Formación de megacristales de feldespato potásico en el sector sur del batolito Cerro Aspero-Alpa Corral (32°40'S y 64°50'W), Sierras Pampeanas, Córdoba, Argentina

The surrounding rocks of studied area are composed by a metamorphic sequence which includes gneisses, schists, amphibolites, marbles and heterogeneous migmatites in non-conformity intruded by a granitic pluton. All this sequence is dated as having late-Precambric to mid-Paleozoic age.Three facies, mostly of monzogranitic composition, were identified. This study focuses on the porphiric facies; detailed petroestructural studies being performed, the orientation of large microcline crystal and associated microgranular enclaves being measured.Different primary flow directions were determined with track variation of microcline megacrystal and enclaves from subvertical to nearly horizontal positions.These changes have been interpreted as a convective system within the pluton.The presence of a marked planar fabric in microcline megacrystals along with phenomena such a size-variation of crystal, synneusis, crystal trending at the enclave's border and crystal accumulation, proves their early magmatic origin. The enclaves show a cinematic of deformation produced by simple shear.El entorno encajante de la zona estudiada está integrado por una secuencia metamórfica que incluye gneises, esquistos, anfibolitas, calizas cristalinas y migmatitas heterogéneas, intruidas discordantemente por el plutón granítico. A este conjunto puede asignársele una edad precámbrica superior-paleozoica media.Se identificaron tres facies, en su mayoría de composición monzogranítica, diques micrograníticos a aplíticos y enclaves. En este trabajo se pone énfasis en la facies porfiroide efectuándose estudios petroestructurales de detalle, tomando como indicadores la orientación de los grandes cristales de microclina y enclaves microgranulares asociados.Se determinaron distintas direcciones de flujo primario con variaciones en la trayectoria de los megacristales de microclina y enclaves desde posiciones subverticales hasta aproximadamente horizontales. Estos cambios han sido interpretados como un sistema convectivo dentro del plutón.La presencia de una marcada fábrica planar en los megacristales de microclina, conjuntamente con fenómenos de gradaciones en el tamaño de cristales, sineusis, alineaciones en los bordes de enclaves y aglomeraciones de cristales evidencian su origen temprano magmático. Los enclaves muestran una cinemática de deformación producida por cizalla simple

Differentiation Between Women With Vulvovaginal Symptoms Who are Positive or Negative for Candida Species by Culture

Objective: To investigate whether clinical criteria could differentiate between women with vulvovaginitis who were culture positive or negative for vaginal Candida species. Methods: Vulvovaginal specimens were obtained from 501 women with a vaginal discharge and/or pruritis. Clinical information and wet mount microscopy findings were obtained. All specimens were sent to a central laboratory for species identification. Results: A positive culture for Candida species was obtained from 364 (72.7%) of the specimens. C. albicans was identified in 86.4% of the positive cultures, followed by C. glabrata in 4.5%, C. parapsilosis in 3.9%, C. tropicalis in 2.7% and other Candida species in 1.4%.Women with a positive Candida culture had an increased utilization of oral contraceptives (26.1% vs. 16.8%, p = 0.02) and antibiotics (8.2% vs. 0.7%, p = 0.001), and were more likely to be pregnant (9.1% vs. 3.6%, p = 0.04) than the culture-negative women. Dyspareunia was more frequent in women without Candida (38.0% vs. 28.3%, p = 0.03) while vaginal erythema (p = 0.01) was more common in women with a positive Candida culture. Conclusions: Although quantitative differences were observed, the presence of vaginal Candida vulvovaginitis cannot be definitively identified by clinical criteria

Stops making sense: translational trade-offs and stop codon reassignment

Background Efficient gene expression involves a trade-off between (i) premature termination of protein synthesis; and (ii) readthrough, where the ribosome fails to dissociate at the terminal stop. Sense codons that are similar in sequence to stop codons are more susceptible to nonsense mutation, and are also likely to be more susceptible to transcriptional or translational errors causing premature termination. We therefore expect this trade-off to be influenced by the number of stop codons in the genetic code. Although genetic codes are highly constrained, stop codon number appears to be their most volatile feature. Results In the human genome, codons readily mutable to stops are underrepresented in coding sequences. We construct a simple mathematical model based on the relative likelihoods of premature termination and readthrough. When readthrough occurs, the resultant protein has a tail of amino acid residues incorrectly added to the C-terminus. Our results depend strongly on the number of stop codons in the genetic code. When the code has more stop codons, premature termination is relatively more likely, particularly for longer genes. When the code has fewer stop codons, the length of the tail added by readthrough will, on average, be longer, and thus more deleterious. Comparative analysis of taxa with a range of stop codon numbers suggests that genomes whose code includes more stop codons have shorter coding sequences. Conclusions We suggest that the differing trade-offs presented by alternative genetic codes may result in differences in genome structure. More speculatively, multiple stop codons may mitigate readthrough, counteracting the disadvantage of a higher rate of nonsense mutation. This could help explain the puzzling overrepresentation of stop codons in the canonical genetic code and most variants

The Palaeocene Cerro Munro tonalite intrusion (Chubut Province, Argentina): A plutonic remnant of explosive volcanism?

The Cerro Munro sub-volcanic intrusion is emplaced in the back-arc (400 km from the trench) as small sub-circular tonalite-granodiorite plutons with abundant radial porphyritic dikes. U-Pb zircon SHRIMP data give an age of crystallization of 57 Ma ± 1.4 Ma. It is located to the east of the North Patagonian Batholith (NPB) that shows a protracted and episodic magmatic history from Cretaceous to Miocene time. The NPB Palaeogene episode is characterized by the lack of magmatic activity at the arc axis, as small plutonic emplacements move to the fore-arc and back-arc. This Palaeogene tectono-magmatic episode is ruled by the detachment of the Aluk plate during the Aluk-Farallon-SAM triple junction, active at that time along northern Patagonia active margin, changing the Cretaceous ?NPB orogenic? setting to a Palaeogene ?Munro transitional? tectono-magmatic setting. Near the contacts, the tonalite contains abundant enclaves of igneous appearance and variable size from several cm to dm, described as autoliths. The study of autoliths and host tonalite reveals interesting results on the processes of fractionation in a thermally zoned magma chamber. Autoliths, and in a large extent the host tonalite, represent disguised cumulates from which a hydrous silicic liquid was extracted. Barometry calculations from mineral chemistry in both autoliths and tonalites record a shallow pressure of emplacement of 0.5 kbar. Rhyolite-dacite flows and ignimbrites, surrounding the northern contact of the Cerro Munro tonalite, may represent the exsolved liquid from the plutonic cumulates. The study by cathodoluminiscence and electron backscattered diffraction techniques from a rhyolite-hosted quartz supports this protracted history of the Cerro Munro magma chamber.Facultad de Ciencias Naturales y MuseoCentro de Investigaciones GeológicasConsejo Nacional de Investigaciones Científicas y Técnica

The Palaeocene Cerro Munro tonalite intrusion (Chubut Province, Argentina): A plutonic remnant of explosive volcanism?

The Cerro Munro sub-volcanic intrusion is emplaced in the back-arc (400 km from the trench) as small sub-circular tonalite-granodiorite plutons with abundant radial porphyritic dikes. U-Pb zircon SHRIMP data give an age of crystallization of 57 Ma ± 1.4 Ma. It is located to the east of the North Patagonian Batholith (NPB) that shows a protracted and episodic magmatic history from Cretaceous to Miocene time. The NPB Palaeogene episode is characterized by the lack of magmatic activity at the arc axis, as small plutonic emplacements move to the fore-arc and back-arc. This Palaeogene tectono-magmatic episode is ruled by the detachment of the Aluk plate during the Aluk-Farallon-SAM triple junction, active at that time along northern Patagonia active margin, changing the Cretaceous ?NPB orogenic? setting to a Palaeogene ?Munro transitional? tectono-magmatic setting. Near the contacts, the tonalite contains abundant enclaves of igneous appearance and variable size from several cm to dm, described as autoliths. The study of autoliths and host tonalite reveals interesting results on the processes of fractionation in a thermally zoned magma chamber. Autoliths, and in a large extent the host tonalite, represent disguised cumulates from which a hydrous silicic liquid was extracted. Barometry calculations from mineral chemistry in both autoliths and tonalites record a shallow pressure of emplacement of 0.5 kbar. Rhyolite-dacite flows and ignimbrites, surrounding the northern contact of the Cerro Munro tonalite, may represent the exsolved liquid from the plutonic cumulates. The study by cathodoluminiscence and electron backscattered diffraction techniques from a rhyolite-hosted quartz supports this protracted history of the Cerro Munro magma chamber.Facultad de Ciencias Naturales y MuseoCentro de Investigaciones GeológicasConsejo Nacional de Investigaciones Científicas y Técnica

Geochemical and metallogenetical study of the pegmatites and associated granites from southern Comechingones pegmatitic field, Córdoba

El distrito pegmatítico Comechingones, ubicado en el faldeo oriental de la sierra homónima, en la provincia de Córdoba, involucra pegmatitas graníticas correspondientes a la clase de Elementos Raros, tipo berilo, subtipo berilo-columbita-fosfatos, algunas en transición a la clase muscovítica, con mineralizaciones de Be-Nb- Ta-U y minerales industriales. Dos tipos de pegmatitas graníticas han sido descriptas en el sector sur del distrito: pegmatitas tipo I, con tamaños que en total pueden alcanzan los 1000 metros de longitud y superar los 50 de ancho, internamente zonadas y portadoras de Be, Nb-Ta y U; y pegmatitas tipo II, de menores dimensiones, no zonadas, ricas en cuarzo de alta pureza, carentes de mineralizaciones metalíferas, y asociadas espacial y genéticamente con leucogranitos aplíticos. En este trabajo se presentan y discuten los datos geoquímicos preliminares de ambos tipos de pegmatitas y granitos asociados. Los datos geoquímicos obtenidos, apoyados con descripciones de campo y petrográficas, permiten establecer que las dos tipologías de pegmatitas corresponden a dos eventos magmáticos diferentes (muy probablemente diacrónicos). El primero generó las pegmatitas tipo I, las cuales de sur a norte presentan un aumento en el grado de fraccionamiento desde pegmatitas poco evolucionadas y sin mineralizaciones de elementos raros, hasta pegmatitas evolucionadas con depósitos metalíferos de interés económico. El segundo evento dio origen a las pegmatitas tipo II y a los granitos aplíticos, y carece de especialización metalogenética, evidenciado por los indicadores de diferenciación magmática sistemáticamente inferiores a los de las pegmatitas tipo I y a la carencia de mineralizaciones metalíferas.The Comechingones pegmatitic field (CPF) is located in the eastern flank of the Sierra de Comechingones, Córdoba province. It is composed of granite pegmatites belonging to the Rare-Element class, beryl type, beryl-columbite-phosphate subtype; some of them are transitional into the Muscovite class. Beryllium, Nb, Ta and U deposits, as well as high-quality industrial mineral deposits, are frequently associated with these pegmatites. In the southern part of the CPF two different pegmatite types have been described. Type I pegmatites constitute large zoned bodies with up to 1000 m long and 50 m thick, and may constitute rare element deposits, whereas type II pegmatites occur as small, unzoned quartz-rich dykes, without metalliferous mineralizations, spatial and genetically associated with aplitic leucogranites. Preliminary geochemical data from both pegmatites types and granites are presented and discussed in this contribution. Geochemical evidences, supported by field and petrographic observations, suggest that the two types of pegmatites identified in the study area represent two different, probably diachronic, magmatic stages. Type I pegmatites display a geochemical gradation in a S-N direction, from barren pegmatites in the south to fractionated pegmatites in the northern part of the study area, and are the lithological product of the first magmatic stage. The second stage lead to the crystallization of aplitic granites and barren type II pegmatites, geochemically less fractionated than type II pegmatites.Centro de Investigaciones Geológica