olog ists ▁to ▁agree ▁on ▁the ▁source ▁of ▁an ▁anom aly . ▁Se ism ic ▁studies ▁of ▁the ▁L acc ad ive ▁Islands ▁in ▁the ▁Indian ▁Ocean ▁revealed ▁a ▁high - vel ocity ▁layer ▁of ▁thick ened ▁cr ust ▁between ▁ 1 6 ▁and ▁ 2 4   km ▁below ▁the ▁surface ; ▁these ▁were ▁cor ro bor ated ▁with ▁tom ographic ▁work ▁in ▁the ▁nearby ▁K utch ▁District , ▁which ▁identified ▁a ▁large ▁ma fic ▁body ▁at ▁depth , ▁close ▁to ▁the ▁mant le . ▁ ▁However , ▁tom ographic ▁studies ▁in ▁Norway ▁undert aken ▁to ▁identify ▁the ▁source ▁of ▁locally ▁thick ened ▁cr ust ▁found ▁une ven ▁thick ness es ▁restricted ▁by ▁several ▁line aments . ▁The ▁morph ology ▁of ▁the ▁lower ▁cr ust ▁was ▁not ▁conclus ively ▁identified ▁as ▁mag m atic ▁under pl ating , ▁and ▁may ▁in ▁fact ▁be ▁the ▁rem n ants ▁of ▁the ▁C aled onian ▁root . ▁ ▁Pro xim ity ▁to ▁large ▁ igne ous ▁provinces ▁may ▁also ▁be ▁helpful ▁in ▁ident ifying ▁mag m atic ▁under pl ating . ▁Un sol id ified ▁areas ▁of ▁mag m atic ▁under pl ating ▁( a ▁mag ma ▁chamber ) ▁may ▁feed ▁mag ma ▁to ▁vol cano es . ▁In ▁the ▁Raj ma hal ▁Tra ps , ▁there ▁is ▁a ▁ 1 0 – 1 5   km ▁thick ▁ igne ous ▁layer ▁at ▁the ▁base ▁of ▁the ▁cr ust ▁beneath ▁this ▁area . ▁The ▁thick ness ▁of ▁the ▁layer ▁is ▁different ▁in ▁various ▁parts ▁of