José R. Martínez Catalán

Variscan accretionary complex of northwest Iberia:Terrane correlation and succession of tectonothermal events

The allochthonous terranes of northwest Iberia can be correlated with specific paleogeographic realms of the continental masses and intervening oceans involved in the Variscan collision. Assuming that the existing ophiolites represent the suture formed by the closure of the Rheic ocean, the units in the footwall to the suture correspond to the outer edge of the Gondwana continental margin, and the units in the hanging wall are interpreted as fragments of the conjugate margin, represented by the Meguma terrane. This correlation establishes a precise link between circum-Atlantic terranes, and makes it possible to draw a relatively simple scenario of the successive tectonothermal events recorded. Following the amalgamation of Avalon to Laurentia, the remaining outboard terranes underwent a progressive accretion to this continent that ended with the collision between Laurentia and Gondwana.

Variscan exhumation of a subducted Paleozoic continental margin: The basal units of the Ordenes Complex, Galicia, NW Spain

A structural and metamorphic study was carried out in the basal units of the Ordenes Complex in Spain, thought to represent a subducted part of the Paleozoic margin of Gondwana. According to their metamorphic evolution, this part of the margin was subducted at the onset of the Variscan Orogeny, becoming part of an accretionary complex developed below a colliding element built previously. Variations in the PT conditions of the first high-pressure metamorphic event along the units indicate a polarity of the subduction to the west. Subsequent underthrusting of more continental material blocked the subduction and triggered the ascent and exhumation of the basal units, whereas the convergence continued. Recumbent folds and thrusts developed along with successive normal detachments. Compressional and extensional structures were synchronous or alternated in time and together induced the thinning and tapering of the orogenic wedge and its lateral spreading. The unroofing took place locally under an inverted temperature gradient caused by a detachment which carried a part of the hot mantle wedge above the subduction zone over the subducted units.

The Vila de Cruces Ophiolite: A Remnant of the Early Rheic Ocean in the Variscan Suture of Galicia (Northwest Iberian Massif)

The Vila de Cruces ophiolite is one of the ophiolitic units involved in the Variscan suture of the northwest Iberian Massif. This ophiolite consists of a tectonically repeated succession of greenschist facies volcanic rocks, common alternations of metasediments of pelitic or siliceous character, and scarce orthogneisses, metagabbros, and serpentinites. The protolith age of a granitic orthogneiss that intruded the mafic rocks is dated at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Provenance constraints from detrital zircon U–Pb ages in the NW Iberian Massif: implications for Palaeozoic plate configuration and Variscan evolution

497\pm 4

The Central Iberian arc, an orocline centered in the Iberian Massif and some implications for the Variscan belt

\end{document} Ma (U‐Pb in zircons). This age can be considered a reference for the generation of the ophiolite. According to their contents of some of the most immobile trace elements, the greenschist and the metagabbros are derived from basaltic magmas with compositions similar to those of island‐arc tholeiites. The influence of a subduction zone in the generation of the original basaltic magmas can be deduced from the marked negative Nb anomaly observed in all the metabasic rocks of this ophiolite. The granitic orthogneisses can also be genetically related to the basic rocks because they are similar to granitic rocks generated in volcanic arcs. The Vila de Cruces ophiolite is interpreted as a suprasubduction zone ophiolite generated in Late Cambrian times, during the early stages of the opening of the Rheic Ocean. The ophiolite was probably generated in a back‐arc basin developed during the first stages of the pulling apart and later drift of one or more peri‐Gondwanan terranes, one of them represented by the upper allochthon of the northwest Iberian Massif.

Correlation of the nappe stack in the Ibero-Armorican arc across the Bay of Biscay: a joint French–Spanish project

Analysis of the Careón Unit in the Ordenes Complex (northwest Iberian Massif) has supplied relevant data concerning the existence of a Paleozoic oceanic lithosphere, probably related to the Rheic realm, and the early subduction‐related events that were obscured along much of the Variscan belt by subsequent collision tectonics. The ophiolite consists of serpentinized harzburgite and dunite in the lower section and a crustal section made up of coarse‐grained and pegmatitic gabbros. An Early Devonian zircon age ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

40Ar/39Ar laserprobe dating of mylonitic fabrics in a polyorogenic terrane of NW Iberia

395\pm 2