TECTONO-METAMORPHIC EVOLUTION OF THE TACONIC OROGEN IN THE NEWFOUNDLAND APPALACHIANS, INSIGHTS FROM THE BAIE VERTE PENINSULA ECLOGITES

The Appalachians are a complex orogen formed by the Cambrian through Permian closures of the Iapetus and Rheic oceans. Newfoundland comprises an exceptionally well-preserved cross-section of the northern Appalachians. In this transect, evidence for the Ordovician Taconic orogeny, the earliest accretionary stage of the Appalachian orogen in the Laurentian realm, is preserved in the Baie Verte Peninsula. The Early Paleozoic Laurentian margin in the Baie Verte Peninsula underwent subduction, collision and exhumation during the Taconic orogeny. This led to the formation and exceptional preservation of eclogite, which is rarely present or preserved elsewhere in the Appalachian orogen.

The complex geologic record of the Taconic orogeny in this area is further complicated by an extensive tectono-metamorphic overprint related to the subsequent, superimposed Salinic and Acadian orogenic cycles. To separate the Taconic structural and metamorphic signature from the widespread but heterogeneous overprint, extensive regional scale mapping and multiscale structural analysis was undertaken, and five deformation stages related to Taconic and post-Taconic tectonic events were recognized.

Research has unveiled exceptionally well-preserved eclogites and eclogites that preserved exhumation-related structures and retrograde metamorphic assemblages. Microstructural and minerochemical analyses revealed that the eclogite high-pressure peak paragenesis was followed by four retrogressive phases of superimposed amphibole growth. Phase equilibria modelling was used to calculate isothermal P-M(H₂O) pseudosections and to assess the relevance of fluids infiltration in promoting metamorphic reactions involving amphibole growth during retrograde metamorphism. Garnet isopleth modelling was implemented to constrain the metamorphic peak and part of the prograde and retrograde metamorphic paths. Defining the metamorphic P–T trajectories of eclogites is essential for unravelling the tectonic processes related to their subduction and subsequent exhumation, which have been constrained by U-Pb age dating of accessory phases.

Mechanisms responsible for the exhumation of the eclogites will be discussed comparing their P-T-t evolution with other exhumed high-pressure terranes and with numerical models.