but overall the lower sub surface crust and plates formed from the bottom!
Are you familiar with Thermodynamics? Heat does not pass from cooler to warmer. The only circumstance your assertion would allow for would be an earth in which the center was solid and progressivly warmer outward. This is demonstrably not true from seismic, volcanic, and thermal gradients from borings and mines among other things.
the slope--triangle would be inverted---pointing down.
Not enough expansion---'lava' to form mountains!
Matter of 'fact'...the top layers would be the actual layers from the sides of the plate but the lower levels would be fresh layers pushed out from underneath to fill the widening cracks!
The diameter of the earth could be increasing and/or the plates just settling---sinking pushing the material up to form the canyon walls/layering!!
The whole thermodynamics would say they were coming up from lower hotter levels---higher pressures!