GeologyRocksDetermine age of rock
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The igneous rock is the
Sun, 06/24/2012 - 08:36The igneous rock is the youngest.
The order is:
- deposit limestone
- deposit sandstone
- intrude sill (the igneous rock)
Contact metamorphism does not extend out a large amount and would not metamorphose the sediments excessively. Sills/dykes a metre wide typically show contact metamorphism only a few centimetres wide. However, the igneous rock contains both limestone and sandstone (xenoliths), so both must have been there (and lithified) when the igneous rock was intruded.
We can test this hypothesis in the field easily too. If that ordering was true, then both the upper and lower surfaces of the igneous rock will have a contact margin (chilled margin in the igenous rock and baked margin on the sediments). If the order was limestone, igneous, sandstone; then only the lower margin would be show baking/chilling.
Hope that helps and makes sense.
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By the way, is it OK if I
Sun, 06/24/2012 - 21:49By the way, is it OK if I ask one more similar question? I'm starting to get the hang of this now, but there is one more problem I am bit unsure of (my book does not provide answers to all the excersies). The problem is as follows:
An igenous rock is situated between two layers of sedimentary rocks. The upper layer is sandstone, the lower layer is limestone. The sandstone contains pieces of the igenous rock. Which rock is the youngest?
Would the correct answer here be that the sandstone is the youngest, since it contains pieces of the igenous rock? (By the law of inclusion)
. Thanks a lot!
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Determine age of rock
Submitted by krje1980 on Sat, 06/23/2012 - 17:49.Hi.
I am a little bit uncertain about the following question:
An igenous rock is situated between two layers of sedimentary rocks. The upper layer consists of sandstone. The lower layer consists of limestone. The igenous rock contains pieces of both sandstone and limestone. Which rock is the youngest?
OK. This one puzzles me. I would assume that the igenous rock is not the youngest, since this would cause the sandstone to become quartzite and the limestone to become marble, right? So this means that either the sandstone or the limestone has to be youngest. And since sandstone is in the upper layer, I would assume that this would perhaps be the youngest. But then there is the fact that the igenous rock contains pieces of both the sandstone and limestone, and this makes me very uncertain. Are igenous rocks so porous that most of the limestone might have seeped through it?
If anyone can help me, I would truly appreciate it! I might be totally wrong in my reasoning over.