Amphibole evolution in uitramafic amphibolites from NE Sardinia, Italy

摘要

Uitramafic amphibolites from NE Sardinia consist of relics of igneous phases and metamorphic minerals formed during the granulite, amphibolite and greenschist facies. Igneous olivine and plagioclase reacted to produce coronas consisting of orthopyroxene, clinopyroxene, green spinel and garnet. The amphibolite stage is dominated by formation of amphiboles, clinochlore, plagioclase and Cr-bearing spinel and talc. Greenschist minerals consist of amphiboles, fayalite, epidote, albite, calcite, dolomite and serpentine. Four types of clinoamphibole have been recognised: brown amphiboles (Caml: magnesiohornblende to pargasite), green amphiboles (Cam2: tschermakite to magnesiohornblende), zoned magnesiohornblende (Cam3), and late stage tremolite (Cam4). Two textural types of orthorhombic amphiboles have been detected. The P-T path of uitramafic amphibolites is characterised by a decrease in both pressure and temperature from the granulite to the greenschist stage. The compositional variation and cation distribution of the amphiboles can be related to the P-T evolution of the uitramafic amphibolites during the regional Hercynian metamorphism.