Hydrogeology of granite rocks in Sardinia

Barrocu, Giovanni

doi:10.1201/9780203945650.pt1

Cited by 5 publications

(5 citation statements)

References 4 publications

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“…Current knowledge on the hydrogeology of the crystalline rocks of Sardinia and Calabria is scarce. General considerations on occurrence of groundwater flow and some studies limited to specific areas are reported in the scientific and technical literature (e.g., Celico et al 2000;Barrocu 2003;Allocca et al 2006;Regione Autonoma della Sardegna 2006a;2006b;Barrocu 2007;Regione Calabria 2008;Baiocchi et al 2014;Baiocchi et al 2015).…”

Section: Current Knowledge About Occurrence and Flow Of Groundwater In Crystalline Rocksmentioning

confidence: 99%

“…However, several springs (few thousands) with a flow rate ranging between 0.1 and 1 L/s are fed by crystalline rocks. Several tens of wells drilled in the fissured layer Special Issue AQUA2015 -DOI: 10.7343/as-2016-195 of granitoid rocks (and in some cases also including their weathered mantle) show yields between 0.1 and 2 L/s, values of transmissivity between 10 -6 and 10 -4 m 2 /s and of storativity between 0.05 and 2 % (Barrocu 2003;2007). In Southern Sardinia, some wells drilled near a faulted zone in the fissured layer of low-grade metamorphic rocks show yields between 1 and 3 L/s, values of transmissivity between 10 -4 and 10 -3 m 2 /s and of storativity between 0.03 and 3 % (Baiocchi et al 2015).…”

Section: Current Knowledge About Occurrence and Flow Of Groundwater In Crystalline Rocksmentioning

confidence: 99%

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Occurrence and flow of groundwater in crystalline rocks of Sardinia and Calabria (Italy): an overview of current knowledge

Baiocchi

Lotti²,

Piscopo

2016

AS-ITJGW

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Crystalline rocks constitute aquifers that are of interest for water supply in many countries. In Italy, the hydrogeological characteristics of crystalline rocks are not well known and the interest in these aquifers is generally scarce. Nevertheless, the large extent of these rocks in Sardinia and Calabria regions and the local scarcity of water resources justify this preliminary analysis. Crossing the information derived by the available data on climate conditions, type of crystalline rock, structural setting, characteristics of wells and springs, base flow of streams and rivers and pumping test results, a preliminary quantification of the potential yield of the crystalline aquifers of both regions was performed. The processing of data involving different aspects confirmed that the crystalline rocks of Sardinia and Calabria form low-permeability aquifers where groundwater circulation occurs in the weathered layer and, mainly, in the most fissured layers closest to the surface. In the heavily fractured zones, it was seen that the groundwater flow is more active and can also occur at a greater depth. Groundwater mainly outflows in the valleys, feeding streams, numerous low discharge springs and surrounding aquifers. Climate, rock covers and tectonic style influence the aquifer yield, which has been evaluated herein to range from 1 to 2 L/s per km2 and from 2 to 12 L/s per km2 in Sardinia and Calabria, respectively. This preliminary characterization shows that there are reasons to deepen the present knowledge on these aquifers in order to optimize the present use of their groundwater resources

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Section: Current Knowledge About Occurrence and Flow Of Groundwater In Crystalline Rocksmentioning

confidence: 99%

Section: Current Knowledge About Occurrence and Flow Of Groundwater In Crystalline Rocksmentioning

confidence: 99%

Occurrence and flow of groundwater in crystalline rocks of Sardinia and Calabria (Italy): an overview of current knowledge

Baiocchi

Lotti²,

Piscopo

2016

AS-ITJGW

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“…Variscan Corsica is extensively fractured and structured by deeply rooted faults that offer efficient fluid migration pathways. 4 He can readily diffuse through these structures (Aldana Martinez, 2018; Barrocu, 2007). Moreover, given that seismic events on a 10,000‐year timescale are common in Corsica (Larroque et al., 2021), the assumption of a steady‐state crustal degassing model offers a valuable initial insight into the 4 He system of Caldanelle and Guagno.…”

Section: Discussionmentioning

confidence: 99%

Assessing the Helium Potential of Variscan Batholiths: Insight From Corsica Island

Dutoit,

Donzé,

Cardoso

et al. 2024

Geochem Geophys Geosyst

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Most of the current helium (He) reserves originate from fortuitous discoveries, mainly made during oil and gas exploration in sedimentary basins. As helium generation depends on U and Th α‐decay, old geological provinces gather key ingredients for high He accumulation. However, numerous He‐rich springs have also been documented in much younger rocks, such as Variscan granites (320–250 Ma). These latter discoveries question the current exploration guidelines and require revisiting some of the longstanding paradigms. Here, is investigated He migration along a major fault rooted in the Corso‐Sardinian batholith (France). Two thermal springs, Caldanelle and Guagno‐Les‐Bains, show significant outgassing activities of crustal sourced He with concentrations up to 1.45 vol% and flow rates of 110 m3 STP 4He/year. Besides He, the gas phase is dominated by N2 (≈98 vol%) and minor CH4. Based on a survey employing multidisciplinary methodologies, it is revealed that (a) Variscan rocks represent efficient 4He source rocks, (b) the main source of He comes from the underlying Eo‐Variscan basement, (c) A deeply rooted fault and dense fractures networks drain the He, (d) the helium loss is limited, (e) faults and fractures may act as partial traps, and finally (f) the presence of an efficient trap could promote a He‐rich reservoir with high flux but low reserves. In that sense, young post‐orogenic granites represent promising helium plays. The geological context in which Caldanelle and Guagno‐Les‐Bains are embedded is ubiquitous in European Variscan batholiths. This case study is therefore intended to serve as a guide for helium exploration and to provide insights into helium behavior within a Variscan geological context.

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“…Whatever fracture and fault zones are present they act as isolated deep conduits for groundwater flow, at places forming an interconnected network for regional and continental deep groundwater movement (Krasny and Sharp, 2007). In Sardinia highly fractured zones were encountered up to 1000 m depth in a borehole and a fracture with high hydrostatic head (18 m amsl) and high temperature groundwater was found at a depth of 735 m bmsl (Barrocu, 2007). In Sardinia highly fractured zones were encountered up to 1000 m depth in a borehole and a fracture with high hydrostatic head (18 m amsl) and high temperature groundwater was found at a depth of 735 m bmsl (Barrocu, 2007).…”

Section: Deeper Fractured Aquifersmentioning

confidence: 99%

Introduction to the hydrogeology of hard rock

2015

Groundwater Geophysics in Hard Rock

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the parent rock that has undergone weathering, type and degree of weathering, tectonic controls, palaeo-climatic history and the geomorphological set up (Gustafson and Krasny, 1993). The fractures, fissures and joints cause exfoliation and climatic conditions help activate chemical processes of weathering. The degree of weathering decreases with depth. With intense fracturing development of weathered zone becomes prominent and deep weathering gets initiated by the structural deformities. In fact, physical processes facilitate the chemical ones and vice versa. However, the mechanical processes predominate in shallow parts and the chemical processes prevail in deeper parts just above the unweathered rock (Braga et al., 2002).Granites, primarily consisting of felsic minerals, like quartz, orthoclase feldspar, and mica (muscovite) with minor amount of other minerals, produce weathered material comprising clays decomposed from feldspars and mica and unaltered residual quartz-sand grains which are resistant to weathering. In general, the thickness of the weathered zone is more in coarse grained granite compared to metamorphics like quartz mica schists and thin-bedded quartzites (Larsson, 1984). Basalts mostly composed of mafic minerals like plagioclase feldspar, olivine and pyroxene produce clay and iron oxides as weathered material (Hamblin and Christiansen, 2009). The mafic minerals generally weather much faster compared to felsic minerals (McQueen, 2009) and therefore weathering in basalt could be deep and faster than granite. The term saprolite is used for the bottom part of the weathered zone where chemical weathering prevails and which retains the fresh bedrock structure and texture (Dosseto et al., 2012, Dixon et al., 2009, Braga et al., 2002. Saprolite is the transition zone of varying thickness between weathered zone and fresh rock. Wright (1992) further divides the saprolite into upper saprolite with a higher proportion of secondary clay and lower saprolite with a greater abundance of primary mineral with early forms of secondary clay. The variation from weathered rock to fresh rock can be transitional (Jones, 1985) or sharp with a weathering front (Twidale and Campbell, 1993, Houston and Lewis, 1988) occupying a minimum of a few centimetres in transition. Hall (1986) reports its development as thick transition zone in humid temperate climate of Scotland and sharp weathered front in warmer environment. In general, weathering occurred across the entire palaeo-surface and gradually extended to depths from a few metres to a few tens of metres through the favourable pre-existing fractured zones (Olesen et al., 2007), joints and cracks. The thickness of weathering varies depending on the irregularity of weathering front and erosion. It was further pointed out by Olesen et al. (2007) that the alteration process initiates at the top and penetrates downward. The intermediate zone between uppermost highly weathered part and deeper saprolite holds horizontal fractures (Lachassagne et al., 2001).Climate and groundwater ...

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Hydrogeology of granite rocks in Sardinia

Cited by 5 publications

References 4 publications

Occurrence and flow of groundwater in crystalline rocks of Sardinia and Calabria (Italy): an overview of current knowledge

Occurrence and flow of groundwater in crystalline rocks of Sardinia and Calabria (Italy): an overview of current knowledge

Assessing the Helium Potential of Variscan Batholiths: Insight From Corsica Island

Introduction to the hydrogeology of hard rock

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