Ann: Drilling Commences at Tres Estados, page-8

Not really my field so I'm just guessing, but maybe the gabbros have floated off a melting subducted ophiolite or ancient mantle. Maybe the subduction zone tapped the asthenosphere somehow. There'll be a bunch of Masters and PhDs in it for lots of students.

An ophiolite is a section of the Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks.