Question

Which force from asthenospher is responsible for isostatic uplift.

Answer 1

“Isostasy itself is based on the opposing influences of two main forces: buoyancy and gravity. For the earth, it is the reason that the relatively rigid lithospheric plates float at certain levels in the underlying ductile asthenosphere.”

Answer 2

Ridge Push from asthenospher is responsible for isostatic uplift.

Explanation:

A driving force for the motion of the plates in plate tectonics which occurs at the mid ocean ridges is called as Ridge push. It is caused due to the rigid lithosphere that slides down from hot and raised asthenosphere under mid ocean ridges.  

The fresh crust and upwelling mantle which are less dense and hotter that the crust and mantle that are surrounding, which are cool and they come in contract with age until equilibrium is reached with the old crust.

This causes an Isostatic response. Due to this the young regions that are nearer to the plate boundary rises above older regions.