João Carlos Nunes

Nitrogen isotopes determination in natural gas: analytical method and first results on magmatic, hydrothermal and soil gas samples †

A continuous-flow GC/IRMS technique has been developed to analyse δ15N values for molecular nitrogen in gas samples. This method provides reliable results with accuracy better than 0.15 ‰ and reproducibility (1σ) within±0.1 ‰ for volumes of N2 between 1.35 (about 56 nmol) and 48.9 μL (about 2 μmol). The method was tested on magmatic and hydrothermal gases as well as on natural gas samples collected from various sites. Since the analysis of nitrogen isotope composition may be prone to atmospheric contamination mainly in samples with low N2 concentration, we set the instrument to determine also N2 and 36Ar contents in a single run. In fact, based on the simultaneously determined N2/36Ar ratios and assuming that 36Ar content in crustal and mantle-derived fluids is negligible with respect to 36Ar concentration in the atmosphere, for each sample, the degree of atmospheric contamination can be accurately evaluated. Therefore, the measured δ15N values can be properly corrected for air contamination.

Geotourism development in the Azores archipelago (Portugal) as an environmental awareness tool

Abstract The Azores archipelago is distinguished by its unique natural beauty and marine setting. Thanks to its volcanic origin, the region has a very rich and remarkable geodiversity that includes a diversity of landscapes with innumerable craters, volcanic lakes, fumaroles, hot springs, volcanic caves, marine fossil deposits and thermal water springs. The recognition of this valuable geological heritage came with the recent integration of the Azores Geopark into the European and Global Geopark Networks. The pressure that the increasing development of tourism have been exerting on these geological sites for the last years, and the need to create alternative forms of tourism, which contribute towards the socio-economic development in rural areas, have highlighted the importance of geotourism as a tool to promote and preserve the geological heritage of the Azores. Geotourism has turned to be an important instrument of environmental awareness through the local and foreign people.

The Azores Archipelago: Islands of Geodiversity

The Azores Archipelago (a Portuguese Autonomous Region) is located in the North Atlantic at the distance of 1,815 km from the Mainland Portugal, and is formed by nine islands and several islets, which are dispersed along a strip with 600 km length and with a WNW-ESE trend.

Geological Heritage Management in Small Islands: the Example of the Azores UNESCO Global Geopark (Portugal)

The geological heritage management should be integrated in spatial and environmental planning policies. In small islands, the isolation, small size, and anthropogenic pressures reduce the resilience of ecosystems and increase their vulnerability to global changes, requiring different integrated solutions in comparison with other territories. This case study demonstrates that the geological heritage management in small islands should be made at a local scale allowing the effectiveness of its implementation and the protection of natural resources. It is proposed that this management should be carried out at two levels: (i) an island level, in a strategic way, with clear boundaries and a well-identified set of actors and (ii) a geosite level, in an operative perspective. This proposal is being applied to the islands of the Azores UNESCO Global Geopark (“9 Islands – 1 Geopark”), where 121 geosites are identified. Most of the geosites are included in the Natural Parks of the Island and the Marine Park of the Azores, so it is proposed an integrated management of the geosites in these structures. This facilitates the coordination with other classified areas of each the island and integrates all the territorial instruments and planning processes applied to the island.

Potentially Reactive Forms of Silica in Volcanic Rocks Using Different Analytical Approaches

Several concrete structures show signs of deterioration resulting from internal chemical reactions, such as the alkali-silica reaction (ASR). It is well known that these swelling reactions occur in the presence of moisture, between some silica mineral phases present in the aggregates and the alkalis of the concrete, leading to the degradation of concrete structures and consequently compromising their safety. In most of the cases, rehabilitation, demolition or even rebuilding of such structures is needed and the effective costs can be very high. Volcanic rocks are commonly used as aggregates in concrete, and they are sometimes the only option due to the unavailability of other rock types. These rocks may contain different forms of silica that are deleterious to concrete, such as opal, chalcedony, cristobalite, tridymite and microto cryptocrystalline quartz, as well as Si-rich volcanic glass. Volcanic rocks are typically very finegrained and their constituting minerals are usually not distinguished under optical microscopy, thus leading to using complementary methods. The objective of this research is to find the more adequate analytical methods to identify silica phases that might be present in volcanic aggregates and cause ASR. The complementary methods used include X-Ray Diffraction (XRD), mineral acid digestion and Scanning Electron Microscopy with Energy Dispersive X-Ray Spectrometry (SEM/EDS), as well as Electron Probe Micro-Analysis (EPMA).

The ReAVA Project: Assessment of the Potential Alkali-Reactivity of Volcanic Aggregates from Azores Islands

Volcanic rocks have been found to be potentially alkali-reactive in a number of countries, including Japan, New Zealand, Iceland and Turkey. In order to characterize the potential reactivity of the volcanic rocks in Azores a project is being carried out, under the support of the Azores Government: the ReAVA Project—“Characterization of Potential Reactivity of the Volcanic Aggregates from the Azores Archipelago: Implications on the Durability of Concrete Structures”. This project comprises mainly: (1) petrographic assessment of the aggregates, (2) assessment of their performance in expansion tests and (3) site inspection of existing large concrete structures. This study has also the support of the IMPROVE Project—“Improvement of Performance of Aggregates in the Inhibition of Alkali-Aggregate Reactions in Concrete”, aiming to minimize the occurrence of alkali aggregate reaction (AAR) in Portugal. The Azorean rocks used as aggregates are mainly basalts and some trachytes. The reactivity of this kind of rocks is usually associated with the presence of volcanic glass, altered minerals and SiO2 content of the rock. The petrographic examinations of the rocks confirmed that one of the basaltic samples contains volcanic glass. The occurrence of microcrystalline quartz as a secondary product filling the interstices of the trachyte sample was confirmed by scanning electron microscope. The results of the concrete expansion test RILEM AAR-3 showed an increasing expansion starting on 140 days and continued to grow after 2 years of laboratory testing, but below the limit of 0.05 % recommended for this method.