Antonio Puccini

Structural map of Variscan northern Sardinia (Italy)

In this paper, we present a geological structural map (1:100,000 scale, ∼2300 km2 surface area) of the Variscan basement of northern Sardinia. The map integrates field structural analysis, extensive gamma-ray spectrometry, and high-resolution ELA-ICP-MS U/Th-Pb zircon and monazite dating. A set of 10 samples of granitic rocks collected from different plutons were characterized for their crystallization age. This provided an accurate timing of magmatic events related to the development of the Corsica-Sardinia Batholith. The structural map, complemented with geochronological results represents a benchmark for future studies on Variscan geodynamics.

Uranium distribution in the Variscan Basement of Northeastern Sardinia

ABSTRACT We present a detailed map of uranium distribution and its uncertainties in the Variscan Basement of Northeastern Sardinia (VBNS) at a scale of 1:100,000. An area of 2100 km2 was investigated by means of 535 data points obtained from laboratory and in situ gamma-ray spectrometry measurements. These data volume corresponds to the highest sampling density of the European Variscides, aimed at studying the genetic processes of the upper crust potentially triggered by an enrichment of radiogenic heat-producing elements. For the first time, the Kriging with Variance of Measurement Error method was used to assign weights to the input data which are based on the degree of confidence associated with the measurements obtained using different gamma-ray spectrometry techniques. A detailed tuning of the model parameters for the adopted Experimental Semi-Variogram led to the identification of a maximum distance of spatial variability coherent to the observed tendency of the experimental data. We demonstrate that the obtained uranium distribution in the VBNS, characterized by several calc-alkaline plutons emplaced within migmatitic massifs and amphibolite-facies metamorphic rocks, is an excellent benchmark for the study of ‘hot’ collisional chains. The uranium map of VBNS, and in particular the Arzachena minor pluton, confirms the emplacement model based on the recognition of the different petrological associations characterizing the Variscan magmatic processes in the Late Paleozoic. Furthermore, the presented model of the uranium content of the geological bedrock is a potential baseline for future mapping of radon-prone areas.

Structural and metallogenic map of late Variscan Arbus Pluton (SW Sardinia, Italy)

ABSTRACT This paper presents the geological, structural and metallogenic map of the Arbus Pluton, a late Variscan composite intrusion belonging to the Corsica-Sardinia Batholith. The pluton is surrounded and crosscut by a wide variety of vein ore deposits. The Arbus Pluton was emplaced at shallow crustal levels at the end of the Variscan Orogeny, along an E–W trending shear zone located in the low-grade external nappe pile of the Sardinian basement. The architecture of the pluton is roughly concentric with a core of cordierite-bearing leucogranites and an outer shell composed of pyroxene-bearing and hornblende granodiorites. New U/Pb dating on zircons of granodiorite yields an emplacement age of 303.7 ± 1.1 which improves previous Rb/Sr and Ar/Ar dating. The map has been compiled on the basis of new geological/structural surveys and petrographical studies coupled with in situ gamma ray spectrometry. All the data-sets have been processed using a geographical information system.

THE LATE VARISCAN MONTE LINAS PLUTON (SW SARDINIA): A SOURCE OF GRANOPHILE ELEMENT ORE

Lucchi, Renata G. ... et. al.-- 87° Congresso della Societa Geologica Italiana e 90° Congresso della Societa Italiana di Mineralogia e Petrologia, The Future of the Italian Geosciences - The Italian Geosciences of the Future, 10-12 September 2014, Milan, Italy.-- 1 pageThe Montellina Spring (370 m a.s.l.) represents an example of groundwater resource in mountain region. It is a significant source of drinking water located in the right side of the Dora Baltea Valley (Northwestern Italy), SW of Quincinetto town. This spring shows a morphological location along a ridge, 400 m from the Renanchio Torrent in the lower sector of the slope. The spring was investigated using various methodologies as geological survey, supported by photo interpretation, structural reconstruction, NaCl and fluorescent tracer tests, discharge measurements. This multidisciplinary approach, necessary due to the complex geological setting, is required for the importance of the Montellina Spring. It is interesting in the hydrogeological context of Western Alps for its high discharge, relatively constant over time (average 150 l/s), and for its location outside a fluvial incision and suspended about 40 m above the Dora Baltea valley floor (Lasagna et al. 2013). According to the geological setting, the hydrogeological reconstruction of the area suggests that the large amount of groundwater in the basin is essentially favoured by a highly fractured bedrock, covered by wide and thick bodies of glacial and gravitational sediments. The emergence of the water along the slope, in the Montellina Spring, is essentially due to a change of permeability between the deep bedrock and the shallow bedrock and/or surficial sediments. The deep bedrock, showing closed fractures and/or fractures filled by glacial deposits, is slightly permeable. The shallow bedrock, strongly loosened as result of gravitational phenomena, and the local gravitational sediments are, on the contrary, highly permeable. The concentration of water at the spring is due to several reasons. a) The spring is immediately downward a detachment niche, dipping towards the spring, that essentially drains the water connected to the change of permeability in the bedrock. b) It is along an important fracture, that carries a part of the losses of the Renanchio Torrent. c) Finally, it is favored by the visible and buried morphology. Although it is located along a ridge, the spring occurs in a small depression between a moraine and a landslide body. It also can be favored by the likely concave trend of buried base of the landslide. At last, tracer tests of the Renanchio Torrent water with fluorescent tracer are performed, with a continuous monitoring in the Montellina Spring. The surveys permit to verify and quantify the spring and torrent hydrogeological relationship, suggesting that only a small fraction of stream losses feeds the spring.