A survey is given of the dimensions and composition of the present continental crust. The abundances of immobile elements in sedimentary rocks are used to establish upper crustal composition. The present upper crustal composition is attributed largely to intracrustal differentiation resulting in the production of granites senso lato. Underplating of the crust by ponded basaltic magmas is probably a major source of heat for intracrustal differentiation. The contrast between the present upper crustal composition and that of the Archean upper crust is emphasized. The nature of the lower crust is examined in the light of evidence from granulites and xenoliths of lower crustal origin. It appears that the protoliths of most granulite facies exposures are more representative of upper or middle crust and that the lower crust has a much more basic composition than the exposed upper crust. There is growing consensus that the crust grows episodically, and it is concluded that at least 60% of the crust was emplaced by the late Archean (ca. 2.7 eons, or 2.7 Ga). There appears to be a relationship between episodes of continental growth and differentiation and supercontinental cycles, probably dating back at least to the late Archean. However, such cycles do not explain the contrast in crustal compositions between Archean and post-Archean. Mechanisms for deriving the crust from the mantle are considered, including the role of present-day plate tectonics and subduction zones. It is concluded that a somewhat different tectonic regime operated in the Archean and was responsible for the growth of much of the continental crust. Archean tonalites and trond-hjemites may have resulted from slab melting and/or from melting of the Archean mantle wedge but at low pressures and high temperatures analogous to modern boninites. In contrast, most andesites and subduction-related rocks, now the main contributors to crustal growth, are derived ultimately from the mantle wedge above subduction zones. The cause of the contrast between the processes responsible for Archean and post-Archean crustal growth is attributed to faster subduction of younger, hotter oceanic crust in the Archean (ultimately due to higher heat flow) compared with subduction of older, cooler oceanic crust in more recent times. A brief survey of the causes of continental breakup reveals that neither plume nor lithospheric stretching is a totally satisfactory explanation. Speculations are presented about crustal development before 4000 m.y. ago. The terrestrial continental crust appears to be unique compared with crusts on other planets and satellites in the solar system, ultimately a consequence of the abundant free water on the Earth.

The geochemical evolution of the continental crust

http://levee.wustl.edu/~rlk/papers/gromet_et_al_1984_gca_nasc.pdf

The 'North American shale composite' - Its compilation, major and trace element characteristics

https://sites.williams.edu/rcox/files/2013/01/MudrockChem.pdf

The influence of sediment recycling and basement composition on evolution of mudrock chemistry in the southwestern United States

Geochemical and NdSr isotopic composition of deep-sea turbidites: Crustal evolution and plate tectonic associations

The rare earth elements (REE) have been mobilised and fractionated during supracrustal alteration of the Torrongo granodiorite. Compared with the parent granodiorite, incipiently and moderately altered rocks are particularly enriched in the heavy REE, while the extremely altered residual products are especially depleted in the heavy REE. Mobilisation of the REE probably results from pH changes of soil and ground waters as they encounter different chemical environments while fractionation may largely result from mineralogical controls. Submarine and subaerial weathering processes may affect REE similarly, producing intensively weathered materials appreciably depleted in the REE. Spilitisation and hydrothermal alteration processes may affect basaltic rocks in much the same way as do weathering processes.

Mobility and fractionation of rare earth elements during weathering of a granodiorite

Rare-earths in size fractions and sedimentary rocks of Pennsylvanian-Permian age from the mid-continent of the U.S.A.

Rare earth distributions in clay minerals and in the clay-sized fraction of the Lower Permian Havensville and Eskridge shales of Kansas and Oklahoma

1 An Introduction to Clay Minerals and Isotope Geochemistry.- 1 Fundamentals of Clay Mineralogy.- 1.1 Definition.- 1.2 Basic Structural Units and Layer Types.- 1.3 Classification of Clay Minerals.- 1.4 Thermodynamic Considerations for Clay Minerals.- 1.5 Clay Separation and Characterization.- 2 Principles of Isotope Geochemistry.- 2.1 Fundamentals of Isotope Geochemistry.- 2.2 Radiogenic Isotope Geochemistry.- 2.3 Stable Isotope Geochemistry.- 3 Specific Aspects of Clay Isotope Geochemistry.- 3.1 Retentivity of Radiogenic Argon.- 3.2 Effects of Mechanical Treatments.- 3.3 Effects of Chemical Treatments.- 3.4 Significance of the Leachates.- 4 Summary.- 2 Isotope Geochemistry of Clay Minerals in Continental Weathering Environments.- 1 Clay Authigenesis in Soil Profiles.- 1.1 Isotope Redistribution in Silicate Precursors During Weathering.- 1.2 Sr Isotopic Compositions of Clay Minerals Derived from Biotite and Feldspars.- 1.3 Sr Isotopic Characteristics of Fluids in Weathering Profiles.- 1.4 A Sr Isotopic Model for Clay Authigenesis in Soil Profiles.- 1.5 Stable Isotope Geochemistry of Clay Minerals from Soil Profiles.- 1.6 Experimental Clay Authigenesis and Evaluation of Mass Transfers in Soil Profiles.- 1.7 Isotopic Dating of Clay Authigenesis in Soil Profiles.- 2 Clay Weathering and Alteration in Soils.- 3. Summary.- 3 Isotope Geochemistry of Clay Minerals in Young Continental and Oceanic Sediments.- 1 Recent Continental Erosional Debris and Clay Sediments.- 1.1 Sr Isotope Geochemistry.- 1.2 Nd Isotope Geochemistry.- 1.3 Ar Isotope Geochemistry.- 1.4 Stable Isotope Geochemistry.- 2 Terrigenous Clays in Young Ocean Basins.- 2.1 Sr Isotope Geochemistry.- 2.2 Ar Isotope Geochemistry.- 2.3 Nd Isotope Geochemistry.- 2.4 Stable Isotope Geochemistry.- 3 Authigenic Clays in Young Deep-Ocean Basins.- 3.1 Isotopic Characteristics of the Present-Day Ocean Waters.- 3.2 Clay Authigenesis and Modification at Ocean Floor Conditions.- 3.3 Evolution and Paleogeography of Deep-Sea Red Clays.- 4 Isotopic Evolution of Clays in Buried Deep-Ocean Sediments.- 4.1 Isotopic Characterization of Sediment Pore Waters.- 4.2 Isotope Composition of Clays in Shallow Buried Ocean Sediments.- 5 Summary.- 4 Isotope Geochemistry of Clays and Clay Minerals from Sedimentary Rocks.- 1 Syndepositional Evolution of Clay Minerals in Argillaceous Sedimentary Rocks.- 1.1 Analyses of Whole-Rock Samples.- 1.2 Dating Sedimentation Times by Analysis of Clay Fractions.- 2 Diagenetic Evolution of Clay Minerals in Deeply Buried Shales and Sandstones.- 2.1 Diagenetic Clay Fractions in Buried Shales.- 2.2 Diagenetic Clay Fractions in Buried Sandstones...- 2.3 Comparative Evolution of Diagenetic Clay Minerals of Buried Shale-Sandstone Associations.- 2.4 Duration of Diagenetic Illite Formation.- 2.5 Reconstruction of Thermal Histories of Sedimentary Basins.- 3 Isotopic Records of Clay Diagenesis in Formation Waters.- 4 Summary.- 5 Isotope Geochemistry of Mica-Type Minerals from Low-Temperature Metamorphic Rocks.- 1 Isotope Geochemistry of Mica-Type Minerals in Different Metamorphic Environments.- 1.1 Regional Thermal Metamorphism.- 1.2 Dynamothermal Metamorphism.- 1.3 Cataclastic Metamorphism.- 1.4 Contact Metamorphism.- 1.5 Retrograde Metamorphism.- 1.6 Multiple Metamorphism.- 2 Isotope Geochemistry of Mica-Type Minerals Related to Metamorphic Rock Lithology.- 2.1 Metapelite-Metavolcanic Association.- 2.2 Metaarkose-Slate Association.- 2.3 Coal Bed-Slate Association.- 3 Isotope Geochemistry of Mica-Type Minerals Under Hydrothermal Conditions.- 3.1 Isotopic Dating of Hydrothermal Activities.- 3.2 Indirect Isotopic Dating of Hydrothermal Ore Deposits.- 4 Summary.- 6 The Frontiers of Clay Isotope Geochemistry.- 1 Isotope Geochemistry as a Dating Tool for Clay Minerals.- 1.1 Depositional Time Indicator.- 1.2 Diagenetic Time Marker.- 1.3 Provenance Tracer.- 1.4 Isotope Dates and Particle Size.- 2 Isotope Geochemistry as a Record of the Physical and Chemical Conditions of Clay Formation.- 2.1 Isotope Geochemistry and the Process of Clay Formation.- 2.2 Isotope Geochemistry as a Record of Closed Versus Open System Behavior.- 3 Can Isotope Geochemistry Elucidate the Concept of Clay Genesis?.- References.

S. Chaudhuri

Papers

Rare-earths in size fractions and sedimentary rocks of Pennsylvanian-Permian age from the mid-continent of the U.S.A.

Rare earth distributions in clay minerals and in the clay-sized fraction of the Lower Permian Havensville and Eskridge shales of Kansas and Oklahoma

Clays in Crustal Environments: Isotope Dating and Tracing

The distribution of rare-earth elements in deeply buried Gulf Coast sediments

Strontium isotopic evolution of oil-field waters from carbonate reservoir rocks in Bindley field, central Kansas, U.S.A