The Tinaquillo Complex is bordered to the south by the Tinaco Complex, and to the north is separated by a thrust fault from the Cordillera de la Costa belt. The Tinaquillo Complex, consisting mainly of harzburgite and metagabbro, was formed at high temperature (up to 14°C) and presumably at great depth in the upper mantle. The Tinaco Complex consists of meta-igneous and metasedimentary rocks. The Tinaquillo Complex was juxtaposed onto the Tinaco Complex at intermediate crustal levels at temperatures of about 65°C. Structures in the Tinaquillo harzburgites indicate that the juxtaposition was caused by northwesterly directed thrusting. The metamorphism in the Tinaco Complex is clearly not of the contact type, as has been suggested previously, but is a regional metamorphism. Although good age dates are not available, it is suggested that the juxtaposition of the two complexes occurred during Late Paleozoic times, probably related to collision of a volcanic island arc with South America. The juxtaposition of both complexes onto the Cordillera de la Costa belt is probably a Late Cretaceous or Tertiary event and may be related to a collision of another volcanic island arc with South America.