In the United States, the accounts for high population growth in the sunbelt states is the immigration.
The Sunbelt is the region in the United States were it expanded across the southern and southwestern part of the country from Florida to California.
At divergent plate boundaries, two lithospheric plates move apart, and new plate (and crust) are created at the boundary. The new crust is created volcanically. This process always produces ocean crust and thus oceanic plate. Thus divergent boundaries ultimately become mid-ocean ridges.