The Tinaquillo peridotite complex is a layered and veined ultramafic-mafic body cropping out in the Cordillera de la Costa in northern Venezuela. Whole rock compositions, textures, and mineral chemistry of the peridotite and associated mafic rocks suggest that the complex underwent two major events before being emplaced into the Cordillera de la Costa. The peridotite first rose adiabatically within the upper mantle, at about 1350¿C and 15--21 kbar pressure. This rise caused a small to medium degree of partial melting, resulting in the formation of a stratified complex of clinopyroxen-rich spinel lherzolites grading to harzburgites, interlayered with pyroxenite. The stratified complex then cooled and reequilibrated at about 800¿--1000¿C. A second upward movement of the peridotite brought it, still hot, from the upper mantle into lower crustal rocks (now called the Tinaco complex), at an estimated 7 kbar pressure, then cooling to 600¿--700¿C. The peridotite contains small amounts (2--5%) of homogeneously distributed pargasite. Locally, it is concentrated in amphibole veins grading into orthopyroxene- and spinel-hornblendite layers.

Amphibolization was associated with metasomatism, and this metasomatic enrichment seems greater in the most depleted peridotite. The Tinaquillo peridotite shares many characteristics with Alpine spinel lherzolites that are believed to be derived from the subcontinental upper mantle and are emplaced within a continental rift, or at the margins of an oceanic rift. These characteristics are low degree of depletion, highly aluminous spinels, abundance of metasomatic facies, and early high-P equilibration followed by reequilibration with maficsilicic continental type rocks within the intermediate-P granulite facies. ¿ American Geophysical Union 1989