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USGS CMG InfoBank: Beams of Electrons

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Comment: 16:33 - 17:33 (01:00)
Source: Annenberg/CPB Resources - Earth Revealed - 12. Minerals: The Materials of Earth
Keywords: "J. Lawford Anderson", electrons, "laboratory analysis", "thin section", "chemical composition", mineral, rock, pressure, depth, granite, "rock origin", "Whipple Mountains", crust, "rock age", magma

Our transcription: Another important analysis involves shooting beams of electrons at thin sections of rock to determine the individual mineral compositions within the rock.
The data derived from these procedures is vital.
It enables Anderson and his colleagues to ascertain the pressure and depth at which the granite formed.
What we found out about the rocks in the Whipple Mountains is that they originated from the middle crust of the Earth some 25 or perhaps even more that 30 kilometers down.
Those minerals were crystallizing from a magma that was in place in that level deep in the Earth crust at their age of 89 million years.
So today we brought the rocks back, they're at the surface now, but they were once deep.
And they record in their composition and in their mineralogy how their middle crust originates.

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