Chapter 9, Problem 1RQ

To determine

The geological features that enable geologists to recognize ancient continental rifting and ancient subduction zones.

Answer to Problem 1RQ

Block faults, mafic and felsic igneous rocks, and thick sedimentary sequences within fault block basins are some geologic features that enable the geologists to recognize ancient continental rifting. The Andes of South America are associated with the Pacific ring of fire. These mountain ranges consist of volcanoes that cover most of the Pacific Ocean and can be used by geologists to recognize ancient subduction zones.

Explanation of Solution

The geologic features that enable the geologists to recognize ancient continental rifting are as follows:

(i) The margins of Red Sea show geologic features that can be used to recognize the early stages of continental rifting. Much of the topography is the result of block faults and the uplifts created by the high rates of heat flow from mantle.

(ii) Thick sedimentary sequences within fault block basins consist of lake deposits, coarse terrestrial deposits, and evaporates followed by oceanic sediments.

(iii) Continental rifting is also characterized by mafic dikes, sills and flood basalts.

The features that enable the geologists to recognize ancient subduction zones are as follows:

(i) The Andes of South America are associated with the Pacific ring of fire composed of deep-sea trench volcanoes. These volcanoes encircle most of the Pacific Ocean.

(ii) Deep-sea trenches are the site, where the slabs of lithosphere descend into asthenosphere. These trenches are associated with two geologic features namely volcanoes and deep-focus earthquakes. Both shallow and deep-sea earthquakes are common, near trenches.