Jordi Carreras

• Autonomous University of Barcelona

The coastal cliffs around the Roses Lighthouse (Cap de Creus, Mediterranean Costa Brava) display deformation structures generated during the emplacement of a syntectonic granodiorite and associated rocks (quartzdiorite enclaves and leucocratic dykes). These rocks were subjected to shearing and spectacular shear zones are present, which have been ob...

The tectonic evolution of orogenic domains may involve the superposition of ductile and brittle deformation. In some cases, banded or foliated rocks that transiently behaved mechanically brittle, developing sets of variably oriented joints, can be subjected to later ductile deformation. The result can be a complex structural pattern of folded and s...

The Cap de Creus massif in the eastern Pyrenees is a renowned late Variscan fold-and-shear zone belt characterized by partitioning of an overall ductile strike-slip-dominated dextral transpression into coeval folding, ductile shearing and localized embrittlement. The local partitioning of deformation mode (fracture vs. ductile flow) can be related...

Complex folding patterns include folds with curved hinges and/or curved axial surfaces. In simple shear zones, folds commonly nucleate with hinges at a high angle to the shear direction and progressively rotate towards parallelism with the shear/extension direction, giving rise to sheath folds. Axial surfaces also change in attitude with increasing...

The existence of an orogenic arc in the Variscan belt of Central Iberia is traced from its first recognition by the Swiss geologist, Rudolf Staub, at the XIV International Geological Congress (Madrid 1926), to the present. A review of the literature exposes the main facts related to Staub’s original interpretation, and its subsequent discussion, re...

The Roc de Frausa Massif, located at the Eastern Pyrenees, is formed by a stratoid Pre-Hercynian deformed granite (orthogneiss) interbedded with metasedimentary series. Hercynian granitoids (St. Llorenç — La Jonquera pluton) surround the southern and eastern part of the massif and Hercynian basic igneous rocks (Ceret stock) occupy the central part...

The Kerdous massif (Anti-Atlas of Morocco) consists of outstanding geological features and landscapes, such as many fascinating erosion landforms. Moreover, the outcropping rocks in the area comprise a unique record of multiple processes in the Earth geological evolution. The first list, resulting of the preliminary inventory of the most relevant a...

Geochronological U-Pb (LA-ICP-MS), geochemical and isotopic data from metavolcanic felsic rocks of the Canigó and Cap de Creus massifs in the Eastern Pyrenees provide evidence of an Ediacaran magmatic event lasting 30 Ma in NE Iberia. These data also constrain the age of the Late Neoproterozoic succession in the Cap de Creus massif, where depositio...

Geochronological U-Pb (LA-ICP-MS) data from metavolcanic felsic rocks of the Canigó and Cap de Creus massifs in the Eastern Pyrenees provide evidence of an Ediacaran magmatic event lasting 30 Ma in NE Iberia. The data constrain the age of the Late Neoproterozoic succession in the Cap de Creus massif, where depositional ages range from 577±3 Ma (nea...

Variscan massifs of NE Iberia occur along the Pyrenees, Catalan Coastal Ranges, Iberian Range and Minorca. Despite the effects of the Alpine cycle, which involve localized reworking, tilting, translation of basement units and blocks drifting, the Variscan evolution can be reconstructed. Geological features evidence significant differences across th...

A structural analysis has been performed in the Upper Permian lamprophyric dyke swarm of Aiguablava (Costa Brava, NE Iberia). Emplacement of sub-vertical dykes is related to the presence of a widespread joint network, mostly developed during the cooling and decompression of the late Variscan leucogranitic host rocks. The joint pattern consists on m...

Tectonic lozenges are elongate bodies bounded by relatively more deformed rocks. The focus of this study is on the 2-D structure of tectonic lozenges developed during ductile shear in rocks with a pre-existing mechanical anisotropy. On the basis of a detailed analysis of shear zones in foliated rocks from the Cap de Creus area (Variscan of the east...

Among the many concepts that have contributed to the development of structural geology in the last half-century, two are particularly important. These are: (i) the link between the symmetry of the structure, the vorticity of the associated deformation process and the tectonic regime, and (ii) the widespread partitioning of strain. However, a clear...

A structural analysis has been performed in the Upper Permian lamprophyric dyke swarm of Aiguablava (NE Spain). Dyke emplacement is related to the presence of a widespread joint network, likely developed during the cooling and decompression of the late Variscan granitic host rocks. In order to characterize the patterns of both the joint system and...

Some geological outcrops have a special scientific or educational value, represent a geological type locality and/or have a considerable aesthetical/photographic value. Such important outcrops require appropriate management to safeguard them from potentially damaging and destructive activities. Damage done to such rock exposures can include drill s...

Some geological outcrops have a special scientific or educational value, represent a geological type locality and/or have a considerable aesthetical/photographic value. Such important outcrops require appropriate management to safeguard them from potentially damaging and destructive activities. Damage done to such rock exposures can include drill s...

The Red Rocks Amphitheatre in Colorado, USA constitutes a paradigm for reconciling contemporary human actions and geological heritage conservation. The Amphitheatre, built upon red beds of the east flank of the Front Range of the Rocky Mountains, was constructed in the late 1930s with close attention to and respect for the existing geological landf...

The effects of postemplacement deformation on originally nonplanar dikes were tested experimentally and compared to field data from the Rainy Lake zone (Ontario, Canada) where irregular fold-like structures are observed. The analyses reveal that two processes are responsible for the irregular dike geometries. First, dikes intrude with varying orien...

Zircon composition (U, Th, rare earth elements, and Hf) was tested as a tracer of petrogenetic processes in a set of metaigneous rocks from two pre-Ordovician massifs in the Pyrenees, Canigó and Albera. Two groups were differentiated after analyzing a number of elements in zircon: (1) Casemí gneiss and Marialles amphibolite and (2) subvolcanic meta...

New geochronological data from the Albera Massif confirm the presence of an Early - Mid Ordovician igneous event (472 - 465Ma) recorded in the pre-Variscan rocks of the Pyrenees. This event resulted in the emplacement of a large granitic body in the lower part of the pre-Upper Ordovician metasedimentary succession and in the intrusion of a series o...

A detailed structural analysis of an anastomosing shear zone network in metagabbros from the Archean Rainy Lake zone (Canada) revealed the existence of prevalent dextral and minor sinistral conjugate shear zones with the obtuse angle (>130°) facing the main shortening direction. A typology of shear zone intersections, confluences, and other feature...

Lozenges are characteristic common structures related to anastomosing networks of shear zones. They are ellipsoid-shaped bodies of undeformed (or less deformed) country rock bounded by mylonites. They have been studied since the 1980's (Bell and Rubenach 1980, Bell 1981, Simpson, 1982, Choukroune and Gapais 1987, Hudleston 1999, Fusseis 2006), and...

New geochronological data from the Canigó massif (Eastern Pyrenees) using U–Pb SIMS on zircon provide evidence of the existence of a Late Ordovician (456–446 Ma) plutonic event that emplaced granitic and dioritic bodies into a Late Neoproterozoic–Early Paleozoic metasedimentary series. These are the first geochronological data documenting this magm...

This paper presents new geochronological, geochemical and isotopic data for Late Ordovician magmatism (455 ± 2 Ma) from the Variscan massifs in the northeastern Iberian Peninsula. This magmatism is mainly composed of aluminous and metaluminous plutonic rocks and a sequence of calc-alkaline ignimbrites and epiclastic volcanic rocks, which were defor...

An investigation on the effects of a strong rheological contrast in the deformation of layered anisotropic rocks is presented. The study focuses on the geometric and kinematic analysis of complex structures developed within and adjacent to a thin marble–metapsammite multilayer unit from the Cap de Creus tectonometamorphic belt (NE Spain). Zones of...

New geochronological data from low- to medium-grade metamorphic areas of the Eastern Pyrenees (Canigó, Roc de Frausa and Cap de Creus massifs) confirm the presence of two significant pre-Variscan igneous events: Ediacaran–Early Cambrian and Early Ordovician. The Ediacaran–Early Cambrian (580–540 Ma) magmatism is characterized by metavolcanic plagio...

Networks of leucocratic veins are widespread in the Rice Bay–Redgut Bay domain of the Rainy Lake zone at the Wabigoon–Quetico subprovince boundary (Archean Superior Province, Canada). Vein geometries and their cross-cutting relationships with host rocks are indicative of syntectonic emplacement within a regional late Archean transpressional deforma...

It has long been recognised that within zones of intense non-coaxial deformation, fold hinges may rotate progressively towards the transport direction ultimately resulting in highly curvilinear sheath folds. However, there is a surprising lack of detailed and systematic field analysis of such “evolving” sheath folds. This case study therefore focus...

Small-scale faults with associated drag folds in brittle-ductile rocks can retain detailed information on the kinematics and amount of deformation the host rock experienced. Measured fault orientation (α), drag angle (β) and the ratio of the thickness of deflected layers at the fault (L) and further away (T) can be compared with α, β and L/T values...

Migmatites from the Cap de Creus tectonometamorphic belt display a wide variety of structures, from those formed when the leucosomes were melt-bearing, to those developed during solid-state deformation. The observed field structures have been modelled by means of analogue experiments. The materials used in the models are layered plasticine as a sch...

Shear bands are geologic structures widely used as kinematic indicators. Despite the large amount of studies about these structures, their mechanical development is not yet well known. This work presents an experimental study of shear band localization and evolution under coaxial deformation. Particular attention is given to the influence of the ob...

The Precambrian inliers in the Anti-Atlas of Morocco are extensively intruded by swarms of dolerite dykes. On the basis of detail analysis of foliation patterns around dykes from Kerdous and Zenaga inliers it is inferred that dyke emplacement was syntectonic with the main Panafrican collisional event. Introducción: marco geotectónico El dominio ant...

Folds in ductile shear zones are common structures that have a variety of origins. These can be pre-existing folds that become modified or folds developed during the shearing event. Among the syn-shearing folds, a second subdivision is based on the relative age of the folded surface, which can be pre-existing or newly formed during the shearing eve...

Intrusive rocks may be arranged in the form of strings of lenses or beads, as found on the Cap de Creus Peninsula, NE Spain, and in the South Finland Migmatite–Granite Belt. These structures first appear to be the result of stretching and boudinage of intrusive sheets or dykes. However, closer examination reveals that they are not boudins, but are...

The Roses granodiorite is a Variscan stock with well developed syn- and post-magmatic deformation structures that crops Out in the Pyrenean Axial Zone. Analysis of structures reveals a continuous deformation history during and after magma cooling. The deformation history is divided on the basis of mechanical behaviour into two stages: an early one...

Field trip on granitic and hypabyssal rocks from the Northern Catalan Coastal Batholith (Costa Brava).

L'aflorament de Cala Pedrosa és el millor exemple de doble emplaçament de granitoides en la modalitat que s'anomena stopping magmatic. Aquest mecanisme consisteix en la fracturació de l'encaixant en blocs angulosos, de tal manera que permet l'infiltració del magma per la xarxa de fractures produïda. La peculiaritat és que aquest mecanisme d'intrusi...

The Northern Cap de Creus shear belt provides fine examples of shear zones developed at different scales in rocks bearing pre-existing penetrative foliations. The shear zones developed under retrograde metamorphic conditions, and they are preferentially located in crystalline schists. Lower grade metasedimentary rocks accommodated deformation by fo...

The structural analysis of a high-strain zone developed in medium- to high-grade metamorphic micaschists from the Cap de Creus area, Spain provides an example of the complex relationships between geometry, strain and kinematics to be found in deep crustal shear zones. This high-strain zone is composed of E-W trending structural domains characterize...

In shear zones developed across foliated rocks the relationships between geometry, strain patterns and kinematics differ from those in isotropic rocks. These differences refer to: In addition to this second point, the presence of a pre-existing foliation induces the development of minor structures arising from buckling instabilities formed at the m...

The Pyrenees are a chain of Cenozoic age with a Hercynian basement. Structurally the Pyrenees are characterized by a fan-like disposition with E-W trending thrusts and folds facing in opposite directions from the fan axis. The fan is asymmetric, with the south-facing structures forming a wider belt than the north-facing ones. The fan axis coincides...

Los Pirineos son una cadena alpina con un basamento hercínico que aflora extensamente a lo largo de su Zona Axial. En el zócalo de dicha unidad se evidencia la deformación alpina, aunque su configuración estructural es dominantemente hercínica. Una de las características de la estructura hercínica es una zonación estructural en profundidad, clásica...

The Vivero fault is a W-dipping, N-S-striking ductile shear zone separating the Ollo de Sapo antiform in its western hangingwall and the Lugo dome in its eastern footwall. Two stages of deformation (F1 and F2) produced nearly coaxial folds with sub-horizontal axes. A crenulation cleavage S2 transposes an older S1. Three sets of shear bands in the h...

The Pyrenees are an Alpine chain with Hercynian basement rocks that outcrop in a large area called the Axial Zone. These rocks have been involved in the Alpine deformation events although their main structural features resulted from the Hercynian orogeny. The Pallaresa Anticlinorium, is a complex Hercynian structural unit whose southern part belong...

Two different structural domains, developed during the main Hercynian deformation events, were recognized by de Sitter & Zwart in the Hercynian basement of the Central Pyrenees. A deep-seated level (infrastructure) made of medium to high-grade metasediments and orthogneisses with dome-shaped gently dipping foliations, contrasts with a shallow level...

The Hercynian structure in the Pyrenees is characterized by the overprinting of several deformational events, each one associated with spatial changes in tectonic style. The variations in tectonic style depend on the lithological setting and on the tectonic regime, both changing in space and time. However, structural zonations also arise from inhom...

An example of coeval development of ductile shear zones and folds in schistose terrains is documented by detailed mapping and structural analysis. Folds and shear zones were formed under retrogressive conditions after the peak of the regional Hercynian metamorphism, and both affect a previous regional schistosity. A gradual change in structural sty...

A detailed local structural map of the Mérens Fault zone at Port Vell (Vall Ferrera) reveals that the main fault-related mylonite band splits westwards into a network of mylonite zones. These consist of bands of highly-strained rocks exhibiting tightened folds, transposed foliations and extensive obliteration of pre-existing structures. Evidence of...

In the eastern Pyrenees mylonite belts are related to a late phase of Hercynian folding leading to the development of an open antiform-tight synform large-scale structure. These belts consist of steep dipping and anastomosing bands ranging in width from a few centimetres to some tens of metres, broadly parallel to the folds and preferentially devel...

In this contribution, shear zones are treated as zones of inhomogeneous deformation in which strain softening has occurred. The mylonites which form in ductile shear zones are the softened medium. The development of mylonite microstructures and fabrics are discussed from this point of view. Seven possible softening processes are discussed. They are...

The progressive c-axis fabric development in quartz-mylonites from the Cap de Creus (NE Spain) shear zones, is briefly summarized and the subsequent effects of fold development on these fabrics is analyzed in more detail. A stable fabric pattern consisting of a girdle lying in, or almost in, a plane perpendicular to both the mylonitic foliation and...