A relict blueschist in meta-ophiolite from the central Norwegian Caledonides - discovery and consequences

Blueschists in ophiolite sequences are meaningful indicators of the kinematics and thermal evolution of ancient subduction zones. Throughout the Caledonian-Appalachian orogen, blueschist occurrences in ophiolites of Early-Middle Ordovician age have been used to decipher the development and destruction of are-subduction settings around the active Paleozoic Iapetus Ocean margin. We describe herein the first occurrence of glaucophane relies within an Early Ordovician meta-ophiolite sequence from the mainland Scandinavian Caledonides within the Trondheim Nappe Complex. The rock contains a relict blueschist assemblage of glaucophane, epidote, and rutile with pervasive retrograde overprint, first under amphibolite-, and subsequently, greenschist-facies conditions. The existence of blueschist in meta-ophiolite from mainland Scandinavia is consistent with the Ordovician intra-oceanic subduction and arc-continent interactions proposed for the Iapetus oceanic realm, generally, and outboard Baltica, in particular. (C) 2002 Elsevier Science B.V All lights reserved.