Smooth seam between abjacend parts of mesh?

Hi. I working on a sphere terrain generator, just for fun. Trying to make quadtree system but dont exactly get how to make seam bebetween two gameobjects containing sphere parts to shade smoothly. I could iterate all vertices in 4leafs of a node and search for vertices with same coords and then get all adjacend tris and colcelate average normal, but Im afraid itll work too slow. Any better way? Will be gratefull for any help.

 

Anyone?( I managed to to do this by iterating through vertices of meshes and calculating average normal for intersected vertices. But Im afraid itll take too much time for terrain mesh. Any faster, noniterative method? Some tips? Someone should have worked on quadtree and smooth shading.