This chapter reviews the present-day composition of the continental crust, the methods employed to derive these estimates, and the implications of the continental crust composition for the formation of the continents, Earth differentiation, and its geochemical inventories. We review the composition of the upper, middle, and lower continental crust. We then examine the bulk crust composition and the implications of this composition for crust generation and modification processes. Finally, we compare the Earth's crust with those of the other terrestrial planets in our solar system and speculate about what unique processes on Earth have given rise to this unusual crustal distribution.

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Composition of the Continental Crust

Changes in Atmospheric Constituents and in Radiative Forcing

This essential reference for graduate students and researchers provides a unified treatment of earthquakes and faulting as two aspects of brittle tectonics at different timescales. The intimate connection between the two is manifested in their scaling laws and populations, which evolve from fracture growth and interactions between fractures. The connection between faults and the seismicity generated is governed by the rate and state dependent friction laws - producing distinctive seismic styles of faulting and a gamut of earthquake phenomena including aftershocks, afterslip, earthquake triggering, and slow slip events. The third edition of this classic treatise presents a wealth of new topics and new observations. These include slow earthquake phenomena; friction of phyllosilicates, and at high sliding velocities; fault structures; relative roles of strong and seismogenic versus weak and creeping faults; dynamic triggering of earthquakes; oceanic earthquakes; megathrust earthquakes in subduction zones; deep earthquakes; and new observations of earthquake precursory phenomena.

The Mechanics of Earthquakes and Faulting

This chapter should be cited as: Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. Coordinating Lead Authors: Gunnar Myhre (Norway), Drew Shindell (USA)

Anthropogenic and Natural Radiative Forcing

A global plate motion model, named NUVEL-1, which describes current plate motions between 12 rigid plates is described, with special attention given to the method, data, and assumptions used Tectonic implications of the patterns that emerged from the results are discussed It is shown that wide plate boundary zones can form not only within the continental lithosphere but also within the oceanic lithosphere; eg, between the Indian and Australian plates and between the North American and South American plates Results of the model also suggest small but significant diffuse deformation of the oceanic lithosphere, which may be confined to small awkwardly shaped salients of major plates

Current plate motions

Reka Moldovan, Catherine L. Johnson, J. Andreas Ritzer, Michael E. Purucker, Sean C. Solomon, Brian J. Anderson, Brett W. Denevi, and Haje Korth. Department of Earth and Ocean Sciences, The University of British Columbia, 6339 Stores Road, Vancouver, V6T 1Z4, Canada (rmoldova@eos.ubc.ca; cjohnson@eos.ubc.ca; aritzer@eos.ubc.ca); Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719-2395; Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771 (michael.e.purucker@nasa.gov); Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, N.W., Washington, DC 20015-1305 (scs@dtm.ciw.edu); Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723 (brian.anderson@jhuapl.edu; Brett.Denevi@jhuapl.edu, Haje.Korth@jhuapl.edu).

/pdf/detecting-crustal-magnetic-fields-on-mercury-with-messenger-3v1lqk65an.pdf

Detecting crustal magnetic fields on mercury with messenger.

To support studies of Mercury’s internal structure, a
MESSENGER mission goal is to measure the shape of
Mercury. Radio-frequency occultation observations
contribute to this objective. We describe here the
techniques used to derive radius measurements from
such observations. We report results from flyby and
early-orbit observations and compare them with
planet-shape measurements by the Mercury Laser
Altimeter.

Mercury's mean radius and shape from radio occultations

Frank Preusker (1), Jürgen Oberst (1), James W. Head (2), Mark S. Robinson (3), Thomas R. Watters (4), and Sean C. Solomon (5). (1) German Aerospace Center, Institute of Planetary Research, D-12489 Berlin, Germany (Frank.Preusker@dlr.de), (2) Department of Geological Sciences, Brown University, Providence, RI 02912, USA; (3) School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA; (4) Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington, DC 20560, USA; (5) Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA.

Topography of Mercury from stereo images: Regionalterrain models from MESSENGER orbital mapping.

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) obtained spectra of much of the surface of Mercury during the first two MESSENGER flybys of the planet [1]. The dataset have not been corrected for any effect due to observing geometry, but only converted to reflectance [2]. The characterization of spectral units is performed by statistical techniques. In order to extract the spectral shapes of the primary surface components exposed in the surface area analyzed, we applied an R-mode factor analysis [3] [4]. That leads to the evaluation of the eigenvectors of the covariance matrix and their abundances along the track. The results indicates that the NIR spectral range is carrying less information than the VIS portion and that the eigenvectors are unchanged if the full wavelength range is selected rather than limiting observations to the VIS. The analysis shows that seven eigenvectors are needed to reconstruct the original data, where each eigenvector can be regarded as a representative of a spectral class that varies in abundance along the track. The first eigenvector always displays a strong positive or “red” slope, carrying the effects associated to the viewing geometry and all eigenvectors show distinctive spectral signatures. The eigenvector abundances show marked geographical variation and a strong correlation with surface units mapped by MESSENGER’s Mercury Dual Imaging System (MDIS). We apply a decorrelation technique (Mahalanobis transformation [5]) to remove dependence on observation angle in the retrieved eigenvector abundances and then used the corrected abundances to classify or cluster the measurements and to identify spectral units. We used three clustering techniques and then we compare the output from the algorithms. At the same time, we make use of newly available high-temperature spectra from our Planetary Emissivity Laboratory [6] to assist in the identification of the components of each unit. Application to data from the first flyby provides us with confidence in the ability of these techniques to extract physical properties of surface materials.

Sean C. Solomon

Papers

Detecting crustal magnetic fields on mercury with messenger.

Mercury's mean radius and shape from radio occultations

Topography of Mercury from stereo images: Regionalterrain models from MESSENGER orbital mapping.

Compositional units on Mercury from MESSENGER spectral observations: comparison of clustering techniques