( ( When ( ( these ( two ( different plates ) ) ) converge ) ) ( , ( ( the more ) ( ( dense ( oceanic crust ) ) ( ( is ( forced ( under ( the ( less ( dense ( continental crust ) ) ) ) ) ) ) . ) ) ) ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT these) (CD two) (JJ different) (NNS plates)) (VP (VB converge)))) (, ,) (X (DT the) (JJR more)) (NP (JJ dense) (JJ oceanic) (NN crust)) (VP (VBZ is) (VP (VBN forced) (PP (IN under) (NP (DT the) (RBR less) (JJ dense) (JJ continental) (NN crust))))) (. .)))
When these two different plates converge, the more dense oceanic crust is forced under the less dense continental crust.
(ROOT (S (NP (NNP Gabbro)) (VP (VBZ is) (NP (NP (DT a) (JJ dark) (JJ dense) (NN rock)) (SBAR (WHNP (WDT that)) (S (VP (MD can) (VP (VB be) (VP (VBN found) (PP (IN in) (NP (DT the) (JJ oceanic) (NN crust)))))))))) (. .)))
Gabbro is a dark dense rock that can be found in the oceanic crust.