serie NOVA TERRA nº 49

52 Different articles have described the structure and general meta- morphic evolution of the arc-derived upper units of the allochthonous complexes of NW Iberia (see Martínez Catalán et al., 2002 andreferences therein), and data also exist on the geochronology of the tectonothermal events andmain magmatic pulses. However, most previous work on the tectonothermalevolutionoftheseunits hasfocussedoneventsrelatedto the accretion of the arc to Laurussia, and its subsequent Variscan history. Details of the arc's tectonothermal evolution during its development at the periphery of Gondwana are less well known. In addition, the locationofthearcwithinperi-Gondwanaandwhetheritwas builtonthe Gondwanan continental margin or was generated above an intra- oceanic subduction zone at some distance from the margin, remain unknown. To help resolve these issues, we present two consecutive papers onaspectsrelated to the initial developmentof thismagmaticarc. The fi rst paper describes the geochemical features, tectonic setting and provenance of the thick low-grade greywacke series that occupies the uppermost structural position intheupperunits of the Órdenes Complex ( Figs. 1 and 2 ) in order to constrain the tectonic setting of the magmatic arc, its internal constitution and its location within peri-Gondwana. The second describes the internal structure of the metagreywacke series and presents new U – Pb age data for a diabasic dyke swarm that intrudes the metasediments ( Díaz García et al., 2010-this issue ). The new age data constrains the origin of the main fabric at the upper structural levels in the Órdenes Complex and its relationship to magmatic arc dynamics. Fig.1. SketchshowingthedistributionofthePaleozoicorogensinareconstructionoftheBaltica – Laurentia – GondwanajunctiondevelopedduringtheassemblyofPangea.Thedistribution of the most important domains described in the Variscan Belt is also shown, together with the position of the Órdenes Complex in NW Iberia. LBM: London-Brabant Massif. From Martínez Catalán et al. (2002) . 339 J.M. Fuenlabrada et al. / Gondwana Research 17 (2010) 338 – 351