1,720,971 research outputs found
Prospecting of industrial minerals: a geophysical approach
Full text linkThis work deals with the evaluation of the electrical resistivity method for the identification and characterization of industrial minerals deposits.The ERT (Electrical Resistivity Tomography) technique is demonstratively applied to 4 different areas of the central and northern Sardinia.The research focused on clays, which generally have conductivity values greater than those of the host lithotypes. In this regard, a bentonite deposit close Ozieri (N-Sardinia) was investigated by 2D and 3D ERT surveys, and a preliminary study was conducted in the northern part of Nurra (NW-Sardinia) in order to discriminate Messinian clay deposits from the underlying bedrock.The ERT method was also tested on cineritic levels, which for their absorption properties are increasingly required as litter for pets. Potentially exploitable cineritic levels have been identified in two different sites of central Sardinia (Macomer and Zerfaliu), within the Oligo-Miocene calcalkaline volcanic sequence.In all the 4 case studies it is attempted: 1) to define the geometry of the deposits; 2) to estimate the reserves and locate the main faults useful to decipher the ore-forming processes; 3) to evaluate the reliability of the ERT method by cross-checking the results with boreholes data.The results indicate that ERT method may represent a relatively cheap and powerful tool to obtain high-resolution geological and stratigraphic information on clayey and cineritic bodies
Exploring the Variscan syn- to post-orogenic tectonics at the Einstein Telescope site of Sardinia (Italy).
No full textThe Variscan tectonics of north-eastern Sardinia is defined by syn-orogenic collision-related middle to high-T metamorphic terrains and by post-orogenic intrusions. The aim of this study lies in the understanding of the relationships between faults and intrusions in an area that has been candidate for hosting the Einstein Telescope (ET), a European third-generation underground interferometric detector of gravitational waves.
Free of regional faults, the ET layout is currently projected as a triangular infrastructure (10 km long sides), whose location has been proposed because of its present-day geodynamic quietness, very low seismicity and anthropogenic seismic noise. Despite previous maps underestimated the presence of faults in the area, new fieldwork has mapped them in higher detail.
The syn-orogenic deformation of the Palaeozoic metamorphic rocks consists of distinguished fold and cleavage generations with at least two ductile phases (D2+3) almost completely transposing the original bedding and the oldest schistosity (S0+1), that is still visible in the south were the thermometamorphic grade is lower. The later brittle fault network affects the metamorphic-plutonic ensemble with faults that mostly run parallel to the orientation of both dykes and plutonic contacts. Fault zones are generally NNW-, and WSW-striking and are associated with either more altered bedrock and/or cataclastic bands that are locally affected by late hydrothermal circulation with thick quartz veins, thin chlorite fibers or pseudotachilites and gouge that can be as thick as a meter each. In the surroundings of the boreholes drilled at two ET vertices, multiscale morphostructural analysis and 2D Electrical resistivity tomographies was carried out. The distribution of fault zone-related morphostructures shows maximum length up to 2.5 kilometres. At depth (ca. 250 m), the
tomographies show also a complex internal resistivity stratification, that consists of up to three electrolayers with variable distribution and thickness. This is related to the occurrence of faults in the bedrock corresponding to the larger morphostructural lineaments.
In conclusion, these results highlight the interaction between the syn- and the post-orogenic features that seem related to the inherited Variscan crust structure, which has a present-day implication in the groundwater flow. Evidence shows that the post-orogenic Variscan structures guided the post-orogenic dyke and vein injection. Further, the main fault zones were site of later hydrothermal circulation, possibly reactivated during the Oligocene-Aquitanian tectonics. Further studies should constrain the contribute of the eventually current differential uplift into reactivating the inherited Variscan structures to exclude the presence of neotectonics in the area
Bone marrow edema in magnetic resonance in scaphoid injury
No full textINTRODUCTION: Post-traumatic bone marrow edema is detected in 36% of patients undergoing wrist magnetic resonance (MRI), and in most cases, it is related to scaphoid fracture. However, the correct attribution of bone marrow edema in an acute setting remains complex. The aim of this study was to gain a better understanding of the origin of acute bone marrow edema in scaphoid injury.EVIDENCE ACQUISITION: All published and unpublished studies on the presence of bone marrow edema in case of scaphoid injury were included. Comprehensive literature searches were conducted (30 June 2020) based on the use of PubMed, Embase, Cochrane and Web of Science database. Potentially relevant articles were selected for full text review. A data extraction worksheet was compiled to acquire and record the observations regarding pathologies related to the presence of bone marrow edema in scaphoid trauma.EVIDENCE SYNTHESIS: The scaphoid is the most fractured carpal bone; on T1- and T2-weighted sequences is seen as a low signal intensity line across the bone with an adjacent marrow edema. In case of disruption of the ligamentous complex holding the scaphoid and lunate together, in the condition called scapholunate (SL) dissociation, MRI reveals bone marrow edema on the carpal-sided of the scaphoid. Bone contusion refers to bone marrow edema without evidence of fractures that occurs in the post-traumatic bone where marrow changes demonstrated on MRI result from a combination of hemorrhage, edema and microtrabecular fractures. The osteochondral lesion represents an osteochondral fracture involving an area of avascular necrosis in the subchondral bone and in the overlying cartilage layer; typical radiographic findings of this condition are sclerosis, fragmentation, erosion and collapse of the proximal pole of the scaphoid, and these findings on MRI are confirmed and classified.CONCLUSIONS: A review of the currently available literature on diagnostic studies of bone marrow edema following scaphoid trauma identified the mode of presentation and associated findings for major underlying diseases. Further studies will be needed to build solid evidence on the clinical usefulness of this information to help identify the appropriate treatment and follow-up pathway
Electrical Resistivity Tomography as a guideline for detecting altered volcanic ash deposits
No full textIn this paper we propose the application of Electrical Resistivity Tomography (ERT) as a guideline to localize and characterize altered volcanic ash deposits quickly and reliable. The geophysical method was tested on an altered epiclastic layer, identified within a composite Oligo-Miocene volcanic succession in central Sardinia (Italy). The equipment employed in continuous current mode (DC) was a Terrameter SAS 1000 (ABEM, Inc.) based on the use of metal electrodes for galvanic coupling. The high resistivity contrast between the epiclastite and the overlying ignimbrite, allowed the ERT method to provide valuable indications about the locations, lateral continuity and thickness of the deposit
Late to Post-Variscan tectonics in the Sardinia Einstein Telescope candidate site (Italy): insights from Structural Survey and Electrical Resistivity Tomography
No full textThe geological characterization preceding the construction of a large-scale underground structure, such as the Einstein Telescope (ET), is a mandatory step of civil engineering studies. The ET Italian candidate site is located in the Variscan basement of Sardinia because of its geodynamic quietness, very low seismicity and anthropogenic seismic noise. The ET layout is currently projected as an underground triangular infrastructure (10 km long sides), whose vertices are located between the villages of Lula, Bitti and Onanì, and is confined within an area not crossed by main regional faults.
The geological features of the Palaeozoic metamorphic rocks are the result of ductile deformation with folds and related planar and linear anisotropies. This polydeformed metamorphic basement was intruded by several granitic bodies and by mafic to acidic dykes, mostly of early Permian age. A brittle to ductile fault network affects the metamorphic-plutonic ensemble. Within such a structural frame it is difficult to accurately predict lithologies at depth by means of the geological survey alone. Thus, we started an integrated multidisciplinary cartographic, structural and Electrical Resistivity Tomography (ERT) study. The results as far obtained are useful to highlight the structural elements at depth, particularly lithological contacts and fault zones, which are relevant for the prediction of mechanic behaviour of the rocks along the tunnels tracks as well as the groundwater occurrence.
We have merged the lithologic information from published maps (also by comparing satellite images) and new data collected in the field. Newly traced morphostructural lineaments mark the distribution of fault zones from the areas that surround the boreholes drilled at two vertices. The analysis of satellite images has thus allowed to define the segmentation of principal faults, whose length is limited at surface to a few kilometers (2.5 km max).
Field structural results provided evidence of at least two ductile phases (D2+3) almost completely transposing the original bedding and the oldest schistosity (S0+1). Faults are mainly NNW-, and WSW-striking and are associated with either more altered bedrock and/or cataclastic bands. The WSW-striking faults are often conjugated with E- to NE-striking faults. Fault zones can be associated with thick quartz veins, or thin chlorite fibers. Locally, they are crossed by intense fracture arrays, pseudotachilites and gouge that can be as thick as a meter.
Near the vertices that were site of drilling (ca. 250 m total depth), ERT tomography was carried out, providing a complex internal resistivity stratification, that consists of up to three levels with variable distribution and thickness. As supported by field observation, we have interpreted the more conductive electrolayer as regolith and alluvial units, while the most resistive electro-layers correspond with the less-altered granitoids. The sudden trend of the isoresistivity line, that also recognized from satellite images or field evidence, was related to saturated fractured zones.
Thus, matching the vertical information provided by the 2D ERT results and the geological information from the study area, we provide a more accurate estimate of satured fault geometry at depth. Beside the ET vertices, similar approach can be adopted in predicting zone of hazards during the tunnel drillings
Integrated Geophysical Surveyes to investigate the Anghelu Ruju necropolis (Northern Sardinia, Italy).
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Geophysical prospection pilot in rock-cut tombs: The case study of Anghelu Ruju necropolis (Sardinia)
No full textElectrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) surveys were conducted in the Anghelu Ruju hypogeic necropolis in northern Sardinia (Italy). The main purpose was to calibrate both techniques on a known and already dug tomb. After the calibration the survey was extended to neighboring unexplored area aiming to evidencing new hypogeic structures. A comparison of the high-resolution GPR and ERT models was made, and their integrated results are discussed in terms of providing a more complete picture that would not be attainable using a single method. Several anomalies were identified that might represent previously unknown rock-cut tombs and burial sites in the central part of the investigated area
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