Detailed Magnetic Survey Research Articles

Finding fault in a shear zone: a magnetic and drill core study in the Valentine Lake Property, Newfoundland, Canada

The Valentine Lake Property in southwestern Newfoundland has five known gold deposits over a distance of 20 km along a northeast to southwest trend and is expected to be the future site for the largest gold mine in Atlantic Canada. The property contains structurally controlled orogenic-type quartz-tourmaline-pyrite veins, which are gold-bearing, occurring along or proximal to the Valentine Lake Shear Zone. The mineralization is found mostly on the northwest side of the shear zone in intrusive rocks and is rare in the conglomerate on the southeast side. The area has many mafic dykes, which show up well when conducting a magnetic survey due to their magnetite content. These dykes, like the mineralization, occur mainly in the intrusive rocks and trend predominantly subparallel to the shear zone, and so can help indicate structure. To constrain the location of the shear zone (and hence the mineralized region) in an area where an offset was suspected, a detailed magnetic survey was conducted over a 200 m x 300 m grid comprising sixteen lines. With the collected data, residual magnetic intensity maps were created and processed. A region was identified where the pattern of linear magnetic highs weaken and appear to terminate near the suspected offset. In combination with drill core information, this location is interpreted as a fault offset of the shear zone. The loss in magnetic intensity is possibly due to alteration or thinning of the mafic dykes near the fault.

Investigation of the Source of Groundwater Contamination Near a Farmland Using the VLF-EM and Magnetic Methods

Groundwater pollution continues to be a major problem in society where there is high level of urbanization, industrialization and conventional/inorganic farming. A detailed ground magnetic survey and VLF-EM was carried out on a site just beside a farmland to investigate the possible causes of the groundwater contamination in the area which lies within the Precambrian Basement Complex of Southwestern Nigeria. The survey was carried out using a proton precision magnetometer kept at a constant height during the survey, accompanied by Very Low Frequency - Electromagnetic Method (VLF-EM). Data for the two methods were acquired on five (5) traverses with the length of 100 m each. The distance between each traverse (inter traverse spacing) is 5 m. The VLF-EM data were interpreted qualitatively, using the Fraser and the Karous–Hjelt filters. The Fraser filtered data and relative current density pseudosections from the VLF-EM data indicate the presence of shallow and deep conductive zones that cross the farmland which are indicative of fractures. The quantitative interpretation of the data was done with a 2-D code that performs the inversion of the data. Magnetic maps were generated using Oasis Montaj, and profiles were plotted using Microsoft Excel software. From the results obtained, some major geological features were identified while linear features suspected to be fault/fractured zones, weathered zones, and bedrock depressions were delineated. Low magnetic intensity indicating presence of weak and incompetent zones were discovered. Earlier chemical analysis of both surface and groundwater collected at some depth on the farmland confirms the presence of water contamination. This knowledge supported the interpretation of the anomalies detected by VLF-EM and magnetic data as a possible cause of the contaminated groundwater flowing in connected fractures. The study concluded that the groundwater contamination originates from the farmland where some samples of the soil were found to contain nitrate chemicals resulting from fertilizer and pesticide used to enhance plant growth. Keywords: Nitrate contamination, groundwater pollution, multiple fractures, contaminant transport, fractured zone, inorganic farming DOI: 10.7176/JEES/12-6-04 Publication date: June 30 th 2022

Комплексные геофизические исследования Западно-Тиманского разлома

In this paper we discuss results of complex geophysical works within the southern and middle segments of the West Timan fault. In the study area, based on the nature of potential fields (magnetic, gravitational), various areas of the West Timan fault were identified: the southern part (Beloborsk block), the central part (Nivshera block), and the northern part (Sindor block). These areas were studied by profile magnetometry on foot and express radon survey. The detailed magnetic survey revealed that the West Timan fault was clearly visible in the gradient sections of the magnetic field, with some degree of conventionality it can be identified within the regional maximum, and it is impossible to trace it in the zone of the regional minimum. Based on the interpretation of seismic data, the location of the West Timan fault has been clarified. The nature of the seismic record does not always allow identifying the exact location of the fold planes, only the difference in the record in individual blocks is clearly noted. The border area sometimes captures 5 km. The express emanation survey showed that the West Timan thrust, in general, was characterized by increased values of radon volumetric activity, where they are further traced to the territory of Timan, while areas of different intensity are distinguished.

Complex shape of the Palaeoproterozoic Serpovidny refolded mega-sheath fold in northern Fennoscandia revealed by magnetic and structural data

The Serpovidny large-scale synform located in the Arctic zone of the north-eastern Fennoscandian Shield was studied with geological mapping and structural analysis, and its core with a ground detailed magnetic survey. This is a tight to isoclinal mega-sheath fold with the strongly thinned lower limb, almost undeformed upper limb, and the ՙcat's eye՚ core. The innermost rift-related sequence of the fold core is a synformal anticline, whilst limbs are composed of Palaeoproterozoic Keivy Group (metamorphosed redeposited products of mainly deep chemical weathering) and form a syncline. The Serpovidny mega-sheath fold formed during progressive non-coaxial, high strain deformation in simple shear/general shear regimes and a northward thrusting under mid-crustal conditions. This mega-sheath fold evolved from a NNE-verging anticline originated at the base of a nappe transported north-northeastwards from the Palaeoproterozoic Imandra-Varzuga Rift-Belt during the 1.9 Ga Lapland-Kola collisional orogeny. After a thrusting of this nappe onto the Keivy Group, one anticline plunged into these rocks and was transformed into the NNE-closing Serpovidny mega-sheath fold. Its geometric parameters and/or kinematic evolution are close to those of mega-sheath folds in Cretaceous rocks in the Oman Mountains, large-scale synformal anticlines in the Helvetic nappes in the Alps, and a Caledonian nappe in northwest Ireland.

Reconstruction of the Settlement Levoberezhnoe Plan of the Bronze Age (South Ural, Russia)

In the Southern Urals in 2015–2019 research was conducted on the fortified settlement of the Bronze Age Levoberezhnoe (Sintashta II). An asphalt road was drawn through the settlement, during the construction of which about a third of the monument’s area was destroyed. Excavations of the monument have been carried out since 2015. It has been established that the settlement is multi-layered; it functioned in the Late Bronze Age from the turn of the 3rd–2nd millennium BC until the last quarter of the second millennium BC. Detailed magnetic and topographic surveys were performed on the territory that remaining survived the construction of the road. The location of the external moat was reliably determined by linear positive magnetic anomalies. The base of the outer wall of the settlement had a thickness of about 4 m, the width of the outer moat was 2–2.5 m. It was also possible to accurately localize a number of walls of buildings. The settlement had a rectangular shape, inside there were 26 dwellings. As a result of a comprehensive analysis of the data and aerial photographs of the last century, the layout of the entire settlement was reconstructed.

Mayan limekilns as geomagnetic field recorders

We report new results from frontier research that relates the methodology and knowledge of geophysics (geomagnetism) with archeology and the data will represent a valuable contribution to both disciplines. A detailed magnetic survey was performed on limekilns from the northern Yucatan peninsula. We used Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) Spectroscopy to determine the temperature of calcination in order to select limekiln samples that were heated above the Curie temperature for common magnetic minerals. Using rock-magnetism, we identified the main carrier of remanent magnetization to be multi-domain or large pseudo-single domain low titanium titanomagnetite. Alternating magnetic field demagnetizations delivered reliable archaeomagnetic directions. Our summary of 12 limekiln ages shows a large span from 707 to 1900 yr AD. Such a wide time range signifies that Maya used limekilns in the Yucatan peninsula area in the Late Classic period (600 AD), and that some of these limekilns were reused in the Colonial period. From a geophysical point of view, information can be used about the behavior of the Earth's magnetic field in the recent historical past in Mesoamerica. In this context, the hundreds of Mayan limekilns which are distributed in large areas, open great opportunities to contribute to both archeology and geomagnetic field fluctuations during the past two millennia.

Geophysical study of subsurface structures of the area surrounding the new port of Jarjob in El-Negila-Marsa Matruh using magnetic data

ABSTRACT The purpose of the current paper is to investigate the subsurface geological active structures, through the analysis of the magnetic data, to conduct a scientific evaluation of the infrastructure of the area surrounding the new port of Jarjob that located on the northern coast about 60 km from the city of Marsa Matruh towards the city of Salloum and sited in the vicinity of the proposed area. The Magnetic data comprise the RTP aeromagnetic map as well as the resulting map from the geomagnetic survey for the part that was chosen in the proposed area. Two Overhauser Magnetometers are used to make a detailed comprehensive land magnetic survey, while the aeromagnetic map is obtained with authorisation from the General Petroleum Company. The necessary reduction-filtering phases like the daily variation, regional gradient, and the time variation are applied to obtain the total intensity anomaly map. Resulting total land magnetic intensity map is then reduced to the north magnetic pole and followed by the application of filtering linear wavelength technique to RTP aeromagnetic map and RTP land magnetic map to isolated the shallower residual components using different grid intervals. The obtained major tectonic trends of the study area show that the regional structures are controlled by the regional deeper structure taken NE-SW and E-W directions. The average calculated depth to the basement surface ranges from 2.6 to 3.2 km. So, the strength and solidity of the infrastructure of the port area, especially land magnetic survey area being studied that occupies a privileged place, which overlooks directly on the port coast and close to the main building, makes it a candidate for the establishment of industrial and economic projects and logistical services in the port.

The magnetic method as a tool in groundwater investigation in a basement complex terrain: Modomo Southwest Nigeria as a case study

A detailed ground magnetic survey was carried out in a basement complex underlain Modomo community in southwestern Nigeria with a view to delineating the subsurface structures, estimate the overburden thicknesses and assess the relevance of the geophysical method in groundwater investigation in the locality. The total field component of the earth’s magnetic field was measured at station intervals of 10–100 m along access routes within the study area. The data were corrected for diurnal variation and offset and subsequently reduced to the magnetic equator (RTE). Data enhancement techniques including the second vertical derivative, total horizontal derivative and Euler deconvolution were applied to the RTE data to map edges and estimate depths to the structures. Overburden thicknesses were estimated from 2D magnetic subsurface modeling along eight profiles. The magnetic survey derived lineaments (structures) and overburden thicknesses were validated with resistivity survey derived 2D structures and overburden thicknesses and borehole log data from the study area. Twenty-four lineaments with lengths ranging from 150 to 777 m were identified from the magnetic map. The lineament orientations were E–W, ENE–WSW, WNW–ESE, NNW–SSE, NW–SE and NE–SW directions. Many of the identified lineaments correlated significantly with structures derived from the 2D resistivity images. Comparable thicknesses were observed between correlated magnetic derived overburden thicknesses (4.41–29.4 m) and depths from wells and boreholes (5.48–27.1 m). The study concluded that the magnetic method could be reliably used for overburden thickness estimation and structure mapping required in groundwater potential assessment in a typical basement complex terrain.

Impact of Lithofacies and Structures on the Hydrogeochemistry of the Lower Miocene Aquifer at Moghra Oasis, North Western Desert, Egypt

The Moghra Oasis is one of the major Egyptian desert-reclamation projects. Understanding the hydrochemistry of the Moghra aquifer is an onus to properly plan and manage the agricultural activities in the North Western desert of Egypt. The basic geologic structure of the area under study was deduced from a detailed land magnetic survey. The resulted magnetic field map was analyzed using different filtering techniques and tomographic inversion. Field observation, stratigraphic setting, sedimentological studies, microfacies analyses and lithologic log of the studied wells were integrated to detect the lithofacies characteristics of the Moghra aquifer. Strong vertical and lateral variations of channel-fill and flat-laminated lithofacies beside several types of diagenetic processes caused the heterogeneity of the Moghra aquifer. The direction of groundwater flow in the heterogeneous Moghra aquifer is controlled by a fault system deduced from the magnetic study. Twenty groundwater samples from around Moghra Lake were collected and were analyzed hydrochemically for major ions and trace elements. The microfacies analysis (primary components and diagenetic processes), spatial variance in pH and ions concentrations, statistical and hydrogeochemical classifications, ionic ratios and relationships and saturation indices were helpful to understand the groundwater hydrogeochemical processes. The main hydrochemical type was Na–Cl. Ion-exchange due to seawater intrusion, sulfate ion reduction, iron-oxides reduction and mineral dissolution were the detected water–rock interaction processes. Dolomite precipitation was also proven. Iron oxides, quartz and carbonate minerals precipitation in the upper saline groundwater were expected. More mineral dissolution for evaporate minerals, silicate minerals and carbonate minerals in the lower saline groundwater is expected to occur.

Interpretation of magnetic anomalies of geological and archaeological origins in a volcanic area (Tusculum site, Lazio, Italy): Methodological proposals

A detailed magnetic survey combined with the study of magnetic properties and spectral analysis in the Tusculum archaeological site (Alban Hills, Italy) indicates the existence of magnetic anomalies (total field and gradient, showing amplitudes up to thousands of nT) resulting from combined geological and archaeological features. In this paper we propose a two-fold analysis based on both manual and automatic procedures for a precise characterization of those elements from total magnetic field and magnetic gradient profiles. The first, automated step consists in spectral analysis of a long (1.2 km) profile to define the dominant wavelengths related to geological and/or archaeological features. The second, manual step consists of the definition of a hierarchical pattern of magnetic anomalies, according to their amplitude and pervasiveness, in the selected (90 × 90 m) area. The defined anomaly pattern includes 1st-order, total field, magnetic anomaly (1000 nT, decreasing towards the North) related to the geological (volcanic) background, 2nd order anomalies (tens to hundreds of nT), showing a marked periodicity, revealed by spectral analysis, in the magnetic gradient in the 1.2 km long profile, and, finally, superimposed 3rd order anomalies (on the order of several nT). Most second-order and some of the third order anomalies are normal dipoles arranged in an orthogonal pattern in plan view, and can be interpreted as linked to the main roman walls of public buildings or roads. The magnetic susceptibility of most materials used in Roman constructions (volcanic tuff and basalt, whose lithology was characterized by means of thin sections) ranges from 600 to 110,000 × 10−6 S.I., contrasting with the overall lower susceptibility of soil fillings between walls, what explains most of the anomalies found. Magnetite and other iron oxides and sulphides are the main ferromagnetic phases in construction materials. Koenigsberger ratios of roman construction materials vary between 0.25 and 107 what explains for magnetic remanence to have played a certain (but limited) role in some particular magnetic anomalies.

Identification of the dynamic subsurface structures and their seismic implications based on geophysical methods at the southern part of Cairo area, Egypt

The main purpose of paper is to detect the active subsurface structures and their seismic implications located at the southern part of Cairo area. To achieve this target, the reduction-to-the-pole (RTP) aeromagnetic, ground magnetic, magnetotelluric, and seismological data were used. The RTP aeromagnetic data was used to delineate the regional extensions of the subsurface structures along a wide area. The activities of the detected structures were confirmed from the distributions of the earthquake epicenters along the investigated area. The type of the fault structures was identified using the focal mechanism analyses for the seismological data. Moreover, the active subsurface structures have been traced using a detailed ground magnetic survey for the study area. In addition, the magnetotelluric survey was carried out crossing the fault structures which detected previously from aeromagnetic. The results show that the selected area is identified as active zone for earthquakes. This zone extends from Gulf of Suez at the east crossing Wadi Araba and Nile River to south Giza and Cairo cities where the 12th October 1992 earthquake’s epicenter exists. Finally, the Curie magnetic depth investigation indicates the activities of these structures where the curie magnetic depths reach less than 8 km.

Geophysical investigation to support characterisation of structurally controlled groundwater flow into an open pit mine

Efficient dewatering operations depend on reliable predictions of expected inflow and likely water level behaviour. These predictions stem from the conceptual understanding of the hydrogeology of the area, which itself is derived from studies into the aquifer extents, hydraulic parameterisation and connectivity with adjacent aquifer units. Due to their isolated nature, structural controls on these inputs to the conceptual understanding are amongst the most challenging to determine. An investigation was undertaken on structurally controlled flow into an open pit iron ore mine in the Pilbara region of Western Australia. Bore yields, groundwater salinity and water level behaviour of in-pit bores unmistakably indicated flows in excess of normal aquifer throughflow. Airborne magnetic data allowed regional identification of a potential lineament which was confirmed with high density grade control drilling results. These indicated the presence of a trough-like mineralised feature likely to enhance connection to a regional aquifer system down dip of the iron ore body, or with a fractured rock aquifer beneath the ore body. A detailed ground magnetic survey was conducted along strike from the interpreted lineament, drastically improving on the aeromagnetic data, further validating the conceptualisation of the structure and providing greater accuracy with which to target future hydrogeological works around the current pit. Subsequent quantitative magnetic modelling constrained with close spaced drilling information and downhole magnetic susceptibility logging, increased the understanding of the characteristic basement magnetic response, and encourages the use of the magnetic method for local hydrogeological studies.

Emplacement of the Triassic Pueblito Pluton, NW Colombia: Implications for the Evolution of the Western Margin of Pangea

We present the first structural geology focused study of a Triassic pluton in the Northern Andes, which provides new insights into the understanding of the tectonically complex northwestern corner of South America. Based on a combination of field structural data (377 stations) and a detailed magnetic susceptibility survey, 159 sites, we studied the structure of the Pueblito Pluton (PP), an original suprasubduction mafic cumulate structure emplaced in the northern part of the Arquia Terrane (western margin of Central Cordillera of Colombia). Even though the PP has resided along an active margin for over 230 million years ago, geochronology suggests no postcrystallization Ar-loss and, probably, no major reset of the original emplacement fabric. The PP magnetic fabric is dominatly parallel to the measured field foliation and formed under submagmatic to high-temperature conditions, at the final stages of cooling. The pluton internal contacts, mylonitic structures along the western margin, shape of the pluton, scalar parameters of the magnetic fabric, the directional field/magnetic data, and the geochronological data are compatible with a sinistral transpressional tectonic regime of emplacement by ca 233 Ma. This regime was regionally extended in the Arquia and Tahami Terranes (western margin of Pangea).

Magnetic survey of archaeological kiln sites with Overhauser magnetometer: A case study of buried Sue ware kilns in Japan

We conducted magnetic surveys using an Overhauser magnetometer, a fast-sampling, high-accuracy magnetometer, at two archaeological sites in central Japan to detect magnetic anomalies associated with buried climbing Sue ware kilns in suburban hill areas. Our magnetic survey was conducted in two stages, a preliminary sweeping survey followed by a detailed mapping survey. The mapping survey at both sites revealed magnetic anomalies of the order of 10–100 nT that were clearly distinguishable from the low background signals due to the basement rocks and soils. After the magnetic surveys, archaeological excavations were conducted on the basis of these magnetic anomalies, where two kilns were successfully discovered. The shape, dimensions, and magnetization of the kilns are consistent with the amplitude and distribution of the magnetic anomalies. These results highlight that the combination of quick sweeping and detailed mapping magnetic surveys is useful for detecting buried kilns in hillslope areas.

Magnetic and Radiometric Signatures over a Proterozoic Massive Sulfide Setting of Northern Fringe of Dalma Volcanics, Eastern India: An implication to Metallogeny

ABSTRACT Magnetic and radiometric surveys were carried out over a felsic dominated rifted margin of Proterozoic volcanic terrain of a mobile belt in the eastern India. The studies were made in blocks I and II of 0.65 sq km and 0.70 sq km respectively over a previously identified conductor in the northern fringe of Dalma Volcanics (DVs). In general, both the blocks show high magnetic signature associated with sulfide mineralisation. The interpretation of magnetic data suggests that nature of the causative source is mainly horizontal cylinder in both the blocks. The depth to the top of the causative source is about 25 m in both the blocks and extends upto 60 m in block I and 40m in block II. Gamma count rate exhibits about a factor of two to three enhancements above the field background for both the blocks. The obtained iso-rad maps are similar to uranium and copper belt in the Singhbhum shear zone south of the study area. The anomalous radiometric signature of the residual soil/rock of the area indicates towards hydrothermal alteration. The detailed magnetic surveys and preliminary iso-rads results seems quite encouraging and may be attributed to VMS setting in the area and potential sulfide mineralisation with uranium mineral association in the DVs province.

Subsurface architecture of Las Bombas volcano circular structure (Southern Mendoza, Argentina) from geophysical studies

The Plio-Pleistocene Llancanelo volcanic field is located in the south-eastern region of the province of Mendoza, Argentina. This wide back-arc lava plateau, with hundreds of monogenetic pyroclastic cones, covers a large area behind the active Andean volcanic arc. Here we focus on the northern Llancanelo volcanic field, particularly in Las Bombas volcano. Las Bombas volcano is an eroded, but still recognizable, scoria cone located in a circular depression surrounded by a basaltic lava flow, suggesting that Las Bombas volcano was there when the lava flow field formed and, therefore, the lava flow engulfed it completely. While this explanation seems reasonable, the common presence of similar landforms in this part of the field justifies the need to establish correctly the stratigraphic relationship between lava flow fields and these circular depressions. The main purpose of this research is to investigate Las Bombas volcano 3D subsurface architecture by means of geophysical methods. We carried out a paleomagnetic study and detailed topographic, magnetic and gravimetric land surveys. Magnetic anomalies of normal and reverse polarity and paleomagnetic results point to the occurrence of two different volcanic episodes. A circular low Bouguer anomaly was detected beneath Las Bombas scoria cone indicating the existence of a mass deficit. A 3D forward gravity model was constructed, which suggests that the mass deficit would be related to the presence of fracture zones below Las Bombas volcano cone, due to sudden degassing of younger magma beneath it, or to a single phreatomagmatic explosion. Our results provide new and detailed information about Las Bombas volcano subsurface architecture.

Magnetic imaging of the Kurungnakh Island ice complex upper layer structure, Lena Delta, Russia

ABSTRACTGround‐based detailed magnetic surveys have so far been minimally used in permafrost research but they have a great potential to explore near‐surface structures and to reveal their hidden features. This study presents the results of a two‐elevation magnetic survey on a Pleistocene ice complex covered by Holocene deposits and penetrated by ice wedges. A polygonal pattern, which is not distinctly visible on the surface, is successfully identified in the anomalous magnetic field. Obtained data allow to allocate confidently the polygon distribution and to discriminate the ice wedges of different thicknesses. Typical values of total magnetic field anomalies related to ice wedges and frozen sediments in between are about several nanoteslas measured at the elevations of 0.4 and 1.15 m above the surface. Magnetic susceptibility of the permafrost samples is on the order of 10‐4. Observed data were modelled using a numerical magnetic model to estimate quantitatively geometrical and magnetic parameters of the ice complex structure. The best‐fitting model provides the following results: the upper part of the Pleistocene and Holocene ice wedges shows a thickness of 8 and 3 m, respectively, and the upper boundary of the Pleistocene ice wedges where they contact with Holocene wedges rests at 1 m depth. The magnetic susceptibility of frozen sediments between ice wedges is about 0.14 × 10‐3. An anomalously high vertical gradient within the study area has been observed. The presumable sources for this anomaly were considered. Our results suggest that detailed magnetometry could be efficient as it is a rapid and non‐invasive reconnaissance permafrost research.

Status of Karur-Kambam-Painavu-Trichur Shear Zone, Southern Granulite Terrain in the Context of Late Mesozoic Dynamic Evolution of Western Ghats:A Geophysical-Geological Perspective

Detailed magnetic and gravity surveys in the Periyar Plateau and adjoining coastal tract (central Kerala) have brought to light a family of four major geophysical lineaments. These include the NNW-SSE trending Idamalayar lineament (LM-1) and the Kerala lineament (LM-2); both housing gabbroic and doleritic dykes dated ~90 Ma and geochemically related to the Marion plume and the NW trending Periyar lineament (LM-3) and Todupuzha lineament (LM-4) housing in part dolerite dykes dated 65 Ma and chemically related to the Reunion plume. The lineaments largely cut across the litho-tectonic framework of the Precambrian basement. Integrating geological evolution of the region, these lineaments seem to have been formed by reactivation of the deep-seated distensional fractures, that facilitated magmatic emplacements during the episodic breakup of Gondwanaland under distinctive mantle thermal regimes of the Late Mesozoic. Possibly, later in the Cenozoic, these lineaments were enlarged to their present dimensions during the uplift of Western Ghats.

The dynamics of a very large intra-plate continental basaltic volcanic province, the Newer Volcanics Province, SE Australia, and implications for other provinces

Abstract The Newer Volcanics Province of SE Australia is a very large continental basaltic province, with an area of >23 000 km 2 , a dense rock equivalent volume of <900 km 3 and >400 monogenetic volcanoes; it has been active since c. 8 Ma. Lava fields, shields, scoria cones are common, and there are >40 maars and volcanic complexes. Maars occur dominantly in the south where magmas erupted through Tertiary sedimentary aquifers, whereas in the north, over Palaeozoic crust, there are few. Complex interactions of the magma volatile content, magma ascent rates, conduit characteristics and the availability and depth of aquifers caused diverse eruption styles. Volcanoes commonly occur close to major crustal faults, which acted as magma conduits. There is no simple age pattern of volcanism across the province. Volcanism was probably triggered by transtensional decompression in the crust where fault sets intersect, affecting hot, hydrated mantle that had welled up through edge-driven convection where the base of the lithosphere thins abruptly at the edge of the continent. Rock compositions range from picritic to basaltic andesitic. Some volcanoes are polymagmatic. Regional geophysical datasets have clarified the regional characteristics of the province, whereas detailed ground magnetic and gravity surveys resulted in new insights into the subsurface structure of maar-diatremes.

Acquisition procedures, processing methodologies and preliminary results of magnetic and ROV data collected during the TOMO-ETNA experiment

<p>The TOMO-ETNA experiment was devised for the investigation of the continental and oceanic crust beneath Mt. Etna volcano and northeastern Sicily up to the Aeolian Islands, through an active source study. In this experiment, a large amount of geophysical data was collected both inland and in the Ionian and Tyrrhenian Seas for identifying the major geological and structural features offshore Mt. Etna and NE Sicily. One of the oceanographic cruises organized within the TOMO-ETNA experiment was carried out on the hydrographic vessel “Galatea” by Italian Navy. During the cruise a detailed magnetic survey and a set of ROV (remotely operated vehicle) dives were performed offshore Mt. Etna. The magnetic survey allowed the compilation of a preliminary magnetic map revealing a clear direct relationship between volcanic structures and high frequency magnetic anomalies. Significant positive magnetic anomalies were identified offshore the Timpa area and along the easternmost portion of the Riposto Ridge <span>and</span> correlated to a primitive volcanic edifice and to shallow volcanic bodies, respectively. On the whole, the magnetic anomaly map highlights a clear SW-NE decreasing trend, where high amplitude positive magnetic anomaly pattern of the SW sector passes, northeastwardly, to a main negative one. ROV dives permitted to directly explore the shallowest sectors of the Riposto Ridge and to collect several videos and seafloor samples, allowing us to identify some locally developed volcanic manifestations.</p>