#All
Hi, Kamron–
>> The whole continental miles deep crust isn't compressing is it?
Yes, it is, in cases of fold mountains like the Appalachians and Himalayas. We
can measure the gravitational differences (and I think the seismic wave
distortions) caused by the "roots" of major mountain chains where the crust
extends unusually deep into the lithosphere (shallow mantle), counterbalancing
the weight of the mountains (acting like a float to hold the mountains up).
The entire plate (crust plus lithosphere) is being compressed when continents
collide. If the lithosphere bulges into the outer mantle, I figure it simply
becomes outer mantle rock, but the crustal bulge remains as fold mountains and
their roots. I do not know if the roots are _precisely_ matched to the
mountains (which would need some filling of spaces vacated by folding) or just
generally matched, as when paper is crumpled (no filling needed).
Fault block mountains have roots too, though they are created differently. Over
time, I expect any mountain without a "float" underneath would simply sink into
the crust, faster than it could erode.
–Doug