Remember that not all of the earth's internal heat is transported by mantle convection, but that part is transported by plumes of very hot rock. Experimental and computer models suggest that when a plume reaches the lithosphere, the plume flattens out against the bottom of the lithosphere, heats it, and causes it to bulge and fracture. Decompression melting converts some of the plume material to lava that rises through cracks to the surface to form a huge flood basalt volcano. Lava rising up the tail and through the plate over a long period of time leaves a trail of shield volcanoes leading away from the huge flood basalt deposit. Since the lavas come from the mantle, the plumes are basaltic in composition and low in dissolved gases.
Plumes come in all different sizes and can occur anywhere.
All of this should sound familiar. Virtually all of these model predictions match features seen in hotspot volcanism, which is why the plume model is the leading hypothesis for hotspot volcanoes. In fact, a volcano did occur recently in one farmer's back yard. In 1943, Dionisio Pulido found a crack spewing out red hot rocks and lava in his cornfield. Paricutin is still active in southwestern Mexico.