Geologic time of sedimentary rocks : LUSENET : Introductory Geology, Oswego State : One Thread

I am really confused on the group activity that we did in class on Wednesday. I am not sure that I understand how the contact metamorphism on the top layers of sandstone effected the ages of the different layers.

-- Kathleen Belus (, April 01, 2001


Contact metamorphism occurs when magma intrudes into pre-existing rocks and cools. As the magma cools, heat is transferred to the pre-existing rock. This heating can cause metamorphism (contact metamorphism) of the surrounding, pre-existing (i.e., older) rock.

In the exercise, the sedimentary rocks above and below the igneous intrusion were contact metamorphosed. This shows that both sed. rocks were formed before (and are therefore older than) the igneous intrusion.

-- Sharon Gabel (, April 03, 2001.

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