25. The centers of most continents contain \"shields\" where very old igneous an

Question

25. The centers of most continents contain "shields" where very old igneous and metamorphic rocks are exposed in flat lying areas. They also contain platforms - areas of flat lying sedimentary rocks on or adjacent to shields. Why are there shields and platforms only in the middles of continents? We find most mountain belts at the edges of continents. Why do mountains mostly only form at the edges of continents? Every once and a while we find mountain ranges in the interior of continents. The Rockys and the Ural Mountains are examples. Explain how they formed (different for each) and ended up where they are. If you looked at a map of the world showing locations of volcanic activity, you would find that most volcanoes are at the edges of continents - just like most mountain ranges are. A few volcanoes are in the middle of oceans, and even fewer in the middle of continents. Explain why volcanoes occur where they do.

Explanation / Answer

Platforms, shields and basements, abundant in sedimenatry, metamorphic and igneous rocks are always found in the middle of the continents. As is evident from their name, they have not been affected by any large-scale tectonic activities. They overlie upon the consolidated rocks of an earlier deformed basement. Thus, they are stable. They are the nucleus of the continents.

Mountains are formed by the collision of continental plates. So, they are created at the edges of continents.

Most of the volcanoes are created in the middle of the oceans. Most of them are deep water volcanoes. But some of them occur in the middle of the continents. They occur as a consequence of intraplate volcanism.

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