The exact same (or rather a very similar type) question occurred to me while driving up to Lake Arrowhead for an organized youth activity with my son and observing the exposed strata along the way: all sedimentary rock consists of much older rock that has been physically broken down and redeposited, so how is radio-dating supposed to work with sedimentary rock?
So I started researching the question. I had already long known of William Smith's empirical observations which formed the basis of stratigraphy, such that observable characteristics of the layer of rock could be used to identify it. Furthermore, I already knew of the Law of Supposition, whereby the age of a given stratum relative to other strata was determined. What I then learned through my research was that the age of a given stratum was further narrowed down by the radio-dating of igneous intrusions and whether they occurred above or below the stratum.
It should be noted here that if we question and research scientific ideas, then we find answers to our questions. That is not at all what we discover when we question and research creationist claims.
I would assume that plate tectonics would be one cause of the rise of the intrusive igneous from the mantel to above the fossil.
One cause. Not the only cause. Certainly, plate boundaries offer more openings for magma to migrate to the surface and we tend to see a lot of volcanic activity around those boundaries; eg, the Pacific "Ring of Fire" -- on Google Earth, check out the Aleutian Islands some time. However, magma may also migrate in the middle of a plate, two famous examples being the mid-Pacific "hot spot" (currently just east of Hawaii) that has created a long chain of islands and seamounts as the Pacific plate moved over it, and the Yellowstone cauldera (http://en.wikipedia.org/wiki/Yellowstone_Caldera#Volcanism):
quote:Yellowstone, like Hawaii, is believed to lie on top of an area called a hotspot where light, hot, molten mantle rock rises towards the surface. While the Yellowstone hotspot is now under the Yellowstone Plateau, it previously helped create the eastern Snake River Plain (to the west of Yellowstone) through a series of huge volcanic eruptions. Although the hotspot's apparent motion is to the east-northeast, the North American Plate is really moving west-southwest over the stationary hotspot deep underneath.
At any rate, the speed of plate tectonic activity or even the very presence of activity has absolutely no bearing on the age of any igneous formations. Rather, it is when those formations had solidified that determines that. Here is an excellent article on isochron dating, http://www.talkorigins.org/faqs/isochron-dating.html, which explains that.
Also, here is a link to a textbook, An Introduction to Physical Science at http://books.google.com/books?id=1LvMLoaN0HQC&pg=PA710&lp.... That page gives an example of interpreting two igneous intrusions -- it's in Google books, so I'm unable to copy-and-paste. The graphic it refers to is on the next page, so simply scroll down a little bit.
If it is the cooled magma rock that is tested by the radiometric dating, does it date differently than the rising magma and if so, why?
That was a trick question, one that nobody else caught, which surprises me. The age of a rock is how long ago it had formed. In the case of igneous rock, which we are talking about here, it formed when it solidified from a molten state. Solidified magma, AKA "igneous rock", has started to age and its age is tested by radiometric dating. Magma has not yet solidified and hence is still molten doesn't need to be tested. We already know its age: zero.
Now, igneous rock that is many millions of years old could be re-melted and mixed thoroughly, in which case its clock has been reset, its age is back to zero and when it solidifies then its clock will start running again.