Were we to understand more about the origin of both basalt and granite, we would have a much better appreciation of how the solid earth functions. The origin of basalt is the easier part. We can see basaltic lava erupting from volcanoes, and its magmatic origin has not seriously been disputed since the later 18th century, when Sir James Hall slowly cooled molten basalt and reproduced the texture of the volcanic rock (Watt, 1804). Most geologists now accept that basalt forms by decompression melting of mantle peridotite beneath mid-ocean ridges or within mantle plumes, or in a...

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