Original paper

Metamorphism and metasomatism in the Jurassic Nain ophiolitic melange, Central Iran

Shirdashtzadeh, Nargess; Torabi, Ghodrat; Arai, Shoji


This ophiolite has experienced several metamorphic events since its formation. During Jurassic times, a regional metamorphism (M1) caused the formation of amphibolitic rocks from the oceanic basic rocks. These amphibolites were often covered by skarns formed during M2 metasomatism of carbonates. There are also evidences claiming a retrograde regional metamorphism (M3) that has affected both skarns and amphibolites. Additionally, some less highly metamorphosed sheeted dykes and pillow lavas occur in this ophiolite. Based on their geochemistry they were originally different from the amphibolitic rocks. Therefore, two phases of magma generation can be recognized: The first one, in Lower Jurassic, led to the formation of the basaltic protolith of the amphibolites. The second one, in Upper Cretaceous, caused the generation of sheeted dykes and pillow lavas.