African Shield
Quick Summary
The African Shield is a large, stable area of low relief in Earth's crust, primarily composed of Precambrian crystalline rocks that are over 540 million years old. This shield, sometimes called the Ethiopian Shield, covers much of Africa and extends into western Saudi Arabia and eastern Madagascar. It is made up of ancient Precambrian cratons, such as the Kaapvaal, Zimbabwe, Tanzania, Congo, and West African cratons, which have been tectonically stable for billions of years. These cratons are bordered by younger fold belts formed between 2 billion and 300 million years ago. The oldest rocks within the shield are Archean, dating back 4.6 to 2.5 billion years, and are found in granite-gneiss-greenstone terrains.12
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The African Shield, sometimes called the Ethiopian Shield, extends eastward to include western Saudi Arabia and the eastern half of Madagascar.
Read MoreThe African Shield, sometimes called the Ethiopian Shield, extends eastward to include western Saudi Arabia and the eastern half of Madagascar.
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PrecambrianOrogenic beltsThis entire shield, called the Arabian-Nubian Shield, is dominated by volcanic lavas, tuffs (consolidated rocks consisting of pyroclastic fragments and ash), and granitic plutons that formed in a variety of island arcs separated by several sutures along which many ophiolite complexes occur. Some of the ophiolites contain a complete stratigraphy…
Read MoreThis entire shield, called the Arabian-Nubian Shield, is dominated by volcanic lavas, tuffs (consolidated rocks consisting of pyroclastic fragments and ash), and granitic plutons that formed in a variety of island arcs separated by several sutures along which many ophiolite complexes occur. Some of the ophiolites contain a complete stratigraphy…
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AfricaGeneral considerations…is recorded in the so-called Arabian-Nubian Shield of northeastern Africa and Arabia. There, large volumes of volcanic and granitoid rocks were generated in an island-arc, marginal-basin setting—an environment similar to that of the present southwestern Pacific Ocean. Rocks were accreted onto the ancient African continent, the margin of which was…
Read More…is recorded in the so-called Arabian-Nubian Shield of northeastern Africa and Arabia. There, large volumes of volcanic and granitoid rocks were generated in an island-arc, marginal-basin setting—an environment similar to that of the present southwestern Pacific Ocean. Rocks were accreted onto the ancient African continent, the margin of which was…
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SaharaPhysiographyThe Sahara sits atop the African Shield, which is composed of heavily folded and denuded Precambrian rocks. Because of the stability of the shield, subsequently deposited Paleozoic formations have remained horizontal and relatively unaltered. Over much of the Sahara, these formations were covered by Mesozoic deposits—including the limestones of Algeria,…
Read MoreThe Sahara sits atop the African Shield, which is composed of heavily folded and denuded Precambrian rocks. Because of the stability of the shield, subsequently deposited Paleozoic formations have remained horizontal and relatively unaltered. Over much of the Sahara, these formations were covered by Mesozoic deposits—including the limestones of Algeria,…
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ArabiaGeology…two main geomorphological areas: the Arabian shield in the west; and sedimentary areas dipping away from the shield to the northeast, east, and southeast into the great basin consisting of lower Iraq, the Persian Gulf, and the eastern part of the Rubʿ al-Khali (“Empty Quarter”) desert. The eastern edge of…
Read More…two main geomorphological areas: the Arabian shield in the west; and sedimentary areas dipping away from the shield to the northeast, east, and southeast into the great basin consisting of lower Iraq, the Persian Gulf, and the eastern part of the Rubʿ al-Khali (“Empty Quarter”) desert. The eastern edge of…
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Arabian DesertGeology of the Arabian Desert…platform (a segment of the African Shield), is in the west. It is composed mainly of Precambrian gneiss (dated to between 2.6 billion and roughly 541 million years ago) and was assembled roughly 900 to 541 million years ago. The second region, in the east, comprises sedimentary rock layers deposited…
Read More…platform (a segment of the African Shield), is in the west. It is composed mainly of Precambrian gneiss (dated to between 2.6 billion and roughly 541 million years ago) and was assembled roughly 900 to 541 million years ago. The second region, in the east, comprises sedimentary rock layers deposited…
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