Basaltic magmas are not formed by the partial melting of granite. They are formed by the partial melting of the mantle, specifically the upper mantle. Here's why:

* Composition: Granite is a felsic igneous rock, rich in silica and aluminum. Basalt is a mafic rock, rich in iron and magnesium. The chemical compositions of these rocks are fundamentally different.

* Melting Point: Granite has a much higher melting point than the minerals found in the mantle. The temperatures required to melt granite are unlikely to be found at the depths where basaltic magmas originate.

* Mantle Processes: The Earth's mantle undergoes various processes that generate basaltic magma. These include:

* Decompression Melting: As hot mantle material rises, the pressure decreases, leading to melting.

* Flux Melting: The introduction of water or other volatiles into the mantle can lower the melting point, triggering melting.

In summary, basaltic magmas form from the partial melting of the mantle, not granite.