, we hypothesize that motion has remained steady to the present and attempt to test this hypothesis with published GPS estimates for Eurasia-North America motion. We find, however, that GPS estimates that are tied to recent versions of the international geodetic reference frame and rely principally on station velocities from Europe give implausible estimates of recent motion, with the most recently published GPS model predicting convergence along the southern Gakkel Ridge and in the Laptev Sea, where seafloor spreading occurs. An alternative GPS estimate that is not tied to the international terrestrial reference frame and employs GPS station velocities from northeastern Asia is marginally consistent with our 6.7-0 Ma motion estimate.

Break-up and seafloor spreading domains in the NE Atlantic

“…6). A change in relative plate motions around 7 Ma has been reported by Merkouriev & DeMets (2008) and was accompanied by a sudden decrease in seafloor spreading rate (Fig. 7e-g).…”

The collision of India with Asia

“…Between 100 and 84 Ma we move India → Australia → Africa → North America → Europe. The Euler poles for the motion of North America → Eurasia were derived from Gaina et al (2002), Merkouriev and DeMets (2008) and Rosenbaum et al (2002) (see Auxiliary Data [A2]). The Euler poles for the motion of Africa → North America were taken from the data presented in Müller et al (1999) and Rosenbaum et al (2002).…”

Reconstructing plate-motion changes in the presence of finite-rotations noise

“…Over the last decades great efforts have been made to reconstruct Earth's plate motions at progressively finer temporal resolution from observations of the ocean-floor spreading 7 . In particular, the kinematics of the Eurasia/North America (EU/NA), India/Somalia (IN/SO) and Pacific/Antarctica (PA/AN) spreading systems since mid-/late Cenozoic have been recently reconstructed at unprecedented temporal resolution [8][9][10] from finite rotations of Earth's ocean-floor. These map the imprints of past geomagnetic inversions, therefore providing the cumulative displacement between two adjacent spreading plates-in the form of total angle opened and average geographical position of the rotation axis from some time in the geological past, through to the present day.…”

“…This yields small noise-tosignal ratios when computing Euler vectors directly by differentiation, with respect to time, of stage rotations obtained from two consecutive finite-rotation matrices. However, as finite rotations are reconstructed at progressively higher temporal resolution ( < 1 Myr) [8][9][10] , data noise becomes a major challenge to overcome. To date there is no solution to this problem, and the standard practise has been to smooth temporal series of single measurements [8][9][10] by averaging over 2 to 5 Myr-long time intervals, in the hope of isolating true plate motions and their temporal changes.…”

“…However, as finite rotations are reconstructed at progressively higher temporal resolution ( < 1 Myr) [8][9][10] , data noise becomes a major challenge to overcome. To date there is no solution to this problem, and the standard practise has been to smooth temporal series of single measurements [8][9][10] by averaging over 2 to 5 Myr-long time intervals, in the hope of isolating true plate motions and their temporal changes. Doing so, however, downgrades the native resolution of data-sets and, more importantly, does not provide unique kinematic reconstructions, because different averaging time-windows would yield different results.…”