Abstract New Rb–Sr isotopic data from South Portuguese Zone (SPZ) turbidites show that the 87 Sr/ 86 Sr( t ) ratio increases from the basal Mértola Formation (Visean–Serpukhovian: 0.706–0.707), through the Mira Formation (Serpukhovian–Bashkirian: 0.706–0.712) to the uppermost Brejeira Formation (Bashkirian–Moscovian: 0.713–0.715). In addition, estimated Nd T DM model ages for the Mértola (1.29–1.09 Ga), Mira (1.58–1.1 Ga) and Brejeira (1.73–1.37 Ga) formations indicate inverted stratigraphy for their isotopic sources. The isotope geochemical data indicate significant changes in the sources from which the SPZ Carboniferous turbidites are derived, consistent with the progressive denudation of a continental magmatic arc built on the Laurussian margin. Mértola turbidites inherited their geochemical and isotopic characteristics from an adjacent dissected Middle–Late Devonian continental magmatic arc with an intermediate–felsic composition: that is a Laurussian (Rheic magmatic arc)-type source. The progressive erosion of its plutonic roots and older host continental basement rocks are indicated in the Mira and Brejeira formations by the increasing contribution of recycled ancient continental crust. The pronounced similarity between the Nd T DM model ages and the detrital zircon populations of the Mira and Brejeira formations (SW Iberia) suggest that they share a common Laurussian (West Avalonia/Meguma terrane)-type source but a contribution from Gondwanan (Ossa-Morena)-type sources cannot be discarded.

The aim of this article is to present a compilation of available information on the Évora Massif based on structural mapping, whole-rock geochemistry, recognition of metamorphic mineral assemblages, and geothermobarometry. In our view, trans-current movements responsible for strong orogen-parallel stretching were dominant and had a major role in the geodynamic evolution of this part of Ossa-Morena zone (southwest Iberian Massif). Cadomian and Variscan orogenic events separated by a period of intense rifting were the cause for the composite distribution of zones with contrasting metamorphic paths, the structural complexity, the variety of lithological associations, and the sequence of deformation events and magmatism. The proposed geodynamic reconstruction for this segment of the northern Gondwana continental margin includes three main stages in chronological order: (1) Neoproterozoic accretion and continental magmatic arc developing, dismantling, and reworking, followed by late-“orogenic” magmatism; (2) Lower Paleozoic crustal thinning, block tilting, and mantle upwelling, induced by generalized rifting, leading to the formation of marine basins with carbonate platform sediments and thick accumulations of volcaniclastic and terrigenous sediments, contemporaneous with normal and enriched mid-oceanic ridge basalt–type magmatism; and (3) Upper Paleozoic transpressional orogenesis resulting from obliquity of convergence and the geometry of the involved blocks. The third stage includes the tectonic inversion of Lower Paleozoic basins, crustal thickening, the exhumation of high- to medium-pressure rocks and partial exhumation of high-grade metamorphic lithologies (controlled by local transtension and major detachments), the formation of synorogenic basins filled with volcanic-sedimentary sequences, and finally, the emplacement of late Variscan granodiorites and granites.

Abstract Field relationships and new U–Pb geochronology data indicate a temporal link between the diverse high-K mafic–intermediate magmas of the Ossa–Morena Zone (OMZ). Ages of c. 338–335 Ma for the Vale de Maceiras gabbro and the Campo Maior microdiorite and quartz-diorite indicate that plutonism took place during a Variscan extensional D 2 deformation event in the OMZ. The syntectonic nature of the Vale de Maceiras pluton is attested to by the orientation of intrusive contacts, magmatic foliation and the growth of contact metamorphic minerals in relation to the Variscan extensional D 2 foliation. The Campo Maior microdiorite, quartz-diorite and orthomigmatites are temporally linked to high-temperature mylonitic gneisses formed simultaneously with the Variscan extensional D 2 deformation event. The geochemical features of the Vale de Maceiras and Campo Maior mafic–intermediate rocks show an affinity with the sanukitoid series. This finding suggests that the observed geochemical variability, from tholeiitic to calc-alkaline and sanukitoid, in the Visean OMZ plutonic rocks ( c. 349–335 Ma) may have been inherited from partially melted mantle domains that were previously contaminated by crustal melts during subduction.

Abstract We present a new structural study of a D 2 –M 2 tectono-thermal structure in SW Iberia (Ponte de Sor–Seda gneiss dome) characterized by a spatial distribution of telescoping isograds providing a record of Buchan-type metamorphic conditions. The gneiss dome comprises an infrastructure made up of a lower gneiss unit (LGU) and an intermediate schist unit (ISU), separated by early D 2 ductile extensional shear zones. The LGU and the ISU are composed of Ediacaran–Cambrian rocks that experienced the highest-grade M 2 metamorphic conditions (amphibolite facies). Late Ediacaran–Early Terreneuvian and Late Miaolingian–Early Furongian protolith ages for LGU (496 ± 3 Ma) and ISU (539 ± 2 Ma) orthogneisses are reported. A superstructure made of Cambrian–Devonian rocks (Upper Slate Unit, USU) deformed under M 2 greenschist facies conditions, tectonically overlies the ISU across a D 2 extensional shear zone. Kinematic criteria associated with D 2 –M 2 fabrics indicate top-to-ESE–SE sense of shear. A late-D 2 brittle-ductile high-angle extensional shear zone (Seda shear zone) crosscuts the gneiss dome. D 3 upright folds, thrusts and transpressive shear zones caused the steepening of D 2 structures and the local crenulation of S 2 foliation. The Mississippian D 2 –M 2 event recorded in the Ossa–Morena Zone may be regarded as a regional-scale phenomenon that markedly influenced the crustal architecture of North Gondwana during the assembly of Pangaea.

Abstract Following a Middle–Late Devonian ( c . 390–360 Ma) phase of crustal shortening and mountain building, continental extension and onset of high-medium-grade metamorphic terrains occurred in the SW Iberian Massif during the Visean ( c . 345–326 Ma). The Évora–Aracena–Lora del Rı́o metamorphic belt extends along the Ossa–Morena Zone southern margin from south Portugal through the south of Spain, a distance of 250 km. This major structural domain is characterized by local development of high-temperature–low-pressure metamorphism ( c . 345–335 Ma) that reached high amphibolite to granulite facies. These high-medium-grade metamorphic terrains consist of strongly sheared Ediacaran and Cambrian–early Ordovician ( c . 600–480 Ma) protoliths. The dominant structure is a widespread steeply-dipping foliation with a gently-plunging stretching lineation generally oriented parallel to the fold axes. Despite of the wrench nature of this collisional orogen, kinematic indicators of left-lateral shearing are locally compatible with an oblique component of extension. These extensional transcurrent movements associated with pervasive mylonitic foliation ( c . 345–335 Ma) explain the exhumation of scarce occurrences of eclogites ( c . 370 Ma). Mafic-intermediate plutonic and hypabyssal rocks ( c . 355–320 Ma), mainly I-type high-K calc-alkaline diorites, tonalites, granodiorites, gabbros and peraluminous biotite granites, are associated with these metamorphic terrains. Volcanic rocks of the same chemical composition and age are preserved in Tournaisian–Visean ( c . 350–335 Ma) marine basins dominated by detrital sequences with local development of syn-sedimentary gravitational collapse structures. This study, supported by new U–Pb zircon dating, demonstrates the importance of intra-orogenic transtension in the Gondwana margin during the Early Carboniferous when the Rheic ocean between Laurussia and Gondwana closed, forming the Appalachian and Variscan mountains.