Geoscience Reference
In-Depth Information
16. Example of a seismic reflection profile of layers and a domed structure within the
Earth's crust.
The rise of granite
As continental rocks pile up, so the base of the continent gets buried deeper and deeper.
As it sinks, it heats up and the rocks at base begin to melt. Many of them are ancient sed-
iments deposited in seas billions of years ago. They contain water chemically bonded into
the rocks. The water helps them to melt and lubricates them so that they rise easily towards
the surface. Unlike volcanic rocks, they're too thick and sticky to erupt from volcanoes. In-
stead, huge bubbles of molten rock, perhaps many thousands of metres across, push up into
the higher layers of the continents, perhaps at quite high speeds. They bake the surround-
ing rock and cool slowly, forming a coarsely crystalline rock of quartz, feldspar, and mica:
granite. Eventually, the surrounding rock wears away to reveal the great granite domes of,
for example, Dartmoor.
