Lithospheric Structure Research Articles

Opening of the North Atlantic Ocean and the rise of Scandinavian mountains

Large-scale topography is usually associated with tectonic plate boundaries, but the Scandinavian mountains (Scandes) are located far from any active tectonic setting, and their origin is unknown. We demonstrate that the Precambrian lithospheric structure of Fennoscandia controlled both the Cenozoic ocean opening and mountain rise in the North Atlantic region. Our new seismic receiver function analysis reveals a block of thick continental crust formed by Proterozoic crustal stacking. We propose that this block created a wide continental shelf bounded by two transform fault systems during continental breakup. This geometry resulted in the formation of lithospheric steps at the continental margin on both sides of the stacked crustal structure, coinciding with the highest Southern and Northern Scandes. We propose that edge-driven convection at these steps caused the mountain rise. This study presents a general model for the formation of high elevation behind passive margins.

Subduction retreat recorded in the southern Beishan orogenic collage of the Central Asian Orogenic Belt: New evidence from deep seismic reflection profiling

The crustal and upper mantle structure of the Beishan orogenic collage, which serves as the southern part of the middle Central Asian Orogenic Belt, provides crucial insights into the history of the multiple openings and closings of the Paleo-Asian Ocean during the Paleozoic. There is considerable dispute over the eventual closure position, timing, and subduction polarity of the Paleo-Asian Ocean, particularly in the southern Beishan orogenic collage. The main cause of these controversies is the lack of a high-resolution lithospheric structure in this area. In this study, we first present a 140-km-long, high-resolution seismic reflection profile taken across the northern Dunhuang Block and the southern Beishan orogenic collage. The seismic imaging provides new constraints on the structure of the lower crust, the Moho, and the upper mantle beneath the southernmost Central Asian Orogenic Belt. A subhorizontal reflector in the middle crust, two sets of north-dipping reflectors from the lower crust to the upper mantle, and several south-dipping reflectors in the upper crust in the northern part of the profile were imaged. Based on our study and other geological, chronological, and geophysical data, we propose that the two sequences of north-dipping reflectors from the lower crust to the upper mantle represent two stages of north-dipping subduction of the southern branch of the Paleo-Asian Ocean. The first stage in the southern Beishan orogenic collage is Late Silurian−Early Devonian, and the second stage is late Carboniferous−Early Permian. The two-stage subduction process gave rise to the Huaniushan arc and the subsequent Shibanshan arc, respectively. These findings provide new constraints on the controversial subduction polarity and the multistage amalgamation of the microcontinental blocks and arcs in the southern Central Asian Orogenic Belt.

Upper mantle flow and crustal deformation patterns beneath the Dangerous Grounds and Borneo where multiple plates converge in South China Sea revealed by 3-D anisotropic magnetotelluric imaging

SUMMARY A large-scale magnetotelluric (MT) study was carried out in offshore Borneo to understand the lithospheric structure in this geologically complex region where three tectonic plates converge and past crustal studies generated long-standing debates. Marine MT data were acquired at 1416 stations with 3 km spacing along 13 regional lines (covering 4677 line-km) with periodicities of 0.1 to 10 000 s. These were inverted in 3-D incorporating electrical anisotropy with cross-gradients constraints between vertical and horizontal resistivities and the results were validated with resistivity well-logs from several exploration wells. The models reveal widespread presence of electrically resistive upper crustal and uppermost mantle layers, each underlain by a laterally varying conductive and anisotropic layer. The geometries of the anisotropic layers suggest large-scale ductile flow, thrusting and folding forming belts of alternating deep roots and thin lithosphere, consistent with multiple underthrusting/subduction. Our results are in agreement with the seismologically detected lithospheric variations in northern Borneo suggesting onshore–offshore continuity and a common lithospheric–asthenospheric origin for the deformation patterns. Over thinned lithosphere, we found consistent low resistivity and high anisotropy anomalies in the mantle above the spatial locations of fast shear-wave bodies imaged by recent seismological workers which we interpret to indicate post-subduction lithospheric–asthenospheric ductile flow in response to multidirectional regional compression. We demonstrate that these zones are spatially correlated with the distribution of mainly Cretaceous ophiolitic rocks and melanges exposed onshore and suggest that serpentinization of mantle peridotite can explain some of the anisotropic conductivity anomalies. The taper zones of these deep anisotropic conductors are also associated with Neogene sub-basins, high thermal gradients, and intrasedimentary magmatic bodies indicating a link between lithospheric thinning and magmatism. We propose that such anomalies could be important pathfinders for geothermal and natural hydrogen systems in the ongoing global drive for carbon-free energy resources.

Lithospheric Structure in the Northern Appalachian Mountains: A Detailed Examination of the Abrupt Change in Crustal Thickness in Northwestern Massachusetts

AbstractPrevious geophysical studies in the New England Appalachians identified a ∼15 km offset in crustal thickness near the surface boundary between Laurentia and the accreted terranes. Here, we investigate crustal structure using data from a denser array: New England Seismic Transects experiment, which deployed stations spaced ∼10 km apart across the Laurentia‐Moretown terrane suture in northwestern Massachusetts. We used receiver function (RF) analysis to detect P to SV converted waves and identified multiple interfaces beneath the transect. We also implemented a harmonic decomposition analysis to identify features at or near the Moho with dipping and/or anisotropic character. Beneath the Laurentian margin, the Ps converted phase from the Moho arrives almost 5.5 s after the initial P wave, whereas beneath the Appalachian terranes, the pulse arrives at 3.5 s, corresponding to ∼48 and ∼31 km depth, respectively. The character of the RF traces beneath stations in the middle of our array suggests a complex transitional zone with dipping and/or anisotropic boundaries extending at least ∼30 km. This extension is measured in our profiles and perpendicular to the suture. We propose one possible crustal geometry model that is consistent with our observations and results from previous studies.

Lithospheric Structure Above the Northern Appalachian Anomaly: Initial Results From the NEST Array

AbstractSeismic tomography observations show a low‐velocity feature in the upper mantle beneath eastern North America known as the Northern Appalachian Anomaly (NAA). Proposed models for the formation of the NAA include a remnant high‐temperature feature resulting from the passage of the Great Meteor Hotspot, edge‐driven convection, and ongoing asthenospheric upwelling. We investigate the structure of the lithosphere above the central portion of the NAA using data from the New England Seismic Transects (NEST) experiment. Ps receiver functions reveal two consistent interfaces beneath the dense northern line of NEST: the Moho (the base of the crust) and a deeper negative velocity gradient (NVG) feature located at depths between 60 and 110 km. We consider several potential explanations for this NVG feature; based on comparisons with previous results, we propose that it likely corresponds to the lithosphere‐asthenosphere boundary. Our results indicate that the lithosphere beneath New England is nonuniform and has likely been thinned.

Driven magmatism and crustal thinning of coastal southern China in response to subduction

Abstract. The late Mesozoic igneous rocks along the coastal South China Block (SCB) exhibit complex parental sources involving a depleted mantle, subducted sediment-derived melt, and melted crust. This period aligns with the magmatic flare-up and lull in the SCB, debating with the compression or extension in coastal region. Our study employs numerical models to investigate the dynamics of the ascent of underplating magma along the Changle–Nan'ao Belt (CNB), simulating its intrusion and cooling processes while disregarding the formational background. The rheological structure of the lithospheric mantle significantly influences magma pathways, dictating the distribution of magmatism. This work reveals that the ascent of magma in the presence of faults is considerably faster than in the absence of faults, and contemporaneous magmatic melts could produce different cooling and diagenetic processes. Additionally, the influence of pre-existing magma accelerated the emplacement of underplating magma. The magma beneath the fault ascended rapidly, reaching the lower crust within 20 million years, with a cooling rate of approximately ∼ 35 °C Myr−1. Conversely, the thickened magma took 40–50 million years to ascend to the lower crust, cooling at a rate of ∼ 10 °C Myr−1. In contrast, magma without thickening and fault would take a considerably longer time to reach the lower crust. The ascent of magma formed a mush-like head, contributing to magmatic circulation beneath the crust and decreasing crustal thickness. Multiphase magmatism increases the geothermal gradient, reducing lithospheric viscosity and promoting underplating magma ascent, leading to magmatic flare-ups and lulls. Our findings suggest that the Cretaceous magmatism at different times in the coastal SCB may be associated with the effects of lithospheric faults under similar subduction conditions. Boundary compression forces delay magma ascent, while rising magma induces a significant circulation, decreasing the crustal thickness of the coastal SCB. This study provides new insights into the complex interplay of magmatic processes during subduction, emphasizing the role of lithospheric structure in shaping the temporal and spatial evolution of coastal magmatism.

High-resolution 3-D lithospheric structure beneath the Qinling-Dabie orogenic belt from joint inversion of receiver functions and ambient noise

Resulting from the convergence of the Yangtze and North China Cratons, the Qinling-Dabie orogenic zone (QD) represents an important element in the central China orogenic system. To fully comprehend the craton evolution and lower crustal flow from the Tibetan Plateau, it is important to understand the crust and mantle structure of the QD. We reconstructed the three-dimensional lithospheric structure beneath the QD with high resolution using the joint inversion of receiver functions and ambient noise. Observations reveal that a high-velocity anomaly in the middle to lower crust beneath the western Qinling (WQL) orogen obstructs the eastward extension of a crustal low-velocity anomaly originating from the Tibetan Plateau. This finding provides unambiguous evidence that the WQL orogen is not crossed by eastward lower crustal flow from the Tibetan Plateau. The lithospheric mantle beneath the Weihe Rift and East Qinling orogen exhibits low-velocity characteristics, indicating that eastward asthenospheric flow from the Tibetan Plateau has caused substantial thermal-chemical erosion in the uppermost mantle beneath these regions. The results additionally indicate that the uppermost mantle high-velocity anomalies beneath the Dabie orogen is confined in a limited area and extends only to a depth of 70 km. We propose that during the Triassic, deeply subducted continental lithosphere returned into the uppermost mantle, forming the high-velocity anomalies beneath the Dabie orogen.

Kinematics of rift linkage between the Eastern and Ethiopian rifts in the Turkana Depression, Africa

AbstractRift initiation within cold, thick, strong lithosphere and the evolving linkage to form a contiguous plate boundary remains debated in part owing to the lack of time–space constraints on kinematics of basement‐involved faults. Different rift sectors initiate diachronously and may eventually link to produce a jigsaw spatial pattern, as in the East African rift, and along the Atlantic Ocean margins. The space–time distribution of earthquakes illuminates the geometry and kinematics of fault zones within the crystalline crust, as well as areas with pressurized magma bodies. We use seismicity and Global Navigation System Satellites (GNSS) data from the Turkana Rift Array Investigating Lithospheric Structure (TRAILS) project in East Africa and a new digital compilation of faults and eruptive centres to evaluate models for the kinematic linkage of two initially separate rift sectors: the Main Ethiopian Rift (MER) and the Eastern rift (ER). The ca. 300 km wide zone of linkage includes failed basins and linkage zones; seismicity outlines active structures. Models of GNSS data indicate that the ca. 250 km‐wide zone of seismically active en echelon basins north of the Turkana Depression is a zone, or block, of distributed strain with small counterclockwise rotation that serves to connect the Main Ethiopian and Eastern rifts. Its western boundary is poorly defined owing to data gaps in South Sudan. Strain across the northern and southern boundaries of this block, and an ca. 50 km‐wide kink in the southern Turkana rift is accommodated by en echelon normal faults linked by short strike‐slip faults in crystalline basement, and relay ramps at the surface. Short segments of obliquely oriented basement structures facilitate across‐rift linkage of faults, but basement shear zones and Mesozoic rift faults are not actively straining. This configuration has existed for at least 2–5 My without the development of localized shear zones or transform faults, documenting the importance of distributed deformation in continental rift tectonics.

Palaeogeography and 3D variability of a dynamically uplifted shelf: Observations from seismic stratigraphy of the Palaeocene East Shetland Platform

AbstractIn the Palaeocene North Sea, pulses in turbidite fan deposition and shelfal progradation have been correlated with episodes of regional uplift caused by a precursor of the Icelandic Plume. In the East Shetland Platform, the specific impacts of dynamic uplift on the regional palaeogeographic evolution are less understood. Using new, high‐resolution 3D seismic data from an underexplored proximal area, we investigate the palaeogeography of the East Shetland Platform in terms of the extent and timing of erosion versus deposition, focusing on how these can be used to reconstruct changes in relative sea‐level along strike. Using a combination of well data, clinoform‐based seismic stratigraphy and seismic attribute analysis of >60,000 km2 of 3D data, we have obtained palaeogeographic maps of multiple Palaeocene to Early Eocene units, with high temporal resolution for the Late Palaeocene–Early Eocene Moray Group. This includes six unconformity‐bounded units marked by prograding clinoforms of the Dornoch Formation, which are covered by backstepping sequences of the Beauly Member (Balder Formation). Temporal and spatial changes in the distribution of downdip depocentres and updip unconformities indicate strong lateral variability in patterns of shelf accommodation/erosion and local sediment supply. This results from a complex interplay among laterally uneven relative sea‐level fall, inherited topography, time‐varied sediment entry point distribution and along‐shore sediment transport regimes. Unconformities and palaeogeographic maps suggest a first‐order control on erosion and sediment distribution promoted by the transiently and differentially uplifted topography of Shetland, which is characterized by an anomalous erosive history in the Bressay High, in the centre of our study area, where the Lower Dornoch Formation has been eroded and marked fluvial incision is observed. Ultimately, results indicate shorter‐wavelength and shorter‐period variations in uplift than what is typically assumed for dynamic topography, perhaps as a result of additional modulation by lithospheric structures or influence of previous rift‐related faults.

Lithospheric rheology in West Tibet and Pamir constrained from the postseismic deformation of the 2005 Mw7.6 Kashmir (Pakistan) earthquake

We study the postseismic deformation of the 2005 Mw7.6 Kashmir earthquake in Pakistan, with a combination of the near- and far-field geodetic observations from the Kashmir Himalaya and the Tibetan Plateau, respectively. We construct a 3D finite-element model that integrates topographic relief, curved fault plane, and layered lithospheric structures to analyze stress-driven afterslip and estimate the rheological parameters of the Tibetan lithosphere. Our findings reveal that the ten-year afterslips of up to 30 cm were primarily localized at the downdip edges of co-seismic slip patches, causing near-field surface deformation of up to ∼5 cm within the first year. In contrast, viscoelastic relaxation in the lower crust of western Tibet and Pamir was required to reproduce far-field displacements of up to 1–2 cm recorded by GPS during the first 7 years. The model that best fits to the GPS displacements suggests a Maxwell viscosity exceeding 1020 Pa s for the Indian lower crust, while a much lower viscosity of ∼4–10×1018 Pa s is inferred for the lower crust beneath Pamir and western Tibet, indicating a softer Tibet and Pamir in response to the continental collision between India and Eurasia.

Along-strike forearc and subducted upper slab structure beneath north Chile: Slow slip implications

We evaluate the lateral variation of the lithospheric structure beneath the forearc of the North Chile subduction zone along strike, extending from Iquique to Valparaiso, to understand a possible seismic structure that hosts deep slow earthquakes by comparing the deep slow slip areas around 60 km depth, using receiver function and inversion method. Relative differences are investigated in seismic velocities around the plate interface, especially underlying the mantle wedge, the upper part of the subducted oceanic crust, and the oceanic mantle along the subduction strike. We estimate and compare the thickness and velocity of subducted oceanic crust, slab top, subducted oceanic Moho, continental Moho, and wedge mantle velocity beneath the seismic stations. The oceanic crustal thickness range from ∼5 to 10 km respectively, and the oceanic Moho depth is ∼40 km–∼90 km. It was observed that the disparities in velocities were more pronounced near the south of the Iquique zone (18°S-25°S), with high subducting oceanic crust velocities. These discrepancies in velocities could be regarded as the presence of fluids from subducted ridges and seamounts, which might alter seismicity in the area, including slow slip.

Relationship between electrical conductivity, metallogeny, and lithospheric structure in south China

The South China Block (SCB) is located at the junction of the Pacific, Eurasian, and Indo-Australian plates. Their interaction led to large-scale multi-stage mineralization in the SCB during the Mesozoic. Several regional ore-concentration areas, such as the Middle-Lower Yangtze Metallogenic Belt (MLYMB), the Qinzhou-Hangzhou Metallogenic Belt (QHMB), the Wuyishan Metallogenic Belt (WYMB), and the Nanling Metallogenic Belt (NLMB) were formed during this process. However, the dominant mineral types of these metallogenic belts are different. To study the deep mechanisms of the different metallogenic types developed in the same tectonic background at almost the same period, the magnetotelluric sounding (MT) data from 691 sites located mainly within the eastern SCB are employed to obtain a regional lithospheric 3-D resistivity model.It could be concluded from the resistivity model that deep low-resistivity anomalies and mantle upwelling channels mainly controlled almost all the Mesozoic deposits. Large-scale low-resistivity bodies extend from the crust to the upper mantle beneath the MLYMB and the QHMB, interpreted as channels of mantle-derived magma and melts/fluids containing metallogenic elements upwelling. However, the MLYMB and the QHMB have different upper crustal ore-conducting and ore-controlling structures, thus forming porphyry copper and copper-bearing tungsten deposits. Small-scale low-resistivity anomalies are invading the high-resistivity crust in the NLMB. And remelting the upper crust, mixing, and intrusion of crust-source magma, enriching tungsten-tin elements near the NLMB. Larger-scale low-resistivity anomalies exist deep in the WYMB, remelting the lower crust and resulting in the formation of porphyry copper in it. Significantly, the upper-mantle low-resistivity anomalies beneath the eastern SCB show a spatial distribution that is gradually shallowing from south to north, probably indicating that the asthenospheric materials are upwelling from south to north, corresponding with the changing progressively of magma and metallogenic activities. We propose that the lithospheric delamination and asthenospheric upwelling caused by the far-field effects of the Paleo-Pacific Plate subduction are the sources of solid magmatic activities and related metallogeny.

Lithospheric structure of the Paraná, Chaco-Paraná, and Pantanal basins: Insights from ambient noise and earthquake-based surface wave tomography

To investigate the lithospheric seismic structure of southern South America beneath the Paraná, Chaco-Paraná, and Pantanal basins, we measure two distinct sets of dispersion curves of Rayleigh waves: the first corresponds to 25,986 phase velocity dispersion curves in the period range 5–50 s, extracted from cross-correlation of the ambient noise between pairs of stations and thus sensitive mainly to crustal structure; the second set is derived from group velocities extracted from earthquake recordings, resulting in 33,888 dispersion curves with periods ranging from 8 to 200 s, allowing us to probe deeper Earth structure. From these data sets, we derive two independent S-wave velocity models following a two-step inversion procedure, resulting in a crustal and a lithospheric mantle model with depths extending up to 50 and 200 km, respectively. Features imaged in our crustal model include low velocity anomalies in agreement with the surface position of the major sedimentary basins and high velocity anomalies within fold-thrust provinces and the basement of the Pantanal basin. In the uppermost mantle, we identify high velocities in the region of the Paraná basin, São Francisco and Amazonian cratons, and Luiz Alves block, and a low velocity feature beneath the Pantanal basin, which suggests a potentially thinner lithosphere under the basin. We also illuminate a strong velocity gradient boundary between the eastern border of the Pantanal basin with the Paraná basin, from crustal to lithospheric mantle depths, which seems to delineate the western and southern borders of the Paraná basin, coinciding with the Western Paraná Suture. Additionally, we construct a Moho depth proxy map for the study area, which has an overall good agreement with previous results, except for a thicker crust beneath the southern Chaco-Paraná basin. This area, together with a thicker crust counterpart in the Paraná basin, has a remarkable correlation with the position of a volcanic layer related to the Paraná Magmatic Province, which leads us to suggest that magmatic processes played an important role in the south Chaco-Paraná basin as well.

Patchwork structure of continental lithosphere captured in 3D body wave images of its anisotropic fabrics

This paper presents an overview of research conducted for more than five decades around Vladislav Babuška and collaborators on large-scale seismic anisotropy in tectonically different regions of continental lithosphere in Europe. A wide range of independent data sets and methods are covered. It also briefly touches laboratory measurements of velocity anisotropy on rock samples from the crust and the upper mantle, and emphasizes the importance of considering anisotropy in studies of the Earth structure. The anisotropy is responsible for even larger velocity variations than those due to composition of the most abundant upper mantle rocks (peridotites). The large-scale in-situ measurements of the upper mantle anisotropy capture fabrics of the mantle lithosphere, and enables mapping lateral changes in its structure. The joint inversion/interpretation of the teleseismic body-wave anisotropic parameters, such as variations of directional terms of relative travel time residuals of P waves, shear-wave splitting or the coupled anisotropic-isotropic teleseismic P-wave tomography, image the continental lithosphere as a mosaic of anisotropic domains. Each of the domains has its own thickness and fossil fabric characterized by tilted symmetry axes. We map boundaries of the domains in dependence on the fabric changes. The boundaries can be either narrow and steep or broader and inclined, with an offset relative to boundaries of the related crustal bocks, which can reach several tens of kilometres. This overview presents the European lithosphere-asthenosphere boundary (LAB) and shows examples of anisotropic fabrics of the mantle lithosphere domains and their boundaries in different parts of the European plate.

Seafloor Rayleigh ellipticity, measured from unoriented data, and its significance for passive seismic imaging in the ocean

SUMMARY Observations of the seafloor Rayleigh ellipticity contribute to seismic imaging in the ocean. To extract such observables from the arbitrarily oriented ocean–bottom seismometer (OBS) data, we develop an orthogonal-regression-based approach to measure the waveform amplitude ratios of the unoriented horizontal and vertical components. The amplitude ratios are then used to calculate the Rayleigh ellipticity (and the sensor orientation angle). The robustness of our method is verified by applications to both the unoriented OBS data and the well oriented on-land seismic data. As we propose to calculate the Rayleigh ellipticity directly from the unoriented three-component data, the measurement process avoids the complexity arising from the surface wave non-great-circle effects and uncertainties of the OBS sensor orientation angles. Overall the Rayleigh ellipticity measurements from our method are systematically higher than those by conventional analysis and show less uncertainties. Our analyses suggest that the Rayleigh ellipticity curve (14–60 s), which could be retrieved from the raw broad-band OBS data, is effective to constrain the oceanic lithosphere structure, and the accurate measurement of Rayleigh ellipticity curve is important. The potential of seafloor Rayleigh ellipticity for seismic imaging in the ocean is evidenced by a case study of the Japan Basin, the Sea of Japan. Considering the insufficient station coverage in the ocean, the single-station measurement of seafloor Rayleigh ellipticity is of significance for OBS community.

Insight into the Evolution of the Eastern Margin of the Wyoming Craton from Complex, Laterally Variable Shear Wave Splitting

Abstract Dense seismic arrays such as EarthScope’s Transportable Array (TA) have enabled high-resolution seismic observations that show the structure of cratonic lithosphere is more heterogeneous and complex than previously assumed. In this study, we pair TA data with data from the Bighorn Arch Seismic Experiment and the Crust and lithosphere Investigation of the Easternmost expression of the Laramide Orogeny (CIELO) to provide unprecedented detail on the seismic anisotropic structure of the eastern margin of the Wyoming Craton, where several orogens emerged from nominally strong cratonic lithosphere during the Laramide Orogeny. In this study, we use the splitting of teleseismic shear waves to characterize fabrics associated with deformation in the Earth’s crust and mantle. We constrain distinct anisotropic domains in the study area, and forward modeling shows that each of these domains can be explained by a single layer of anisotropy. Most significantly, we find a fast direction in the southern part of the Powder River Basin, which we refer to as the Thunder Basin Block (TBB), that deviates from absolute plate motion (APM). This change in splitting behavior coincides with changes in other modeled geophysical observations, such as active source P-wave velocity models, potential field modeling, and seismic attenuation analysis, which all show a significant change moving from the Bighorn Mountains to the TBB. We argue that these results correspond to structure predating the Laramide Orogeny, and most likely indicate a Neoarchean boundary preserved within the lithosphere.

A translithospheric magmatic system revealed beneath Changbaishan volcano

Abstract Changbaishan volcano (CBV), located on the border between China and North Korea, has undergone violent eruptions since the Oligocene, making it one of the most captivating and explosive volcanoes on Earth. However, the lack of precise characterization regarding the magmatic system makes it difficult to decipher its eruption risk and mechanism, despite its significant size and past devastating effects. In this study, we employed newly developed teleseismic receiver function techniques, including Ps and Sp waves, to construct a lithospheric structure model beneath the CBV region. The results show a thick crust (~37 km) and a weak, thin lithosphere under the CBV, with a low-amplitude width of 80 km at the Moho depth and 200 km at the depth of the lithosphere-asthenosphere boundary. These features depict the seismological response of a translithospheric magmatic system beneath the CBV, where hot upwelling material rises through the lithospheric mantle, underplates at the base of the crust, and forms the magma chamber(s) at shallow depth. Such magmatic system features can be taken as a unifying paradigm for large volcanic regions worldwide.

The thermal structure of the Colombian lithosphere: A regional and basin-scale analysis

It is well-established that the thermal state of the lithosphere strongly influences various regional and local geological processes, including crustal deformation, hydrocarbon maturation, hydrogen generation, and geothermal phenomena. Moreover, the thermal structure exhibits high sensitivity to tectonic features, a property of particular significance in Colombia, where three main tectonic plates converge, and lithospheric tearing has been documented. In this contribution, we focus on elucidating the impact of plate architecture on the thermal field in central-eastern Colombia at both shallow and deep levels. To accomplish this, we constructed a series of two-dimensional profiles and derived a numerical solution of the heat equation using the conservative finite difference method. As constraints, we incorporate an inferred distribution of rocks in the deep crust and upper mantle based on global and local lithospheric thickness models. Material parameters for the various rocks, both exposed and inferred, were obtained from the literature. Additionally, we used superficial heat flow estimates and apparent geothermal gradients compiled by the Colombian Geological Survey.Our results suggest a significant influence of the lithospheric Caldas tear on the thermal state of Colombia, with the breaking off occurring in the Nazca plate under the Eastern Cordillera range around 5°N. The modeled asthenospheric heat flow remains approximately 25 mWm−2, except in the northern Eastern Cordillera range, where the background heat flow increases rapidly to 40 mWm−2. Consequently, our model predicts partial melting in the lower crust to the north and a thermally unstable lower crust to the south of the Caldas tear. The material parameters that best fit the surface data suggest the presence of a basement moderately enriched in radioactive elements in the Eastern Llanos basin. After accounting for compaction, we also confirm a strong influence of the tectonic setting on the thermal state of sedimentary basins.

What controls structural variations along the Zagros Collision Zone? Insights from geophysical observations and thermo-mechanical modelling

The Zagros Collision Zone is a complex tectonic region formed as a consequence of the collision between Arabia and Eurasia after the subduction of the Neo-Tethys ocean. The NW-SE striking Zagros orogen consists of the following parallel tectonic units (from SW to NE): Zagros Fold and Thrust Belt (ZFTB), Sanandaj–Sirjan Metamorphic Zone (SSZ), and Urumieh–Dokhtar Magmatic Arc (UDMA). In this study, we perform a combined analysis of recent geophysical data, revealing pronounced differences in the crustal and lithospheric structure along the Zagros Mountains. The northwestern sector shows a fairly uniform crustal thickening across the broad symmetric orogen from the ZFTB to the UDMA. In contrast, in the central Zagros, the transition from a relatively narrow zone of high elevations and high-frequency relief in the ZFTB to a smoother surface topography of the SSZ and UDMA occurs with an abrupt increase in Moho depth below the SSZ. The last observation has recently been interpreted as a result of “relamination” process, where the felsic upper crust of the Arabian plate underthrust the mafic crust of the Iranian plate. We present geodynamic numerical models of crustal relamination during continental collision and compute static gravity field of the resulting structures. We show that oblique closure of the Neo-Tethys affects lateral variations in the style and extent of crustal relamination, which control the observed along-strike changes in crustal configuration and orogen altitude. In particular, a narrow and higher orogen (as in the central Zagros) develops in the experiments with a young and wide oceanic plate, whereas an old and narrow subducting plate tends to form a broad and lower topography (as in the northwestern Zagros). This is geometrically consistent with the progressive closure of the Neo-Tethys from NW to SE during the oblique continental collision between Arabia and Eurasia.

Is There a Carbonated Mid‐Lithosphere Discontinuity in Cratons?

AbstractThe mid‐lithosphere discontinuity (MLD), identified by a sharp velocity drop at ∼70–100 km depths within the cratonic lithosphere is key to comprehending the chemical composition and thermal structure of the cratonic lithosphere. The MLD is widely accepted to be caused by composition anomalies, such as hydrous minerals, which show low velocities and high electrical conductivities. However, noticeable high‐electrical conductivity anomalies have not been detected in the most cratonic lithosphere. Dolomite has an electrical conductivity similar to olivine and can be originated by carbonatitic melts trapped at ∼80–140 km depths. Here we investigated the elasticity of dolomite under mantle conditions using ab initio calculations and found dolomite exhibits significantly lower velocities than the primary minerals in the lithospheric mantle. Therefore, the dolomite enrichment might provide a good explanation for the observed velocity drop of the MLD in cratonic regions where no high‐conductivity anomaly has been detected, such as the northern Slave craton.