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Understanding Ancient Tectonic Settings: Cratons, Orogenic Belts, and Hot Spots

This chapter explores the fundamental elements of continental tectonics, including cratons, shields, platforms, and orogenic belts. It delves into hot spots, which are manifestations of mantle plumes that create geological features as they rise through the Earth’s crust. The concepts of continental rifts, specifically the East African Rift, and the associated deep structures of continental shelves are examined, alongside the dynamics of failed rifts and their implications. The relationship between tectonic processes and sediment deposition is also discussed, highlighting the cyclical nature of ocean creation and destruction.

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Understanding Ancient Tectonic Settings: Cratons, Orogenic Belts, and Hot Spots

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  1. Chapter 8 Intro Ancient Tectonics Settings

  2. Principle tectonic elements of a continent • Craton - Shield - Platform • Orogenic belt

  3. Hot Spots Hot spots are the product of mantle diapirs (diapirein, Greek to perforate) or plumes (because of their shape) that rise through the mantle as finger-shaped hot currents and penetrate the crust.

  4. Continent- Continent Continental Rifts

  5. Model for East African Rift

  6. Continental Shelf Profile of deep structure of continental shelf off Atlantic coast of eastern North America -- ?typical of passive continental margins. (Based on gravity, magnetics and seismic data) Critical points regarding this profile are (a) the large thickness of post-rift sediments of Mesozoic-Tertiary age, up to 15 km, and (b) that most of these sediments are shallow-water type. Note: volcanics and evaporites and reef (or carbonate banks)

  7. Continent- Continent Continental Rifts

  8. Large young graben systems on Earth

  9. Rio Grande Rift Generalized block diagram showing the components of Earth’s crust and upper mantle.

  10. Rio Grande Rift

  11. Aulacogene • Burke & Whiteman (1973), following the doming hypothesis, suggested that in these domalregions three rifts would develop, forming an 'rrr' triple junction. Although it is possible that all three rifts might develop into an ocean ('RRR'), it is more likely that two of these rifts would develop into an ocean ('RRr'), leaving the third rift as a 'failed arm'. They demonstrated / speculated that on many continents it was possible to recognize these RRr junctions. The 'failed arm' rift would eventually subside as the thermal anomaly decayed and become the site of a major depositional basin, or a major river channel and delta.When oceans eventually close it is possible to recognize these failed arms as depositional basins oriented perpendicular to the collision mountain belt (most basins tend to be aligned parallel to mountain belts). These are termed 'aulacogens'.

  12. Triple Junctions

  13. Ancient Ocean-Ocean Divergent Margins

  14. Ophiolite

  15. Ancient Subduction Zones

  16. Subduction Zone

  17. Continent- Continent Collision

  18. Accretion

  19. Accretion

  20. The Wilson Cycle The relatively young Mesozoic-Cenozoic age of the current ocean basins implies that there have been many cycles of ocean creation and destruction during the Earth’s history.

  21. Map of Global distribution of hot spots Volcano chains formed by the hot spots (dashed lines) indicate the plate movement over the hot spots.

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