In comparison to the rock it intrudes, what is the relative age of a dike?
always older than the last layer it intrudes
always older than the rock it intrudes
always younger than the rock it intrudes
always older than the very top layer
it intrudes
To determine the relative age of a dike compared to the rock it intrudes, you can apply the principle of cross-cutting relationships. This principle states that a rock feature, such as a dike, is younger than the rocks it cuts across or intrudes.
To establish the relative age of a dike, follow these steps:
1. Examine the sequence of rock layers or formations. Pay attention to any intrusive features like dikes, which are igneous rock bodies that cut across existing rock layers.
2. Identify the dike in question and note the rock it cuts across.
3. Determine the various ages of the rocks or layers you're working with. This may involve researching or consulting geologic maps, stratigraphic records, or other sources of information.
4. Compare the ages of the dike and the rock it intrudes. Based on the principle of cross-cutting relationships, the dike will always be younger than the rock it intersects. Therefore, the correct answer to your question is: the dike is always younger than the rock it intrudes.
Remember, these relative age relationships rely on the assumption that the various rock layers have been deposited in a continuous and undisturbed sequence, without significant faulting or erosion.