Buzsaw writes:
What forces cause the lava to rise to the extent that it raises the plates?
The plates don't "rise"
per se. They "float", as it were, on the magma. The weight of the plates forces magma up into cracks in the plates. (Think of walking on a frozen-over puddle. The ice cracks and water comes up through the cracks.)
Buzsaw writes:
How far above the planet's mantel does the magma rise before it becomes cooled enough to harden into intrusive igneous rock?
The magma can harden
inside the rocks of the crust, in which case it is an
intrusion, or it can harden
outside the crust as lava, in which case it is an
extrusion. Geologists can tell the difference between an intrusion and an extrusion. Only the extrusions would be used as dating layers.
Buzsaw writes:
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?
The rate of cooling would depend on the initial temperature of the magma/lava, the temperature of the surrounding material, etc. My guess is that lava on the surface would cool more rapidly than magma below the surface.
But it's the
sequence of the layers that matters, not the rate of cooling. The bottom layer would have cooled to the point of closure before sedimentary layers were deposited on top of it, so the lower layer will always date older than the higher layer.
If you have nothing to say, you could have done so much more concisely. -- Dr Adequate