Ultramafic rocks occur scattered along a 300 km long NNW-SSE trending belt, lying parallel to the central Peruvian Andean direction in the Cordillera Oriental, from Tarma (Junín Dept.) to Huánuco and Tingo María (Huánuco Dept.). The Tarma occurrences (Tapo and Acobamba) are studied, as first step of a broader research. The Tapo massif comprises strongly tectonised serpentinites with scarce peridotitic relics, amphibolites and podiform chromitites. It is overthrust on the lower carboniferous metasediments of the andean basement (Ambo Group), and it shows evidences of a pre-andean deformational history, not found in the Ambo Group; the basal thrust plane is folded by Andean tectonics. The two smaller Acobamba occurrences are also allochtonous and show similar tectonic characteristica. Major and trace element compositions of the amphibolites point to a tholeiitic basalt (to picrobasalt)...

pp. 429-437

Páginas 75-78.

Páginas 59-62.

Metamorphosed chromite crystals in massive chromitite ore-bodies from the Tapo ultramafic massif (Peru) show distinct petrographic features and chemical patterns of zoning different from those exhibited by disseminated chromites. The observed differences can be explained in terms of prograde metamorphism up to the lower-amphibolite facies, under the control of the chromite/silicate ratio, chromite grain size and degree of fracturing.

Páginas 51-54.