GENERAL GEOLOGY

Detailed explanation-1: -Cratons are the oldest and most stable part of the continental lithosphere. These parts of the continental crust are usually found deep in the interior of most continents. Cratons are divided into two categories. Shields are cratons in which the ancient basement rock crops out into the atmosphere.

Detailed explanation-2: -The ancient core of a continent, at and beneath the surface, is its craton. The cratonic rock that is seen at the surface is called the shield. Where the shield is covered by younger sediments is the platform.

Detailed explanation-3: -These areas of Precambrian rocks are termed, appropriately, the Indian Shield, the Australian Shield, and the Antarctic Shield. In Asia the name Angaran Shield is applied to a large stable block bounded by the Lena and Yenisey rivers on the east and west and by the Arctic Ocean and Lake Baikal to the north and south.

Detailed explanation-4: -A shield is a large area of exposed Precambrian-age crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas. In all cases, the age of these rocks is greater than 570 million years and sometimes dates back 2 to over 4 billion years.

Detailed explanation-5: -A shield is that part of a craton in which the usually Precambrian basement rocks crop out extensively at the surface. In contrast, the platform of the basement is overlain by horizontal or subhorizontal sediments. Cratons are subdivided geographically into geologic provinces.