The magmatic evolution of Graciosa and Corvo oceanic islands, Azores Archipielago

El archipiélago de las Azores se encuentra localizado en el Océano Atlántico, entre las latitudes 37º y 40º N y las longitudes 25º y 31º O. Está constituido por nueve islas y varios montículos submarinos construidos sobre la plataforma de las Azores. Dos de estas islas han sido objeto de estudio en la presente Tesis Doctoral: Graciosa, al este de la dorsal centro-atlántica, y Corvo, al oeste de la misma. Dado que los estudios previos sobre estas islas son escasos y se han limitado a la descripción geológica y petrológica de las diferentes unidades volcánicas, la presente investigación aborda un completo estudio de la petrología, la mineralogía y la geoquímica de las distintas unidades volcánicas, así como de los procesos magmáticos ocurridos. En la Isla de Graciosa se han estudiado diferentes coladas de lava y xenolitos de gabros (alcalinos y subalcalinos), de sienitas y de dunitas, pertenecientes a los complejos volcánicos de Serra das Fontes, Serra Branca y Vitória - Vulcão Central. Se ha demostrado que las coladas de lava de los tres complejos volcánicos, junto con los gabros de composición alcalina (cumulados) y las sienitas (frozen liquids), están relacionados mediante un proceso de cristalización fraccionada polibárica, que comenzó en una cámara magmática situada a unos 15 km de profundidad. Además, la alternancia temporal de rocas de composición básica y ácida se explica a través de la existencia de varias recargas magmáticas del sistema. Por el contrario, los gabros de composición subalcalina, que son descritos por primera vez en el archipiélago de las Azores, se interpretan como cumulados relacionados con un proceso de fraccionación de fundidos altamente refractarios en niveles más someros (~ 3 km). En la Isla Corvo, se han muestreado también todas las unidades volcanoestratigráficas (Pre-, Sin- y Post-caldera), que incluyen coladas de lava, diques y xenolitos de gabro. Tanto algunas de las coladas, como algunos de los diques, presentan antecristales no cogenéticos que fueron incorporados al fundido previamente a la erupción. Se ha puesto de manifiesto, por primera vez en Azores, que la composición geoquímica de roca total está altamente influenciada por la acumulación de estos antecristales, lo que produce un enmascaramiento de los procesos magmáticos de diferenciación que han dado lugar a la formación de estas rocas. Por ello, para identificar los procesos que han dado lugar a la formación de la isla tan solo se han considerado rocas sin antecristales. De este modo, las coladas de lava y los diques sin antecristales, junto con los xenolitos de gabro (cumulados) están relacionados mediante un proceso de cristalización polibárica, que comenzó en una cámara magmática situada a unos 15 km de profundidad y en la que tuvieron lugar procesos de recarga constantes con fundidos más profundos y de gran carga cristalina. Por lo tanto, se propone que la Isla de Corvo ha sido formada a partir de un complejo sistema magmático en el que los diferentes fundidos y su carga de antecristales provienen de diferentes profundidades y han estado en constante interacción a los largo de toda la evolución de la isla. La Isla de Graciosa ha sido estudiada desde un punto de vista isotópico, para adecuar el conocimiento de la isla con las demás islas del Rift de Terceira. La edades 40Ar/39Ar han permitido establecer la evolución temporal de la isla a lo largo del Pleistoceno y el Holoceno, desde los 1056 ± 28.0 ka hasta los 3.9 ± 1.4 ka, en contraste con las edades previas obtenidas por K-Ar y 14C (620 ka a 2 ka). Las composiciones isotópicas de Sr-Nd-Pb han permitido la caracterización de la fuente del manto de los fundidos, señalando una mezcla entre un componente empobrecido de tipo MORB y un componente enriquecido de tipo HIMU. Estos datos son similares a la composición de manto recientemente redefinida como FOZO, la cual parece estar presente en la signatura isotópica de la mayor parte de islas oceánicas

The Systematics of Olivine CaO + Cr-Spinel in High-Mg# Arc Volcanic Rocks: Evidence for in-Situ Mantle Wedge Depletion at the Arc Volcanic Front

We investigated the state of the arc background mantle (i.e. mantle wedge without slab component) by means of olivine CaO and its Cr-spinel inclusions in a series of high-Mg# volcanic rocks from the Quaternary Trans-Mexican Volcanic Belt. Olivine CaO was paired with the Cr# [molar Cr/(Cr + Al) *100] of Cr-spinel inclusions, and 337 olivine+Cr-spinel pairs were obtained from 33 calc-alkaline, high-K and OIB-type arc front volcanic rocks, and three monogenetic rear-arc basalts that lack subduction signatures. Olivine+Cr-spinels display coherent elemental and He–O isotopic systematics that contrast with the compositional diversity of the bulk rocks. All arc front olivines have low CaO (0.135 ± 0.029 wt %) relative to rear-arc olivines which have the higher CaO (0.248 ± 0.028 wt %) of olivines from mid-ocean ridge basalts. Olivine 3He/4He–δ18O isotope systematics confirm that the olivine+Cr-spinels are not, or negligibly, affected by crustal basement contamination, and thus preserve compositional characteristics of primary arc magmas. Variations in melt H2O contents in the arc front series and the decoupling of olivine CaO and Ni are inconsistent with controls on the olivine CaO by melt water and/or secondary mantle pyroxenites. Instead, we propose that low olivine CaO reflects the typical low melt CaO of high-Mg# arc magmas erupting through thick crust. We interpret the inverse correlation of olivine CaO and Cr-spinel Cr# over a broad range of Cr# (~10–70) as co-variations of CaO, Al and Cr of their (near) primary host melts, which derived from a mantle that has been variably depleted by slab-flux driven serial melt extraction. Our results obviate the need for advecting depleted residual mantle from rear- and back-arc region, but do not upset the larger underlying global variations of melt CaO high-Mg# arc magmas worldwide, despite leading to considerable regional variations of melt CaO at the arc front of the Trans-Mexican Volcanic Belt

Family violence, war, and natural disasters: A study of the effect of extreme stress on children's mental health in Sri Lanka

Catani C, Jacob N, Schauer E, Kohila M, Neuner F. Family violence, war, and natural disasters: a study of the effect of extreme stress on children's mental health in Sri Lanka. BMC Psychiatry. 2008;8(1): 33.BACKGROUND: The consequences of war violence and natural disasters on the mental health of children as well as on family dynamics remain poorly understood. Aim of the present investigation was to establish the prevalence and predictors of traumatic stress related to war, family violence and the recent Tsunami experience in children living in a region affected by a long-lasting violent conflict. In addition, the study looked at whether higher levels of war violence would be related to higher levels of violence within the family and whether this would result in higher rates of psychological problems in the affected children. METHODS: 296 Tamil school children in Sri Lanka's North-Eastern provinces were randomly selected for the survey. Diagnostic interviews were carried out by extensively trained local Master level counselors. PTSD symptoms were established by means of a validated Tamil version of the UCLA PTSD Index. Additionally, participants completed a detailed checklist of event types related to organized and family violence. RESULTS: 82.4% of the children had experienced at least one war-related event. 95.6% reported at least one aversive experience out of the family violence spectrum. The consequences are reflected in a 30.4% PTSD and a 19.6% Major Depression prevalence. Linear regression analyses showed that fathers' alcohol intake and previous exposure to war were significantly linked to the amount of maltreatment reported by the child. A clear dose-effect relationship between exposure to various stressful experiences and PTSD was found in the examined children. CONCLUSION: Data argue for a relationship between war violence and violent behavior inflicted on children in their families. Both of these factors, together with the experience of the recent Tsunami, resulted as significant predictors of PTSD in children, thus highlighting the detrimental effect that the experience of cumulative stress can have on children's mental health

Plasmodium falciparum Nucleosomes Exhibit Reduced Stability and Lost Sequence Dependent Nucleosome Positioning

The packaging and organization of genomic DNA into chromatin represents an additional regulatory layer of gene expression, with specific nucleosome positions that restrict the accessibility of regulatory DNA elements. The mechanisms that position nucleosomes in vivo are thought to depend on the biophysical properties of the histones, sequence patterns, like phased di-nucleotide repeats and the architecture of the histone octamer that folds DNA in 1.65 tight turns. Comparative studies of human and P. falciparum histones reveal that the latter have a strongly reduced ability to recognize internal sequence dependent nucleosome positioning signals. In contrast, the nucleosomes are positioned by AT-repeat sequences flanking nucleosomes in vivo and in vitro. Further, the strong sequence variations in the plasmodium histones, compared to other mammalian histones, do not present adaptations to its AT-rich genome. Human and parasite histones bind with higher affinity to GC-rich DNA and with lower affinity to AT-rich DNA. However, the plasmodium nucleosomes are overall less stable, with increased temperature induced mobility, decreased salt stability of the histones H2A and H2B and considerable reduced binding affinity to GC-rich DNA, as compared with the human nucleosomes. In addition, we show that plasmodium histone octamers form the shortest known nucleosome repeat length (155bp) in vitro and in vivo. Our data suggest that the biochemical properties of the parasite histones are distinct from the typical characteristics of other eukaryotic histones and these properties reflect the increased accessibility of the P. falciparum genome

Sources of atmospheric pollution in the rust belt, Ohio, USA

Industrial regions in the rust belt are sites of significant legacy atmospheric pollution, and despite recent regulations, continue to be sites of ongoing atmospheric emissions of toxic metals. Source attribution in such areas is complicated by the presence of multiple potential point sources, including steel production plants and coal fired power plants. This study focuses on a region in Ohio, USA, in the vicinity of a steel manufacturing plant and coke production facility. Scanning electron microscopy of atmospheric particulate matter, combined with major and trace element and Pb and Os isotopic analysis of dust, lichen and tree bark, have been employed to identify the primary contributors to the atmospheric metal load. Our results suggest that steel production, coal burning, and traffic emissions are all significant sources of metals to the local environment

Crystals reveal magma convection and melt transport in dyke-fed eruptions

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Crystals reveal magma convection and melt transport in dyke‑fed eruptions

The processes and ranges of intensive variables that control magma transport and dyke propagation through the crust are poorly understood. Here we show that textural and compositional data of olivine crystals (Mg/Fe, Ni and P) from the tephra of the first months of Paricutin volcano monogenetic eruption (Mexico, 1943-1952) record fast growth and large temperature and oxygen fugacity gradients. We interpret that these gradients are due to convective magma transport in a propagating dyke to the Earth's surface in less than a few days. The shortest time we have obtained is 0.1 day, and more than 50% of the calculated timescales are<2 days for the earliest erupted tephra, which implies magma ascent rates of about 0.1 and 1 m s(-1). The olivine zoning patterns change with the eruptive stratigraphy, and record a transition towards a more steady magma flow before the transition from explosive to effusive dynamics. Our results can inform numerical and experimental analogue models of dyke propagation, and thus facilitate a better understanding of the seismicity and other precursors of dyke-fed eruptions.National Research Foundation Investigatorship Award from Singapore NRF-NRFI2017-06 National Science Foundation (NSF) EAR 1019798 Dirección General de Asuntos del Personal Académico through project UNAM-DGAPA IN-10361

Magmatic processes and the role of antecrysts in the genesis of Corvo island (Azores Archipelago, Portugal)

Corvo island is one of two Azorean islands located to the west of the Mid-Atlantic Ridge. Its small size and the existence of a single main eruptive center make it an ideal island for an in-depth study of the magmatic processes controlling its evolution.This study presents detailed petrographic and geochemical data for representative samples of the complete volcanostratigraphic sequence (Pre-, Synand Post-caldera stages), including lava flows, dikes and cumulate gabbroic xenoliths hosted in a Pre-caldera lava flow. Some lava flows and dikes contain large crystals that are not in equilibrium with the host magma. These crystals are antecrysts crystallized from progenitor magmas that have been reincorporated into the host lava before eruption.We note for the first time that the accumulation of antecrysts in Azorean magmas strongly affects the bulk composition of the rocks. Antecryst contents as high as 50-60% can result in whole-rocks with MgO contents of 15 wt %. This accumulation process obscures the magmatic processes responsible for the differentiation of the volcanic products. Accordingly, only antecryst-free samples are considered to identify the magmatic processes involved in the generation of the island. The least evolved antecryst-free rock was used as the closest composition to the primary magma for modeling of major element (MELTS) and trace element variations; our results establish a petrogenetic relationship between Corvo antecryst-free lava flows, dikes and cumulate xenoliths, all of which are products of polybaric fractional crystallization. Pre- and Post-caldera products are related to an ~ 15 km deep magma chamber, whereas the Syn-caldera evolved products are related to a shallower magma chamber. These results suggest that Corvo island developed from a complex magmatic plumbing system in which magmas and their crystal cargo, derived from variable depths, have interacted and been tapped throughout the evolution of the island

Magmatic evolution of Graciosa (Azores, Portugal)

Graciosa is the westernmost island of theTerceira Rift, located to the east of the Mid-Atlantic Ridge, in the Azores archipelago. The three volcanic complexes recognized in the island have been characterized, including the study of lava flows, gabbroic xenoliths (alkaline and subalkaline), syenites and dunites. A detailed study of mineral compositions and whole-rock major and trace element concentrations has allowed the characterization of volcanic units and the investigation of the magmatic and temporal evolution of the island. Lava flows from the three volcanic complexes, alkaline gabbros (cumulate origin) and syenites (bulk trachyte liquid origin) can be related by polybaric fractional crystallization starting at ~15 km depth; to explain the alternation of mafic and evolved products with time, magma chamber replenishment by primitive melts is needed. In contrast, the origin of the subalkaline gabbros, found for the first time in the Azores, appears to be related to fractionation of highly refractory melts at shallower levels (~3 km).The lack of significant crustal assimilation in most Graciosa samples suggests that the range in Sr-Nd-Pb isotope compositions probably reflects those of a predominantly FOZO-like mantle source. Enriched (EMI- and EMII-type) mantle source components, similar to those of São Miguel and Faial, have also been recognized for the first time in Graciosa