Buoyancy-driven, rapid exhumation of ultrahigh-pressure metamorphosed continental crust

Preservation of ultrahigh-pressure (UHP) minerals formed at depths of 90–125 km require unusual conditions. Our subduction model involves underflow of a salient (250 ± 150 km wide, 90–125 km long) of continental crust embedded in cold, largely oceanic crust-capped lithosphere; loss of leading portions of the high-density oceanic lithosphere by slab break-off, as increasing volumes of microcontinental material enter the subduction zone; buoyancy-driven return toward midcrustal levels of a thin (2–15 km thick), low-density slice; finally, uplift, backfolding, normal faulting, and exposure of the UHP terrane. Sustained over ≈20 million years, rapid (≈5 mm/year) exhumation of the thin-aspect ratio UHP sialic sheet caught between cooler hanging-wall plate and refrigerating, downgoing lithosphere allows withdrawal of heat along both its upper and lower surfaces. The intracratonal position of most UHP complexes reflects consumption of an intervening ocean basin and introduction of a sialic promontory into the subduction zone. UHP metamorphic terranes consist chiefly of transformed, yet relatively low-density continental crust compared with displaced mantle material—otherwise such complexes could not return to shallow depths. Relatively rare metabasaltic, metagabbroic, and metacherty lithologies retain traces of phases characteristic of UHP conditions because they are massive, virtually impervious to fluids, and nearly anhydrous. In contrast, H2O-rich quartzofeldspathic, gneissose/schistose, more permeable metasedimentary and metagranitic units have backreacted thoroughly, so coesite and other UHP silicates are exceedingly rare. Because of the initial presence of biogenic carbon, and its especially sluggish transformation rate, UHP paragneisses contain the most abundantly preserved crustal diamonds.

Dinoflagellate cysts analyses from sediment cores of the Po River discharge plume over the last two centuries

To obtain insight into the natural and/or human-induced changes in the trophic state of the distal portion of the Po River discharge plume over the last two centuries, high temporal resolution dinoflagellate cyst records were established at three sites. Cyst production rates appear to reflect the natural variability in the river's discharge, whereas cyst associations reflect the trophic state of the upper waters, which in turn can be related to agricultural development. The increased abundances of Lingulodinium machaerophorum and Stelladinium stellatum found as early as 1890 and 1920 correspond to the beginning of the industrial revolution in Italy and the first chemical production and dispersion of ammonia throughout Europe. After 1955, the increased abundances of these species and of Polykrikos schwartzii, Brigantedinium spp. and Pentapharsodinium dalei correspond to agriculturally induced alterations of the hypertrophic conditions. A slight improvement in water quality can be observed from 1987 onward.

Illustrations of northern antiquities, from the earlier Tentonie and Scandinavian romances; being an abstract of the Book of heroes, and Nibelungen lay; with translation of metrical tales, from the Old German, Danish, Swedish, and Icelandie languages; with notes and dissertations.

Abstract of the Eyrbiggiasaga; being the early annals of that district of Iecland lying around the promontory called Snæfells, by W. S. [i.e. Sir Walter Scott] Glossary, by R. Jamieson.

Um olhar sobre o castelo de Noudar: do castelo medieval à ruína: Proposta de valorização do lugar

O Castelo de Noudar está implantado num íngreme promontório da herdade da Coitadinha, a Noroeste de Barrancos, integrando o atual Parque da Natureza de Noudar. Construído a partir de 1303, foi alvo de diversas transformações ao longo do tempo, para responder às exigências militares de cada época, e chega aos nossos dias num avançado estado de decadência física. A investigação desenvolvida assenta, em grande parte, no desenho: de Noudar a uma escala territorial, como elemento que participa numa rede fortificada complexa; da evolução morfológica e funcional, que nos permite ter noção das várias configurações do castelo ao longo dos séculos; num desenho propositivo que desenvolve uma estratégia para valorização do lugar e do seu património material e imaterial. Hoje é fundamental compreender como as valências do Parque e da fortaleza se podem cruzar? Este trabalho pretende refletir sobre possibilidades de valorização para contrariar a degradação em que a fortaleza se encontra; ABSTRACT: The Noudar Castle is located in a steep promontory in the herdade da Coitadinha, Northeast from Barrancos, part of the Natural Park of Noudar. Its construction began in 1303, and underwent several transformations throughout its existence, adapting to the military advancements thru out the ages. Today, it shows an advanced state of decay. The investigation is focused on the design of Noudar on a territorial scale, taking part in a complex network of fortified systems; its functional and morphological evolution, which allows us to comprehend the configurations of the castle throughout the centuries; and on a proposed design that develops a strategy to enhance and bring value to this place and its material and non-material heritage. Today it's crucial to comprehend how can the values of the Park and fortress intertwine. This thesis reflects on the possibilities of valuing this site, counter acting the decay which has fallen upon it.

Arrábida

Dissertação para obtenção do grau de Mestre em Arquitectura, apresentada na Universidade de Lisboa - Faculdade de Arquitectura.

A Review of the Arcuate Structures in the Iberian Variscides; Constraints and Genetical Models

In the Iberian Variscides several first order arcuate structures have been considered. In spite of being highly studied their characterization, formation mechanisms and even existence is still debatable. Themain Ibero-Armorican Arc (IAA) is essentially defined by a predominantNW–SE trend in the Iberian branch and an E–Wtrend in the Brittany one. However, in northern Spain it presents a 180° rotation, sometimes known as the Cantabrian Arc (CA). The relation between both arcs is controversial, being considered either as a single arc due to one tectonic event, or as the result of a polyphasic process. According to the last assumption, there is a later arcuate structure (CA), overlapping a previousmajor one (IAA). Whatever themodels, they must be able to explain the presence of a Variscan sinistral transpression in Iberia and a dextral one in Armorica, and a deformation spanning from the Devonian to the Upper Carboniferous. Another arcuate structure, in continuity with the CA, the Central-Iberian Arc (CIA) was recently proposed mainly based upon on magnetic anomalies, geometry of major folds and Ordovician paleocurrents. The critical review of the structural, stratigraphic and geophysical data supports both the IAA and the CA, but as independent structures. However, the presence of a CIA is highly questionable and could not be supported. The complex strain pattern of the IAA and the CA could be explained by a Devonian — Carboniferous polyphasic indentation of a Gondwana promontory. In thismodel the CA is essentially a thin-skinned arc,while the IAA has a more complex and longer evolution that has led to a thick-skinned first order structure. Nevertheless, both arcs are essentially the result of a lithospheric bending process during the Iberian Variscides.