what is shield area?
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Answers
A sʜɪᴇʟᴅ ɪs ᴀ ʟᴀʀɢᴇ ᴀʀᴇᴀ ᴏғ ᴇxᴘᴏsᴇᴅ Pʀᴇᴄᴀᴍʙʀɪᴀɴ ᴄʀʏsᴛᴀʟʟɪɴᴇ ɪɢɴᴇᴏᴜs ᴀɴᴅ ʜɪɢʜ-ɢʀᴀᴅᴇ ᴍᴇᴛᴀᴍᴏʀᴘʜɪᴄ ʀᴏᴄᴋs ᴛʜᴀᴛ ғᴏʀᴍ ᴛᴇᴄᴛᴏɴɪᴄᴀʟʟʏ sᴛᴀʙʟᴇ ᴀʀᴇᴀs. Tʜᴇsᴇ ʀᴏᴄᴋs ᴀʀᴇ ᴏʟᴅᴇʀ ᴛʜᴀɴ 570 ᴍɪʟʟɪᴏɴ ʏᴇᴀʀs ᴀɴᴅ sᴏᴍᴇᴛɪᴍᴇs ᴅᴀᴛᴇ ʙᴀᴄᴋ 2 ᴛᴏ 3.5 ʙɪʟʟɪᴏɴ ʏᴇᴀʀs. ... Sʜɪᴇʟᴅs ᴏᴄᴄᴜʀ ᴏɴ ᴀʟʟ ᴄᴏɴᴛɪɴᴇɴᴛs.
A shield is a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas.[1] These rocks are older than 570 million years and sometimes date back 2 to 3.5 billion years.[citation needed] They have been little affected by tectonic events following the end of the Precambrian, and are relatively flat regions where mountain building, faulting, and other tectonic processes are minor, compared with the activity at their margins and between tectonic plates.
Geologic provinces of the world (USGS)
Shield
Platform
Orogen
Basin
Large igneous province
Extended crust
Oceanic crust:
0–20 Ma
20–65 Ma
>65 Ma