▁sub duct ing ▁under ▁contin ental ▁cr ust . ▁Under pl ating ▁is ▁the ▁result ▁of ▁partial ▁mel ts ▁being ▁produced ▁in ▁the ▁mant le ▁w edge ▁above ▁a ▁sub duct ing ▁plate . ▁The ▁partial ▁mel ting ▁is ▁induced ▁by ▁a ▁lower ing ▁of ▁the ▁mel ting ▁temperature , ▁the ▁solid us , ▁by ▁the ▁input ▁of ▁water ▁and ▁other ▁vol at iles ▁supplied ▁by ▁phase ▁trans itions ▁in ▁the ▁sub duct ing ▁sl ab . ▁When ▁the ▁bu oy ant ▁partial ▁m elt ▁r ises ▁up wards ▁through ▁the ▁mant le , ▁it ▁will ▁usually ▁st all ▁at ▁the ▁base ▁of ▁the ▁cr ust ▁and ▁p ond ▁there . ▁This ▁is ▁because ▁the ▁cr ust ▁is ▁usually ▁less ▁dense ▁than ▁the ▁under pl ating ▁mag ma , ▁and ▁this ▁is ▁the ▁point ▁at ▁which ▁the ▁asc ending ▁mag ma ▁reaches ▁a ▁level ▁of ▁neutral ▁bu oy ancy . ▁ ▁The ▁evol ving ▁m elt ▁will ▁remain ▁here ▁until ▁it ▁fraction ates ▁enough ▁( through ▁mel ting - ass im ilation - storage - hom ogen ization ▁( MA SH ) ▁processes ) ▁that ▁the ▁remaining ▁m elt ▁is ▁less ▁dense ▁than ▁the ▁surrounding ▁rock ; ▁the ▁m elt ▁will ▁then ▁continue ▁up ▁into ▁the ▁cr ust , ▁leaving ▁behind ▁the ▁heav ier ▁ma fic ▁min er als ▁which ▁were ▁cry st all ized ▁during ▁fraction al ▁cry st all ization . ▁The ▁assemb lage ▁of ▁min er als ▁remaining ▁behind ▁are ▁typically ▁ma fic ▁or ▁ul tr am af ic ,