J. Martínez-Frías

Nucleation, growth and oxidation of framboidal pyrite associated with hydrocarbon-derived submarine chimneys: lessons learned from the Gulf of Cadiz

In order to establish the history and conditions of nucleation and growth of pyrite formed inside methane-derived carbonate chimneys collected in the seafloor of the Gulf of Cadiz, we compared the size distributions, morphologies, textures and geochemical compositions of framboidal and euhedral pyrite as well as iron oxyhydroxides pseudomorphs. More than 2400 framboids and crystals were measured and four types of statistical populations were identified. Framboid size (diameter) ranges from 6 to 12.5 μm with a mean size of 10.4 μm and a maximum value of 27.9 μm, whereas euhedral crystal size (maximum dimension) ranges from 6.3 to 9 μm with a mean size of 7.2 μm and a maximum value of 21.6 μm. Crystal size distributions (CSD) of different populations of framboidal iron oxyhydroxides show strongly negatively skewed shapes, close to the universal steady-state CSD curve for Ostwald ripening, an unequivocal signal of closed-system growth. Euhedral crystal populations of pyrite and iron oxyhydroxides present CSDs with lognormal or slightly negatively skewed lognormal shapes and low size variances, indications of open-system growth. This was confirmed by simulating framboidal and euhedral crystal populations with different growth mechanisms using the GALOPER (Growth According to the Law of Proportionate Effect) program. From CSDs shapes and the values of α and β 2 , the populations of framboids are inferred to have grown initially in an open system (surface and then transport-controlled) and then in a closed system (Ostwald ripening) and the populations of euhedral crystals only in an open system. In this case, the initial stage of surface-controlled growth is shorter than that deduced for the framboidal populations. We suggest that: (1) the concentration and availability of reactive iron and hydrogen sulphide are the main factors controlling the morphology and growth of pyrite, and (2) the higher reactive surface of framboidal textures would govern their preferential oxidation, dissolution and recrystallization during the closed-system growth and consequently the development of higher sizes in comparison with euhedral forms.

The volcanism-related multistage hydrothermal system of El Jaroso (SE Spain): Implications for the exploration of Mars

The SE Mediterranean margin of Spain is an extremely interesting area of synchronous interaction of tectonic, volcanic, evaporitic and mineralizing hydrothermal processes. This works tackles the multiple relations among these processes by the study of a specific and representative case: the ‘Jaroso Hydrothermal System’. The hydrothermal fluids were genetically linked with the late episodes of the Upper Miocene calc-alkaline and shoshonitic volcanism of the area. The ascent of the fluids was mainly controlled by the Palomares fault in Sierra Almagrera. In the shallow-marine basin of Las Herrerias, the movement of the acid solutions was controlled by both NNE-SSW and N150E normal faults and WNW-ESE wrench reverse faults. At least three mineralising stages were identified, although the particular formation of jarosite could be associated with both hypogenic and supergenic processes. We suggest that the multistage hydrothermal system of El Jaroso (Sierra Almagrera, Almería province, SE Spain), which is responsible for both the Jaroso ores (especially rich in jarosite) and the Las Herrerias sulfate-rich, shallowmarine laminites, could be exploited as a potential model with important implications for the exploration of Mars.

New application of microwave digestion–inductively coupled plasma-mass spectrometry for multi-element analysis in komatiites

A new method using microwave digestion combined with inductively coupled plasma-mass spectrometry (ICP-MS) was studied to analyze the elemental composition of a variety of komatiites samples. Microwave digestion consisted in two-stage heating and pressurizing acid treatments for maximum dissolution of the samples. We report here different quality control measurements (external and internal calibration, monitoring of reference materials) which involve standard deviation calculations and recovery examinations in order to test the precision and accuracy of the analytical procedure. Data for 17 elements (Na, P, K, T, V Cr, Mn, Co, Ni, Cu, Zn, Zr, Pb, Al, F, Ca and Mg) in eight komatiite samples and two USGS basalt reference samples (BCR-2 and BHVO-2) are presented. We evaluate our new digestion and instrumental procedure. The element concentration obtained for BCR-2 and BHVO-2 agreed well with the certified values, the relative standard deviations were lower than 5% and recoveries were good. Our analytical results demonstrate that it reproduces accurately the concentrations of minor and trace elements in komatiites. The ease of digestion of the samples and the speed (less than 12 h) to digest the komatiite material makes this technique an efficient method to be used easily and routinely for preparing and analyzing komatiites samples for multiple elements determination.

Raman spectroscopic study of four Spanish shocked ordinary chondrites: Cañellas, Olmedilla de Alarcón, Reliegos and Olivenza

Shock metamorphism in chondritic parent bodies produces typical textures, visible under the microscope, which are a consequence of structural deformation of the crystals. Such deformations can be studied with Raman spectroscopy. The vibrational characteristics of olivines and pyroxenes, structurally deformed by weak-to-moderate shock metamorphism, have been determined on four Spanish ordinary chondrites (Cañellas, Olmedilla de Alarcón, Reliegos and Olivenza). Such deformations would affect, in principle, the band positions and widths of the Raman spectra peaks. The measured band positions and relative intensities are consistent with chemical composition for olivines and pyroxenes, but show little influence on the degree of shock. However, the full spectral band width of the silicate internal modes shows some dependence on the impact grade, which could be attributed to inhomogeneous effects produced by the impacts.

Micro-Raman spectroscopic study of extremely large atmospheric ice conglomerations (megacryometeors)

For the first time, micro-Raman spectroscopy has been applied to the structural study of four megacryometeors (extremely large atmospheric ice conglomerations that fall in general under blue-sky atmospheric conditions) that fell in Spain. The Raman spectra taken on the megacryometeor cores have been compared with those obtained from an in situ and online study performed on the crystallization process of water in the laboratory. A detailed comparison of the band profiles obtained made it possible to place the formation of the megacryometeors within a particular range of temperatures (−10 to −20°C), which in turn can be related with the altitude of formation in the atmosphere. These results have also been compared with isotope concentrations (δ18O and δD) previously obtained in these cores. The two sets of results show a close correlation.

Insights Into Speleothems From Lava Tubes Of The Galapagos Islands (Ecuador): Mineralogy And Biogenicity

7 paginas.-- 3 figuras.-- 21 referencias.-- Comunicacion oral presentada en el 7th International Symposium of Vulcan speleology At Ocean View, Big Island, Hawaii (USA) February 6-12, (2016)

A Mathematical Algorithm to Simulate the Growth and Transformation of Framboidal Pyrite: Characterization of the Biogenic Influence in Their Size Distributions

We developed and implemented a mathematical algorithm to model the growth of sedimentary framboidal pyrite simulating diverse natural mechanisms. The algorithm starts with growth in open system, based in the Proportional Effect Law, and finishes with growth in closed system at constant volume, following processes of dissolution, interstitial spaces infilling and framboidal and prismatic overgrowth. The algorithm was implemented varying more than 30 variables including: (1) an initial framboid diameter to simulate aggregation over pre-existing spherical surfaces and then the likely induction of the spherical morphology by microorganisms, (2) the decrease of microcrystal size from core to rim simulating the fall of supersaturation when growth advances, (3) packing coefficient to reproduce the inclusion of organic matter and other small substances inside framboids. Results obtained show that: (1) the microcrystal aggregation over spherical surfaces influences significantly the shape of the framboidal size distribution generating narrow populations in the sense of small size variation; (2) this effect can be masked by the decrease of the microcrystal size when supersaturation falls and by the decrease of the packing coefficient by particles trapped in framboidal structure. The main conclusion of this study is that mathematical computer simulation of the growth of framboidal pyrite allows the easy generation of large framboid populations with size distribution similar to that observed in nature, simulating the biogenic influence in the acquisition of the spherical morphology, the main question remained in the theory of framboidal pyrite formation.

Atmospheric Megacryometeor Events versus Small Meteorite Impacts: Scientific and Human Perspective of a Potential Natural Hazard

It is important to differentiate between a natural hazard and a natural disaster. A natural hazard is an unexpected or uncontrollable natural event of unusual magnitude that threatens the activities of people or people themselves (NHERC 2004). A natural disaster is a natural hazard event that actually results in widespread destruction of property or causes injury and/or death. Only a very small fraction of the actual meteorite events are observed as falls in any given year. It has been predicted that 5800 meteorite events (with ground masses greater than 0.1 kg) should occur per year on the total land mass of the Earth. In a recent work, Cockell (2003) emphasizes the scientific and social importance of giving a coordinated and multidisciplinary response to events related with the entrance of small asteroidal bodies that could potentially collide with the Earth. In fact, it can be said that the recovery of small meteorites between 1 kg to 200 kg is relatively common; in Spain alone there are four meteorites in the collection of the National Museum of Natural History, weighing more than 30 kg (e.g. Colomera iron meteorite). But what would happen if the impact bodies, despite weighing up to 200 kg, would melt?

A review of the contributions of Albert Einstein to Earth Sciences—in commemoration of the World Year of Physics

The World Year of Physics (2005) is an international celebration to commemorate the 100th anniversary of Einstein’s “Annus Mirabilis.” The United Nations has officially declared 2005 as the International Year of Physics. However, the impact of Einstein’s ideas was not restricted to physics. Among numerous other disciplines, Einstein also made significant and specific contributions to Earth Sciences. His geosciences-related letters, comments, and scientific articles are dispersed, not easily accessible, and are poorly known. The present review attempts to integrate them as a tribute to Einstein in commemoration of this centenary. These contributions can be classified into three basic areas: geodynamics, geological (planetary) catastrophism, and fluvial geomorphology. Regarding geodynamics, Einstein essentially supported Hapgood’s very controversial theory called Earth Crust Displacement. With respect to geological (planetary) catastrophism, it is shown how the ideas of Einstein about Velikovsky’s proposals evolved from 1946 to 1955. Finally, in relation to fluvial geodynamics, the review incorporates the elegant work in which Einstein explains the formation of meandering rivers. A general analysis of his contributions is also carried out from today’s perspective. Given the interdisciplinarity and implications of Einstein’s achievements to multiple fields of knowledge, we propose that the year 2005 serve, rather than to confine his universal figure within a specific scientific area, to broaden it for a better appreciation of this brilliant scientist in all of his dimensions.

Computational Models and Simulations of Meteor Impacts as Tools for Analysing and Evaluating Management of Crisis Scenarios

The geological record evidences that cosmic impacts have accompanied the geobiological evolution of our planet. There is a general agreement that the largest risk of impact (and the highest difficulty of observation and monitoring) is focussed on “small objects” with sizes ranging from 10 to 300 m. Computer simulation and modelling offer new insight into the formation of impact craters, not only helping to understand ancient impact events, but also providing a way for analyzing and evaluating management issues related to future crisis scenarios. Very recent events, such as the Chelyabinsk meteor event (Russia, 15 february, 2013) confirm the significance of being aware about these astrogeological hazards, as well as of having appropriate methodological tools and protocols which help us minimize their effects. A set of twenty possible crisis scenarios, related to different types of impactors, have been simulated and evaluated.