Dynamics and timing of metamorphic processes in exhumation channels at thecontinent-continent interface:comparative target areas in NW Newfoundland and W Argentina

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In the northern Appalachians at the NE margin of the N-American continent a collage of four different terranes (from north to south Dashwood, Ganderia, Avalonia, Meguma) occur. There, continental magmatic arcs evolved which were subsequently separated from the involved major continental plates (Gondwana, Laurentia) (Abb.1; van Staal 2009; Zagorevski et al. 2010). Especially in Newfoundland this collage is coherently exposed being an excellent natural laboratory to study collisional processes involving microplates. These microplates collided subsequently with the margin of Laurentia. For instance, the Dashwood terrane was firstly accreted to Laurentia along the Baie Vert-Brompton Line (BVBL) in the Ordovizian. The following accretion of further microplates south of the Dashwood terrane led to additional deformation and crustal thickening even at this old collisional zone. The structure and the early geological history of these microplates including the structure of the collisional zones had been already investigated in detail (van Staal 2007; Zagorevski et al. 2010).West of the BVBL eclogite bodies, which are enveloped by gneisses, and medium-grade high-pressure metapelites occur. According to the view of the applicant, these rocks were exhumed in an exhumation channel. East of the BVBL very low to low grade rocks of the upper plate are exposed. Only rough information exist on the metamorphic conditions and the corresponding ages of the high-pressure rocks (Jamieson, 1990; e.g. Ar/Ar cooling ages of 429-375 Ma). The study of such high-pressure rocks (see 1.2 of the proposal) in the frame of this DFG project has confirmed the idea of the exhumation channel, which is of major importance to understand collisional processes on a global scale. Additional high-pressure rocks will be investigated during the applied additional research year.