Discussion
Which of the following tectonic settings are primarily characterized by thin crust, normal faults, shallow earthquakes and basalt and rhyolite magmatism ?
Answer: B
These features characterise continental rifts.
Where continental lithosphere is stretched, as in the East African Rift, the Rio Grande Rift or the Basin and Range, the crust thins, normal faults bound grabens and horsts, and earthquakes are shallow. Melting of the upwelling mantle gives basalt, and that basalt in turn melts the continental crust to give rhyolite, producing the bimodal basalt-rhyolite suite typical of rifts.
Mid-ocean ridges also have normal faults and shallow earthquakes, but their magmatism is basalt only, since there is no continental crust to melt. Convergent boundaries have thick crust, thrust faults and andesitic magmatism. Transform boundaries have strike-slip faults and little magmatism.
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