The Salamón gold deposit (León, Spain)

Located 55 km NE of the provincial capital León, Salamón deposit, discovered in 1985, is located on the southern slope of the Cantabrian Mountains, in the north of the Iberian Peninsula. The deposit is located on the León fault, which is a late-Variscan, E–W trending, deep structure extending for more than 100 km. The León fault has a complex history, and many mines and occurrences are located near it. The deposit is also close to small stocks and dykes of igneous rocks with intermediate to basic composition to which the mineralisation is related. The mineralisation is hosted mainly by the limestones and bituminous shales of the Lena Group (Namurian–Westphalian). There is also some mineralisation in other stratigraphic units of the Upper Carboniferous, such as the Maraña Group or the Stephanian B sediments.Apart from local and regional exploration, a detailed mineralogical and metallogenic research has been carried out. The epithermal mineralisation of Salamón was developed in two phases: an early dominant and extensive stage, with very fine crystalline gold-bearing sulphides, mainly pyrite, arsenic-bearing pyrite and arsenopyrite, in a matrix of quartz–chalcedony (jasperoid) and dolomite, and a later stage, of a larger crystal size, which occurs replacing the early stage or in pockets and veins, with greater mineralogical variety. Last of all there is a stage of supergene mineralisation, a product of the oxidant action of meteoric waters over the previous minerals. The hydrothermal alterations of the host rocks related to the orebodies are fundamentally decarbonatisation–dolomitisation, silicification and argillitisation. The early stages of mineralisation were produced in a temperature of 148–241°C, while that in the later stages occurred at 86–123°C. The early stage has been dated as 269±5 Ma, and this agrees with the ages of the other deposits of the district, which lay between 292 and 263 Ma, and the igneous rocks of the Peña Prieta stock (277±1 Ma), all which are of Permian age.The results of the studies carried out until now lead to the conclusion that Salamón is a Carlin-type gold deposit.     

Multiple dolomitization events along the Pozalagua Fault (Pozalagua Quarry,Basque–Cantabrian Basin,Northern Spain)

The Pozalagua Quarry in the Basque–Cantabrian Basin of northern Spain exposes a unique set of fault‐associated dolomites that can be studied on a decametre scale. The dolomites developed along the Pozalagua Fault system in slope‐deposited limestones of Albian age. Following marine phreatic diagenesis, the limestones were subject to meteoric karst formation. The resulting cavities were filled either by angular limestone fragments in a black clay‐rich matrix, or by cave floor/pond (now dolomitized) sediments. The subsequent diagenetic history reflects repeated periods of fracturing, fluid expulsion, dissolution and cementation. Contrasting fluid pulses resulted in the formation of a network of hydrothermal karst and the subsequent development of coarse‐crystalline calcite cement, zebra dolomite, recrystallized coarse‐crystalline dolomite, elongated blue–grey coarse‐crystalline dolomite cement in the open fault and, finally, coarse‐crystalline saddle dolomite. Decimetre‐size reworked host‐rock fragments present in the latter two dolomite phases probably reflect roof collapse fragments of a cave system that developed along the Pozalagua Fault system. However, there are also metre‐scale host‐rock fragments that apparently ‘float’ in the coarse‐crystalline saddle dolomites, implying that either fragment assimilation was a widespread process or violent expulsion of fluids occurred along the Pozalagua Fault system. The presence of pre‐dolomite and post‐dolomite stylolites, parallel to bedding, supports a linkage between the diagenetic events and the Late Albian tectonism that affected the region.     

The last deglaciation in the Picos de Europa National Park (Cantabrian Mountains,northern Spain)

A sedimentological and geochemical study of the Lago Enol sequence (Cantabrian Mountains, northern Spain), together with detailed geomorphological mapping, provides a first record of glacier evolution and climate change over the last 40 ka in the Picos de Europa National Park. The Enol glacier retreated from its maximum extent prior to 40 ka BP as demonstrated by the onset of proglacial lacustrine sedimentation in two glaciated depressions: the Comella hollow to the north (before 40 ka BP) and the Lago Enol (before 38 ka BP). These results support previous evidence that the maximum extent of southern European glaciers occurred earlier than in northern Europe. Alternation of homogeneous and laminated proglacial sediments during the glacier retreat illustrate a dynamic glacial evolution during the Marine Isotope Stage (MIS) 3 (40–26 ka BP). A slight warming is detected at 26 ka ago with the change from proglacial sediments (in a lake located in contact to the glacier) to glaciolacustrine sedimentation (in a non‐contact or distal lake). Finally, the onset of organic‐rich sediments took place at 18 ka ago. This last transition occurred in two phases, similarly to the North Atlantic Last Termination, suggesting a link between North Atlantic Deep Water formation oscillations and palaeohydrological variability in the Cantabrian Mountains. Copyright © 2009 John Wiley & Sons, Ltd.     

A strike-slip fault corridor within the Alpujarra Mountains (Betic Cordilleras,Spain)

In a long »corridor« in the internal zone of the Betic Cordilleras, bounded to the north by the Sierra Nevada and to the south by the Sierras Lujar, Contraviesa and Gador, two discernible bands of strike-slip faults exist: These bands lie in an approximately E-W direction and are well exposed throughout and beyond the 85 km long belt.The characteristic features of strike-slip faults, such as cataclastic rocks composed of variously textured fault breccia, which also include fragments of rocks up to several metres in size, incipient foliation, and striation demonstrate the right-lateral nature of the displacement. There are also fractures which run in a NW-SE and NNE-SSW direction, and apparently originated after formation of the E-W faults. The magnitude of lateral displacements is difficult to calculate. Evidence of considerable vertical movement can be found locally.These strike-slip displacements have essentially occurred since the middle Miocene period and might still be taking place.

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Zusammenfassung In einem langen Korridor in der Internzone der Betischen Kordilleren, der im Norden durch die Sierra Nevada und im Süden von den Sierren Lujar, Contraviesa und Gador begrenzt wird, sind zwei Streifen mit Blattverschiebungen zu beobachten. Sie streichen etwa E-W und sind gut entlang des 85-km-langen Gürtels aufgeschlossen.Die charakteristischen Merkmale von Blattverschiebungen wie etwa kataklastische Gesteine mit verschiedenen texturierten Verwerfungsbrekzien, welche auch bis zu mehreren Metern große Gesteinsblöcke enthalten, beginnende Schieferung und Harnischbildung, zeigen die dextrale Natur der Bewegung. Daneben treten NW-SE und NNE-SSW streichende Störungen auf, die offensichtlich nach der Bildung der E-W verlaufenden Blattverschiebungen entstanden sind. Das Ausmaß des lateralen Versatzes ist schwer abzuschätzen.Diese Bewegungen finden seit dem mittleren Miozän statt und sind möglicherweise immer noch aktiv.

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Résumé Dans un long couloir situé dans la zone interne des Chaînes Bétiques et limité au Nord par la Sierra Névada et au Sud par les Sierras de Lujar, Contraviesa et Gador, s'observent deux trains de failles de décrochements. Ces trains ont une direction à peu près E-W et sont bien exposés tout au long des 85 Km de cette zone.Les traits caractéristiques des décrochements, tels que cataclasites, brèche de faille avec fragments de roches jusqu'à plusieurs mètres de longueur, schistosité naissante et striation, démontrent la nature dextre du déplacement. Il existe aussi des fractures de direction NW-SE et NNW-SSW qui se sont vraisemblablement formées postérieurement aux failles E-W. La valeur du déplacement latéral est difficile à estimer. On rèléve localement des indices de mouvements verticaux importants.Ces décrochements se sont produits essentiellement à partir du Miocène moyen et peuvent encore se poursuivre aujourd'hui.

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Depositional facies and stratal geometry of an Upper Carboniferous prograding and aggrading high-relief carbonate platform (Cantabrian Mountains, N Spain)

Seismic‐scale continuous exposures of an Upper Carboniferous (Bashkirian–Moscovian) carbonate platform (N Spain) provide detailed information about the lithofacies and stratal geometries (quantified with differential global positioning system measurements) of microbial boundstone‐dominated, steep prograding and aggrading platform margins. Progradational and aggradational platform‐to‐slope transects are characterized by distinct lithological features and stratal patterns that can be applied to the understanding of geometrically comparable, high‐relief depositional systems. The Bashkirian is characterized by rapid progradation at rates of 415–970 m My^?1. Characteristic outer‐platform facies are high‐energy grainstones with coated intraclasts, ooids and pisoids, moderate‐energy algal‐skeletal grainstones to packstones and lower energy algal packstone and boundstone units. The Moscovian aggradational phase is characterized by aggradation rates of 108 m My^?1. Coated‐grain shoals are less common, whereas crinoidal bars nucleated in well‐circulated settings below wave‐base. Boundstones form a belt (30–300 m wide) at the platform break and interfinger inwards with massive algal‐skeletal wackestones (mud‐rich banks). The progradational phase has divergent outer‐platform strata with basinward dips of 12° to 2°. Steep clinoforms with dips of 20–28° are 650–750 m in relief and possibly sigmoidal to concave in the lower part. The basinward‐dipping outer‐platform strata might be depositional for less than 6°, consistent with lithofacies deepening seaward. The basinward dip is attributed to the downward shift of upper‐slope boundstone, forced by late highstand and relative sea‐level fall, and to compaction‐induced differential subsidence during progradation. The aggradational phase is characterized by horizontally layered platform strata. Clinoforms steepen to 30–45° reaching heights of 850 m and are planar to concave. The evolution from progradation to aggradation, at the Bashkirian–Moscovian boundary, is attributed to increased foreland‐basin subsidence and decreased boundstone accumulation rates. Progradation was primarily controlled by boundstone growth rather than by highstand shedding from the platform top. Within the major phases, aggradational–progradational increments are produced by third‐ to fourth‐order relative sea‐level fluctuations.     

Periglacial features of the Subbetic Mountains of southern Spain (Córdoba Province)

Three types of periglacial deposits (breccias, stratified breccias and grèzes litées are described from Córdoba Province in southern Spain. Their physico-chemical properties, in particular clay mineralogy in relation to terra rossas in the area, indicate two different ages for these deposits. Younger terra rossas and younger periglacial deposits contain illite and kaolinite whereas older terra rossas and older periglacial deposits contain vermiculite and kaolinite. Geomorphological evidence (altitude and relationships to the surfaces described by earlier authors in southern Spain) indicate approximate ages for the deposits. Secondary carbonate from one of the younger breccias gave a uranium series date of 80 000 yr BP, suggesting that some of the younger breccias were deposited in a periglacial climate before 80 000 BP. © 1997 John Wiley & Sons, Ltd.     

8000 years of vegetation history in the northern Iberian Peninsula inferred from the palaeoenvironmental study of the Zalama ombrotrophic bog (Basque‐Cantabrian Mountains,Spain)

This paper focuses on pollen, spores, non‐pollen palynomorphs (NPPs) and certain geochemical elements from the ombrotrophic blanket bog of Zalama (Basque‐Cantabrian Mountains, northern Iberian Peninsula), with the support of a robust chronology based on 17 AMS ¹⁴C dates. The main results related to the last 8000 years show that, during the early middle Holocene, pines and deciduous forests were the most extensive tree formations. At the beginning of the succession, pines reach 44%, showing regional presence, whereas after 7600 cal. a BP, deciduous forests were particularly abundant. From c. 6500 cal. a BP the pollen diagram constructed from our samples shows the first anthropogenic evidence, linked with the new economic practices related to the Neolithic of the Basque‐Cantabrian Mountains. From 3300 cal. a BP the expansion of Fagus sylvatica is particularly clear, and has since then become one of the dominant forest species in this region. We also discuss the Holocene evolution of other noteworthy plant communities in southwestern Europe, such as Taxus baccata, Juglans and shrublands.     

Tectonic and liquefaction structures in the Loreto basin,Baja California (Mexico) : synsedimentary deformation along a fossil fault plane

Abstract

Complex fault assemblages associated to liquefaction structures have been analyzed in a Pliocene basin located along the Gulf of California. The studied outcrop shows a fossil fault plane formed ill soft flat lying sediments. The liquefaction and fluidification structures have been recognized in voleaniclastic layers deposited ill a lagoonal environment and are potentially related to seismic wave shaking and to successive dewatering along fractures. This strati-graphic record is explained by the progressive development of a seismic fault zone, related to the transtensional regime still active in the Gulf. The present analysis can he considered as an useful case study for the reconnaissance of the different types of structures formed during synsedimentary deformation in hydroplastic conditions.     

Granites built by sheeting in a fault stepover (the Sanabria Massifs, Variscan Orogen, NW Spain)

The Sanabria region (Central Iberian Zone, Variscan belt of Spain) shows an asymmetric thermal dome marked by migmatites accompanied by the Ribadelago and the Sotillo plutons. These small plutons display pronounced mineralogical variations. Biotite granodiorites and tonalites prevail, and granites and gabbros are common. Both plutons are confined in the releasing stepover of a transpressional shear zone that strikes 120°E and dips 70°SW. Most of the igneous rocks form sheets parallel to the shear zone. Magnetic foliations and lineations in the igneous rocks are parallel, respectively, to the shear bands and stretching lineations observed in the shear zone. The formation of these igneous sheets at high angle to the main axis of the regional field stress is explained by a combination of the fault-valve behaviour of the shear zone with the power of melt overpressure to open and ascend through previously formed planar structures, like S- or C-planes.     

New radiometric and geomorphologic evidences of a last glacial maximum older than 18 ka in SW European mountains: the example of Redes Natural Park (Cantabrian Mountains,NW Spain)

The first numerical age determinations from radiocarbon dating establish the chronology of glacial events in Redes Natural Park (Cantabrian Mountain, NW Spain). A core drilled in an ice-dammed deposit provided a minimum age of 28 990 ± 230 years BP for the maximum glacial expansion (phase I). Another core from a cirque bottom-fill provided organic sediment with 20 640 ± 300 years BP, a minimum age for the first glacial retreat (phase II). Radiometric dating of proglacial deposits interpreted as synchronous with the last glacial maximum phase in neighbouring Comella basin (Picos de Europa), yield ages of 40 480 ± 820 years BP. The chronological data presented in this work are consistent with the model of glacier evolution established in the Pyrénées, with a glacial maximum phase for the last glacial period older than 18 ka.     

Hydrogeologic evidence for a continuous basal shear zone within a deep-seated gravitational slope deformation (Eastern Alps, Tyrol, Austria)

The currently inactive deep-seated gravitational slope deformation (DGSD) Sagspitz in Tyrol, Austria, covers an area of 3 km² and originated along a glacially over-steepened slope composed mainly of phyllites belonging to the Innsbruck Quartzphyllite Complex. Past mass movement processes caused the formation of fracture systems and slump bodies which consequently form the aquifers of relatively large springs in a rock type with generally very low permeability and poor porosity. Analysis of water chemistry, oxygen isotope, and field parameters of the springs emerging from the DGSD imply that multilevel aquifers exist and enabled the detection of continuous deep flow paths through the entire length of the mass movement from the main scarp to the toe of the slope. It is shown that the aquifer boundaries and spring emergences throughout the loosened rock mass can be correlated to the internal and basal shear zones of the DGSD so that this hydrogeological approach proved to be useful for evaluating the mass movement structure.     

Tectonothermal evolution of a foreland fold and thrust belt: the Cantabrian Zone (Iberian Variscan belt,NW Spain)

Analysis of the conodont colour alteration index and the Kübler index of illite allowed us the characterization of four types of very low‐ or low‐grade metamorphism in the Cantabrian Zone (CZ) and determination of their regional and temporal distribution. These types are: (1) an orogenic Variscan metamorphism present only in restricted areas of the western and north‐western parts of the CZ where epizonal conditions are reached; (2) a burial metamorphism that appears in the basal part of some nappes, where anchizonal conditions are sometimes achieved; the thermal peak preceded emplacement of the nappes; (3) a late‐Variscan metamorphism in the southern and south‐eastern parts of the CZ; a cleavage, cutting most of the Variscan folds, is associated with this metamorphism, which has been related to an extensional episode; (4) a contact metamorphism and hydrothermal activity associated with minor intrusive bodies. The extension continued after the Variscan deformation giving rise to hydrothermal activity during Permian times.     

The last major earthquakes along the Magallanes–Fagnano fault system recorded by disturbed trees (Tierra del Fuego,South America)

Forests situated above active fault zones may record hillslope evolution, thus holding information about recent seismic events. Lenga trees (Nothofagus pumilio) extend across the Magallanes–Fagnano fault system (MFFS), the active transform boundary between the South American and Scotia plates. Coseismic surface ruptures along the fault scarp tilt trees located uphill. During the interseismic period, tree growth curves the trunks. Annual tree rings from the study area show abrupt changes from concentric to asymmetric, allowing the timing of major historical earthquakes to be established. In this case, tree‐ring analysis suggests rupture on the MFFS fault scarp in 1883 ± 5 and 1941 ± 10, coinciding with the February 1, 1879 (Modified Mercalli Scale, VI) and the December 17, 1949 (Ms 7.8) earthquakes in Tierra del Fuego. Our results provide evidence that this fault system was the source of these earthquakes, which has implications for seismic hazard in the study region.     

Active transfer fault zone linking a segmented extensional system (Betics, southern Spain): Insight into heterogeneous extension driven by edge delamination

Pliocene and Quaternary tectonic structures mainly consisting of segmented northwest–southeast normal faults, and associated seismicity in the central Betics do not agree with the transpressive tectonic nature of the Africa–Eurasia plate boundary in the Ibero-Maghrebian region. Active extensional deformation here is heterogeneous, individual segmented normal faults being linked by relay ramps and transfer faults, including oblique-slip and both dextral and sinistral strike-slip faults. Normal faults extend the hanging wall of an extensional detachment that is the active segment of a complex system of successive WSW-directed extensional detachments which have thinned the Betic upper crust since middle Miocene. Two areas, which are connected by an active 40-km long dextral strike-slip transfer fault zone, concentrate present-day extension. Both the seismicity distribution and focal mechanisms agree with the position and regime of the observed faults. The activity of the transfer zone during middle Miocene to present implies a mode of extension which must have remained substantially the same over the entire period. Thus, the mechanisms driving extension should still be operating. Both the westward migration of the extensional loci and the high asymmetry of the extensional systems can be related to edge delamination below the south Iberian margin coupled with roll-back under the Alborán Sea; involving the asymmetric westward inflow of asthenospheric material under the margins.     

New radiometric and geomorphologic evidences of a last glacial maximum older than 18 ka in SW European mountains: the example of Redes Natural Park (Cantabrian Mountains,NW Spain)

Abstract

The first numerical age determinations from radiocarbon dating establish the chronology of glacial events in Redes Natural Park (Cantabrian Mountain, NW Spain). A core drilled in an ice-dammed deposit provided a minimum age of 28 990 ± 230 years BP for the maximum glacial expansion (phase I). Another core from a cirque bottom-fill provided organic sediment with 20 640 ± 300 years BP, a minimum age for the first glacial retreat (phase II). Radiometric dating of proglacial deposits interpreted as synchronous with the last glacial maximum phase in neighbouring Cornelia basin (Picos de Europa), yield ages of 40 480 ± 820 years BP. The chronological data presented in this work are consistent with the model of glacier evolution established in the Pyrénées, with a glacial maximum phase for the last glacial period older than 18 ka. © 2002 Éditions scientifiques et médicales Elsevier SAS. AU rights reserved.