Fractional crystallization of olivine and pyroxene typically leads to the formation of gabbro or norite.

Here's why:

* Olivine and pyroxene are the first minerals to crystallize from a mafic magma (magma rich in magnesium and iron).

* Fractional crystallization is a process where minerals crystallize from a magma at different temperatures. The crystals are removed from the magma, leaving behind a magma with a different composition.

* As olivine and pyroxene crystallize and are removed, the remaining magma becomes enriched in other elements like sodium, calcium, and aluminum.

* This enriched magma then cools and crystallizes, forming gabbro (rich in plagioclase feldspar and pyroxene) or norite (rich in plagioclase feldspar and hypersthene, a type of pyroxene).

So, in short, the removal of early-crystallizing minerals like olivine and pyroxene through fractional crystallization results in the formation of gabbro or norite.