Interpretation Of Magnetic Data Research Articles

Structure and geological history of the Congo Basin: an integrated interpretation of gravity, magnetic and reflection seismic data

The stratigraphic, paleogeographic and tectonic evolution of the intracratonic Congo Basin in Central Africa has been revised on the basis of an integrated interpretation of gravity, magnetic and reflection seismic data, together with a literature review of papers sometimes old and difficult to access, map compilation and partial reexamination of outcrop and core samples stored in the Royal Museum for Central Africa (RMCA). The Congo Basin has a long and complex evolution starting in the Neoproterozoic and governed by the interplay of tectonic and climatic factors, in a variety of depositional environments.This multidisciplinary study involving 2D gravity and magnetic modeling as additional constraints for the interpretation of seismic profiles appears to be a powerful tool to investigate sedimentary basins where seismic data alone may be difficult to interpret. The tectonic deformations detected in the Congo Basin after the 1970–1984 hydrocarbon exploration campaign in the Democratic Republic of Congo (DRC) have been attributed to crustal contraction and basement uplift at the center of the basin, following a transpressional inversion of earlier graben structures. Two-dimensional gravity and magnetic models run along key seismic lines suggest the presence of evaporite sequences in some of the deeper units of the stratigraphic succession, in the lateral continuity with those observed in the Mbandaka and Gilson exploration wells. The poorly defined seismic facies that led to the previous basement uplift interpretation of the crystalline basement is shown to correspond to salt-rich formations that have been tectonically de-stabilized. These features may be related to vertical salt-tectonics connected to the near/far-field effects of the late Pan-African and the Permo-Triassic compressive tectonic events that affected this African part of Gondwana.

Use of non-linear filtering for the regional–residual separation of potential field data

Abstract Regional–residual separation is essential in gravity and magnetic data interpretation and a variety of techniques have been proposed. Graphical determination of the regional allows geological information to be taken into account. Upward continuation can be used to obtain the regional field either empirically or using some hypothesis about the geology. In some cases, a matched filter can be designed and used to separate deep and shallow sources. Simple low pass filtering has also been used but without much success. Here we propose to use a non-linear filter approach to remove gravity and magnetic anomalies smaller than a given width. This technique attempts to mimic the graphical separation method. The results from synthetic models are presented as well as the results from a case study in eastern Canada and compared to regional gravity and magnetic anomalies obtained by other techniques. Contrary to the regional fields obtained by upward continuation, non-linear filtering does not have any physical meaning. However, its main advantage is that it gives a regional component of the gravity or magnetic field similar to the one obtained from a graphical separation.

Structural correlates of active-staining following magnetic resonance microscopy in the mouse brain

Extensive worldwide efforts are underway to produce knockout mice for each of the ~25,000 mouse genes, which may give new insights into the underlying pathophysiology of neurological disease. Microscopic magnetic resonance imaging (μMRI) is a key method for non-invasive morphological phenotyping, capable of producing high-resolution 3D images of ex-vivo brains, after fixation with an MR contrast agent. These agents have been suggested to act as active-stains, enhancing structures not normally visible on MRI. In this study, we investigated the structural correlates of the MRI agent Gd-DTPA, together with the optimal preparation and scan parameters for contrast-enhanced gradient-echo imaging of the mouse brain. We observed that in-situ preparation was preferential to ex-situ due to the degree of extraction damage. In-situ brains scanned with optimised parameters, enabled images with a high signal-to-noise-ratio (SNR ~30) and comprehensive anatomical delineation. Direct correlation of the MR brain structures to histology, detailed fine histoarchitecture in the cortex, cerebellum, olfactory bulb and hippocampus. Neurofilament staining demonstrated that regions of negative MR contrast strongly correlated to myelinated white-matter structures, whilst structures of more positive MR contrast corresponded to areas with high grey matter content. We were able to identify many sub-regions, particularly within the hippocampus, such as the unmyelinated mossy fibres (stratum lucidum) and their region of synapse in the stratum pyramidale, together with the granular layer of the dentate gyrus, an area of densely packed cell bodies, which was clearly visible as a region of hyperintensity. This suggests that cellular structure influences the site-specific distribution of the MR contrast agent, resulting in local variations in T2*, which leads to enhanced tissue discrimination. Our findings provide insights not only into the cellular distribution and mechanism of MR active-staining, but also allow for three dimensional analysis, which enables interpretation of magnetic resonance microscopy brain data and highlights cellular structure for investigation of disease processes in development and disease.

Magnetization reversal of nanodots with different magnetic anisotropy and magnetostatic energy

The arrays of circle and square nanodots were prepared by Ga+ ion-beam etching of thing cobalt films with induced uniaxial magnetic anisotropy. The size of researched nanodots was d=600, 450 and 250 nm that equal or less then radius of ferromagnetic correlation for continuous Co film. The distances l=2d and 3d between center of nanodots in the arrays were taken. The interpretation of experimental magnetic force microscopy data was done by means of micromagnetic simulation and MFM-experiment simulation. Each nanodot of arrays with d=600 nm has multidomain structure at demagnetisation state for l=3d and magnetic vortex for l=2d. For arrays with size of element d<600 nm and l=2d and 3d at same condition occurred only vortex state.

Interprétation des données magnétiques du chapeau de fer de Laachach (Jebilets centrales, Maroc): Implications minières

In the hercynian massif of Central Jebilets (Morocco), outcrop a large number of gossans which sometimes top economical orebodies (Kettara, Draa Sfar, etc.). The present study is devoted to the interpretation of magnetic data covering one of these iron hats, located near of the Laachach village, at about thirty kilometres north-westward of Marrakech. The magnetic map of Laachach highlights several anomalies which coincide with the outcrop of the gossan. Detailed analysis of reduced to the pole data allows us to conclude that these anomalies may be due to submeridian magnetic structures cut by a set of dextral transverse faults. These structures are generally dipping westward but they can be locally sub vertical. The Euler deconvolution of the magnetic data gives moderately deeping solutions (22 to 254 m). The quantitative interpretation of the two principal magnetic anomalies highlighted in the study area lead to better characterising of the deep structure of the Laachach magnetic bodies, that may correspond to massive sulphide occurrences, according to the geological and mining context of the study area. The two modelled bodies constitute priority recognition targets for any mining exploration program to be car ried out on the Laachach site.

Integrated Interpretation of FALCON Airborne Gravity Gradiometer, Magnetic and Seismic data acquired over the Chirete Block, Argentina

Integrated Interpretation of FALCON Airborne Gravity Gradiometer, Magnetic and Seismic data acquired over the Chirete Block, Argentina

GEOPHYSICAL MODELLING OF THE MOLOPO FARMS COMPLEX IN SOUTHERN BOTSWANA; IMPLICATIONS FOR ITS EMPLACEMENT WITHIN THE 2 GA LARGE IGNEOUS PROVINCES OF SOUTHERN AND CENTRAL AFRICA

The Molopo Farms Complex is an extremely poorly exposed, major, ultramafic-mafic layered intrusion straddling the southern border of Botswana with South Africa. It lies within the south-western part of the ~2.0 Ga large igneous province of southern and central Africa that includes the better known Bushveld Complex. Integrated interpretation of regional gravity data and new high-resolution airborne magnetic data have constrained the geometry of the Molopo Farms Complex in southern Botswana as a strongly faulted, polyphase intrusion compartmentalised by regional ductile shear zones. Previous models showing that the Complex was emplaced in at least two discrete stages are supported. Ultramafic rocks were initially emplaced as a semi-coherent lopolithic sheet up to about 4 km in thickness cutting across Transvaal Supergroup strata that had already been folded into open eastwest trending dome and basin structures with wavelengths of about 4 km. Steeply dipping, dyke-like ultramafic bodies adjacent to, and within major shears are inferred to be solidified feeders to the main lopolithic part of the MFC. It is likely that the initial ultramafic sheet was emplaced at a high crustal level (<3 km depth) into an attenuated Transvaal Supergroup sequence. This lack of a thick hanging wall sequence is thought to be significant for the emplacement of the succeeding mafic sheets. The ultramafic sheet thermally altered its wall rock and also created a complex fracture system in its hanging wall rocks. Differentiation within the ultramafic sheet produced basal harzburgites overlain by bronzites and possibly mafic sheets. Later mafic/basic sheets and dykes, again fed along shear-controlled, steeply dipping zones, spread into the fracture network created by the initial emplacement of the ultramafic lopolith to form a distinctive spider’s-web pattern on high-resolution airborne magnetic maps. It is proposed that either post-emplacement regional folding or gravitational collapse of the basal ultramafic lopolith produced a major basin with a ~40 km eastwest diameter, north of the Jwaneng-Makopong Shear Zone and smaller basin to the southeast. The newly postulated, steeply dipping ultramafic/mafic feeders, as well as the ultramafic lopolith and areas with anomalous nickel values in soils are considered to be prospective for PGE-bearing magmatic nickel-copper sulphide mineralisation. Magmatic rocks dated at about 2.0 Ga are a common feature, not only of the Kaapvaal Craton, but of all the African cratonic blocks south of the Equator. Reactivated intracratonic faults and shears appear to control emplacement of individual magmatic complexes although a sub-continental thermal anomaly unconfined by lithospheric plate boundaries is a likely driving force for the widespread magmatism.

Three‐dimensional structure of the submarine flanks of La Réunion inferred from geophysical data

La Réunion (Indian Ocean) constitutes a huge volcanic oceanic system of which most of the volume is submerged. We present a study of its submarine part based on the interpretation of magnetic and gravity data compiled from old and recent surveys. A model of the submarine internal structure is derived from 3‐D and 2‐D models using constraints from previous geological and geophysical studies. Two large‐scale, previously unknown, buried volcanic construction zones are discovered in continuation of the island's construction. To the east, the Alizés submarine zone is interpreted as the remnants of Les Alizés volcano eastward flank whose center is marked by a large hypovolcanic intrusion complex. To the southwest, the Etang Salé submarine zone is interpreted as an extension of Piton des Neiges, probably fed by a volcanic rift zone over a large extent. They were predominantly built during the Matuyama period and thus probably belong to early volcanism. A correlation exists between their top and seismic horizons recognized in previous studies and interpreted as the base of the volcanic edifice. Their morphology suggested a lithospheric bulging beneath La Réunion, not required to explain our data, since the seismic interfaces match the top of our volcanic constructions. The coastal shelf coincides with a negative Bouguer anomaly belt, often associated with magnetic anomalies, suggesting a shelf built by hyaloclastites. A detailed analysis of the offshore continuation of La Montagne Massif to the north confirms this hypothesis. The gravity analysis confirms that the bathymetric bulges, forming the northern, eastern, southern, and western submarine flanks, are predominantly built by debris avalanche deposits at the surface.

Reduction to the Pole at the Geomagnetic Equator

AbstractReduction to the pole (RTP) is a standard part of magnetic data processing method, especially for large‐scale mapping. RTP operation can transform a magnetic anomaly caused by an arbitrary source into the anomaly that the same source would produce if it is located at the pole and magnetized by induction only. Interpretation of magnetic data can further be helped by RTP in order to remove the influence of magnetic latitude on the anomalies, which is significant for anomalies caused by crust. The solution of RTP in the wave number domain faces a long standing difficulty of instability when the observed data are acquired at low latitudes especially at the geomagnetic equator. We present a new solution to this problem that allows stable reconstruction of the RTP field with a high fidelity at the magnetic equator, combining the reduction to the equator (RTE) and the phase reversal interpretation method for ∆T anomalies at low latitudes. The operation with RTE can transform theoretical magnetic anomalies located at the pole and magnetized by induction only into the observed magnetic anomalies. RTE used in our RTP procedure named SRTE is an absolutely stable potential field transformation. The principle of method is very simple, it can transform the observed magnetic anomaly at geomagnetic equator into the anomaly that would have been measured if the magnetization and ambient field were both vertical. It is a stable RTP operation at geomagnetic equator and performs a high computation speed with a reasonable accuracy. Theoretical models and the practical magnetic field data located at the magnetic equator show that the operator of RTP solution is stable and accurate.

Automation of the SLUTH method: a novel approach to airborne magnetic data interpretation

ABSTRACTA useful property of the anomalous magnetic field associated with some simple geological bodies is that the field is homogeneous with respect to horizontal distance and height. Its horizontal and vertical derivatives are also homogeneous fields so the angle ratio of the lateral gradient over the vertical gradient is constant along rays emanating outward from a single point that represents the body location. Hence drawing these raypaths, which connect the same values at different upward continued heights along a profile, can be used to identify the location and depth of the source. This is the basis for the source location using the total‐field homogeneity (SLUTH) method. A six‐step procedure is proposed to automate the SLUTH method, allowing large amounts of data to be interpreted quickly and easily. Furthermore, the rate of decay of the field along these raypaths provides a means to estimate the type of body that is the cause of the anomaly. Once the type of body is known, a quantity related to the susceptibility can be estimated.An analysis of the results in the case when there is interaction between two proximal magnetic sheets shows a distortion when the bodies are within 600 m of each other. A similar distortion is seen when analysing field data from Timmins, Ontario, Canada, which consists of many other magnetic body models such as contacts and thin sheets. Adding noise to synthetic data shows that the estimates we obtain for the source parameters are robust for the typical noise levels seen in survey data.Because a lot of information about the characteristics of the causative geologic body can be determined using the method, it is a challenge to summarize the results on a single map. Our approach is to use different shaped symbols for each type of body, with the size of the symbol being proportional to the susceptibility‐thickness and the shade indicative of the error in estimating the position. Data from Chibougamau, Quebec, Canada are used to illustrate these display techniques.

Low-temperature magnetic properties of iron-bearing sulfides and their contribution to magnetism of cometary bodies

In this study we present a review of low-temperature magnetic properties of alabandite (Fe, Mn)S, daubreelite FeCr 2S 4, pyrrhotite Fe 1− x S and troilite FeS updated with new experimental data. The results indicate that besides FeNi alloys mainly daubreelite with its Curie temperature T C ∼ 150 K and strong induced and remanent magnetizations may be a significant magnetic mineral in cold environments and may complement that of FeNi or even dominate magnetic properties of sulfide rich bodies at temperatures below T C . Comets are known to contain iron-bearing sulfides within dusty fraction and their surfaces are subject to temperature variations in the range of 100–200 K down to the depth of several meters while the cometary interior is thermally stable at several tens of Kelvin which is within the temperature range where alabandite, daubreelite or troilite are “magnetic”. Thus not only FeNi alloys, but also sulfides have to be considered in the interpretation of magnetic data from cometary objects such as will be delivered by Rosetta mission. Modeling indicates that magnetic interactions between cometary nucleus containing iron-bearing sulfides and interplanetary magnetic field would be difficult, but not impossible, to detect from orbit. Rosetta’s Philae lander present on the surface would provide more reliable signal.

The deep interior of Venus, Mars, and the Earth: A brief review and the need for planetary surface-based measurements

A comparison of the internal structure of Earth-like planets is unavoidable to understand the formation and evolution of the solar system, and the differences between Earth’s, Mars’, and Venus’ atmospheres, surfaces and tectonic behaviors. Recent studies point at the role of core structure and dynamics in the evolution of the atmosphere, mantle and crust. On Earth, the crust thickness and the radius and physical state of the cores are known for almost one century, since the advent of seismological observations, but the lack of long-term surface-based geodetic, electromagnetic and seismological observations on the other planets, results in very large uncertainties on the crust thickness, on the temperature and composition of their mantle, and on the size and physical state of their cores. According to the currently available geodetic data, Mars’ dimensionless mean-moment-of-inertia ratio is equal to 0.3653±0.0008. When combined with geochemical observations and with the inputs of laboratory experiments on planetary materials at high pressure and high temperature, this result constrains a narrow range of density values for Mars’ mantle and favors a light [6200–6765 kg m −3] sulfur-rich core, but it still allows for a 1600–1750 km range for the core radius, i.e. an uncertainty at least ten times larger than the precision obtained in 1913 by Gutenberg for the Earth’s core. Mars’ mantle density distribution may be explained by a large range of temperatures and mineralogical compositions, either olivine- or pyroxene-rich. The unknown mean thickness of Mars’ crust makes necessary a number of working assumptions for the interpretation of gravimetric and magnetic data. The situation is worse for Venus, and the most conservative model of its deep interior is a transposition of the Earth’s structure scaled to Venus’ radius and mass. The temperature conditions at the surface of this planet hardly make possible long-term ground-based measurements, but this is indeed feasible at the surface of Mars. Precise measurements of Mars’ crust thickness, core radius and structure, and the proof of the existence or absence of an inner core, would put tight constraints on mantle dynamics and thermal evolution, and on possible scenarios leading to the extinction of Mars’ magnetic field about 4.0 Ga ago. Long-lasting surface-based geodetic, seismological and magnetic observations would provide this information, as well as the distributions as a function of depth of the density, elastic and anelastic parameters, and electrical conductivity. Current studies on the structure of Earth’s deep interior demonstrate that the latter data set, when constrained by laboratory experiments, may be inverted in terms of temperature, chemical, and mineralogical compositions.

Detection of Metabolites by Proton Ex Vivo NMR, in Vivo MR Spectroscopy Peaks and Tissue Content Analysis: Biochemical-Magnetic Resonance Correlation: Preliminary Results

Abstract*Aim*: Metabolite concentrations by in vivo magnetic resonance spectroscopy and ex vivo NMR spectroscopy were compared with excised normal human tissue relaxation times and tissue homogenate contents.*Hypothesis*: Biochemical analysis combined with NMR and MR spectroscopy defines better tissue analysis. Materials and Methods: Metabolites were measured using peak area, amplitude and molecular weights of metabolites in the reference solutions. In normal brain and heart autopsy, muscle and liver biopsy tissue ex vivo NMR peaks and spin-lattice (T1) and spin-spin (T2) relaxation times, were compared with diseased tissue NMR data in meningioma brain, myocardial infarct heart, duchene-muscular-dystrophy muscle and diffused-liver-injury liver after respective in vivo proton MR spectroscopy was done. NMR data was compared with tissue homogenate contents and serum levels of biochemical parameters.*Results*: The quantitation of smaller NMR visible metabolites was feasible for both ex vivo NMR and in vivo MR spectroscopy. Ex vivo H-1 NMR and in vivo MRS metabolite characteristic peaks (disease/normal data represented as fold change), T1 and T2, and metabolites in tissue homogenate and serum indicated muscle fibrosis in DMD, cardiac energy depletion in MI heart, neuronal dysfunction in meningioma brain and carbohydrate-lipid metabolic crisis in DLI liver tissues.*Conclusion*: This preliminary report highlights the biochemical-magnetic resonance correlation as basis of magnetic resonance spectroscopic imaging data interpretation of disease.

Computationally inexpensive interpretation of magnetic data for finite spin clusters

We show that high-temperature expansion of the partition function is a computationally convenient tool to interpretation of magnetic properties of spin clusters wherein the spin centers are interacting via an isotropic Heisenberg exchange operator. High-temperature expansions up to order 12 are used to reproduce temperature dependent magnetic susceptibilities of a Cr(III) tetramer, a decanuclear Fe(III) wheel, a 3x3 grid arrangement of nine Mn(II) ions, and a dodecanuclear Ni(II) wheel. Excellent agreement with experiments as well as with results from computationally more elaborate methods is achieved.

Magneto-seismic interpretation of subsurface volcanism in the Gaeta Gulf (Italy, Tyrrhenian Sea)

The occurrence of a former subaerial volcanic edifice off the Volturno River (Tyrrhenian Sea, Gulf of Gaeta) in the 41°N parallel is suggested by joint interpretation of multichannel seismic lines and ship-borne magnetic data. In the Campanian region igneous (volcanic) rocks are very close to the carbonate Mesozoic basement and seismics cannot always discriminate between them. A joint seismic-magnetic analysis was very effective in assessing the lithological nature of the bodies evidenced by both geophysical methods. Distortion analysis showed that the main magnetic source in the area is characterised by a not normal-polarity direction of the magnetization, similar to oth- er Pleistocene volcanoes in the Tyrrhenian region. Hence we argued that the overall magmatic emplacement for this source occurred during a reverse-polarity chron, very likely the 0.78-1.78 Ma time span. This magnetically-derived time constraint is in agreement with seismic stratigraphy that shows that the entire volcano is sealed by the Volturno River prograding delta from Middle Pleistocene to Present in age. Our interpreted volcano belongs to a set of in- ferred onshore and offshore volcanic edifices all lying along the 41°N parallel.

Geophysical exploration for gold and associated minerals, case study: Wadi El Beida area, South Eastern Desert, Egypt

The occurrences of gold and disseminated sulfides lie as a part of the shearing fault zone that extends from the north to the south of the study area for a length of about 25 km. The gold and disseminated sulfides are located on the alteration shear zone which is composed of quartz–feldspathic highly ferruginated rock (gossans) occupying the eastern and central parts of the area. Mineralogical analyses that were done on bedrock samples of the oxidized and alteration zones indicated that there are two anomalous spots of gold contents; the first one has values ranging from 5 to 49 g ton−1 and the second anomaly has values ranging from 150 to 502.5 g ton−1. Magnetic, self-potential, resistivity and induced polarization surveys were applied at Wadi El Beida area to delineate the mineral ore deposits in terms of depths and extensions through the structural shearing zone. The quantitative interpretation of magnetic data was carried out by using two techniques; the first is 3D magnetic inversion using Euler deconvolution and the second is magnetic models using the MAGMOD program. The results of the magnetic interpretation indicated that the depths of such ore deposits range from 35.9 to 52.7 m and the half width ranged from 27.2 to 87.8 m. The SP contour maps show negative anomalies with ranges from −70 to 20 mV. Most of these anomalies occupy the shear, silicified zones, alterations and rock contacts. The SP anomalies are correlated with other geophysical ones and also with the geological sources. Quantitative interpretation was done on the selected anomalies along the coded lines on the normal SP contour map. The quantitative interpretation of self-potential anomalies (SP) was carried out using two techniques; the first is a new algorithm constructed by Monteiro Santos (2009) using particle swarm optimization (PSO) and the second is the code constructed by Caglar (2000). The depths range from 20 to 60 m. The gradient resistivity survey was carried out simultaneously with IP measurements. The low-resistivity zones coincide with the altered and sheared acidic meta-volcanics. The quantitative interpretation technique determined the conductive bodies' parameters using the Schulz method (1985) where the depth to the top of the ore body ranged from 21 to 62 m while the maximum width ranged from 52 to 165 m. The induced polarization-chargeability data were measured in the time domain. The positive anomalies on the IP-chargeability map coincide with the sites of alterations, shears and contact zones. Four dipole–dipole sections were carried out along the anomalous sites selected from the constructed maps in the study area and were inverted using the RES2DINV program. The results of resistivity and IP inversions indicated that there are conductive and chargeable bodies at depths ranging from 15 to 65 m. According to the integrated geophysical results, two suggested borehole sites were selected before carrying out any future mining projects.

Principal faults in the Shatsky Rise and their influence upon the evolution of the geological structure in the East Black Sea Region

A fault was traced along the southwestern margin of the Shatsky Rise. It extends to land where it crosses the Mountainous Crimea. Interpretation and analysis of marine seismic and magnetic survey data, as well as geological data on land, allow stating that the fault originated during the rift evolution stage of the East Black Sea Basin. Currently, the fault is in the sea and is a channel for migrating hydrocarbon fluids. Another fault was traced from the West Caucasus into the sea, where it separates the Shatsky Rise into two structural units.

Evolution of the Girilambone regolith landscape, central-western New South Wales

A model of regolith and landscape evolution for the Girilambone region is derived from regolith–landform mapping and interpretation of drillhole information, the latter being underpinned by detailed petrography and Portable Infrared Mineral Analyser (PIMA) characterisation. The model is partly constrained by the interpretation of palynological, paleomagnetic, apatite fission-track, and airborne magnetic data. The model interprets the architecture of the three main sediment sequences and explains their derivation: a possible Late Jurassic fluvial sequence, an Early Cretaceous estuarine–shallow-marine and fluviolacustrine sequence (both sequences being part of the Surat Basin), and a Late Pliocene to Holocene colluvial–alluvial sequence. Implications of this model are that much, if not all, of the Cobar Uplands was covered by a shallow sea in the Early Cretaceous, and that neotectonic reactivation of north-trending Paleozoic faults caused the formation of the north-plunging depressed zone that contains the Mulga–Tindarey Paleovalley System.

The R-approximation method and its application to the interpretation of detailed gravity and magnetic data

The application of the R-approximation method based on the use of the Radon integral transform within the framework of the method of linear integral representations to the interpretation of detailed gravity and magnetic data is considered in this paper. The results are presented for some research areas located in Russia and in the Crimea (Ukraine). The method determines the distribution of anomalous field elements, construction of the analytical continuation of fields, and their linear transformations with a sufficiently high degree of accuracy.

Subsidence and crustal roughness of ultra-slow spreading ridges in the northern North Atlantic and the Arctic Ocean

SUMMARY Five basin-wide seismic reflection profiles of up to 550 km each were acquired in the Arctic Ocean and the northern North Atlantic in 2001 and 2002. The main objective was to investigate the depth to the basement and to analyse the crustal structure, morphology and roughness of ultra-slow spreading ridges of the Gakkel, Molloy and Knipovich ridges. To date, little is known to date of the ultra-slow spectrum of such spreading ridges. The seismic profiles of all investigated ridges show similar morphological characteristics with deep axial valleys and rough basement topography. Magnetic data compilation and interpretation suggests that the ultra-slow spreading systems are fairly stable and existed during the entire evolution of the basins to the north of the Greenland Fracture Zone. The thermal subsidence curve was calculated and corrected for sediment loads, and crustal roughness values are estimated for all five profiles. The resulting roughness values append the global roughness data set for ultra-slow spreading systems. The results are higher than those predicted by interpolating existing global roughness. This study confirms the presence of a global relationship between crustal roughness, ridge morphology and spreading rates. New curve fits, supporting the global relationship, are discussed. Data on present spreading rates, ridge morphology, subsidence and roughness provide a better insight into the development of the axial ridge morphology in the study area. The results show that the basins to the north of the Greenland Fracture Zone were formed at ultra-slow spreading axial rift valleys and continued spreading at ultra-slow rates to the present day configuration.