Mode Of Extension Research Articles

Late Quaternary deformation on the island on Pantelleria: New constraints for the recent tectonic evolution of the Sicily Channel Rift (southern Italy)

Abstract Structural observations carried out on the volcanic Island of Pantelleria show that the tectonic setting is dominated by NNE trending normal faults and by NW-striking right-lateral strike-slip faults with normal component of motion controlled by a ≈N 100°E oriented extension. This mode of deformation also controls the development of the eruptive fissures, dykes and eruptive centres along NNE–SSW belts that may thus represent the surface response to crustal cracking with associated magma intrusions. Magmatic intrusions are also responsible for the impressive vertical deformations that affect during the Late Quaternary the south-eastern segment of the island and producing a large dome within the Pantelleria caldera complex. The results of the structural analysis carried out on the Island of Pantelleria also improves the general knowledge on the Late Quaternary tectonics of the entire Sicily Channel. ESE–WNW directed extension, responsible for both the tectonic and volcano-tectonic features of the Pantelleria Island, also characterizes, at a greater scale, the entire channel as shown by available geodetic and seismological data. This mode of extension reactivates the older NW–SE trending fault segments bounding the tectonic troughs of the Channel as right-lateral strike-slip faults and produces new NNE trending pure extensional features (normal faulting and cracking) that preferentially develop at the tip of the major strike-slip fault zones. We thus relate the Late Quaternary volcanism of the Pelagian Block magmatism to dilatational strain on the NNE-striking extensional features that develop on the pre-existing stretched area and propagate throughout the entire continental crust linking the already up-welled mantle with the surface.

Low lower crustal velocity across Ethiopia: Is the Main Ethiopian Rift a narrow rift in a hot craton?

The Main Ethiopian Rift (MER) is a classic narrow rift that developed in hot, weak lithosphere, not in the initially cold, thick, and strong lithosphere that would be predicted by common models of rift mode formation. Our new 1‐D seismic velocity profiles from Rayleigh wave/receiver function joint inversion across the MER and the Ethiopian Plateau indicate that hot lower crust and upper mantle are present throughout the broad region affected by Oligocene flood basalt volcanism, including both the present rift and the adjacent Ethiopian Plateau hundreds of kilometers from the rift valley. The region of hot lithosphere closely corresponds to the region of flood basalt volcanism, and we interpret that the volcanism and thermal perturbation were jointly caused by impingement of the Afar plume head. Across the affected region, Vs is 3.6–3.8 km/s in the lowermost crust and ≤4.3 km/s in the uppermost mantle, both ∼0.3 km/s lower than in the eastern and western branches of the East African Rift System to the south. We interpret the low Vs in the lower crust and upper mantle as indicative of hot lithosphere with partial melt. Our results lead to a hybrid rift mode, in which the brittle upper crust has developed as a narrow rift along the Neoproterozoic suture between East and West Gondwana, while at depth lithospheric deformation is distributed over the broad region (∼400 km wide) thermally perturbed by the broad thermal upwelling associated with the Afar plume head. Development of both the East African Rift System to the south (in cold, strong lithosphere) and the MER to the north (in hot, weak lithosphere) as narrow rifts, despite their vastly different initial thermal states and depth‐integrated lithospheric strength, indicates that common models of rift mode formation that focus only on temperature, thickness, and vertical strength profiles do not apply to these classic continental rifts. Instead, inherited structure and associated lithospheric weaknesses are the primary control on the mode of extension.

Metamorphic and age constraints on the Alakeçi shear zone: Implications for the extensional exhumation history of the northern Kazdağ Massif, NW Turkey

The Kazdağ Massif exposes an extensional metamorphic dome in the Biga Peninsula of northwest Turkey, bounded on both flanks by detachments and/or shear zones. The northern flank is marked by the extensional Alakeçi shear zone (ASZ), with poorly known P–T–t path. We therefore focus on metamorphic conditions and temporal history of the ASZ to determine its tectono-metamorphic evolution. ASZ mylonites were derived from both the footwall Kazdağ Massif core metamorphic rocks and the hanging wall Çetmi mélange lithologies. The mylonitic fabrics in the ASZ depict a top-to-the NNE shearing, parallel to the NNE-plunging stretching lineation and NNW-dipping mylonitic foliation. This geometry implies normal sense movement i.e. north-side down-dip extensional displacement along this flank of the Kazdağ Massif. The northward transition from ductile to brittle–ductile shear regime through the ASZ shows that the non-coaxial deformation occurred at decreasing temperatures and degree of metamorphism. The paragenesis in equilibrium of the mylonitic gneisses and schists contains quartz + feldspar + muscovite + biotite + garnet ±staurolite, with late retrogressive chlorite after biotite and garnet. Calculated thermo-barometric conditions for ASZ rocks yielded pressures between 6.9 and 5.7 kbar and temperatures between 706 and 587 °C, which constrain the peak metamorphism. The mylonitic rocks supplied isochron 39Ar/ 40Ar mica ages between 26.97 and 24.19 Ma, which we interpret to date the cooling of the mylonites following the P–T decrease across the ASZ. The metamorphic data support the structural record and strengthen the extensional character of the ASZ. The transition from sillimanite-bearing footwall Kazdağ Massif core gneisses in the deeper structural levels to chlorite schists towards the shallow structural levels at the top of the ASZ, is consistent with an extensional exhumation of the metamorphic pile. These data allow us to determine the peak P–T conditions and the temporal evolution in the northern flank of the Kazdağ Massif, where Late Oligocene extensional exhumation was assisted by NNE-directed ductile–brittle ASZ, which had operated from amphibolite to greenschist facies. The ASZ, together with similar time-constrained ductile–brittle activity of SW-directed detachment along the southern flank of the massif, collectively indicates a bivergent mode of extension in the western Kazdağ Massif. The latter is likely influenced by magmatic activity spatially and temporally related to these extensional zones. At the regional scale, the bivergent tectono-metamorphic pattern of the Kazdağ Massif is similar to those observed on other places of the north-central Aegean domain.

Temperature compensated cuts in LGT crystal microresonators using length extensional mode

In this letter, experimental investigation of frequency-temperature effects in langatate rectangular cross-section beams are presented. It is shown that a first-order temperature compensated cut exists for the first vibrating mode of length extension.

Modes of the southern extension of the East Madagascar Current

Data sets from satellite observations and a nested high‐resolution model are used to study a source region of the Agulhas Current. Altimeter‐derived geostrophic surface currents are averaged over varying periods, providing evidence of the persistence of flow patterns in the extension of the southern branch of the East Madagascar Current (SEMC). South of Madagascar, the SEMC separates into one branch toward the Agulhas Current and into a second branch retroflecting and connecting to the Subtropical Indian Ocean Countercurrent (SICC). Good agreement is found between long‐term mean patterns of observational and model dynamic heights. Two basic modes are identified in the SEMC extension, with anticyclonic motion favoring retroflection in the northern Mozambique Basin when the extension is in a southwestward direction and cyclonic motion occurring in the case of the SEMC flowing westward along the southern Madagascar slope. A cross‐correlation sequence between model SEMC transports and the modal changes in the extension region displays a correlation at about 1‐month lag which agrees with eddy propagation time from the SEMC to the outflow region. Mean model SEMC transports are determined using floats released at 21°S, and the contribution of the SEMC to the SICC is obtained using floats injected at 55°E with the model running backward. Almost half of the SEMC volume transport contributes to the Agulhas system, and about 40% of SICC water originates from the SEMC.

A Methodology for the Quantitative Assessment of the Primary Social Impact of Agricultural Technologies

Present methodologies for the assessment of the social impact of agricultural technologies and their modes of extension are merely comparative or often qualitative. A hierarchical clustering based ...

Subduction, convergence and the mode of backarc extension in the Mediterranean region

Abstract30-35 Ma ago a major change occurred in the Mediterranean region, from a regionally compressional subduction coeval with the formation of Alpine mountain belts, to extensional subduction and backarc rifting. Backarc extension was accompanied by gravitational spreading of the mountain belts formed before this Oligocene revolution. Syn-rift basins formed during this process above detachments and low-angle normal faults. Parameters that control the formation and the kinematics of such flat-lying detachments are still poorly understood. From the Aegean Sea to the Tyrrhenian Sea and the Alboran Sea, we have analysed onshore the deformation and P-T-t evolution of the ductile crust exhumed by extension, and the transition from ductile to brittle conditions as well as the relations between deep deformation and basin formation. We show that the sense of shear along crustal-scale detachments is toward the trench when subduction proceeds with little or no convergence (northern Tyrrhenian and Alboran after 20 Ma) and away from the trench in the case of true convergence (Aegean). We tentatively propose a scheme explaining how interactions between the subducting slab and the mantle control the basal shear below the upper plate and the geometry and distribution of detachments and associated sedimentary basins. We propose that ablative subduction below the Aegean is responsible for the observed kinematics on detachments (i.e. away from the trench). The example of the Betic Cordillera and the Rif orogen, where the directions of stretching were different in the lower and the upper crust and changed through time, is also discussed following this hypothesis.

The Lebombo monocline and associated feeder dyke swarm: Diagnostic of a successful and highly volcanic rifted margin?

As part of the Karoo large igneous province (LIP), the ∼ 700 km-long and ∼ 182 Ma-old Lebombo monocline outcrops inland of a younger Mozambique Lowland cover that separates it from the Indian Ocean. Detailed mapping of a particularly well exposed Olifant River traverse across this monocline correlates basaltic and rhyodacitic lava units within the Lebombo Group to at least three hosted generations of intrusions within the monocline-parallel Northern Lebombo dyke swarm, implying that a much denser feeder dyke swarm is covered by younger flows. Measured attitudes and thicknesses of up to 197 lavas and 791 dykes statistically quantify a structural cross section, from which a properly weighted lava log of nearly 5 km basalts inter-bedded with an overlying > 3.5 km of rhyodacites is constructed. The geological section is compatible with a slightly deeper (sub-lava) section through the innermost ∼ 30 km's of a relatively narrow East Greenland margin, to which the Lebombo monocline can be rigorously compared. In both cases, field relationships are consistent with early tectonic extension being overwhelmed by dyke dilation within margin-parallel swarm segments that may have been injected laterally from central magma chambers. Thus, it is argued that the Lebombo monocline is part of a successfully rifted margin that, furthermore, belongs to a distinct class of highly volcanic and relatively narrow margins, which only form proximal to classical triple rift LIP centers, where an elevated magma flux sustains a magmatic mode of extension. For the Karoo LIP, this conforms with (1) a tight Gondwana reconstruction of Africa with Antarctica, (2) successful breakup during intense ∼ 182 Ma emplacement of the Lebombo Group, (3) triple rift formation, together with a short-lived (∼ 181–178 Ma) Okavango dyke swarm, and (4) anomalously thick igneous crust formation during continued ∼ 2.5 cm/yr separation into a loose ∼ 155 Ma plate configuration of Africa and Antarctica.

Geologic, structural, and thermochronologic constraints on the tectonic evolution of the Sierra Mazatán core complex, Sonora, Mexico: New insights into metamorphic core complex formation

The Sierra Mazatán in northwestern Mexico is the southernmost metamorphic core complex in the North American Cordillera. Large‐magnitude Tertiary extension at Sierra Mazatán involved both ductile and brittle slip along a major normal fault that presently dips 10°–15° west. Extension was polyphase and involved an early period of extension from 25 to 23 Ma followed by major slip from 21 to 16 Ma. Total slip was ≤20 km and occurred at rates of 3–4 mm/a. This extension predated the plate boundary change to transtension at ∼12 Ma and was largely decoupled from relative Pacific–North American plate motion. Numerous lines of evidence suggest that the presently low‐angle normal fault initiated at a steep dip (50°–60°) and was rotated to lower angles during slip. When corrected for this tilting, fault corrugations at Sierra Mazatán had a similar geometry to the segmentation of many active normal faults, which is compatible with their origin as primary fault features. Many aspects of the Sierra Mazatán are comparable to large active normal faults, indicating that this core complex formed owing to prolonged extension on an otherwise typical high‐angle normal fault. Therefore, core complexes need not represent a fundamentally unique mode of crustal extension.

Modes of Extension: Comments on Kit Fine's ‘In Defence of Three-Dimensionalism’

The debate between 3- and 4-dimensionalists is one of the most lively and pervasive in current metaphysics. At stake is a glittering prize: the correct metaphysical analysis of material things and other objects commonly thought to persist in time by enduring. Since we count ourselves among such objects the outcome of the debate is of more than merely academic interest to us. Obviously the ramifications of the debate, even of the points raised by Kit Fine, go far beyond what I can discuss here, so I shall simply select some salient issues and comment on them from my own somewhat heterodox point of view.

Dissipation analysis as a guide to mode selection during crustal extension and implications for the styles of sedimentary basins

We analyze the initial modes of continental extension with the aim of providing an improved understanding of the dynamic development of sedimentary basins. We first examine simple two‐layer crustal‐scale models which consist of a frictional‐plastic upper crust bonded to a linear viscous lower crust of equal thickness. The mode of deformation is predicted by using an analytical analysis of the rate of internal dissipation of energy and the gravitational rate of work. It is assumed that models deform in the mode in which the total rate of work is minimized. For strain‐softening models we predict the following modes of crustal extension: (1) pure shear, (2) multiple conjugate or parallel shear zones, (3) two shear zones, which form either one symmetric basin or two asymmetric basins, and (4) a single shear zone forming an asymmetric basin. The transitions between these modes are shown to depend on the trade off between “gains” that reduce the rate of energy dissipation and “penalties” that increase it. A single asymmetric basin is preferred for a strong brittle layer which has a high amount of strain softening (high plastic gain), a weak viscous layer and slow extension (low viscous penalty). A decrease in the plastic gain and/or an increase in the viscous penalty leads to modes with more shear zones in the upper crust. The pure shear mode is found for low strain softening, a high viscosity, and/or fast extension. Results of finite element calculations of equivalent simple two‐layer models agree with the analytical mode predictions.

Lithospheric dismemberment and magmatic processes of the Great Basin–Colorado Plateau transition, Utah, implied from magnetotellurics

To illuminate rifting processes across the Transition Zone between the extensional Great Basin and stable Colorado Plateau interior, we collected an east‐west profile of 117 wideband and 30 long‐period magnetotelluric (MT) soundings along latitude 38.5°N from southeastern Nevada across Utah to the Colorado border. Regularized two‐dimensional inversion shows a strong lower crustal conductor below the Great Basin and its Transition Zone in the 15–35 km depth range interpreted as reflecting modern basaltic underplating, hybridization, and hydrothermal fluid release. This structure explains most of the geomagnetic variation anomaly in the region first measured in the late 1960s. Hence, the Transition Zone, while historically included with the Colorado Plateau physiographically, possesses a deep thermal regime and tectonic activity like that of the Great Basin. The deep crustal conductor is consistent with a rheological profile of a brittle upper crust over a weak lower crust, in turn on a stronger upper mantle (jelly sandwich model). Under the incipiently faulted Transition Zone, the conductor implies a vertically nonuniform mode of extension resembling early stages of continental margin formation. Colorado Plateau lithosphere begins sharply below the western boundary of Capitol Reef National Park as a resistive keel in the deep crust and upper mantle, with only a thin and weak Moho‐level crustal conductor near 45 km depth. Several narrow, steep conductors connect conductive lower crust with major surface faulting, some including modern geothermal systems, and in the context of other Great Basin MT surveying suggest connections between deep magma‐sourced fluids and the upper crustal meteoric regime. The MT data also suggest anisotropically interconnected melt over a broad zone in the upper mantle of the eastern Great Basin which has supplied magma to the lower crust, consistent with extensional mantle melting models and local shear wave splitting observations. We support a hypothesis that the Transition Zone location and geometry ultimately reflect the middle Proterozoic suturing between the stronger Yavapai lithosphere to the east and the somewhat weaker Mojave terrane to the west. We conclude that strength heterogeneity is the primary control on locus of deformation across the Transition Zone, with modulating force components.

Strain localisation and weakening of the lithosphere during extension

We explore the sensitivity of extensional systems to the thermal structure of the lithosphere using numerical simulations that fully couple the energy, momentum and continuity equations. The rheology of the lithosphere is controlled by weakening processes, such as shear heating, that localises strain into shear zones and faults. Numerical models show that during extension of an initially unpatterned lithosphere, structures develop spontaneously out of basic thermodynamic energy fluxes, and without the imposition of ad hoc rules on strain localisation. This contrasts with the classical Mohr–Coulomb theory for brittle localisation, which prescribes the angles of faults by a mathematical rule. Our results show that the mode of extension is sensitive to subtle changes in rheology, heat flux and geometry of the system. This sensitivity lies at the core of the variety and complexity observed in extensional systems. Localisation processes make the lithosphere weaker than previously estimated from the Brace–Goetze quasi-static approach. Consequently, typical estimates for plate tectonic forces are capable of splitting the lithosphere under extension, even without the role of active magmatism.

Seismic structure of the southern Gulf of California from Los Cabos block to the East Pacific Rise

Multichannel reflection and coincident wide‐angle seismic data collected during the 2002 Premier Experiment, Sea of Cortez, Addressing the Development of Oblique Rifting (PESCADOR) experiment provide the most detailed seismic structure to date of the southern Gulf of California. Multichannel seismic (MCS) data were recorded with a 6‐km‐long streamer, 480‐channel, aboard the R/V Maurice Ewing, and wide‐angle data was recorded by 19 instruments spaced every ∼12 km along the transect. The MCS and wide‐angle data reveal the seismic structure across the continent‐ocean transition of the rifted margin. Typical continental and oceanic crust are separated by a ∼75‐km‐wide zone of extended continental crust dominated by block‐faulted basement. Little lateral variation in crustal thicknesses and seismic velocities is observed in the oceanic crust, suggesting a constant rate of magmatic productivity since seafloor spreading began. Oceanic crustal thickness and mean crustal velocities suggest normal mantle temperature (1300°C) and passive mantle upwelling at the early stages of seafloor spreading. The crustal thickness, width of extended continental crust, and predicted temperature conditions all indicate a narrow rift mode of extension. On the basis of upper and lower crust stretching factors, an excess of lower crust was found in the extended continental crust. Total extension along transect 5W is estimated to be ∼35 km. Following crustal extension, new oceanic crust ∼6.4‐km‐thick was formed at a rate of ∼48 mm a−1 to accommodate plate separation.

Hudson on Location

Chapter 4 of Hud Hudson's stimulating book The Metaphysics of Hyperspace (2005) contains an discussion of the notion of location in a container spacetime. Hudson uses this idea to define a number of modes of extension or ways of being extended. A pertended object is what most people think of as a typical object it is made up of spatial parts, one part for each region the object pervades. An entended object is an simple (or a complex object made up of simples). Elsewhere, (2007) I've argued that nothing about the concept of extended rules out entension. Hudson thinks that I did not go far enough. Besides pertended and entended objects, he also sees conceptual room for what he calls spanners and multiply located objects. These last two ways of being are even more exotic than simples. Imagining a museum display of objects enjoying different modes of extension, he says:

Begriffliche und psychologische Ordnung bei Spinoza

Spinoza's metaphysical thesis that there is only one substance in the universe but a plurality of modes, each of them falling under an attribute, raises a crucial question. How are modes of thinking, i.e. ideas, related to modes of extension? This paper intends to show that there are at least two answers, depending on an understanding of the equivocal term ‘idea’. If ideas are taken to be mental acts, they are identical with modes of extension. If, however, they are understood in the “objective” way, namely as the conceptual content of mental acts, they correspond to modes of extension. It is argued that this method of disambiguating the term ‘idea’ not only helps to understand Spinoza's famous doctrine of parallelism but that it also provides a solution to two puzzling problems: the possibility of “active affects” and the existence of an eternal mind.

The Nature of Neural Invasion by Pancreatic Cancer

Neural invasion is one of the most important modes of tumor extension in pancreatobiliary tract cancer. However, the precise pattern of neural invasion and the relationship between neural invasion and nodal involvement are unknown. Using 8 surgical specimens from patients with pancreatic cancer, 4973 sections were created and examined histopathologically. A total of 961 sections of VX2 tumor grown in the retroperitoneum of rabbits also were examined histologically. The precise mechanism by which neural invasion occurs and the relationship between nerve fascicle and lymph node involvement were determined by histological examination of serial sections. Histological evaluation of the surgical specimens revealed continuity between the cancer cells between the inside and the outside of the perineurium. Tumor cells grew mainly in a continuous fashion along the branches of nerves. An advancing tip of the tumor cells was identified. The pattern of tumor spread in the experimental study was similar to that in the clinical study. Continuity was found between the cancer cells inside some lymph nodes and the cancer cells within the perineural space. This finding suggests that neural invasion might be a pathway to lymphatic involvement. Neural invasion is a common, but not a specific, feature of pancreatic cancer. Tumor cells in the perineural space grow in a continuous fashion and may be responsible for some cases of lymphatic spread.

Modelling the extension of heterogeneous hot lithosphere

The consequences of weak heterogeneities in the extension of soft and hot lithosphere without significant previous crustal thickening has been analysed in a series of centrifuge models. The experiments examined the effects of i) the location of heterogeneities in the ductile crust and/or in the lithospheric mantle, and ii) their orientation, perpendicular or oblique to the direction of bulk extension. The observed deformation patterns are all relevant to the so-called “wide rifting” mode of extension. Weak zones located in the ductile crust exert a more pronounced influence on localisation of deformation in the brittle layer than those located in the lithospheric mantle: the former localise faulting in the brittle crust whereas the latter tend to distribute faulting over a wider area. This latter behaviour depends in turn upon the decoupling provided by the ductile crust. Localised thinning in the brittle crust is accompanied by ductile doming of both crust and mantle. Domains of maximum thinning in the brittle crust and ductile crust and mantle are in opposition. Lateral differences in brittle crust thinning are accommodated by lateral flow in the ductile crust and mantle. This contrasts with “cold and strong” lithospheres whose high strength sub-Moho mantle triggers a necking instability at the lithosphere-scale. This also differs from the extension of thickened hot and soft lithospheres whose ductile crust is thick enough to give birth to metamorphic core complexes. Thus, for the given lithospheric rheology, the models have relevance to backarc type extensional systems, such as the Aegean and the Tyrrhenian domains.

Predicted extension, compression and shearing of optic nerve head tissues

Glaucomatous optic neuropathy may be in part due to an altered biomechanical environment within the optic nerve head (ONH) produced by an elevated intraocular pressure (IOP). Previous work has characterized the magnitude of the IOP-induced deformation of ONH tissues but has not focused specifically on the mode of deformation (strain), i.e. whether the ONH tissues and cells are stretched, compressed or sheared. Circumstantial evidence indicates that the mode of deformation has biological consequences. Here we use computational models to study the different modes of deformation that occur in an ONH as a result of an increase in IOP. One generic and three individual-specific 3D models of the human ONH were reconstructed as previously described. Each model consisted of five tissue regions: pre and post-laminar neural tissue, lamina cribrosa, sclera and pia mater. Finite element methods were then used to predict the biomechanical response to changes in IOP. For each model we computed six local measures of strain, including the magnitude and direction of maximum stretching, maximum compression and maximum shearing strain. We compared the spatial and population distributions of the various measures of strain by using semi-quantitative (contour plots) and quantitative (histograms) methods. For all models, as IOP increased, the tissues of the ONH were subjected simultaneously to various modes of strain, including compression, extension and shearing. The highest magnitudes of all modes of strain occurred within the neural tissue regions. There were substantial differences in the magnitudes of the various modes of strain, with the largest strains being in compression, followed by shearing and finally by extension. The biomechanical response of an individual-specific ONH to changes in IOP is complex and cannot be fully captured by one measure of deformation. We predict that cells within the ONH are subjected to very different modes of deformation as IOP increases. The largest deformations are compressive, followed by shearing and stretching. Models of IOP-induced RGC damage need to be further refined by characterizing the cellular response to these different modes of strain.

Cervicothoracic goitre: an anatomical or radiological definition? Report of 223 surgical cases

To analyse and compare chest radiographs and cervicothoracic computed tomography scans taken prior to thyroid surgery, in order to locate and predict thoracic extension of substernal goitres. This eight-year, retrospective study included 223 patients who had undergone total thyroidectomy for benign, substernal, multinodular goitres. Chest radiographs and computed tomography scans were reviewed by two physicians (a senior ENT surgeon and a senior radiologist). The most frequent mode of extension was anterior or prevascular, seen in 76 per cent of cases, especially on the left side. Fifty-nine per cent of goitres did not reach the aortic arch and 11 per cent extended beyond the aortic arch. A cervical surgical approach was performed in approximately 99 per cent of cases. Thorough examination of computed tomography scans is essential in order to identify and classify substernal goitres and to decide the best surgical procedure. A cervical surgical procedure is almost always sufficient and safe for the surgical management of substernal goitres. Computed tomography appears to be the best imaging modality for identifying and characterising substernal goitres. Surgical management is almost always via a cervical approach and does not differ from that used for benign cervical goitres. In the future, magnetic resonance imaging may be used; its results would need to be compared with those of computed tomography.