Egidio Armadillo - Profile on Academia.edu (original) (raw)

Papers by Egidio Armadillo

Magnetic anomalies caused by 2D polygonal structures with uniform arbitrary polarization: new insights from analytical/numerical comparison among available algorithm formulations

Tantalising new magnetic views of Precambrian and Pan-African age crustal architecture in interior East Antarctica

&... more &am…

Magnetic and gravity views of crust and lithosphere heterogeneity in the Wilkes Subglacial Basin of East Antarctica

<p&amp... more <p>The Wilkes Subglacial Basin (WSB) is a major intraplate tectonic feature in East Antarctica. It stretches for ca 1400 km from the edge of the Southern Ocean, where it is up to 600 km wide towards South Pole, where it is less than 100 km wide. Recent modelling of its subice topography (Paxman et al., 2019, JGR) lends support to a long-standing hypothesis predicting that the wide basin is linked to flexure of more rigid and mostly Precambrian cratonic lithosphere induced by the Cenozoic uplift of the adjacent Trasantarctic Mountains,. However, there is also mounting evidence from potential field and radar exploration that its narrower structurally controlled sub-basins may have formed in response to more localised Mesozoic to Cenozoic extension and transtension that preferentially steered glacial erosion (Paxman et al., 2018, GRL).  </p><p>Here we exploit recent advancements in regional aerogeophysical data compilations and continental scale satellite gravity gradient imaging with the overarching aim of helping unveil the degree of 4D heterogeneity in the crust and lithosphere beneath the WSB. New views of crustal and lithosphere thickness stem from 3D satellite gravity modelling (Pappa et al., 2019, JGR) and these can be compared with predictions from previous flexural modelling and seismological results. By stripping out the computed effects of crustal and lithosphere thickness variations we then obtain residual intra-crustal gravity anomalies. These are in turn compared with a suite of enhanced aeromagnetic anomaly images. We then calculate depth to magnetic and gravity source estimates and use these results to help constrain the first combined 2D magnetic and gravity models for two selected regions within the WSB.</p><p>One first model reveals a major lithospheric scale boundary along the eastern margin of the northern WSB. It separates the Cambro-Ordovician Ross Orogen from a newly defined composite Precambrian Wilkes Terrane that forms the unexposed crustal basement buried beneath partially exposed early Cambrian metasediments and more recent Devonian to Jurassic sediments.</p><p>Our second model investigates a sector of the WSB further south, where the proposed Precambrian basement is modelled as being both shallower and of more felsic bulk composition. Although the lack of drilling precludes direct sampling of this cryptic basement, aeromagnetic anomaly patterns suggest that it may be akin to late Paleoproterozoic to Mesoproterozoic igneous basement exposed in part of the Gawler and Curnamona cratons in South Australia. We conclude that these first order differences in basement depth, bulk composition and thickness of metasediment/sediment cover are a key and previously un-appreciated intra-crustal boundary condition, which is likely to affect geothermal heat flux variability beneath different sectors of the WSB, with potential cascading effects on subglacial hydrology and the flow of the overlying East Antarctic Ice Sheet.</p>

Crustal architecture of the largest pull-apart basin in East Antarctica unveiled

<p>The West Antarctic Rift System (WARS) is known to have experienced distributed/w... more <p>The West Antarctic Rift System (WARS) is known to have experienced distributed/wide mode extension in the Cretaceous, followed by narrow mode and variably oblique extension/transtension in the Cenozoic, the latter potentially linked to the onset of oceanic seafloor spreading within the Adare Basin (Davey et al., 2016, GRL). However, onshore the extent and impact of Cenozoic extension and transtension within the Transantarctic Mountains sector of East Antarctica is currently much less well-constrained from a geophysical perspective.</p> <p>Here we combine aeromagnetic, aerogravity, land-gravity and bedrock topography imaging to help constrain the extent, architecture and kinematics of the largest Cenozoic pull-apart basin recognised so far in East Antarctica, the Rennick Graben (RG).</p> <p>Enhanced potential field imaging reveals the extent of a Jurassic tholeiitic Large Igneous Province preserved within the RG and the inherited structural architecture of its basement, including remnants of uplifted ca 530-500 Ma arc basement in the northern Wilson Terrane and a ca 490-460 Ma subglacial thrust fault belt separating the Cenozoic western flank of the RG from the eastern margin of Wilkes Subglacial Basin (WSB).</p> <p>The architecture of the RG is best explained in terms of a major composite right-lateral pull-part basin that extends from the Oates Coast to the Southern Cross Mountains block. We propose that Cenozoic strike-slip deformation kinematically connected the RG with both the western edge of the WARS and the eastern margin of the WSB. An earlier phase of left-lateral strike slip deformation is also emerging from recent geological field work in the study region but only relatively subtle offsets in aeromagnetic anomaly patterns are visible in currently available regional datasets.</p> <p>We conclude that the RG is part of a wider distributed region of the continental lithosphere in East Antarctica that was deformed in response to an evolving Cenozoic transtensional tectonic setting that may have also affected enigmatic sub-basins such as the Cook Basins in the adjacent WSB region.</p>

Journal of Geophysical Research: Earth Surface

Reconstructions of the bedrock topography of Antarctica since the Eocene-Oligocene Boundary (appr... more Reconstructions of the bedrock topography of Antarctica since the Eocene-Oligocene Boundary (approximately 34 Ma) provide important constraints for modeling Antarctic ice sheet evolution. This is particularly important in regions where the bedrock lies below sea level, since in these sectors the overlying ice sheet is thought to be most susceptible to past and future change. Here we use 3-D flexural modeling to reconstruct the evolution of the topography of the Wilkes Subglacial Basin (WSB) and Transantarctic Mountains (TAM) in East Antarctica. We estimate the spatial distribution of glacial erosion beneath the East Antarctic Ice Sheet, and restore this material to the topography, which is also adjusted for associated flexural isostatic responses. We independently constrain our post-34 Ma erosion estimates using offshore sediment stratigraphy interpretations. Our reconstructions provide a better-defined topographic boundary condition for modeling early East Antarctic Ice Sheet history. We show that the majority of glacial erosion and landscape evolution occurred prior to 14 Ma, which we interpret to reflect more dynamic and erosive early ice sheet behavior. In addition, we use closely spaced 2-D flexural models to test previously proposed hypotheses for a flexural origin of the TAM and WSB. The pre-34 Ma topography shows lateral variations along the length of the TAM and WSB that cannot be explained by uniform flexure along the front of the TAM. We show that some of these variations may be explained by additional flexural uplift along the southwestern flank of the WSB and the Rennick Graben in northern Victoria Land.

Geophysical Research Letters

East Antarctica hosts large subglacial basins into which the East Antarctic Ice Sheet (EAIS) like... more East Antarctica hosts large subglacial basins into which the East Antarctic Ice Sheet (EAIS) likely retreated during past warmer climates. However, the extent of retreat remains poorly constrained, making quantifying past and predicted future contributions to global sea level rise from these marine basins challenging. Geomorphological analysis and flexural modeling within the Wilkes Subglacial Basin are used to reconstruct the ice margin during warm intervals of the Oligocene-Miocene. Flat-lying bedrock plateaus are indicative of an ice sheet margin positioned >400-500 km inland of the modern grounding zone for extended periods of the Oligocene-Miocene, equivalent to a 2-m rise in global sea level. Our findings imply that if major EAIS retreat occurs in the future, isostatic rebound will enable the plateau surfaces to act as seeding points for extensive ice rises, thus limiting extensive ice margin retreat of the scale seen during the early EAIS. Plain Language Summary The Wilkes Subglacial Basin is a large, low-lying topographic depression situated beneath the Antarctic Ice Sheet. Because the land surface of the basin is currently situated below sea level, it is a potential site of ice sheet collapse and rapid retreat in a warming world. Understanding this landscape and how it has evolved through time in relation to past climate and sea level is therefore key to understanding the future dynamics of this part of the ice sheet. Here we report the discovery, using ice-penetrating radar data sets, of extensive subglacial bedrock plateaus within the Wilkes Subglacial Basin. We analyze the geomorphology of these plateau surfaces and reconstruct the evolution of the subglacial landscape through time. Our results indicate that this part of the Wilkes Subglacial Basin was free of ice for extensive and prolonged periods of time during the early stages of ice sheet development. These constraints on past ice sheet extent, together with our landscape reconstruction, can be used by the ice sheet modeling community to better understand the likely future dynamics of this part of the Antarctic Ice Sheet.

High Resolution AeroMagnetic surveys (HRAM) are a novel tool experimented in several countries fo... more High Resolution AeroMagnetic surveys (HRAM) are a novel tool experimented in several countries for volcano and earthquake hazard re-assessment, ground water exploration and mitigation, hazardous waste site characterization and accurate location of buried ferrous objects (drums, UXO, pipelines). The improvements achieved by HRAM stem from lower terrain clearance coupled with accurately positioned, real-time differential navigation on closely spaced flight grids. In field cultural noise filtering, advanced data processing, imaging and improved interpretation techniques enhance data information content. Development of HRAM approaches might also contribute to mitigate environmental hazards present throughout the Italian territory. Hence an HRAM field test was performed in July 2000 in Friuli, NorthEastern Italy to assess the capabilities and limitations of HRAM over a buried pipeline and a domestic waste site. A Cesium magnetometer in towed bird configuration was used on two separate grids. Profile line spacing was 50-100 m and bird nominal ground clearance was set to 50 m. Microlevelled total field magnetic anomaly data forms the basis for subsequent advanced processing products including 3D analytic signal, maximum horizontal gradient of pseudo-gravity and 3D Euler Deconvolution. The magnetic signatures we detected and enhanced over the environmental test site area in Friuli are also compared with similar but more extensive HRAM signatures recently observed in other countries.

A high-resolution aeromagnetic survey (altitude 125 m asl, spacing 500 m , area 800 km 2) was car... more A high-resolution aeromagnetic survey (altitude 125 m asl, spacing 500 m , area 800 km 2) was carried out in 1994 offshore of Cape Roberts by the GITARA (German ITalian Aeromagnetic Research in Antarctica) Group. The availability from drilling of whole-core physical properties logs for magnetic susceptibility, P-wave velocity and density/porosity data allows new insights to be inferred from reprocessed and reviewed HRAM aeromagnetic data. Aeromagnetic data have been reprocessed to image with greater detail the structural framework along the western flank of the Victoria Land Basin. New processing includes 2D Werner and 3D Euler deconvolution, the production of maps of the maximum horizontal gradient of pseudo-gravity, and 2D, 3D modelling. Magnetic trends and anomalies are discussed in conjunction with now available drilling results from the CRP, existing bathymetric data and recently published interpretations of a multichannel seismic reflection survey.

GDS (Geomagnetic Depth Sounding) in Italy: Applications and perspectives

The analysis of geomagnetic field variations is a useful tool to detect electrical conductivity c... more The analysis of geomagnetic field variations is a useful tool to detect electrical conductivity contrasts within the Earth. Lateral resolution of outlined patterns depends on the array dimensions and density of measurement sites over the investigated area. The inspection ...

A geomagnetic depth sounding investigation in the period range 20-250 s has been carried out alon... more A geomagnetic depth sounding investigation in the period range 20-250 s has been carried out along the Oates Coast and across the Rennick Graben (RG) to get geophysical independent constraints on the deep structure of the Oates Land. Along the former profile the coast effect hinders structural interpretation; on the contrary, the latter profile across the RG shows a well characterized regional bidimensional pattern with induction arrows trend perpendicular to the graben and the main structural lineaments. Interpretations by induction arrows analysis and 2D inversion suggest a clear differentiation of the investigated area in three crustal blocks separated by the Daniels Range and the Bowers Mts., in close relation with main known structural lineaments. The thickening of the shallow resistivity layer from the East to the West of the RG could indicate a thickening of the resistive upper crust which usually overlays the enhanced conductive layer in the lower continental crust. At depth over 15 km, two electrical conductivity anomalies are located at both the sides of the RG which on the contrary is not affected by electrical conductivity enhancement, suggesting a recent reactivation of the shoulders rather than of the graben itself. A shallow conductivity anomaly below the Bowers Mts. is associated with strong positive gravimetric and magnetic signatures.

Large Subsurface Hollows Revealed by Means of Electrical Resistivity Tomography : The Case of Mt. Armetta Karst Area, Italy

In this work we show the results of a resistivity tomography performed over the shallow part of a... more In this work we show the results of a resistivity tomography performed over the shallow part of a large cave system in the Mt.Armetta karst, Pennavaira valley northwestern Italy. The cave has been explored and surveyed by the authors themselves, thus a precise knowledge of size and shape of the subsurface voids is available. The cave, whose shallowest part exhibits narrow passages and large chambers, was developed in the Mesozoic sedimentary cover(Caprauna Armetta tectonic unit), an allochtonous nappe characterized by four deformation phases. The main target of the experiment is a region located at about 30 m below surface precisely spotted by ve 235m long ERT sections. Since cave develops in a windy summit area, the long-term stability of an eolic power plant tower, located over a karst void, is also considered. As a matter of fact, the footings of the eolic towers (approx 100 m high) may interfere with unpredictable shallow hollows, whose presence, in the power plant area, is more...

Key words petrophysics -thermal and magnetic properties -radioactive heat production -volcanic rocks

Statistical analysis of the polar electrojet influence on geomagnetic transfer functions estimate... more Statistical analysis of the polar electrojet influence on geomagnetic transfer functions estimates over wide time and space scales. D.Rizzello(1),E.Armadillo(1),A.Manzella(2) 1)DISTAV - University of Genoa,Italy. 2)Institute of Geosciences and Earth Resources - CNR, Pisa, Italy. Magnetotelluric (MT) and magnetovariational (MV) investigations can provide original information and constraints on the electrical conductivity, thermal state and structure of the crust and mantle at the base of the polar ice sheets. These methods provide depth resolution, lacking in potential field methods, and can reach high investigation depth, an invaluable advantage where very difficult logistic conditions prevent or limit the use of active methods such as seismic surveys. However, MT/MV surveys have not been applied extensively in polar areas mainly because electromagnetic data could be biased by the polar electrojet current systems (PEJ) occurring at high geomagnetic latitude. In fact, close to the au...

Time-series of radon concentration and environmental parameters were recently recorded in a urani... more Time-series of radon concentration and environmental parameters were recently recorded in a uranium mine gallery, located in the Maritime Alps (NW Italy). The mine was bored in metarhyolites and porphyric schists mainly composed by quartz, feldspar, sericite and fluorite. U-bearing minerals are generally concentrated in veins heterogeneously spaced and made of crystals of metaautunite and metatorbernite. Radon air concentration monitoring was performed with an ionization chamber which was placed at the bottom of the gallery. Hourly mean values of temperature, pressure, and relative humidity were also measured. External data of atmospheric temperature, pressure and rainfall were also available from a meteorological station located nearby, at a similar altitude of the mine. The analysis of the time series recorded showed variation of radon concentration, of large amplitude, exhibiting daily and half-daily periods, which do not seem correlated with meteorological records. Searching for...

Integrated MVG and ERT Survey Over a Shallow Cave

An integrated geophysical MVG (Microgravity Vertical Gradient) and ERT (Electrical Resistivity To... more An integrated geophysical MVG (Microgravity Vertical Gradient) and ERT (Electrical Resistivity Tomography) survey was performed over a shallow cave in the Armetta Mountain karst area, close to the Liguria-Piedmont watershed (Tanaro valley). The aim of this study is to test the response of a known shallow karst cave. The cave was developed in the Mesozoic sedimentary cover (dolostones and limestones

Thermal, radioactive and magnetic properties of the lavas of the Mt Melbourne Volcanic Field (Victoria Land, Antarctica)

We present the results of measurements of physical properties carried out on mafic lavas from the... more We present the results of measurements of physical properties carried out on mafic lavas from the Mt MelbourneVolcanic Field, useful for interpretation of geophysical surveys designed to shed light on the structure of thecrust. The thermal conductivity is comparable to that of glass and shows a clear negative dependence on porosity.The volume heat capacity and the thermal diffusivity are less variable. The concentration of the thermallyimportant natural radioactive isotopes was determined by gamma-ray spectrometry. Lavas denoted a rather lowheat-production rate, and the largest concentration of heat-producing elements (potassium, uranium, thorium)was found in the trachyte samples. The magnetic susceptibility is more variable than the other physical propertiesand, among the several iron-titanium oxides, it appears primarily controlled by the ulvöspinel-magnetite solidsolution series.

Earth, Planets and Space, 2001

A Geomagnetic Depth Sounding (GDS) survey covering the Northern Apennines of Italy has been carri... more A Geomagnetic Depth Sounding (GDS) survey covering the Northern Apennines of Italy has been carried out in the period 1992-94. Induction arrows maps and hypothetical event Fourier maps were constructed to obtain an electromagnetic imaging of this area. Since the two dimensional (2-D) character comes out from those maps for periods greater than 32 minutes, a 2-D inverse modeling was carried out. The model responses show that a deep conductive layer (>5000 S) underlies the Apennine chain at about 20 km depth. The transition between the Adriatic and the Tyrrhenian domains is marked by a rather sharp vertical offset in this conducting layer. In the northwest sector of the studied area an anomalous high conductivity behavior is superimposed on the regional trend, which corresponds to the geothermal field of Larderello-Travale.

Imaging deep and shallow structures by electromagnetic soundings moving from the Transantarctic Mountains to the Wilkes Subglacial Basin

Magnetic anomalies caused by 2D polygonal structures with uniform arbitrary polarization: new insights from analytical/numerical comparison among available algorithm formulations

Tantalising new magnetic views of Precambrian and Pan-African age crustal architecture in interior East Antarctica

&... more &am…

Magnetic and gravity views of crust and lithosphere heterogeneity in the Wilkes Subglacial Basin of East Antarctica

<p&amp... more <p>The Wilkes Subglacial Basin (WSB) is a major intraplate tectonic feature in East Antarctica. It stretches for ca 1400 km from the edge of the Southern Ocean, where it is up to 600 km wide towards South Pole, where it is less than 100 km wide. Recent modelling of its subice topography (Paxman et al., 2019, JGR) lends support to a long-standing hypothesis predicting that the wide basin is linked to flexure of more rigid and mostly Precambrian cratonic lithosphere induced by the Cenozoic uplift of the adjacent Trasantarctic Mountains,. However, there is also mounting evidence from potential field and radar exploration that its narrower structurally controlled sub-basins may have formed in response to more localised Mesozoic to Cenozoic extension and transtension that preferentially steered glacial erosion (Paxman et al., 2018, GRL).  </p><p>Here we exploit recent advancements in regional aerogeophysical data compilations and continental scale satellite gravity gradient imaging with the overarching aim of helping unveil the degree of 4D heterogeneity in the crust and lithosphere beneath the WSB. New views of crustal and lithosphere thickness stem from 3D satellite gravity modelling (Pappa et al., 2019, JGR) and these can be compared with predictions from previous flexural modelling and seismological results. By stripping out the computed effects of crustal and lithosphere thickness variations we then obtain residual intra-crustal gravity anomalies. These are in turn compared with a suite of enhanced aeromagnetic anomaly images. We then calculate depth to magnetic and gravity source estimates and use these results to help constrain the first combined 2D magnetic and gravity models for two selected regions within the WSB.</p><p>One first model reveals a major lithospheric scale boundary along the eastern margin of the northern WSB. It separates the Cambro-Ordovician Ross Orogen from a newly defined composite Precambrian Wilkes Terrane that forms the unexposed crustal basement buried beneath partially exposed early Cambrian metasediments and more recent Devonian to Jurassic sediments.</p><p>Our second model investigates a sector of the WSB further south, where the proposed Precambrian basement is modelled as being both shallower and of more felsic bulk composition. Although the lack of drilling precludes direct sampling of this cryptic basement, aeromagnetic anomaly patterns suggest that it may be akin to late Paleoproterozoic to Mesoproterozoic igneous basement exposed in part of the Gawler and Curnamona cratons in South Australia. We conclude that these first order differences in basement depth, bulk composition and thickness of metasediment/sediment cover are a key and previously un-appreciated intra-crustal boundary condition, which is likely to affect geothermal heat flux variability beneath different sectors of the WSB, with potential cascading effects on subglacial hydrology and the flow of the overlying East Antarctic Ice Sheet.</p>

Crustal architecture of the largest pull-apart basin in East Antarctica unveiled

<p>The West Antarctic Rift System (WARS) is known to have experienced distributed/w... more <p>The West Antarctic Rift System (WARS) is known to have experienced distributed/wide mode extension in the Cretaceous, followed by narrow mode and variably oblique extension/transtension in the Cenozoic, the latter potentially linked to the onset of oceanic seafloor spreading within the Adare Basin (Davey et al., 2016, GRL). However, onshore the extent and impact of Cenozoic extension and transtension within the Transantarctic Mountains sector of East Antarctica is currently much less well-constrained from a geophysical perspective.</p> <p>Here we combine aeromagnetic, aerogravity, land-gravity and bedrock topography imaging to help constrain the extent, architecture and kinematics of the largest Cenozoic pull-apart basin recognised so far in East Antarctica, the Rennick Graben (RG).</p> <p>Enhanced potential field imaging reveals the extent of a Jurassic tholeiitic Large Igneous Province preserved within the RG and the inherited structural architecture of its basement, including remnants of uplifted ca 530-500 Ma arc basement in the northern Wilson Terrane and a ca 490-460 Ma subglacial thrust fault belt separating the Cenozoic western flank of the RG from the eastern margin of Wilkes Subglacial Basin (WSB).</p> <p>The architecture of the RG is best explained in terms of a major composite right-lateral pull-part basin that extends from the Oates Coast to the Southern Cross Mountains block. We propose that Cenozoic strike-slip deformation kinematically connected the RG with both the western edge of the WARS and the eastern margin of the WSB. An earlier phase of left-lateral strike slip deformation is also emerging from recent geological field work in the study region but only relatively subtle offsets in aeromagnetic anomaly patterns are visible in currently available regional datasets.</p> <p>We conclude that the RG is part of a wider distributed region of the continental lithosphere in East Antarctica that was deformed in response to an evolving Cenozoic transtensional tectonic setting that may have also affected enigmatic sub-basins such as the Cook Basins in the adjacent WSB region.</p>

Journal of Geophysical Research: Earth Surface

Reconstructions of the bedrock topography of Antarctica since the Eocene-Oligocene Boundary (appr... more Reconstructions of the bedrock topography of Antarctica since the Eocene-Oligocene Boundary (approximately 34 Ma) provide important constraints for modeling Antarctic ice sheet evolution. This is particularly important in regions where the bedrock lies below sea level, since in these sectors the overlying ice sheet is thought to be most susceptible to past and future change. Here we use 3-D flexural modeling to reconstruct the evolution of the topography of the Wilkes Subglacial Basin (WSB) and Transantarctic Mountains (TAM) in East Antarctica. We estimate the spatial distribution of glacial erosion beneath the East Antarctic Ice Sheet, and restore this material to the topography, which is also adjusted for associated flexural isostatic responses. We independently constrain our post-34 Ma erosion estimates using offshore sediment stratigraphy interpretations. Our reconstructions provide a better-defined topographic boundary condition for modeling early East Antarctic Ice Sheet history. We show that the majority of glacial erosion and landscape evolution occurred prior to 14 Ma, which we interpret to reflect more dynamic and erosive early ice sheet behavior. In addition, we use closely spaced 2-D flexural models to test previously proposed hypotheses for a flexural origin of the TAM and WSB. The pre-34 Ma topography shows lateral variations along the length of the TAM and WSB that cannot be explained by uniform flexure along the front of the TAM. We show that some of these variations may be explained by additional flexural uplift along the southwestern flank of the WSB and the Rennick Graben in northern Victoria Land.

Geophysical Research Letters

East Antarctica hosts large subglacial basins into which the East Antarctic Ice Sheet (EAIS) like... more East Antarctica hosts large subglacial basins into which the East Antarctic Ice Sheet (EAIS) likely retreated during past warmer climates. However, the extent of retreat remains poorly constrained, making quantifying past and predicted future contributions to global sea level rise from these marine basins challenging. Geomorphological analysis and flexural modeling within the Wilkes Subglacial Basin are used to reconstruct the ice margin during warm intervals of the Oligocene-Miocene. Flat-lying bedrock plateaus are indicative of an ice sheet margin positioned >400-500 km inland of the modern grounding zone for extended periods of the Oligocene-Miocene, equivalent to a 2-m rise in global sea level. Our findings imply that if major EAIS retreat occurs in the future, isostatic rebound will enable the plateau surfaces to act as seeding points for extensive ice rises, thus limiting extensive ice margin retreat of the scale seen during the early EAIS. Plain Language Summary The Wilkes Subglacial Basin is a large, low-lying topographic depression situated beneath the Antarctic Ice Sheet. Because the land surface of the basin is currently situated below sea level, it is a potential site of ice sheet collapse and rapid retreat in a warming world. Understanding this landscape and how it has evolved through time in relation to past climate and sea level is therefore key to understanding the future dynamics of this part of the ice sheet. Here we report the discovery, using ice-penetrating radar data sets, of extensive subglacial bedrock plateaus within the Wilkes Subglacial Basin. We analyze the geomorphology of these plateau surfaces and reconstruct the evolution of the subglacial landscape through time. Our results indicate that this part of the Wilkes Subglacial Basin was free of ice for extensive and prolonged periods of time during the early stages of ice sheet development. These constraints on past ice sheet extent, together with our landscape reconstruction, can be used by the ice sheet modeling community to better understand the likely future dynamics of this part of the Antarctic Ice Sheet.

High Resolution AeroMagnetic surveys (HRAM) are a novel tool experimented in several countries fo... more High Resolution AeroMagnetic surveys (HRAM) are a novel tool experimented in several countries for volcano and earthquake hazard re-assessment, ground water exploration and mitigation, hazardous waste site characterization and accurate location of buried ferrous objects (drums, UXO, pipelines). The improvements achieved by HRAM stem from lower terrain clearance coupled with accurately positioned, real-time differential navigation on closely spaced flight grids. In field cultural noise filtering, advanced data processing, imaging and improved interpretation techniques enhance data information content. Development of HRAM approaches might also contribute to mitigate environmental hazards present throughout the Italian territory. Hence an HRAM field test was performed in July 2000 in Friuli, NorthEastern Italy to assess the capabilities and limitations of HRAM over a buried pipeline and a domestic waste site. A Cesium magnetometer in towed bird configuration was used on two separate grids. Profile line spacing was 50-100 m and bird nominal ground clearance was set to 50 m. Microlevelled total field magnetic anomaly data forms the basis for subsequent advanced processing products including 3D analytic signal, maximum horizontal gradient of pseudo-gravity and 3D Euler Deconvolution. The magnetic signatures we detected and enhanced over the environmental test site area in Friuli are also compared with similar but more extensive HRAM signatures recently observed in other countries.

A high-resolution aeromagnetic survey (altitude 125 m asl, spacing 500 m , area 800 km 2) was car... more A high-resolution aeromagnetic survey (altitude 125 m asl, spacing 500 m , area 800 km 2) was carried out in 1994 offshore of Cape Roberts by the GITARA (German ITalian Aeromagnetic Research in Antarctica) Group. The availability from drilling of whole-core physical properties logs for magnetic susceptibility, P-wave velocity and density/porosity data allows new insights to be inferred from reprocessed and reviewed HRAM aeromagnetic data. Aeromagnetic data have been reprocessed to image with greater detail the structural framework along the western flank of the Victoria Land Basin. New processing includes 2D Werner and 3D Euler deconvolution, the production of maps of the maximum horizontal gradient of pseudo-gravity, and 2D, 3D modelling. Magnetic trends and anomalies are discussed in conjunction with now available drilling results from the CRP, existing bathymetric data and recently published interpretations of a multichannel seismic reflection survey.

GDS (Geomagnetic Depth Sounding) in Italy: Applications and perspectives

The analysis of geomagnetic field variations is a useful tool to detect electrical conductivity c... more The analysis of geomagnetic field variations is a useful tool to detect electrical conductivity contrasts within the Earth. Lateral resolution of outlined patterns depends on the array dimensions and density of measurement sites over the investigated area. The inspection ...

A geomagnetic depth sounding investigation in the period range 20-250 s has been carried out alon... more A geomagnetic depth sounding investigation in the period range 20-250 s has been carried out along the Oates Coast and across the Rennick Graben (RG) to get geophysical independent constraints on the deep structure of the Oates Land. Along the former profile the coast effect hinders structural interpretation; on the contrary, the latter profile across the RG shows a well characterized regional bidimensional pattern with induction arrows trend perpendicular to the graben and the main structural lineaments. Interpretations by induction arrows analysis and 2D inversion suggest a clear differentiation of the investigated area in three crustal blocks separated by the Daniels Range and the Bowers Mts., in close relation with main known structural lineaments. The thickening of the shallow resistivity layer from the East to the West of the RG could indicate a thickening of the resistive upper crust which usually overlays the enhanced conductive layer in the lower continental crust. At depth over 15 km, two electrical conductivity anomalies are located at both the sides of the RG which on the contrary is not affected by electrical conductivity enhancement, suggesting a recent reactivation of the shoulders rather than of the graben itself. A shallow conductivity anomaly below the Bowers Mts. is associated with strong positive gravimetric and magnetic signatures.

Large Subsurface Hollows Revealed by Means of Electrical Resistivity Tomography : The Case of Mt. Armetta Karst Area, Italy

In this work we show the results of a resistivity tomography performed over the shallow part of a... more In this work we show the results of a resistivity tomography performed over the shallow part of a large cave system in the Mt.Armetta karst, Pennavaira valley northwestern Italy. The cave has been explored and surveyed by the authors themselves, thus a precise knowledge of size and shape of the subsurface voids is available. The cave, whose shallowest part exhibits narrow passages and large chambers, was developed in the Mesozoic sedimentary cover(Caprauna Armetta tectonic unit), an allochtonous nappe characterized by four deformation phases. The main target of the experiment is a region located at about 30 m below surface precisely spotted by ve 235m long ERT sections. Since cave develops in a windy summit area, the long-term stability of an eolic power plant tower, located over a karst void, is also considered. As a matter of fact, the footings of the eolic towers (approx 100 m high) may interfere with unpredictable shallow hollows, whose presence, in the power plant area, is more...

Key words petrophysics -thermal and magnetic properties -radioactive heat production -volcanic rocks

Statistical analysis of the polar electrojet influence on geomagnetic transfer functions estimate... more Statistical analysis of the polar electrojet influence on geomagnetic transfer functions estimates over wide time and space scales. D.Rizzello(1),E.Armadillo(1),A.Manzella(2) 1)DISTAV - University of Genoa,Italy. 2)Institute of Geosciences and Earth Resources - CNR, Pisa, Italy. Magnetotelluric (MT) and magnetovariational (MV) investigations can provide original information and constraints on the electrical conductivity, thermal state and structure of the crust and mantle at the base of the polar ice sheets. These methods provide depth resolution, lacking in potential field methods, and can reach high investigation depth, an invaluable advantage where very difficult logistic conditions prevent or limit the use of active methods such as seismic surveys. However, MT/MV surveys have not been applied extensively in polar areas mainly because electromagnetic data could be biased by the polar electrojet current systems (PEJ) occurring at high geomagnetic latitude. In fact, close to the au...

Time-series of radon concentration and environmental parameters were recently recorded in a urani... more Time-series of radon concentration and environmental parameters were recently recorded in a uranium mine gallery, located in the Maritime Alps (NW Italy). The mine was bored in metarhyolites and porphyric schists mainly composed by quartz, feldspar, sericite and fluorite. U-bearing minerals are generally concentrated in veins heterogeneously spaced and made of crystals of metaautunite and metatorbernite. Radon air concentration monitoring was performed with an ionization chamber which was placed at the bottom of the gallery. Hourly mean values of temperature, pressure, and relative humidity were also measured. External data of atmospheric temperature, pressure and rainfall were also available from a meteorological station located nearby, at a similar altitude of the mine. The analysis of the time series recorded showed variation of radon concentration, of large amplitude, exhibiting daily and half-daily periods, which do not seem correlated with meteorological records. Searching for...

Integrated MVG and ERT Survey Over a Shallow Cave

An integrated geophysical MVG (Microgravity Vertical Gradient) and ERT (Electrical Resistivity To... more An integrated geophysical MVG (Microgravity Vertical Gradient) and ERT (Electrical Resistivity Tomography) survey was performed over a shallow cave in the Armetta Mountain karst area, close to the Liguria-Piedmont watershed (Tanaro valley). The aim of this study is to test the response of a known shallow karst cave. The cave was developed in the Mesozoic sedimentary cover (dolostones and limestones

Thermal, radioactive and magnetic properties of the lavas of the Mt Melbourne Volcanic Field (Victoria Land, Antarctica)

We present the results of measurements of physical properties carried out on mafic lavas from the... more We present the results of measurements of physical properties carried out on mafic lavas from the Mt MelbourneVolcanic Field, useful for interpretation of geophysical surveys designed to shed light on the structure of thecrust. The thermal conductivity is comparable to that of glass and shows a clear negative dependence on porosity.The volume heat capacity and the thermal diffusivity are less variable. The concentration of the thermallyimportant natural radioactive isotopes was determined by gamma-ray spectrometry. Lavas denoted a rather lowheat-production rate, and the largest concentration of heat-producing elements (potassium, uranium, thorium)was found in the trachyte samples. The magnetic susceptibility is more variable than the other physical propertiesand, among the several iron-titanium oxides, it appears primarily controlled by the ulvöspinel-magnetite solidsolution series.

Earth, Planets and Space, 2001

A Geomagnetic Depth Sounding (GDS) survey covering the Northern Apennines of Italy has been carri... more A Geomagnetic Depth Sounding (GDS) survey covering the Northern Apennines of Italy has been carried out in the period 1992-94. Induction arrows maps and hypothetical event Fourier maps were constructed to obtain an electromagnetic imaging of this area. Since the two dimensional (2-D) character comes out from those maps for periods greater than 32 minutes, a 2-D inverse modeling was carried out. The model responses show that a deep conductive layer (>5000 S) underlies the Apennine chain at about 20 km depth. The transition between the Adriatic and the Tyrrhenian domains is marked by a rather sharp vertical offset in this conducting layer. In the northwest sector of the studied area an anomalous high conductivity behavior is superimposed on the regional trend, which corresponds to the geothermal field of Larderello-Travale.

Imaging deep and shallow structures by electromagnetic soundings moving from the Transantarctic Mountains to the Wilkes Subglacial Basin