Multistage crystallization of tonalitic enclaves in granitoid rocks (Hercynian belt,Spain): implications for magma mixing

The crystallization sequence, nucleation density and crystal index (n = nucleation density/mode) of tonalitic enclaves from different granitoids of the Hercynian orogeny indicate that they are pieces of magma partially crystallized in the interior of synplutonic bodies of basic magma, which was injected into a silicic magma chamber. A rapid cooling stage can be identified from the high nucleation density and high n-values of minerals. A final stage of slow cooling, is identified by a low nucleation density and low n-values. At this stage a residual melt crystallized in thermal equilibrium to the cooling rate of the whole magma chamber. Thermal equilibrium and convection are necessary conditions for mixing. Enclaves can be interpreted as the remaining, non-disaggregated portions of an early injected mafic magma, which in turn underwent hybridization during injection. Their presence indicates the existence of magma mixing processes and the possibility that the host granitoid was a hybrid rock.

---

Zusammenfassung Die Kristallisationsabfolge, Keimdichte und der Kristallindex (n = Keimdichte/Modus) von tonalitischen Einschlüssen verschiedener Granitoide des variszischen Orogens zeigen, daß sie Teile eines Magmas sind, das teilweise im Inneren von basischen synplutonischen Magmenkörpern auskristallisierte und in eine silikatische Magmenkammer injiziert wurde. Eine Zeit schnellen Abkühlens kann an Hand der hohen Keimdichte und der niedrigen n-Werte festgestellt werden. Zu diesem Zeitpunkt kristallisierte eine Restschmelze unter thermischen Gleichgewichtsbedingungen und der Abkühlungsgeschwindigkeit der ganzen Magmenkammer aus. Thermisches Gleichgewicht und Konvektion sind für das Mischen notwendig. Einschlüsse können als nichtzerfallene Reste eines früh injizierten mafischen Magmas angesehen werden, welches während der Injizierung eine Hybridisierung erfuhr. Ihre Gegenwart zeigen das Vorhandensein von Magmenmischungsvorgängen und die Möglichkeit, daß der Muttergranitoid ein Hybridgestein war, an.

---

Resumen La secuencia de cristalización, densidad de nucleación e índice cristalino (n = densidad de nucleación/moda) de enclaves tonalíticos de diferentes granitoides hercínicos, indican que dichos enclaves representan fragmentas de magma parcialmente cristalizados en el interior de cuerpos simplutónicos de magma básico, que originalmente fue inyectado en una cámara magmática félsica. Se puede identificar una etapa de enfriamiento rápido a partir de los altos valores de n y alta densidad de nucleación de los minerales. Una etapa final de enfriamiento lento es detectada por una baja densidad de nucleación y bajos valores de n de determinados minerales. Un líquido residual cristalizó en esta etapa lenta en equilibrio térmico y a la misma tasa de enfriamiento que toda la cámara magmática en conjunto. Equilibrio térmico y convección son condiciones necesarias para que se produzca mezcla. Los enclaves pueden ser interpretados como porciones no hibridadas de magma que han sido homogéneamente distribuidos dentro del granitoide encajante. Su presencia indicaría la existencia de procesos de mezcla de magmas y la posibilidad de que el granitoide encajante sea una roca híbrida.

---

, (n = /) , , , . . . . , , . , , , , .

     

Caii H and K spectroscopic observations in active binary systems

We have performed high resolution spectroscopic observations of five active binary systems in the Caii H and K lines at La Palma Observatory. We present the absolute fluxes calculated at the surface of the stars and we discuss the spectral characteristics observed, presence of double emissions and phase variations.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Suspended-sediment response to pulses in river flow and semidiurnal and fortnightly tidal variations in a mesotidal estuary

The effects of the tidal regime and high river flows on the suspended sediment concentration field have been separated and the retention time of fluvial sediment has been determined. The study was carried out in the upper Sado estuary, Portugal, and included surveys at high and low tide in different semidiurnal tide ranges every month for 1 year, including contrasting freshwater discharge. DDT and its metabolites (DDD and DDE) were determined in the suspended sediment and in the whole soft tissues of oysters, and they have been used as tracers of the derived flood material in the upper estuary. The tide is responsible for the relatively slow relaxation time following a winter runoff event.     

Undrained expansion of a cylindrical cavity in clays with fabric anisotropy: theoretical solution

This paper presents a novel, exact, semi-analytical solution for the quasi-static undrained expansion of a cylindrical cavity in soft soils with fabric anisotropy. This is the first theoretical solution of the undrained expansion of a cylindrical cavity under plane strain conditions for soft soils with anisotropic behaviour of plastic nature. The solution is rigorously developed in detail, introducing a new stress invariant to deal with the soil fabric. The semi-analytical solution requires numerical evaluation of a system of six first-order ordinary differential equations. The results agree with finite element analyses and show the influence of anisotropic plastic behaviour. The effective stresses at critical state are constant, and they may be analytically related to the undrained shear strength. The initial vertical cross-anisotropy caused by soil deposition changes towards a radial cross-anisotropy after cavity expansion. The analysis of the stress paths shows that proper modelling of anisotropic plastic behaviour involves modelling not only the initial fabric anisotropy but also its evolution with plastic straining.     

Review: Hydrogeology of Northern Mendoza (Argentina), from the Andes to the eastern plains,in the context of climate change

Hydrogeology Journal - In the drylands of Northern Mendoza, Argentina, water supply depends on rivers and groundwater. Climate change makes this region vulnerable due to the snow-glacial-melt...     

Numerical Analysis of Infiltration in One-Dimensional Unsaturated Soil–Geotextile Column

Geotechnical and Geological Engineering - Numerical modelling development for capillary barrier investigation considering unsaturated soil–geotextile interface has been studied and evaluated...     

Age constraints to the relationships between magmatism, metamorphism and tectonism in the Aracena metamorphic belt, southern Spain

 The Aracena metamorphic belt (AMB), southwest Iberian peninsula, is characterized by the following geological elements: (a) a high-temperature/low-pressure (HT/LP) metamorphic belt a few kilometres wide and more than 200 km long; (b) a linear belt of oceanic amphibolites with a low-pressure inverted metamorphic gradient; (c) crustal-scale ductile shear zones; and (d) mafic, noritic intrusions of high-Mg andesite (boninite) composition. The relationships between these elements led to the proposal of a model of ridge subduction for this sector of the Hercynian belt of Europe. This interpretation is supported by the age relationships displayed between the main rock units considered representative of the main tectonic and petrological processes responsible for the geological elements mentioned previously. The results of a geochronological study (Ar–Ar, Rb–Sr and Sm–Nd) clearly support a Late Paleozoic tectonic evolution at an active continental margin. The time evolution of the metamorphism in the oceanic domain, ranging from 342.6±0.6 Ma in the west to 328.4±1.2 Ma in the east, over a distance of 70 km along the metamorphic belt, support a tectonic model of triple-junction migration responsible for the creation at depth of a slab-free window with decisive consequences for the thermal evolution of the region. The origin of the linear metamorphic belt of HT/LP regime may be explained by the migration along a continental margin of a punctual thermal anomaly induced by the creation of a triple-junction at the continental margin. Received: 9 March 1998 / Accepted: 9 December 1998     

Representivity of incompletely sampled fall deposits in estimating eruption source parameters: a test using the 12–13 January 2011 lava fountain deposit from Mt. Etna volcano,Italy

The Southeast Crater (SEC) of Mt. Etna, Italy, is renowned for its high activity, mainly long-lived eruptions consisting of sequences of individual paroxysmal episodes which have produced more than 150 eruptive events since 1998. Each episode typically forms eruption columns followed by tephra fallout over distances of up to about 100 km from the vent. One of the last sequences consisted of 25 lava fountaining events, which took place between January 2011 and April 2012 from a pit-vent on the eastern flank of the SEC and built a new scoria cone renamed New Southeast Crater. The first episode on 12–13 January 2011 produced tephra fallout which was unusually dispersed toward to the South extending out over the Mediterranean Sea. The southerly deposition of tephra permitted an extensive survey at distances between ~1 and ~100 km, providing an excellent characterization of the tephra deposit. Here, we document the stratigraphy of the 12–13 January fallout deposit, draw its dispersal, and reconstruct its isopleth map. These data are then used to estimate the main eruption source parameters. The total erupted mass (TEM) was calculated by using four different methodologies which give a mean value of 1.5?±?0.4?×?10⁸ kg. The mass eruption rate (MER) is 2.5?±?0.7?×?10⁴ kg/s using eruption duration of 100 min. The total grain-size (TGS) distribution, peaked at ?3 phi, ranges between ?5 and 5 phi and has a median value of ?1.4 phi. Further, for the eruption column height, we obtained respective values of 6.8–13.8 km by using the method of Carey and Sparks (1986) and 3.4?±?0.3 km by using the methods of Wilson and Walker (1987), Mastin et al. (2009), and Pistolesi et al. (2011) and considering the mean value of MER from the deposit. We also evaluated the uncertainty and reliability of TEM and TGS for scenarios where the proximal and distal samples are not obtainable. This is achieved by only using a sector spanning the downwind distances between 6 and 23 km. This scenario is typical for Etna when the tephra plume is dispersed eastward, i.e., in the prevailing wind direction. Our results show that, if the analyzed deposit has poorer sample coverage than presented in this study, the TEM (3.4?×?10⁷ kg) is 22 % than the TEM obtained from the whole deposit. The lack of the proximal (<6 km) deposit may cause more significant differences in the TGS estimations.     

Code‐based record selection methods for seismic performance assessment of buildings

The recent concerns regarding the seismic safety of the existing building stock have highlighted the need for an improvement of current seismic assessment procedures. Alongside with the development of more advanced commercial software tools and computational capacities, nonlinear dynamic analysis is progressively becoming a common and preferable procedure in the seismic assessment of buildings. Besides the complexity associated with the formulation of the mathematical model, major issues arise related with the definition of the seismic action, which can lead to different levels of uncertainty in terms of local and global building response. Aiming to address this issue, a comparative study of different code‐based record selection methods proposed by Eurocode 8, ASCE41‐13 and NZS1170.5:2004 is presented herein. The various methods are employed in the seismic assessment of four steel buildings, designed according to different criteria, and the obtained results are compared and discussed. Special attention is devoted to the influence of the number of real ground motion records selected on the estimation of the mean seismic response and, importantly, to the efficiency that is achieved when an additional selection criteria, based on the control of the spectral mismatch of each individual record with respect to the reference response spectrum, is adopted. The sufficiency of the methods with respect to the pairs of M–R of the selected group of records and the robustness of the scaling procedure are also examined. The paper closes with a study which demonstrates the suitability of a simplified probability‐based approach recently proposed for estimating mean seismic demands. Copyright © 2015 John Wiley & Sons, Ltd.