Using full-colour palaeogeographical maps from the Cambrian to the present, this interdisciplinary volume explains how plate motions and surface volcanism are linked to processes in the Earth's mantle, and to climate change and the evolution of the Earth's biota. These new and very detailed maps provide a complete and integrated Phanerozoic story of palaeogeography. They illustrate the development of all the major mountain-building orogenies. Old lands, seas, ice caps, volcanic regions, reefs, and coal beds are highlighted on the maps, as well as faunal and floral provinces. Many other original diagrams show sections from the Earth's core, through the mantle, and up to the lithosphere, and how Large Igneous Provinces are generated, helping to understand how plates have appeared, moved, and vanished through time. Supplementary resources are available online, making this an invaluable reference for researchers, graduate students, professional geoscientists and anyone interested in the geological history of the Earth.

Earth History and Palaeogeography

[1] Sp and Ps converted seismic waves at 93 permanent seismic stations are used to image upper mantle velocity discontinuities across the contiguous United States and portions of southeast Canada and northwest Mexico. Receiver functions are calculated with frequency-domain deconvolution and migrated with 1D models that account for variations in crustal structure and mantle velocities between stations. Strong positive Ps phases from the Moho are observed and agree well with previous crustal thickness estimates. In the tectonically active western U.S., high amplitude, negative Sp phases are interpreted as the lithosphere-asthenosphere boundary (LAB) at depths of 51–104 km. These phases indicate a large and rapid LAB velocity gradient and are consistent with an anomalously hot asthenosphere that is rich in water or contains partial melt. In the regions of the Phanerozoic southern and eastern U.S where Sp phases are interpretable as the LAB, the discontinuity lies at depths of 75–111 km and is also too sharp to be explained by temperature alone. In contrast, no Sp phases are observed at depths comparable to the base of the thick high velocity lithosphere that lies beneath cratonic North America and certain portions of the Phanerozoic eastern U.S. At these stations, negative Sp phases occur at depths of 59–113 km and are interpreted as the top of a low velocity zone internal to the lithosphere. The absence of an observable LAB discontinuity in regions of thick lithosphere indicates that the LAB velocity gradient is distributed over more than 50–70 km in depth and is consistent with a purely thermal boundary.

/pdf/north-american-lithospheric-discontinuity-structure-imaged-2y9mzt4saj.pdf

North American lithospheric discontinuity structure imaged by Ps and Sp receiver functions

http://cascadiageo.org/documentation/literature/cascadia_papers/schmandt_humphreys_2010_subduction_convection_tomography_west_US.pdf

Complex subduction and small-scale convection revealed by body-wave tomography of the western United States upper mantle

[1] Ambient noise tomography and multiple plane wave earthquake tomography are new methods of surface wave analysis that yield much more highly refined information about the crust and uppermost mantle than traditional surface wave techniques. Applied together to data observed at more than 300 broadband seismic stations from the Transportable Array component of the EarthScope USArray, these methods yield surface wave dispersion curves from 8 to 100 s period across the entire western United States with unprecedented resolution. We use the local Rayleigh wave phase speed curves to construct a unified isotropic 3-D Vs model to a depth of about 150 km. Crustal and uppermost mantle features that underlie the western United States are revealed in striking relief. As the USArray continues to sweep eastward across the United States, the substructure of the entire country will be unveiled.

http://ciei.colorado.edu/pubs/2008/2008JB005833.pdf

Structure of the crust and uppermost mantle beneath the western United States revealed by ambient noise and earthquake tomography

SUMMARY

The relation between the complex geological history of the western margin of the North American plate and the processes in the mantle is still not fully documented and understood. Several pre-USArray local seismic studies showed how the characteristics of key geological features such as the Colorado Plateau and the Yellowstone Snake River Plains are linked to their deep mantle structure. Recent body-wave models based on the deployment of the high density, large aperture USArray have provided far more details on the mantle structure while surface-wave tomography (ballistic waves and noise correlations) informs us on the shallow structure. Here we combine constraints from these two data sets to image and study the link between the geology of the western United States, the shallow structure of the Earth and the convective processes in mantle. Our multiphase DNA10-S model provides new constraints on the extent of the Archean lithosphere imaged as a large, deeply rooted fast body that encompasses the stable Great Plains and a large portion of the Northern and Central Rocky Mountains. Widespread slow anomalies are found in the lower crust and upper mantle, suggesting that low-density rocks isostatically sustain part of the high topography of the western United States. The Yellowstone anomaly is imaged as a large slow body rising from the lower mantle, intruding the overlying lithosphere and controlling locally the seismicity and the topography. The large E–W extent of the USArray used in this study allows imaging the ‘slab graveyard’, a sequence of Farallon fragments aligned with the currently subducting Juan de Fuca Slab, north of the Mendocino Triple Junction. The lithospheric root of the Colorado Plateau has apparently been weakened and partly removed through dripping. The distribution of the slower regions around the Colorado Plateau and other rigid blocks follows closely the trend of Cenozoic volcanic fields and ancient lithospheric sutures, suggesting that the later exert a control on the locus of magmato-tectonic activity today. The DNA velocity models are available for download and slicing at http://dna.berkeley.edu.

/pdf/lithosphere-asthenosphere-interaction-beneath-the-western-25dcy3tvnr.pdf

Lithosphere-asthenosphere interaction beneath the western United States from the joint inversion of body-wave traveltimes and surface-wave phase velocities

We present a new set of contour maps of the seismic structure of North America and the surrounding ocean basins. These maps include the crustal thickness, whole-crustal average P-wave and S-wave velocity, and seismic velocity of the up- permost mantle, that is, Pn and Sn. We found the following: (1) The average thickness of the crust under North America is 36.7 km (standard deviation (s.d.) 8.4 km), which is 2.5 km thinner than the world average of 39.2 km (s.d. 8.5) for continental crust; (2) Histograms of whole-crustal P- and S-wave velocities for the North Amer- ican crust are bimodal, with the lower peak occurring for crust without a high-velocity (6.9-7.3 km/sec) lower crustal layer; (3) Regions with anomalously high average crustal P-wave velocities correlate with Precambrian and Paleozoic orogens; low average crustal velocities are correlated with modern extensional regimes; (4) The average Pn velocity beneath North America is 8.03 km/sec (s.d. 0.19 km/sec); (5) the well-known thin crust beneath the western United States extends into north- west Canada; (6) the average P-wave velocity of layer 3 of oceanic crust is 6.61 km/ sec (s.d. 0.47 km/sec). However, the average crustal P-wave velocity under the eastern Pacific seafloor is higher than the western Atlantic seafloor due to the thicker sediment layer on the older Atlantic seafloor.

/pdf/seismic-structure-of-the-crust-and-uppermost-mantle-of-north-5c6trwqvh6.pdf

Seismic Structure of the Crust and Uppermost Mantle of North America and Adjacent Oceanic Basins: A Synthesis

https://escweb.wr.usgs.gov/share/mooney/145.pdf

Seismic structure of the crust and uppermost mantle of South America and surrounding oceanic basins

We summarize geophysical information from North America and India, and find many similarities in the deep crustal structure of the two continents. From this, we infer that similar processes have operated, particularly in the accretion and stabilization of the cratonic regions. Seismic images and other data suggest that plate tectonic processes have been active, both in the North American and Indian shields, since the late Archean. Precambrian orogens and high-pressure granulite terrains of both regions have developed nearly identically through time since about 2500 Ma. Such similarities invite direct comparisons of deep crustal structure. Here we present results from work in North America including: maps of crustal thickness, maps of average P-wave velocity of the crystalline crust, maps of average P n (sub-Moho) velocity, and statistical analysis of crustal properties.

/pdf/comparison-of-the-deep-crustal-structure-and-seismicity-of-4lf4zjcjy2.pdf

Gary S. Chulick

Papers

Seismic Structure of the Crust and Uppermost Mantle of North America and Adjacent Oceanic Basins: A Synthesis

Seismic structure of the crust and uppermost mantle of South America and surrounding oceanic basins

Comparison of the deep crustal structure and seismicity of North America with the Indian subcontinent