This dataset contains supplementary materials to the manuscripts “Interpreting inverse magnetic fabric in Miocene dikes from Eastern Iceland” by Trippanera et al., (submitted to JGR) and “Anatomy of an extinct magmatic system along a divergent plate boundary: Alftafjordur, Iceland” by Urbani et al. 2015. These works present an extensive multi-scale and multi-disciplinary study focused on the magnetic fabric of dikes belonging to the Alftafjordur volcanic system in Eastern Iceland. Eastern Iceland is one of the most suitable places to analyze the roots of the volcanic systems that are composed of central volcanoes and fissure swarms. We sampled 19 NNE-SSW oriented dikes (for a total of 383 samples) belonging to the exhumed fissure swarm portion of Alftafjordur volcanic system, aiming at understanding the direction of magma propagation in the swarm by using Anisotropy of Magnetic Susceptibility (AMS) analysis. However, most of the samples (80% out of the measured cores) show an inverse geometric magnetic fabric (kmax is perpendicular to the dike margins and sub-horizontal)- therefore the study of the flow direction is complicated. Nevertheless, this result poses the problem of why the geometrically inverse fabric is present and widespread in the whole dike swarm. In order to understand the origin of this inverse fabric, besides standard AMS measurements, we also performed additional analysis such as different field and temperature AMS, Anisotropy of Anhystheretic Remanent Magnetization (AARM), Hysteresis loops and First-order reversal curves (FORC), Scanning Electron Microscope (SEM) and Optic microscope images analysis.
This dataset includes the following materials: • Location of the sampled sites (.kml) • AMS measurements at room temperature by using H=300 A/m for all samples (.ran) • AMS measurements at room temperature by using H=200 A/m and H=600 A/m for selected samples (.ran) • AMS measurements at different temperature (from 20 to 580 ℃) for selected samples (.ran) • AARM measurements for selected samples (.ran) • DayPlots data for selected samples (.xls or .csv) • SEM and Optical microscope images of thin sections of selected samples.
AMS and AARM data can be opened through Anisoft open-source software provided by Agico (Chadima and Jelinek, 2009; https://www.agico.com/text/software/anisoft/anisoft.php). Data have been acquired at: Roma Tre University (Rome, Italy), Istuto di Geofisica e Vulcanologia (INGV, Rome, Italy) and Laboratoire des Sciences du Climat et de l'Environnement, CEA, CNRS, UVSQ (Gif-sur-Yvette Cedex, France).
For the interpretation of the data refer to Urbani et al., 2015 and Trippanera et al., (submitted). The description of each dataset is provided in the description file.
This data publication includes movies and figures of twenty-six analogue models which are used to investigate what controls sill emplacement, defining a hierarchy among a selection of the proposed factors: compressive stresses, interface strength between layers, rigidity contrast between layers, density layering, ratio of layer thickness, magma flow rate and driving buoyancy pressure (Sili et al., 2019).Crust layering is simulated by pig-skin gelatin layers and magma intrusions is simulated by colored water. The experimental set-up is composed of a 40.5 X 29 X 40 cm3 clear-Perspex tank where a mobile wall applies a deviatoric compressive stress (C, in Table 1) to the solid gelatin (Figure 1). In each experiment is imposed two layers with different density and rigidity, separated by a weak or strong interface, excluding two experiments characterized by homogeneous gelatin (experiment 4 and 12). Three different rigidity contrast (1, 1.3, 1.8) between the two layers are imposed, defined as the ratio between the Young’s moduli of the upper (Eu) and lower (El) layer. By using NaCl and gelatin concentration, two layers with same rigidity but different densities are obtained, investigating the influence of the density contrasts on sill emplacement. The effects of the ratio between layer thicknesses (i.e. the ratio between upper and lower layer thickness: Thu/Thl) was simulated by changing only the thickness of the upper layer; while magma flow rate are studied changing the flow rate of peristaltic pump.Water density was increased by adding NaCl to analyze the effect of changing driving buoyancy pressure (Pm) that depends on the density difference between host rock and magma (Δρ), gravitational acceleration (g) and intrusion length (H). In the table different colors indicate the experiment result: black = dike; red = sill and blue = sheet. The here provided material includes time-lapse movies showing intrusion propagation of the twenty-six models with a velocity of 5 times higher compared to the real time (1 second in the movie is 25 real seconds). These visualizations are side (XZ or YZ plane in Figure 1) and/or top views (XY plane in Figure 1).
Objective: Aim: to determine the physical properties of the granitic basement in the soultz hdr borehole. General information: description: the core samples obtained from the granite section of the soultz gpk-1 borehole will be analysed to determine the properties of the granite such as strength and fracture toughness, thermal parameters, heat production (radiogenic content), and acoustic, electrical and magnetic properties. Achievements: The results of studies carried out on cores and cutting materials of three boreholes to a depth of 3.6 km are summarised. The physical property programme included measurements of density, ultrasonic velocities, seismic anisotropy, elasticity, fracture behaviour, electric and magnetic parameters, thermal properties including radioactive heat production, and radioactive age dating. Heat production in the Soultz granite is 2 to 3 times greater than that in other granites at the surface, although all surface granites in the vicinity show the same intrusion age. The physical property measurement programme has demonstrated that continuous measurements on cores and cuttings are essential for both operational drilling procedures and down hole condition assessment in crystalline rock formations. The European Geothermal Project involved teams from France and Germany who collaborated to test a site in the Upper Rhine Valley for its suitability for terrestrial heat mining (hot dry rock (HDR) energy production). Some British scientists participated in specific tasks. The site was chosen near Soulz-sous-Forets in Alsace at the location of the old oil field of Pechelbronn which was the first oil field exploited in Europe since the 18th century. It is situated on 1 of the summits of a very large thermic anomaly (200 km long and 20 km wide) where the mean geothermal gradient between the surface and 1500 m is known to be higher than 6.5 C/100 m. The programme began in July 1987 with a 2000 m deep borehole. Below at 1375 m thick sediment cover, the granitic basement was penetrated to a depth of 2000 m. The temperature at the bottom of the hole was 140 C. The geothermal gradient within the sediments was unusually high (10 C per 100 m) and diminished to a normal after a series of fractures inside the Buntsandstein producing some water at 116 C with a total salinity 98 g/l. At the depth of 1820 m, hydraulically active natural fissure was reached. The artesian outflow from this zone was 0.15 l/s, with well head pressure of 1.6 bars. The thermal water produced from the well had a high chloride contents and clearly had an identical origin with the fluid collected from the Buntsandstein just above the granite. During the water injection tests, a second active natural fissure was detected normally closed out but which seemed to aquire a noticeable permeability at a well head pressure of about 40 bars.