Discussion
If the dark portion is on a vanishing stage and is recognised by dark schlieren streaks within the granitic portion (Leucosome), this migmatite is known as :
Answer: C
This migmatite is a nebulite.
In a nebulitic migmatite, melting and mixing have gone so far that the dark, older portion (the melanosome or palaeosome) has almost disappeared. It survives only as faint, cloudy dark schlieren and streaks within the light granitic leucosome, giving the rock a nebulous appearance close to a granite.
An agmatite is a breccia-like migmatite in which angular dark blocks remain distinct within a granitic network. The melanosome is the dark, mafic part of a migmatite, not a type of migmatite. The neosome is the newly formed part, leucosome plus melanosome, again a component rather than a type.
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