Laura Marinoni

Injection and arrest of dykes : implications for volcanic hazards

Dykes are the principal channels through which magma reaches the surface in volcanic eruptions. For this reason dykes observed in the field are commonly assumed to be feeders to lava flows. The actual proportion of dykes reaching the surface is, however, poorly known. In order to develop models for the purpose of estimating volcanic hazard, this proportion must be known. This follows because such models should not only consider the probability of dykes being injected from magma chambers during periods of unrest in the associated volcanoes, but also the probability of the injected dykes being arrested. This paper presents field data on several thousand dykes from Iceland and Tenerife (Canary Islands) indicating that many, and probably most, dykes become arrested at various crustal levels and never reach the surface to feed eruptions. Using the results of analytical and numerical models, it is shown that, for common loading conditions, the stress field in the vicinity of a magma chamber may favour the injection and propagation of dykes while the stress field at a certain distance from the chamber favours dyke arrest. This means that many dykes that are injected from the chamber propagate only for a very limited distance from the chamber to the point where they become arrested. The implication is that during periods of unrest in volcanoes, the probability of volcanic eruption is only a small fraction of the probability of dyke injection from the source magma chamber.

Tectonic evolution of the emergent part of a volcanic ocean island: Lanzarote, Canary Islands

Abstract A reconstruction of the structural evolution of Lanzarote confirms the existence of two principal stages of construction of the island, separated by a main erosional event. The first (pre-erosional) is the shield stage, Miocene-Pliocene in age, which is divided in three stratigraphic groups, where different formations can be distinguished using unconformities mappable over the whole area of outcrop. In the second (post-erosional) stage, developed during the Quaternary, nine stratigraphic levels are tentatively identified and are grouped in two phases of volcanic activity (Shields phase and Pyroclastic cones phase). Data from 580 photogeologic lineaments, as well as field data from 204 fault planes (195 with sense of movement), 273 dykes, and 45 volcanic alignments, are presented. The tectonic style of the deformations is brittle and polyphasic. Strike-slip faults are dominant, but normal and reverse faults are also present. Both the so-called “Atlantic” and “African” directions are well developed in trends of strike-slip faults and volcanic indicators. At least two deformation phases can be identified from the geometrical analysis of faults and from the stress tensor calculated using lineations on fault planes. The reconstructed stress field responsible for the measured deformations changed orientation during the evolution of the island of Lanzarote. It is suggested that a permutation between principal stress axes σ1, and σ3 occurred subparallel to the length of the island between the pre-erosional and post-erosional stages.

Tuning Physical Properties of Tomato Puree by Fortification with Grape Skin Antioxidant Dietary Fiber

Grape skins recovered from winemaking by-products were investigated for use as sustainable, antioxidant fiber-rich ingredient for the innovation of low-energy dense tomato puree. Six tomato purees fortified with grape skin antioxidant fiber, with varying particle size distribution, and two control tomato purees were studied. Physical parameters of purees were analyzed upon mixing and either an intensive heat treatment or an optimized heat treatment designed to achieve six decimal reductions of a target microorganism (Alicyclobacillus acidoterrestris) as recommended for pasteurization of acidic fruit products. Mixing of grape skin antioxidant fiber with tomato purees led to a decrease in both surface-weighted mean diameter (Sauter mean diameter, d(3,2)) and volume-weighted mean diameter (d(4,3)) values and an increase in span. Changes in these descriptors were most significant in purees added with the smallest particle sizes. Thermal stabilization of purees slightly decreased the d(3,2) values further and increased d(4,3) values, suggesting concomitant occurrence of particle disaggregation and formation of flocs within the food matrix. Phenolic solubility was inversely correlated to d(3,2) values. Bostwick consistency, storage (G′) and loss (G″) moduli, and complex viscosity (η*) increased in the fortified purees. The η* values displayed a positive correlation with d(4,3) values. Variations in Hunter colorimetric parameters were within the acceptability threshold. Overall, the information obtained provides knowledge to assist development of fiber-rich, low-energy dense fruit purees.

Quantification of casein fractions and of some of their genetic variants in phosphate buffer by near infrared spectroscopy

Milk casein and casein fraction contents have a great influence on milk rennet properties and cheese yield so that the selection of dairy cattle with genetic characteristics suitable for milk transformation is of great interest to dairy farms and firms. The possibility of a rapid and accurate determination of these parameters would be very useful to predict milk aptitude to cheese making. This work aimed to determine casein fractions and their genetic variants content using near infrared (NIR) spectroscopy in reconstituted casein samples by comparing the performance of different NIR equipment (a monochromator instrument and a Fourier transform instrument) and different modes of measurement (reflectance and transflectance) in order to evaluate the best operative conditions for this application. Fifty-eight raw milk samples, collected from different farms in the Asturias region, Spain, were analysed for protein (TP%) and non caseinic nitrogen (NCN%) content using the Kjeldahl method. Casein content was calculated as the difference between TP and NCN content. Casein fractions (αs0-, αs1-, αs2-, κ-casein) and genetic variants of β-casein (βB- βA1-, βA2-casein) were determined by a capillary electrophoresis system. Samples were ultra-centrifuged to obtain native casein and then reconstituted in phosphate buffer (pH = 6.8) at the same original milk concentration, previously determined by the Kjeldahl method. Spectra were collected at 37°C with a FT-NIR instrument in transflectance mode and a monochrometer in both transflectance and reflectance mode. Partial least square (PLS) analyses performed on transflectance spectra showed good prediction ability for all variables—(min R2 = 0.80 for κ-casein; max R2 = 0.94 for βA2–casein), with the exception of αs2-casein. NIR spectroscopy has the ability to determine and quantify casein genetic variants and could be used to select milk for its final purpose and to predict the aptitude of milk to cheese-making.

Testing the suitability of different high-performance liquid chromatographic methods to determine aflatoxin M1 in a soft fresh Italian cheese.

Aflatoxin M1 (AFM1) is a toxic undesirable compound in milk. AFM1 affinity for caseins causes a concentration effect during milk process for dairy transformation. In spite of this, no official method of analysis, nor maximum tolerance level for aflatoxin M1 in cheese have been established. Thus, the aim of this work was to test the suitability of different HPLC methods for the AFM1 quantification in soft cheese samples at three different contamination levels (low, medium and high, at respectively nearly 30, 100 and 250 ng/kg). Nine participants were selected among Italian laboratories accredited by the Italian accreditation body (ACCREDIA) for HPLC toxin analysis. They were asked to analyze samples applying the method routinely used. The different applied methods were compared, and precision and accuracy parameters were evaluated. The main differences among HPLC procedures were registered at the level of extraction step. The use of an enzymatic digestion for the extraction of the toxin from cheese seemed to be particularly advantageous and the use of immunoaffinity columns seemed to be determinant for the improvement of sensitivity at low contamination levels. In general, the applied methods well discriminated the 3 levels of contamination, even though they performed better at the medium and high concentration levels (100 and 250 ng/kg) than at the low one (30 ng/kg). In fact relative standard deviation for reproducibility at low level was higher (60.1%) than the same value at medium and high levels (22.8% and 28.9%, respectively).

Reply to Comment on ‘Dykes, faults and paleostresses in the Teno and Anaga massifs of Tenerife (Canary Islands)’ by J.A. Rodrı́guez-Losada and A. Hernández-Pacheco

Abstract We welcome the comment by Rodriguez-Losada and Hernandez-Pacheco (hereafter LP) and we are pleased that they have ‘no objections to the conclusions’ of Marinoni and Gudmundsson (2000 ; hereafter MG). The LP comment deals only with the Anaga massif and mostly with (1) dykes supposed to be folded by post-emplacement ductile deformation, (2) tilting of the oldest part of the Anaga succession, (3) selection of profiles, (4) the horizontal extension due to dykes, and (5) the paleostress field of Anaga. We reply briefly to these points below.