Geological structure of a long‐living geothermal system,Larderello, Italy

We have examined the data of 600 geothermal wells and re‐interpreted approximately 500 km seismic profiles through the field of Larderello, Italy. We conclude that the two main seismic reflectors present below the geothermal area host two different fluids: (1) superheated steam in the upper H‐horizon (reached by drillholes) and (2) supercritical fluid in the deeper K‐horizon (reached by few unproductive or damaged wells). The superheated steam has the physical and chemical connotation of the geothermal fluid exploited so far at Larderello, whereas the supercritical fluid represents a potential unconventional deep‐seated resource still to be assessed. The high temperatures existing in correspondence of the K‐horizon suggest that the silica‐rich rocks are close to a plastic state and the fluids should remain confined in a medium sealed to the confining rocks, unless occasional fluid overpressure and abrupt high strain rates occur.     

Discovery of Late Jurassic fossils inside modern sediments at Gorringe Bank (Eastern Atlantic Ocean) and some geological implications.

During a recent expedition at the Gorringe Bank (eastern Atlantic, 150 miles SW off Portugal), one of the rare sites in the ocean where mantle rocks crop out at very shallow depths (? 30 m), the Gettysburg and Ormonde seamounts, the two summits on the Gorringe Bank, were surveyed in detail. At Gettysburg seamount, within the modern bioclastic material, which is continually produced on the summit and exported to deep water, several examples of Mesozoic cephalopods were found. These fossils, reworked ‘in situ’, gave an age spanning from Kimmeridgian–Tithonian to Hauterivian (145–155 Ma) and recall some condensed Jurassic sequences of the Thetyan region compatible with shallow water (< 200 m). The serendipitous discovery of such ancient faunas within modern sediments suggests that Gorringe Bank was a seamount at the early opening of the Atlantic Ocean and requires us to reassess the age of rifting along the Iberian margin and the importance of vertical tectonics for non‐volcanic, mantle‐rooted seamounts.     

A quantitative approach to the influence of pyrite separation on Cu-processing tailings: a case study at Reps,Mirdita district,Albania

Sulfide-rich tailings are a well-known environmental threat due to their production of acid drainage (AD) and release of potential toxic elements (PTE) to the local environment. The presence of heterogeneous materials produces complex environmental signatures and complicates the quantitative prediction of contamination. The present work provides a method of quantifying such heterogeneities, starting from mineral processing data of the Reps, Mirdita (Albania) site. A quantitative flow sheet (QF) method was applied to a selected dump site of the Mirdita copper mining district where secondary pyrite separation had been used in the past. The site is subject to long-lasting (10³ years) AD processes with significant release of PTE into the local environment. The tailings at the Reps site are divided into two classes based on the sulfide S content, respectively, represented by high-sulfide-content (S > 10 wt%) materials (hS) and low-sulfide-content (S < 3 wt%) material (lS). The reconstruction of the QF allowed us to identify the hS tailings as the discharge of single-flotation processing lines. This material accounts for about 82% of the total potential H₂SO₄ production, even though it represents < 20% of the entire tailing discard. The QF is a useful tool for the evaluation of heterogeneity and consequently for the modeling of waste management within abandoned sites and in working plants. Given a good quantification, heterogeneity can in fact support the setting of pyrite separation lines or the separate management of pyrite-rich tailing dumps.     

Comparative soil CO2 flux measurements and geostatistical estimation methods on Masaya volcano, Nicaragua

We present a comparative study of soil CO₂ flux () measured by five groups (Groups 1–5) at the IAVCEI-CCVG Eighth Workshop on Volcanic Gases on Masaya volcano, Nicaragua. Groups 1–5 measured using the accumulation chamber method at 5-m spacing within a 900 m² grid during a morning (AM) period. These measurements were repeated by Groups 1–3 during an afternoon (PM) period. Measured ranged from 218 to 14,719 g m⁻² day⁻¹. The variability of the five measurements made at each grid point ranged from ±5 to 167%. However, the arithmetic means of fluxes measured over the entire grid and associated total CO₂ emission rate estimates varied between groups by only ±22%. All three groups that made PM measurements reported an 8–19% increase in total emissions over the AM results. Based on a comparison of measurements made during AM and PM times, we argue that this change is due in large part to natural temporal variability of gas flow, rather than to measurement error. In order to estimate the mean and associated CO₂ emission rate of one data set and to map the spatial distribution, we compared six geostatistical methods: arithmetic and minimum variance unbiased estimator means of uninterpolated data, and arithmetic means of data interpolated by the multiquadric radial basis function, ordinary kriging, multi-Gaussian kriging, and sequential Gaussian simulation methods. While the total CO₂ emission rates estimated using the different techniques only varied by ±4.4%, the maps showed important differences. We suggest that the sequential Gaussian simulation method yields the most realistic representation of the spatial distribution of , but a variety of geostatistical methods are appropriate to estimate the total CO₂ emission rate from a study area, which is a primary goal in volcano monitoring research.Editorial responsibility: H Shinohara     

Multi-stage melt–rock interaction in the Mt. Maggiore (Corsica, France) ophiolitic peridotites: microstructural and geochemical evidence

Spinel and plagioclase peridotites from the Mt.Maggiore (Corsica, France) ophiolitic massif record a composite asthenosphere–lithosphere history of partial melting and subsequent multi-stage melt–rock interaction. Cpx-poor spinel lherzolites are consistent with mantle residues after low-degree fractional melting (F = 5–10%). Opx + spinel symplectites at the rims of orthopyroxene porphyroclasts indicate post-melting lithospheric cooling (T = 970–1,100°C); this was followed by formation of olivine embayments within pyroxene porphyroclasts by melt–rock interaction. Enrichment in modal olivine (up to 85 wt%) at constant bulk Mg values, and variable absolute REE contents (at constant LREE/HREE) indicate olivine precipitation and pyroxene dissolution during reactive porous melt flow. This stage occurred at spinel-facies depths, after incorporation of the peridotites in the thermal lithosphere. Plagioclase-enriched peridotites show melt impregnation microtextures, like opx + plag intergrowths replacing exsolved cpx porphyroclasts and interstitial gabbronoritic veinlets. This second melt–rock interaction stage caused systematic chemical changes in clinopyroxene (e.g. Ti, REE, Zr, Y increase), related to the concomitant effects of local melt–rock interaction at decreasing melt mass, and crystallization of small (<3%) trapped melt fractions. LREE depletion in minerals of the gabbronoritic veinlets indicates that the impregnating melts were more depleted than normal MORB. Preserved microtextural evidence of previous melt–rock interaction in the impregnated peridotites suggests that they were progressively uplifted in response to lithosphere extension and thinning. Migrating melts were likely produced by mantle upwelling and melting related to extension; they were modified from olivine-saturated to opx-saturated compositions, and caused different styles of melt–rock interaction (reactive spinel harzburgites, vs. impregnated plagioclase peridotites) depending on the lithospheric depths at which interaction occurred. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Spectroscopic Investigation on Hydrophobic and Hydrophilic Fractions of Dissolved Organic Matter Extracted from Soils at Different Salinities

Organic matter can be considered one of the most important indicators of the extent of soil desertification processes. Among the causes of desertification, salinization induced by different factors is raising the greatest concern in the Mediterranean area. In the present research, hydrophilic (HI) and hydrophobic (HO) fractions of dissolved organic matter (DOM) extracted from soils at different degrees of salinization have been investigated by means of spectroscopic techniques such as tridimensional fluorescence spectroscopy in the mode of emission excitation matrix (EEM) and Fourier transform infrared spectroscopy (FT‐IR). The FT‐IR spectra were distinctive in differentiating HI from HO fractions and each DOM fraction as a function of soil salinity. The EEM spectra of HO fractions exhibited a shift toward longer emission wavelengths and higher fluorescence intensity (FI) values as compared to that of the HI fractions. These results could be ascribed to the different molecular complexities of HI and HO fractions. Further, a marked quenching effect was observed in the FI of both the DOM fractions with increasing soil salinity, which allowed to obtain immediate information on the soil salinity degree by comparing the fluorescence intensity.     

Multitemporal Landsat-MODIS fusion for cropland drought monitoring in El Salvador

Abstract

This study aims to develop an approach to characterize cropland drought conditions in El Salvador, Central America. The data were processed for 2016–2017 through three main steps: (1) reconstructing MODIS land-surface temperature (LST), (2) Landsat-MODIS data fusion and (3) drought delineation using the temperature vegetation dryness index (TVDI). The results of LST reconstruction using the random forests (RF) indicated the median RMSE value of 0.5?°C. The fusion results achieved from the STARFM compared with the reference Landsat data revealed close agreement with the correlation coefficient (r) values higher than 0.84. The TVDI results verified with that from the reference Landsat data indicated r values of 0.85 and 0.75 for 2016 and 2017, respectively. The larger very dry area was observed for the 2016 primera season due to prolonged droughts. Approximately 11.5% and 10.7% of croplands were, respectively, associated with very dry moisture condition in the 2016 and 2017 primera seasons.     

Linear relationship between thermo-dehydroxylation and induced-strain by mechanical processing in vacuum: The case of industrial kaolinite, talc and montmorillonite

The thermal behaviour and the structural properties of three important industrial phyllosilicates, such as kaolinite, talc and Ca-rich montmorillonite, have been examined after mechanical treatment in a specifically built planetary ball mill working in vacuum (P = 0.13 Pa) at room temperature (25 °C). It is found that, on increasing the grinding time, the temperature of the dehydroxylation reaction decreases linearly as a result of a decrease of the crystallite size and structural order. To be noted that the mechanical treatment in our milling conditions did not induce significant amorphization. The temperature at which there is the maximum of dehydroxylation and the weight losses of the intralayer OH are linearly related to the increase of the FWHM of the 001 basal plane. These results are useful for predicting the thermal behaviour of layer silicates to be subjected to mechanical processing in industrial application.