An investigation into the controls of granite plutonism in the Sierra da Freita region, Northern Portugal

The Serra da Freita region of north central Portugal was chosen for study as it displays the complex relationships between regional structure, plutonism, regional and contact metamorphism typical of this part of Iberia. The region was mapped on a scale of 1:10000. The Serra da Freita pluton, which intrudes the core of the Porto-Viseu metamorphic belt developed in the late Pre-Cambrian - Cambrian Beira Schists, is shown to lie in a sinistral transpressive shear zone, the Serra da Freita shear zone. Early structures are progressively modified over a protracted period by shear zone deformation, during which time metamorphism reached a peak and the granite was emplaced. Mapping of the intrusive contacts of the granite show that following initial intrusion of a steeply inclined sheet of magma into the zone of highest strain, magmas were injected into a region of progressively lower strain where the magma was acconunodated as a nearly flat sheet. The distal end of this mass ballooned upvards to form the small intrusion of Castanheira which has abundant biotite nodules which acted as near perfect strain markers. The main pluton is shown to intrude obliquely the core of a narrow metamorphic belt characterized by parageneses of biotite, andalusite/staurolite, sillimanite, which maps distinctly from a younger cordierite sillimanite contact aureole around an adjacent quartz diorite body. Several facies of granite within the pluton have been recognized; petrographical and structural studies allow the interpreted emplacemen~ mechanism of these units to be integrated within a more general model for the evolution of the shear zone. Geochemical analyses of major and trace elements show that certain compositional trends within these facies cannot be simply related as part of a fractionation sequence. A model is put forward in which repeated melting of a heterogeneous source is followed by sequential emplacement of discrete batches of magma as sheets and wedges wi thin the acti ve shear zone. A Rb-Sr whole rock isochron age of 324 Ma was obtained and this dates not only the emplacement age of the syn-tectonic granite, but also constrains the time of movement along the shear zone. Radiogenic and stable isotope data strongly point to the local high grade Beira Schists as being sui table source rocks for generation of magmas wi th marked S-type characteristics which now form the Serra da Freita pluton. 180 values for the granites of 10.64 ± 0.24 - 13.00 ± 0.12 overlap those of the schists which lie in the range 12.38 ± 0.24 - 14.15 ± 0.4. The whole rock Rb-Sr isochron for the granite has an initial ratio of 0.7136 ± 0.0008 (MSWD = 3.2). A regional and tectonothennal model is put forward in which end-Palaeozoic oblique strike slip collision took place in the Ibero-Armorican Arc. The resulting peturbation in continental heat flow, coupled with the possible effects of shear heating, fluid concentration and local high ductility contrasts in the heterogeneous metasediments, are invoked as being responsible for causing anatexis of the Beira Schists at a depth of 10-12 km, and the generation of granitic melts. Emplacement of these bodies gave rise to the Porto-Viseu metamorphic belt, into which later smaller higher-level melts were injected. It is argued that some of these later magmas which reached higher levels are now exposed as the constituent facies of the Serra da Freita pluton. The Serra cia Freita shear zone, active throughout metamorphism, anatexis and magma emplacement was a dominant feature of the geological history of the region

An insight on the polyphase thermal history of the Internal Rif (Northern Morocco) through Raman micro-spectroscopy investigation

We are greatly indebted with M.N. Zaghloul for fruitful discussions and for introduce us to Rif geology. We kindly acknowledge the Editor in chief Federico Rossetti, the associated editor Giulio Viola and two anonymous reviewers for their constructive criticisms that improved the original version of this paper.Peer reviewedPostprin

Illite crystallinity patterns in the Anti-Atlas of Morocco

The low-grade metamorphism of the sedimentary cover of the Moroccan Anti-Atlas is investigated using Illite crystallinity (IC) method. More than 200 samples from three key areas (southwestern, central and eastern Anti-Atlas) have been taken from a maximum of different stratigraphic levels and have been analysed. The metamorphism is of low to very low degree throughout the southern flank of the Anti-Atlas. It increases from northeast to southwest. Whereas in the eastern Anti-Atlas diagenetic and anchizonal IC-values are predominant, in the western and central Anti-Atlas also epizonal IC-values are found. In every respective area the IC improves with stratigraphic age. At the scale of the entire Palaeozoic Anti-Atlas basin the IC correlates best with estimated paleo-overburden. However, burial metamorphism cannot be the cause even though considering missing sedimentary pile of Late Carboniferous age. The ‘abnormal' paleo-geothermal gradient of 43-35 °C/km we evidenced for the Carboniferous is a true one, and has to be related to a basement sequence enriched in heat producing elements such as series of the West African Crato

Exceptional Concentrations of Gold Nanoparticles in 1,7 Ga Fluid Inclusions From the Kola Superdeep Borehole, Northwest Russia

In the drill core of the Kola super-deep borehole (SG-3, 12,262 m depth) gold-bearing rocks of Archaean age have been located at depths of 9,500 to 11,000 m. In veins, between 9,052 and 10,744 m, within this gold zone, quartz contains fluid inclusions with gold nanoparticles. There are 4 types of fluid inclusions (1) gas inclusions of dense CO2, (2) liquid-vapor two-phase aqueous inclusions, (3) three-phase inclusions with NaCl daughter crystals, and (4) CO2-aqueous inclusions. In all inclusion types, there are extremely high concentrations of gold. The highest gold concentrations were found in the type 3 and 4 fluid inclusions with an average concentration of c. 750 ppm and may be as high as 6,000 ppm. The presence of gold as nanoparticles in the solutions of these fluid inclusions was determined by optical and spectroscopic methods. We suggest that these fluids could be a precursor of “orogenic gold fluids” which, at the gold concentrations determined, would reduce the requirements for large volumes of metamorphic fluids to form orogenic ore deposits. Further, as nanoparticles, gold could be transported in larger amounts than in true solution

Groundwater and Geological assessment in Eritrea: A Cooperation project in Ademzemat village (Asmara district).

Il seguente lavoro si inserisce nell’ambito di un progetto di cooperazione, la cui finalità è quella di fornire una risorsa d’acqua pulita per il villaggio di Admzemat, situato nell’altipiano Eritreo. Lo studio condotto vuole definire l’assetto geologico ed idrogeologico dell’area dove si trova il villaggio, in modo da fornire uno studio preliminare su cui basare i successivi sviluppi del progetto. A tale scopo, è stato necessario affrontare un inquadramento generale dell’altopiano Eritreo, seguito da un’analisi da remoto di immagini satellitari e da uno studio di campagna. Alla luce di quanto acquisito è stata presa visione dei dati prodotti durante un’indagine geofisica dell’Aprile 2010. In particolare si è cercato di analizzare la potenzialità del sito che, durante la geofisica del 2010, è stato indicato come punto di trivellazione per un nuovo pozzo

Softening the Lower Crust: Modes of Syn-Transport Transposition Around and Adjacent to a Deep Crustal Granulite Nappe, Parry Sound Domain, Grenville Province, Ontario, Canada

The Parry Sound domain is a granulite nappe-stack transported cratonward during reactivation of the ductile lower and middle crust in the late convergence of the Mesoproterozoic Grenville orogeny. Field observations suggest the following with respect to the ductile sheath: (1) Formation of a carapace of transposed amphibolite facies gneiss derived from and enveloping the western extremity of the Parry Sound domain and separating it from high-strain gneiss of adjacent allochthons. This ductile sheath formed dynamically around the moving granulite nappe through the development of systems of progressively linked shear zones. (2) Transposition initiated by hydration (amphibolization) of granulite facies gneiss by introduction of fluid along cracks accompanying pegmatite emplacement. Shear zones nucleated along pegmatite margins and subsequently linked and rotated. The source of the pegmatites was most likely subjacent migmatitic and pegmatite-rich units or units over which Parry Sound domain was transported. Comparison of gneisses of the ductile sheath with high-strain layered gneiss of adjacent allochthons show the mode of transposition of penetratively layered gneiss depended on whether or not the gneiss protoliths were amphibolite or granulite facies tectonites before initiation of transposition, resulting in, e.g., folding before shearing, no folding before shearing, respectively. Meter-scale truncation along high-strain gradients at the margins of both types of transposition-related shear zones observed within and marginal to Parry Sound domain mimic features at kilometer scales, implying that apparent truncation by transposition originating in a manner similar to the ductile sheath may be a common feature of deep crustal ductile reworking. Citation: Culshaw, N., C. Gerbi, and J. Marsh (2010), Softening the lower crust: Modes of syn-transport transposition around and adjacent to a deep crustal granulite nappe, Parry Sound domain, Grenville Province, Ontario, Canada, Tectonics, 29, TC5013, doi:10.1029/2009TC002537

Malignant melanoma of the urethra: a rare histologic subdivision of vulvar cancer with a poor prognosis

Malignant melanoma of the urethra is a rare tumour that is difficult to diagnose and treat, resulting in a poor prognosis. In this paper, we present the case of a 65-year-old woman who was referred to a gynaecologist because of a urethral mass that mimicked a caruncle. The tumour was removed by local excision, and a pathological analysis revealed a malignant melanoma. Distal urethrectomy was performed after three months with no evidence of residual tumour. There was no evidence of disease at a six-year followup. In this paper, we compare the epidemiology, treatment, staging, and prognosis of vulvar cancer in general to malignant melanoma of the vulva in particular