ALBERT

Description: In contrast to oceanic lithosphere, the continents are manifestly composed of the products of tectonic processes whose cumulative duration spans much of the Earths history. Most continents contain Archaean nuclei that are enclosed by Proterozoic and Phanerozoic tectonic domains. The evolution of post-Archaean continental volumes has included additions of new continental material, but it has also involved repeated modification of parts of the existing continental lithosphere during periods of tectonic rejuvenation. This generally involves processes such as the formation of new structural fabrics, the over-printing of metamorphic assemblages and the generation and emplacement of magmas. Such behaviour can occur repeatedly throughout the geological record because the quartzofeldspathic continental crust cannot be subducted due to its relative buoyancy and weakness compared with its oceanic counterpart and the underlying lithospheric mantle. Thus, the character of the continents is significantly influenced by the way in which the existing lithosphere responds to new tectonothermal events that follow geologically significant cessations of activity for millions to hundreds of millions of years (Sutton & Watson 1986). Existing continental lithosphere may be modified during its incorporation into new collisional systems, for example the involvement of the Hercynian basement' in the Alpine collision. However, the most dramatic manifestations of continental tectonic rejuvenation occur during intraplate orogeny, where a coherent pre-existing lithospheric volume undergoes large-scale failure. Notable modern examples of intraplate orogeny are the Cenozoic Tien Shan and the Mongolian Alti in north Asia, which are forming in response to the Himalayan collision (e.g. Hendrix et al. 1992; Dickson ... This 250-word extract was created in the absence of an abstract.