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Although motions at the surface of tectonic plates are well determined, the accompanying horizontal mantle flow is not. We have combined observations of surface deformation and upper mantle seismic anisotropy to estimate this flow field for western North America. We find that the mantle velocity is 5.5 ± 1.5 centimeters per year due east in a hot spot reference frame, nearly opposite to the direction of North American plate motion (west-southwest). The flow is only weakly coupled to the motion of the surface plate, producing a small drag force. This flow field is probably due to heterogeneity in mantle density associated with the former Farallon oceanic plate beneath North America., It is surprising that after more than three decades into the plate tectonic revolution, we have so little direct observation of the mantle flow field that accompanies plate motion. The [...]

U-Pb ages of paleosol samples from cyclothemic sections in the Sacramento Mountains of New Mexico and the Permian basin of West Texas bracket the Pennsylvanian-Permian and Carboniferous-Permian boundaries. Linear interpolation and extrapolation to boundaries are accomplished by using cyclothems as periodic subdivisions. The Carboniferous-Permian boundary is 301 [+ or -] Ma (2[Sigma]), the Pennsylvanian-Permian boundary is 302 [+ or -] 2.4 (2[Sigma]), and the Missourian-Virgilian boundary is 307 [+ or -] 3 Ma (2[Sigma]). These ages are within the uncertainties of recent estimates for the boundaries but are significantly more precise. The average cycle duration for this Upper Pennsylvanian and Lower Permian interval is 143 [+ or -] 64 ka (2[Sigma]), within the uncertainty of the [approximately]100 k.y. cycle that dominated Pleistocene sea-level history. This new estimate, which is much shorter than those published previously, suggests that the Pennsylvanian and Early Permian cyclothems may have been driven in a manner similar to that which caused glacio-eustatic cycles of the Pleistocene.

Use of borehole, seismic and gravity data in the examination of the development of the Taranaki Basin in New Zealand suggests that foreland thrust loading resulted in the formation of the foreland basin structure. Hydrodynamic forces linked to subduction are responsible for the initial water depth in the foreland generated by a long-wavelength platform subsidence. Three different mechanisms of three distinct wavelengths, platform subsidence, flexure and ductile thickening in the lower crust, are responsible for crustal deformation at the eastern margin of the South Taranaki Basin.

A study of the link between subduction initiation and platform subsidence in New Zealand revealed that flexural foredeep was not responsible for the observed 1500 meter subsidence due to a broad wavelength, which was greater than 200 kilometers. Viscous mantle flow models predict that platform subsidence, which occurs above subduction zones, may cause depression that are two kilometers deep and 500 to 1000 kilometers wide.

A fifth-order polynomial function is used to obtain the relative velocities and rotations occurring in the regions surrounding the Eastern Himalayan syntaxis. This method is also applied to strain rates obtained from both modern and historic earthquakes. Lastly, instantaneous rotation rates within the deforming region, extrapolated over 20-40 million years, are in rough agreement with the paleomagnetic rotations measured in Cretaceous-aged rocks.

Sets of polynomials, consistent with the observed seismic strain rate in Asia, facilitate the derivation of velocity fields that suggest strain in the seismogenic protein of the lithosphere. The equations suggested accurately predict the strike directions of the uniform fault model of McKenzie and Jackson. Westaway assumes that occurrence of uniaxial extension is below the seismogenic layer while the strain rates observed are within the seismogenic layer.

Observes the directions of shear in the crustal strain field in Tibet. Alignment between crustal deformation field in Tibet with directions of shear-wave polarization; Correlation between crustal and mantle strain fields; Nature of lithospheric mantle deformation; Link between crustal and upper mantle deformation fields.