Original paper

First results from thermobarometric investigations of the Chila and Rama plutons (N' Ethiopia)

Jungmann, Olga; Dietl, Carlo; de Wal, Helga; Pandie, Manoish

Abstract

New PT data for the ca. 800 Ma old Pan-African Chila and Rama plutons are provided. By utilizing the AI-in-hornblende barometer pressures from 4.5 kbar for the Chila pluton and from 2.7 kbar for the Rama pluton were calculated. Crystallisation temperatures of hornblende were derived from the amphibole-plagioclasethermometer. Calculatedtemperatures in the Chila pluton are slightly above the granite solidus, whereas those of the Rama pluton lie in part distinctly below it, pointing to post-emplacement equilibration of the Rama hornblendes. Our results indicate that both plutons, although of similar age, intmded into different crustal levels and may belong to two different crustal terranes. This finding is in disagreement with the general assumption that both the plutons intmded the same tectonostratigraphicblock, the so-calledChila block.