Abstract
Eclogite-facies rocks are very rare in the Montagne Noire, the local typical metamorphism being a low-pressure type with extensive development of migmatites. The Cabardès and Le Jounié eclogites (garnet + omphacite + quartz + rutile, 700–800°C, 9 ± 2 kbar) derive from tholeiitic basalts interbedded in paragneisses very close to the orthogneissic basement. Both are strongly retromorphosed and re-equilibrated in the conditions of the amphibolite-facies metamorphism of the surrounding gneisses. The eclogite-facies garnet ultramafite of the Airette pod derives from a ferromagnesian calc-alkalic cumulate; its reactional mineral associations show a complex polyphase evolution: a primary spinel websterite (Cpx + Opx + pleonaste + chromite) is reset in the eclogite facies, where garnet develops as coronas on the spinel. A further retromorphic evolution leads to a paragenesis (hornblende + tremolite + picotite + olivine (Fo 70) ± phlogopite) and finally to the paragenesis chlorite + amphibole. Those rocks may be interpreted either as tectonically emplaced slabs or as the only remnants of a medium- to high-pressure regional metamorphism. But it must be pointed out that all these rocks occur only in the southern part of the axial zone of the Montagne Noire, i.e. in the “root zone” of the large Penninic nappes which characterize this part of the Hercynian belt.
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