South Portuguese Research Articles

Changing mantle sources in a suture zone in the heart of Pangea: implications for collisional tectonics during the waning stages of ocean closure

The formation and emplacement of syn-collisional mafic dykes that intrude suture zones and their association with orogenic processes are enigmatic. Southern Iberia records the Late Paleozoic amalgamation of Pangea and exposes today a fragment of Laurussia (South Portuguese Zone), which is spatially juxtaposed with autochthonous Gondwana. Fault-bounded oceanic metasedimentary rocks, melanges and ophiolite complexes characterize the suture zone and are in turn crosscut by intrusive granitoid rocks and mafic dykes. The generation and emplacement of these mafic dykes and their relationship to the suture zone are undetermined. Field evidence shows the dykes were emplaced at high angles to pre-existing orogenic fabrics in the melange, granitoid and metasedimentary rocks. Geochemical analyses (major, trace, rare earth elements) indicate the dykes exhibit a mid-ocean ridge basalt signature. U/Pb zircon geochronology reveals the crystallization age of the dykes is ca. 316 Ma and Sm–Nd isotopic analysis suggests a deep mantle source. Taken together, these data support existing temporal constraints on events leading up to the amalgamation of Pangea, and suggest progressive lower crustal delamination during the waning stages of continent–continent collision.

Geochemistry of the Peramora Mélange and Pulo do Lobo schist: geochemical investigation and tectonic interpretation of mafic mélange in the Pangean suture zone, Southern Iberia

The Peramora Melange is part of an accretionary complex between the South Portuguese Zone (a fragment of Laurussia) and the Ossa Morena Zone (para-autochthonous Gondwana) and is an expression of the Pangean suture zone in southwestern Iberia. The suture zone is characterized by fault-bounded units of metasedimentary rocks, melanges, and mafic complexes. Detailed geologic mapping of the Peramora Melange reveals a complex pattern of imbricated schists and mafic block-in-matrix melanges. Geochemical signatures of the Pulo do Lobo schist (PDL) are consistent with derivation from both mafic and continental sources. The mafic block-in-matrix melange displays normal mid-ocean ridge basalt (NMORB) geochemical signature, juvenile Sm–Nd isotopic compositions, and a range of zircon ages similar to those observed in the PDL, suggesting a sedimentary component. Taken together, these data suggest a complex tectonic history characterized by erosion of a NMORB source, melange formation, and imbrication during underplating occurring during the final stages of continent–continent collision.

Relations between total mercury, methylmercury and selenium in five tissues of Sepia officinalis captured in the south Portuguese coast

Mercury, methylmercury and selenium were determined in digestive gland, branchial hearts, mantle, kidney and gills of Sepia officinalis from two areas of the south Portuguese coast. To the best of our knowledge these are the first data on Hg, MeHg and Se in branchial hearts, kidney and gills of cuttlefish. Digestive gland, branchial hearts and kidney presented higher levels of Hg and Se than mantle and gills. Methylmercury was significantly higher in digestive gland, branchial hearts and mantle. The enhanced levels of Hg in digestive gland and branchial heart reinforce the elevated storage capacity of these two tissues. The percentage of MeHg varied from 6.1% in gills to 92% in mantle. Linear and positive MeHg–Hg relations were obtained for the five tissues, being the better relation and higher slope observed for mantle, followed by branchial hearts, digestive gland, kidney and gills. The Se:Hg molar ratios showed a surplus of Se in all tissues. Calculations based on the equimolarity of Se:Hg point that 95–99% of Se are not linked to Hg (Se free). The negligible quantity of Se associated with Hg suggests that the mechanism of MeHg demethylation was not triggered in none of the tissues, presumably because the threshold for MeHg toxicity was not achieved.

Low HLA DQB1 0602 in portuguese narcoleptics

Narcolepsy is a rare sleep disorder characterized by episodes of excessive sleepiness. Symptoms such as cataplexy sleep paralysis, REM sleep onset and hypnopompic or hypnagogic hallucinations can also occur. The ICSD-2 classifies this sleep disturbance in several subtypes, namely: Narcolepsy with Cataplexy, Narcolepsy without cataplexy, Narcolepsy due to medical condition and Narcolepsy non-specific. The diagnosis implies the existence of excessive sleepiness with or without cataplexy, and the recording of two SOREM’s (Sleep Onset Rapid Eye Movement) in the Multiple Sleep Latency Test (MSLT). The symptoms described above should also be considered. In Brazil HLA DQB1*0602 allele is prevalent in 95% of patients with cat- aplexy, and has been highlighted in less than 50% of patients without cataplexy (Coelho F., et al., 2010); these data are in line with other international data. In Portugal there are about 47 in every 100 000 inhabitants with Narcolepsy (Ohayon et al., 2002), i.e., similar to other European countries, however HLA DQB1*0602 prevalence has been found around 60% in Narcolepsy with cataplexy (Viegas et al. 2013). OBJECTIVES The aim of this study was to enlarge the database to other regions of the country in order to better determine the prevalence of HLA DQB1 0602 and HLA DRB1 1501 in cases of Narcolepsy with (NC) and without cataplexy (NnoC). 183 patients were selected; 117 with cataplexy and 66 without cataplexy. All patients were diagnosed according to standard criteria (ICSD2), using a clinical interview, a cataplexy questionnaire and Type 1 PSG followed by MSLT. HLA typing was performed in officially recognized laboratories. Data were obtained in Center and South Portuguese regions. 54% of the NC are males against 42% of the NnoC. The statistical differences between the 2 groups were: average age of the symptoms onset (24.46 years for NC and 26.81 for NnoC; diagnostic delay took a mean of 16 years for NC while for NnoC it was only 8.29 years. Prevalence of sleep paralysis and hallucinations are statistically different among groups: 44% of the narcoleptic with cataplexy have sleep paralysis against 24.5 of the narcoleptic without cataplexy; 60% of the narcoleptic with cataplexy have hallucinations when compared to 28% of the patients without cataplexy. The mean latency in the MSLT is low for both groups: 4.11 ± 2.52 min for NC and 4.32 ± 2.06 min for NnoC. The patients with cataplexy had an average of 1.98 ± 1.51 SOREMS and those without cataplexy have about 2.16 ± 1.057 SOREMS. The HLA DQB1 0602 was more prevalent in NC: 51% for the NC have HLA DQB10602, while only 31% of the NnoC have this allele. The HLA DRB11501 is prevalent in 42% of the subjects with cataplexy and 25% of those without cataplexy. The low HLA prevalence of DQB1 0602 in NC in our population has so far no clear explanation. It is tempting to assume that the high miscegenation started many centuries ago - it’s a possible explanation. In a National study of HLA prevalence clear differences in allele frequency do exist between North, Center and South regions, in spite of the relatively short differences in KM (Spinola et al. 2005). Furthermore these authors propose a marked influence of African and European genes, with African genes more prevalent in South regions. The high prevalence of HLA DQB1 0602 in NC detected in a São Paulo, Brazilian study renders this explanation eventually difficult, taking into account many similarities between both countries. However 2 aspects may be open for discussion: the reduced number of brazilian cases and the possibility that in Brazil there are strong territorial differences. The questions raised by this study deserve further research. (1) Ohayon, M.M., Priest R.G., Zulley J., Smirne S., Paiva T. (2002). Prevalence of narcolepsy symptomatology and diagnosis in the European general population. Neurology, 58: 1826–1833. (2) Morrish E., King M.A., Smith I.E., Shneerson J.M. (2004). Factors associated with a delay in the diagnosis of narcolepsy. Sleep Medicine, 5: 37–41. (3) David A, Constantino F, Santos JM, Paiva T. Health-related quality of life in Portuguese patients with narcolepsy. Sleep Med. 2012 Jan 24. (4) Coelho F.M.S, Pradella-Hallinan M., Pedrazzoli M., Soares C.A.S., Fernandes G.B.P., Gonçalves A.L., Tufik S. & Bittencourt L.R.A. (2010). Traditional biomarkers in narcolepsy – experience of a brazilian sleep centre. Arq Neuropsiquiatr, 68 (5): 712 – 715. (5) Spínola H, Middleton D, Brehm A. (2005). HLA genes in Portugal inferred from sequence-based typing: in the crossroad between Europe and Africa. Tissue Antigens. 66(1):26–36.

Magnetic evidence of a crustal fault affecting a linear laccolith: The Guadiana Fault and the Monchique Alkaline Complex (SW Iberian Peninsula)

Magnetic anomalies can help reveal the structure of the upper crust in regions with intermediate or basic igneous rocks, and their continuity is essential to determine the position of crustal faults. The southwestern Iberian Peninsula constitutes the foreland of the Betic Cordillera and is characterized by an elongated E-W dipole extending 200km toward its external zones. The anomaly is related to the outcropping Monchique Alkaline Complex, characterized by rocks of moderate magnetic susceptibility (0.029 SI) intruding into the metapelitic host rock of the South Portuguese Zone. Analysis of aeromagnetic and field magnetic anomalies serves to constrain the geometry of this laccolith. Toward the east, the magnetic dipole has a 60km long N-S sharp boundary that coincides with the southern part of the Guadiana River. Field magnetic and gravity anomalies confirm the presence of this structure. It is produced by a sharp step in the elongated anomalous body, with an E downthrown block, interpreted as the offset produced by a deep N-S crustal fault—the Guadiana Fault. Therefore, the Guadiana River has three long linear segments near its mouth, locally coinciding with a N-S trending joint set, that support the presence of this major fault. To date, no evidence of this tectonic discontinuity, coinciding with the Spanish-Portuguese border, has been reported. Magnetic research is essential for understanding the structure of wide regions intruded by intermediate and/or basic igneous rocks.

Complication infectieuse après chirurgie arthroscopique de l’épaule

This work is focused on the turbiditic sediments from the Carboniferous Baixo Alentejo Flysch Group (BAFG) in the South Portuguese Zone, an external zone of the Iberian Variscides. The aim of this work is to constrain the provenance and tectonic setting of these sediments in a context of a complex evolution of SW Iberian Variscides. For this purpose, we performed a systematic study of petrographical and geochemical signatures of greywackes and shales from the three BAFG formations: Mértola, Mira and Brejeira. Major and trace element composition and ratios suggest heterogeneous source area composition for BAFG shales and greywackes. For the oldest Mértola Formation greywackes, source area is dominated by granitoid rocks with minor mafic input. The latter becomes residual in the Mira Formation. The youngest Brejeira Formation greywackes show clear felsic affiliation associated with an increase in recycled components. The shales of all three BAFG formations denote a granodioritic affiliation. Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration (PIA) values suggest moderate weathering in the source areas of Mértola and Mira formations. These indices, together with A–CN–K relations, point out to steady-state weathering conditions in the source areas of both formations. In contrast, both CIA and PIA values for the Brejeira Formation indicate variable conditions of palaeoweathering, from moderate to intense, as a consequence of non-steady-state conditions probably triggered by tectonic instability in the provenance area. Compared to the greywackes, the shales of all three BAFG formations exhibit higher CIA and PIA values, as well as low K2O/Al2O3 (~ 0.2) and index of compositional variability (< 1), reflecting the cumulative effect of multiple cycles of sedimentary recycling and prolonged chemical weathering history. Major and trace element distribution and upper continental crust-normalized multi-element plots suggest that the sediments of BAFG were derived mainly from a continental arc/active margin with minor contribution from old continental crust. Together, our geochemical data are compatible with BAFG sediments derived mainly from SW border of the Ossa Morena Zone (Gondwanan affinity), with possible contribution from an external (Avalonian) source.

Cu- and Zn-Soil Anomalies in the NE Border of the South Portuguese Zone (Iberian Variscides, Portugal) Identified by Multifractal and Geostatistical Analyses

Extensive Cu- and Zn-soil geochemical data in the Albernoa/Entradas–S. Domingos region (NE border of the Iberian Pyrite Belt, South Portuguese Zone) were examined to separate anomalies from background using the concentration–area fractal model. Distribution patterns of Cu and Zn concentrations in soil are primarily influenced by bedrock. The regional threshold values of Cu- and Zn-soil contents over metasedimentary sequences are 20–25 and 20–60 ppm, respectively, becoming 30–50 and 20–90 ppm, respectively, when metavolcanic rocks are present. The first-order threshold values for Cu are 80–90 ppm in soils over metasediments and 70–80 ppm in soils over sequences bearing metavolcanics. For Zn, the first-order threshold values are 40–80 and 90–100 ppm in soils over metasediments and metavolcanic rocks, respectively. Metasediments and metavolcanics comprising significant sulphide disseminations are outlined by Cu- and Zn-soil values above 100 and 300 ppm in soil, respectively. On the basis of these results, Alvares and Albernoa/Entradas areas emerge as the first priority targets for exploration. The observed non-coincidence of Cu- and Zn-soil anomalies in soil in the area could reflect difference in element dispersion during weathering, they mostly indicate distinct metal sources related to the original composition of different rock types or to chemical changes developed during Variscan deformation/re-crystallization path. The established regional baseline data can be used as reference for environmental studies.

Microbiological monitoring of Ruditapes decussatus from Ria Formosa Lagoon (South of Portugal)

Ria Formosa Lagoon is the most important bivalve production region of the South Portuguese coast. However, the microbial contamination has been increasing in the northwest area of the lagoon. This study assesses the microbiological contamination of clams Ruditapes decussatus from the most contaminated area for 1 year period. Escherichia coli levels were weekly determined and related with variations in several environmental parameters: precipitation, atmospheric temperature, solar radiation, wind velocity, humidity and tide height. Highest E. coli levels in clams were associated with periods of heaviest rainfall and lowest temperature, mainly due to diffuse sources of faecal discharges. A seasonal trend was observed: microbial contamination in clams was lowest in summer, with highest temperatures, intense solar radiation and dry weather and higher in the remaining seasons, especially in winter due to the runoff of faecal contaminated waters. Several measurements not only to protect the quality of the lagoon, but also to protect public health were recommended. The most imperative will be to detect and extinguish the diffuse contamination sources. Otherwise it might be necessary to implement an interdiction period of bivalve harvesting after heavy rainfalls.

Variability over time in the sources of South Portuguese Zone turbidites: evidence of denudation of different crustal blocks during the assembly of Pangaea

This study combines geochemical and geochronological data in order to decipher the provenance of Carboniferous turbidites from the South Portuguese Zone (SW Iberia). Major and trace elements of 25 samples of graywackes and mudstones from the Mertola (Visean), Mira (Serpukhovian), and Brejeira (Moscovian) Formations were analyzed, and 363 U-Pb ages were obtained on detrital zircons from five samples of graywackes from the Mira and Brejeira Formations using LA-ICPMS. The results indicate that turbiditic sedimentation during the Carboniferous was marked by variability in the sources, involving the denudation of different crustal blocks and a break in synorogenic volcanism. The Visean is characterized by the accumulation of immature turbidites (Mertola Formation and the base of the Mira Formation) inherited from a terrane with intermediate to mafic source rocks. These source rocks were probably formed in relation to Devonian magmatic arcs poorly influenced by sedimentary recycling, as indicated by the almost total absence of pre-Devonian zircons typical of the Gondwana and/or Laurussia basements. The presence of Carboniferous grains in Visean turbidites indicates that volcanism was active at this time. Later, Serpukhovian to Moscovian turbiditic sedimentation (Mira and Brejeira Formations) included sedimentary detritus derived from felsic mature source rocks situated far from active magmatism. The abundance of Precambrian and Paleozoic zircons reveals strong recycling of the Gondwana and/or Laurussia basements. A peri-Gondwanan provenance is indicated by zircon populations with Neoproterozoic (Cadomian-Avalonian and Pan-African zircon-forming events), Paleoproterozoic, and Archean ages. The presence of late Ordovician and Silurian detrital zircons in Brejeira turbidites, which have no correspondence in the Gondwana basement of SW Iberia, indicates Laurussia as their most probable source.

High-pressure metamorphism in the Early Variscan subduction complex of the SW Iberian Massif

Several units exposed in the boundary area of the Ossa Morena Zone (OMZ) and the South Portuguese Zone (SPZ) preserve petrographic and thermobarometric evidence for an early metamorphic episode (M1), developed under a high-P, low to intermediate-T gradient, related to Early Variscan subduction in the SW Iberian Massif. In the OMZ, these are the Cubito–Moura Unit (Pmin~9.2kbar and T=395±45°C), blueschists from its basal mélange (Pmin~12.4kbar and T=310±11°C), and the underlying Fuenteheridos Group (P=10.9±0.4kbar and T=449±31°C). The equivalent units in the SPZ are the La Minilla Formation (P=8.7±0.4kbar and T=388±16°C) and the lawsonite pseudomorphs-bearing Pulo do Lobo Formation. All these units formed part of an approximately NE verging orogenic wedge (present coordinates) developed by the accretion of subducted slabs of the outermost margin of Gondwana and other elements of the Rheic Ocean realm, from at least the Middle Devonian to the lowermost Tournaisian. High-pressure rocks were subsequently emplaced on more internal zones of the OMZ that only experienced a younger high-T, low to intermediate-P metamorphism (M2). This high-T event was coeval with magmatic activity from the uppermost Devonian to the Middle Mississippian, probably as a consequence of transtensional lithospheric thinning and/or delamination of the lower crust and mantle lithosphere of the Gondwana margin. Pre-Late Devonian synorogenic sedimentation in forearc and back-arc basins of the subduction complex evolved to a Late Devonian–Middle Mississippian foreland basin system in early collisional stages. Finally, a new Middle–Late Mississippian fold-and-thrust belt with opposite (SW) vergence and new foreland basins developed during late collisional stages.

Palynology, Stratigraphy and Geometry of the Pennsylvanian continental Santa Susana Basin (SW Portugal)

The continental Pennsylvanian Santa Susana Basin (SSB) is located along an important N-S strike shear zone (Santa Susana Shear Zone - SSSZ) that separates the Ossa-Morena and South Portuguese Zones (SW Portugal). This shear zone controlled the sedimentation of the basin and probably its post-sedimentary evolution. The lower (basal) unit is mostly conglomeratic and is known essentially from drill-hole data while the upper unit, that covers most of the current surface area, is composed by sandstones, shales and some coal beds. Fluvial sedimentary rocks seem to prevail, but evidences of lacustrine sedimentation can be found in restricted areas within the upper unit. Palynological data indicate that at least part of the sedimentation took place during the Early Kasimovian (Cantabrian) but the sporomorph content of different localities suggest that significantly older sediments (Late Moscovian -Early Bashkirian) may be present. Geometrical, structural, and cartographical evidences indicate that the SSB formed as a pull-apart basin along the SSSZ and was later partially uplifted during latest Varsican and Alpine orogenies.>

Occurrences of the amphi-Atlantic brown mussel Perna perna (Linné, 1758) (Mollusca, Bivalvia) in South Portugal since the Atlantic “climatic optimum”

The large, edible, and near-cosmopolitan brown mussel Perna perna (Linné, 1758) has a history of few and infrequent occurrences in Portugal since the Atlantic “climatic optimum” of the Holocene. Moreover, it is likely that some previous citations of Mytilus spp. from other Holocene deposits, including kitchen middens, may represent true Perna specimens. The species was recently found by Lourenço et al. (2012) in the south Portuguese coastal localities of Ilha do Farol and Vila Moura. Here, we summarize these and other previously published occurrences of P. perna in the areas of Armação de Pêra, Lagos and Aljezur, discussing morphologic, ecologic and biogeographic aspects of this species in the Portuguese fauna. The brown mussel is also known from archaeological records from Padrão I (Sagres – Vila do Bispo, Ancient Neolithic) and Arrifana (Aljezur, XII century). These chronologies are contemporaneous with the climatic warming intervals of the Atlantic Period (circa 8000-5000 BP) and “Medieval Warm Period” (circa 1000- 1200 AD). During these and other related intervals of warmer coastal surface waters, it is very likely that this subtropical “warm guest” colonized open marine rocky areas of the South and Southwest Portuguese coast, with settlement of stable and permanent populations.&#x0D; Ocorrências do mexilhão castanho anfiatlântico Perna perna (Linné, 1758) (Mollusca, Bivalvia) no sul de Portugal desde o “ótimo climático” Atlântico - O mitilídeo Perna perna (Linné, 1758), espécie comestível de dimensão apreciável e repartição quase cosmopolita, apresenta um historial escasso de ocorrências em Portugal desde o “ótimo climático” Atlântico do Holocénico. É provável, também, que algumas das ocorrências publicadas de Mytilus spp. noutros depósitos holocénicos, incluindo concheiros, possam corresponder a espécimes de Perna. Recolhas recentes na costa sul de Portugal, mencionadas por Lourenço et al. (2012) ampliam as ocorrências conhecidas às localidades de Ilha do Farol e de Vila Moura, em paralelo com citações mais antigas para Armação de Pêra, Lagos e Aljezur. Estas ocorrências são sumariadas no presente estudo, assim como discutidos aspetos de ordem morfológica, ecológica e biogeográfica relativos à presença desta espécie na fauna portuguesa. No registo arqueológico, o mexilhão castanho é conhecido nos arqueossítios de Padrão I (Sagres – Vila do Bispo, Neolítico Antigo) e Arrifana (Aljezur, século XII). Estas cronologias são coevas com os intervalos de melhoria climática do período Atlântico (circa 8000-5000 BP) e de finais da IdadeMédia (circa 1000-1200 DC). Durante estes e outros intervalos comparativos de melhoria das condições hidroclimáticas das águas superficiais costeiras, considera-se bastante provável que este “warm guest” subtropical tenha atingido, por diversas vezes, áreas não restritas do litoral rochoso do sul e sudoeste dePortugal, com o estabelecimento de populações estáveis e permanentes.

Geochemistry and provenance of the Carboniferous Baixo Alentejo Flysch Group, South Portuguese Zone

This work is focused on the turbiditic sediments from the Carboniferous Baixo Alentejo Flysch Group (BAFG) in the South Portuguese Zone, an external zone of the Iberian Variscides. The aim of this work is to constrain the provenance and tectonic setting of these sediments in a context of a complex evolution of SW Iberian Variscides. For this purpose, we performed a systematic study of petrographical and geochemical signatures of greywackes and shales from the three BAFG formations: Mértola, Mira and Brejeira. Major and trace element composition and ratios suggest heterogeneous source area composition for BAFG shales and greywackes. For the oldest Mértola Formation greywackes, source area is dominated by granitoid rocks with minor mafic input. The latter becomes residual in the Mira Formation. The youngest Brejeira Formation greywackes show clear felsic affiliation associated with an increase in recycled components. The shales of all three BAFG formations denote a granodioritic affiliation. Chemical Index of Alteration (CIA) and Plagioclase Index of Alteration (PIA) values suggest moderate weathering in the source areas of Mértola and Mira formations. These indices, together with A–CN–K relations, point out to steady-state weathering conditions in the source areas of both formations. In contrast, both CIA and PIA values for the Brejeira Formation indicate variable conditions of palaeoweathering, from moderate to intense, as a consequence of non-steady-state conditions probably triggered by tectonic instability in the provenance area. Compared to the greywackes, the shales of all three BAFG formations exhibit higher CIA and PIA values, as well as low K2O/Al2O3 (~0.2) and index of compositional variability (<1), reflecting the cumulative effect of multiple cycles of sedimentary recycling and prolonged chemical weathering history. Major and trace element distribution and upper continental crust-normalized multi-element plots suggest that the sediments of BAFG were derived mainly from a continental arc/active margin with minor contribution from old continental crust. Together, our geochemical data are compatible with BAFG sediments derived mainly from SW border of the Ossa Morena Zone (Gondwanan affinity), with possible contribution from an external (Avalonian) source.

Chlorophyll a and chemical signatures during an upwelling event off the South Portuguese coast (SW Iberia)

The present paper describes the chemical characteristics and biological implications during an upwelling event that took place in the beginning of October 2006 off the South Portuguese coast. The study is based on a total of 90 CTD casts regularly distributed in 10 meridional 35km long sections, along with wind and current ADCP velocity measurements. Stations were sampled from the surface to a maximum depth of 900dbar. Five sections covering the entire region, including the main areas of influence of rivers outflow, were selected for characterization of dissolved oxygen, chlorophyll a and nutrients (nitrate, phosphate and silicate). Previous and during the cruise time, northwesterly winds, with an upwelling favourable component, were predominant and upwelling extended far eastward into the Gulf of Cadiz, which is uncommon for this time of the year, in the end of the upwelling season. In the coastal stations, cold low salinity waters with high chlorophyll a (maximum 3.1μgl−1) and low nutrient concentrations were observed, particularly in the retention area close to the western limit of the Gulf of Cadiz. No influence from rivers discharges was observed, since the survey was carried out during a dry period in autumn. Offshore, warmer and saltier waters recirculating from the Gulf of Cadiz, typically oligotrophic (low concentrations of chlorophyll a and nutrients), were observed. Deeper waters along the continental slope, at levels close to 400dbar, reveal the influence of the Mediterranean outflow, characterised by an increase of temperature and salinity along with a decrease of nutrients. The present study reveals that although the inhomogeneities observed along the South Portuguese coast, the water characteristics are in conformity with those of the Gulf of Cadiz and similar to those observed in the NW Iberia and NW Africa, showing a continuity of the upper layers of northern branch of the Canary Upwelling System.

New evidence concerning the thermal history of Devonian and Carboniferous rocks in the South Portuguese Zone

The Late Palaeozoic rocks of southern Portugal have a complex thermal history. Vitrinite reflectance determinations from 90 samples confirm that the organic maturity of Late Palaeozoic rocks in SW Portugal is very high, mainly corresponding to meta-anthracite coal rank. The optic fabric of vitrinite in oriented coal samples from the Brejeira Formation suggests maturation under simple, non-tectonic, burial conditions with peak temperatures being attained prior to Variscan deformation. The lack of any increase in vitrinite reflectance with depth through c . 1 km of section in borehole AC-1 is not consistent with conductive heat transfer and is interpreted as the result of late synorogenic to post-orogenic advective heating. This heating episode generated temperatures sufficiently high to produce levels of maturity corresponding to meta-anthracite coal rank through much of the terrane now exposed, but not high enough to result in overprinting of the pre-deformation optic fabric of vitrinite in the thin coals. The slightly lower maturity of older, platform-facies rocks in the Aljezur–Bordeira area may reflect either deposition on a basement high followed by less burial than adjacent parts of the basin, or the area being the site of a sink for descending relatively cool fluids.

Large, deepwater slope failures: Implications for landslide-generated tsunamis

Research Article| October 01, 2012 Large, deepwater slope failures: Implications for landslide-generated tsunamis Claudio Lo Iacono; Claudio Lo Iacono * 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain2National Oceanography Centre, Southampton SO14 3ZH, UK *E-mails: loiacono@utm.csic.es; cllo@noc.ac.uk. Search for other works by this author on: GSW Google Scholar Eulàlia Gràcia; Eulàlia Gràcia 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Search for other works by this author on: GSW Google Scholar Filippo Zaniboni; Filippo Zaniboni 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Search for other works by this author on: GSW Google Scholar Gianluca Pagnoni; Gianluca Pagnoni 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Search for other works by this author on: GSW Google Scholar Stefano Tinti; Stefano Tinti 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Search for other works by this author on: GSW Google Scholar Rafael Bartolomé; Rafael Bartolomé 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Search for other works by this author on: GSW Google Scholar Douglas G. Masson; Douglas G. Masson 2National Oceanography Centre, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar Russell B. Wynn; Russell B. Wynn 2National Oceanography Centre, Southampton SO14 3ZH, UK Search for other works by this author on: GSW Google Scholar Nuno Lourenço; Nuno Lourenço 4Estrutura de Missão para a Extensão da Plataforma Continental, P-2770047 Paco De Arcos, Portugal Search for other works by this author on: GSW Google Scholar Manuel Pinto de Abreu; Manuel Pinto de Abreu 4Estrutura de Missão para a Extensão da Plataforma Continental, P-2770047 Paco De Arcos, Portugal Search for other works by this author on: GSW Google Scholar Juan José Dañobeitia; Juan José Dañobeitia 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Search for other works by this author on: GSW Google Scholar Nevio Zitellini Nevio Zitellini 5Istituto di Scienze Marine, CNR, 40129 Bologna, Italy Search for other works by this author on: GSW Google Scholar Author and Article Information Claudio Lo Iacono * 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain2National Oceanography Centre, Southampton SO14 3ZH, UK Eulàlia Gràcia 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Filippo Zaniboni 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Gianluca Pagnoni 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Stefano Tinti 3Universitá di Bologna, Departimento di Fisica e Astronomia, 40127 Bologna, Italy Rafael Bartolomé 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Douglas G. Masson 2National Oceanography Centre, Southampton SO14 3ZH, UK Russell B. Wynn 2National Oceanography Centre, Southampton SO14 3ZH, UK Nuno Lourenço 4Estrutura de Missão para a Extensão da Plataforma Continental, P-2770047 Paco De Arcos, Portugal Manuel Pinto de Abreu 4Estrutura de Missão para a Extensão da Plataforma Continental, P-2770047 Paco De Arcos, Portugal Juan José Dañobeitia 1Unidad de Tecnología Marina, CSIC, 08003 Barcelona, Spain Nevio Zitellini 5Istituto di Scienze Marine, CNR, 40129 Bologna, Italy *E-mails: loiacono@utm.csic.es; cllo@noc.ac.uk. Publisher: Geological Society of America Received: 22 Mar 2012 Accepted: 23 Apr 2012 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2012 Geological Society of America Geology (2012) 40 (10): 931–934. https://doi.org/10.1130/G33446.1 Article history Received: 22 Mar 2012 Accepted: 23 Apr 2012 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Claudio Lo Iacono, Eulàlia Gràcia, Filippo Zaniboni, Gianluca Pagnoni, Stefano Tinti, Rafael Bartolomé, Douglas G. Masson, Russell B. Wynn, Nuno Lourenço, Manuel Pinto de Abreu, Juan José Dañobeitia, Nevio Zitellini; Large, deepwater slope failures: Implications for landslide-generated tsunamis. Geology 2012;; 40 (10): 931–934. doi: https://doi.org/10.1130/G33446.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Deepwater landslides are often underestimated as potential tsunami triggers. The North Gorringe avalanche (NGA) is a large (∼80 km3 and 35 km runout) newly discovered and deepwater (2900 m to 5100 m depth) mass failure located at the northern flank of Gorringe Bank on the southwest Iberian margin. Steep slopes and pervasive fracturing are suggested as the main preconditioning factors for the NGA, while an earthquake is the most likely trigger mechanism. Near-field tsunami simulations show that a mass failure similar to the NGA could generate a wave >15 m high that would hit the south Portuguese coasts in ∼30 min. This suggests that deepwater landslides require more attention in geo-hazard assessment models of southern Europe, as well as, at a global scale, in seismically active margins. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Multifractal analysis of geochemical anomalies: A tool for assessing prospectivity at the SE border of the Ossa Morena Zone, Variscan Massif (Spain)

The aim of this paper is to demonstrate discrimination of geochemical anomalies by application of multifractal analysis techniques to a stream sediment geochemical data (774 samples) from a geologically complex area at the boundary between the Ossa Morena (OMZ) and South Portuguese (SPZ) zones of the Iberian Variscan Massif. In this area, which is poorly investigated up to now, small to medium size iron–oxide–copper–gold (IOCG-type) and PbZnCu mineralizations are known to exist. The use of multifractal techniques highlighted weak anomalies not manifested by using conventional methods. The use of the C–A method has been very helpful for establishing thresholds separate anomalies of elements from the regional background, but local anomalies could not be identified as clearly as with the singularity mapping method. The characterization of selected elements (Fe, Cu, Pb, and Zn) is based on the use of multifractal spectrum curves f(α) and indices such as R, Δα and M (multifractality). These have proved to be very useful for characterizing different geochemical behaviors (e.g. depletion or enrichment of elements) as well as spatial distribution and singularity. The singularity (α) maps of the studied elements show areas more accurately compared to conventional geochemical maps, and reveal that local anomalies are not only spatially associated with known occurrences but also are disposed along trends consistent with structures known to be linked to mineralization. Therefore, singularity maps used as spatial evidence for integration with other layers of spatial evidence in mineral prospectivity mapping to provide a useful input for decision-making about further mineral exploration in the study area.

Geochemical Constraints on the Origin of the Ni–Cu Sulfide Ores in the Tejadillas Prospect (Cortegana Igneous Complex, SW Spain)

AbstractAfter the discovery of the Aguablanca ore deposit (the unique Ni–Cu mine operating in SW Europe), a number of mafic‐ultramafic intrusions bearing Ni–Cu magmatic sulfides have been found in the Ossa–Morena Zone of the Iberian Massif (SW Iberian Peninsula). The Tejadillas prospect is one of these intrusions, situated close to the border between the Ossa–Morena Zone and the South Portuguese Zone of the Iberian Massif. This prospect contains an average grade of 0.16 wt % Ni and 0.08 wt % Cu with peaks of 1.2 wt % Ni and 0.2 wt % Cu. It forms part of the Cortegana Igneous Complex, a group of small mafic‐ultramafic igneous bodies located 65 km west of the Aguablanca deposit. In spite of good initial results, exploration work has revealed that sulfide mineralization is much less abundant than in Aguablanca. A comparative study using whole‐rock geochemical data between Aguablanca and Tejadillas shows that the Tejadillas igneous rocks present a lower degree of crustal contamination than those of Aguablanca. The low crustal contamination of the Tejadillas magmas inhibited the assimilation of significant amounts of crustal sulfur to the silicate magmas, resulting in the sparse formation of sulfides. In addition, Tejadillas sulfides are strongly depleted in PGE, with total PGE contents ranging from 14 to 81 ppb, the sum of Pd and Pt, since Os, Ir, Ru and Rh are usually below or close to the detection limit (2 ppb). High Cu/Pd ratios (9700–146,000) and depleted mantle‐normalized PGE patterns suggest that the Tejadillas sulfides formed from PGE‐depleted silicate magmas. Modeling has led us to establish that these sulfides segregated under R‐factors between 1000 and 10,000 from a silicate melt that previously experienced 0.015% of sulfide extraction. All these results highlight the importance of contamination processes with S‐rich crustal rocks and multiple episodes of sulfide segregations in the genesis of high‐tenor Ni–Cu–PGE ore deposits in mafic‐ultramafic intrusions of the region.

Metamorphism and kinematics of the early deformation in the Variscan suture of SW Iberia

AbstractThe early (Devonian) collisional stage in SW Iberia has been investigated through the analysis of deformation in the Cubito‐Moura schists, the main lithology of an Allochthonous Complex putatively rooted in the suture between the Ossa‐Morena and South Portuguese zones. The first deformation in these schists (D1) is recorded as a S1‐L1 mylonitic fabric well preserved in early quartz veins. Subsequent D2 deformation caused the main folds and the main (S2) foliation. After restoration, the stretching lineation (L1) trends at a small angle with the Ossa‐Morena/South Portuguese suture. This trend, together with the top‐to‐the‐east kinematics determined from quartz microfabric is indicative of an oblique left‐lateral collisional scenario in SW Iberia. Chlorite–white K‐mica–quartz ± chloritoid multi‐equilibrium calculations yield P–T conditions in the range 0.9–1.2 GPa and 300–400 °C, during the first collisional stage. P–T conditions during D2 were 0.3–0.8 GPa and 400–450 °C, thus indicating an important stage of exhumation of the Allochthonous Complex during these two collisional events, after subduction of the Ossa‐Morena Zone margin under the South Portuguese Zone continental crust. In the general context of the Variscan orogen, dominated by dextral collision, the left‐lateral convergence in SW Iberia can be explained in terms of the Avalonian salient represented by the South Portuguese Zone, which would impinge between Iberia and Morocco.

The missing Rheic Ocean magmatic arcs: Provenance analysis of Late Paleozoic sedimentary clastic rocks of SW Iberia

Early Carboniferous turbiditic sedimentary rocks in synorogenic basins located on both sides of the Rheic suture in SW Iberia were studied for provenance analysis. An enigmatic feature of this suture, which resulted from closure of the Rheic Ocean with the amalgamation of Pangea in the Late Carboniferous, is that there are no recognizable mid- to Late Devonian subduction-related magmatic rocks, which should have been generated during the process of subduction, on either side of it. U–Pb LA–ICP-MS geochronology of detrital zircons from Early Carboniferous turbidites in the vicinity of the Rheic suture in SW Iberia, where it separates the Ossa–Morena Zone (with Gondwana continental basement) to the north from the South Portuguese Zone (with unknown/Meguma? continental basement) to the south, reveals the abundance of mid- to Late Devonian (51–81%) and Early Carboniferous (13–25%) ages. The Cabrela and Mértola turbidites of the Ossa–Morena and South Portuguese zones, respectively, are largely devoid of older zircons, differing from the age spectra of detrital zircons in the oldest (Late Devonian) strata in the underlying South Portuguese Zone, which contain abundant Cambrian and Neoproterozoic ages. Mid- to Late Devonian zircons in the Cabrela Formation (age cluster at c. 391Ma, Eifelian–Givetian transition) and Mértola Formation (age clusters at c. 369Ma and at c. 387Ma, Famennian and Givetian respectively) are attributable to a source terrane made up of magmatic rocks with a simple geological history lacking both multiple tectonic events and older continental basement. The terrane capable of sourcing sediments dispersed on both sides of the suture is interpreted to have been completely removed by erosion in SW Iberia. Given that closure of the Rheic Ocean required subduction of its oceanic lithosphere and the absence of significant arc magmatism on either side of the Rheic suture, we suggest: 1) the source of the zircons in the SW Iberia basins was a short-lived Rheic ocean magmatic arc, and 2) given the lack of older zircons in the SW Iberia basins, this short-lived arc was probably developed in an intra-oceanic environment.