Crustal Architecture Research Articles

Gravity and Magnetic Survey in Southwestern Part of Cuddapah Basin, India and its Implication for Shallow Crustal Architecture and Mineralization

ABSTRACT Gravity and magnetic surveys were carried out in southwestern part of Cuddapah basin (CB) covering an area of ~3660 km2. Southwestern part of CB gained lot of attention after discovery of second most important uranium province in India. Some non-metallic industrial minerals and base metal occurrence are also reported in the study area. Present study with high spatial resolution gravity-magnetic survey aims to decipher detail basin geometry, nature of sediments, along with possible mineral deposits in SW part of CB. The gravity survey comprising short and long wavelength anomalies brought out sedimentary characteristics and basement architecture underneath the sediments. The long wavelength features of the gravity map shows gneissic basement, which is characterized by both basic and acid magmatic intrusive. Residual gravity anomaly map shows good correspondence with the exposed high density basaltic rock units and also brought out occurrence of concealed high density litho-units, which have significance for mineral prospecting. The magnetic map shows that both sediments and underneath basement are non-magnetic in nature except SW part of the study area, where study suggests occurrence of concealed mafic lensoid body. Euler solutions and combined gravity-magnetic modelling further facilitated for understanding of structural feature and basement geometry. Based on the integrated gravity and magnetic study mineral prospecting zones have been delineated for further detailed study.

Dynamics of crustal overthrust versus underthrust in the continental collision zones: Numerical modelling

AbstractTrans‐plate crustal overthrust and underthrust are two unusual crustal architectures in nature, the mechanisms of which remain debated. Here, we construct a series of 2D numerical models to investigate the dynamics of trans‐plate crustal overthrust and underthrust. Model results indicate that the favourable conditions of crustal overthrust include low convergence rate, plastically strong crust, rheologically strong upper crust and hot subducting plate, which meanwhile contribute to the formation of ‘crocodile’ crustal structure. In contrast, a combination of a strong and buoyant subducting plate with a hot overriding plate facilitates crustal underthrust. The development of crustal overthrust shows no correlation with the subduction mode of lithospheric mantle, whereas crustal underthrust normally occurs in an advancing subduction system. Development conditions and crustal structures of the modelled overthrust and underthrust are consistent, on the first order, with the natural Dinarides orogen and the southern Tibetan plateau respectively.

Crustal architecture and Moho topography beneath the eastern Indian and Bangladesh margins – new insights on rift evolution and the continent–ocean boundary

The thick sedimentary cover (≤18 km) along the Eastern Continental Margin of India (ECMI) and over the Bay of Bengal has hindered understanding of the mechanisms of rifting that operated on the eastern Indian and Bangladesh margins. Analysis of multichannel seismic reflection data, together with 3D gravity inversion and 2D gravity forward modelling, illuminates basement configuration, crustal thickness and Moho topography, thereby revealing the modes of rift evolution and the location of the continent–ocean boundary (COB) along these margins. The basement, particularly in the shelf and slope regions of eastern peninsular India, is traversed by nearly coast-perpendicular graben, and their seaward continuity is delineated up to 125 km from the coastline. Three different types of continental margin are present along the ECMI: (1) sheared rift on the southern segment of the ECMI, up to 14° N latitude (offshore the Southern Granulite Terrain); (2) hyper-extended rift in the central segment between 14° N and 17° N (offshore the Dharwar Craton); and (3) hypo-extended rift on the northern segment between 17° N and 20° N (offshore the Eastern Ghats Mobile Belt). The graben terminations, crustal thickness and Moho topography of both the ECMI and offshore Bengal Basin clearly suggest that the COB runs nearly parallel to the coastline of peninsular India, but takes an orthogonal turn offshore in the Bengal Basin and connects the palaeo-continental shelf and the Rajmahal–Sylhet Line onshore in the Bengal Basin. Crustal thickness (8–10 km) and depth to the Moho discontinuity (≤28 km) beneath the Bangladesh margin are unusual because the crustal thickness increased through interaction of the Kerguelen plume with the existing oceanic lithosphere. The Moho deepened largely due to the load of the Bengal Fan sediments. The absence of rifted crustal blocks on the Bangladesh margin and the continuity of the COB into the onshore Bengal Basin together imply that the present Bangladesh region was under marine conditions at least until the beginning of Bengal Fan sedimentation (i.e. no less than 23 Ma).

A revised position for the rotated Falkland Islands microplate

The early stages of transform margin formation are associated with crustal fragmentation and block rotation. The restricted size of the resultant microcontinental blocks precludes palaeogeographical reconstructions and reliable estimations of the amount of rotation they can undergo. An example considered here is the Falkland Plateau. This is located adjacent to the Agulhas–Falkland Fracture Zone and its westernmost province is the Falkland Islands microcontinent. The position of the plateau and the islands prior to Gondwana break-up remains contentious. This study integrates seismic reflection and gravity data to propose a revised position of the Falkland Islands microcontinent constrained by (1) the presence of a mega-décollement, controlling the Gondwanide Orogen, described north of the Falkland Islands and underneath South Africa and the Outeniqua Basin, and (2) the similar architecture of fault networks mapped north of the islands and in the northernmost Outeniqua Basin. This revised position requires a re-evaluation of the timing and rate of rotation of the Falkland Islands microcontinent and affects the expected crustal architecture adjacent to the islands. Our model yields rotation rates between 5.5° and 8° Ma −1 and two potential times for rotation, and predicts more unstretched crust beneath the basin east of the Falkland Islands than previous models.

Oil prospects in the Mozambique Channel: where incipient subduction meets passive margin

After several major gas discoveries made offshore Tanzania and northern Mozambique, the entire East Africa margin has been assumed to be a gas province. We present evidence for a new oil province along this margin based on an interpretation of Spectrum’s recently acquired modern Broadband 2D seismic data in the offshore Angoche/Mozambique Basin. The new seismic data lying south of the Rovuma Basin and across the Davie Ridge in the Mozambique Channel (Figure 1) are considered together with an integration with sea surface oil slicks identified on satellite imagery and other direct hydrocarbon indicators (DHIs). Understanding the nature and origin of crustal architecture in the Angoche Basin and Davie Ridge is a vital input to plate reconstruction, as well as enabling an assessment of petroleum potential. We discuss potential source rocks and variation in geothermal gradient in the region and evaluate various plays in the light of the new geological findings within the new Broadband 2D seismic dataset.

Archean crust and metallogenic zones in the Amazonian Craton sensed by satellite gravity data

The formation of ore deposits has been extensively studied from a shallow crust perspective. In contrast, the association of mineral systems with deep crustal structure of their host terranes remains relatively undisclosed, and there is evidence that processes throughout the lithosphere are coupled for their evolution. The current debate centers on the control of the regional deep crustal architecture in focusing and transferring fluids between geochemical reservoirs. Defining such architecture is not unequivocal, and involves combining indirect information in order to constrain its physical properties and evolution. Herein, based on evidence from satellite gravity, constrained by airborne potential field data (gravity and magnetics), we provide an example on how the lithosphere geometry controlled the location of copper and gold systems in the world-class Archean Carajás Mineral Province (Amazonian Craton, South America). Validation with information from passive seismic (wave speeds, crustal and lithospheric thickness) and geochronologic data (model, crystallization ages, and Neodymium isotope ratio determinations) portrays a significantly enlarged, poly-phase, Archean crust that exerted geometric control on the location of the mineral systems within and adjacent to the province during tectonic quiescence and switches. This new geologic scenario impacts the understanding of the Amazonian Craton. Synergy between multi-source data, as experimented here, can provide robust models efficiently and, conceivably, help to unveil similar terrains elsewhere.

Geological interpretation of the 2008 seismic reflection, refraction and magnetotelluric data from the northern Eyre Peninsula, Gawler Craton

A deep seismic reflection profile and coincident refraction and magnetotelluric data were acquired across the northern Eyre Peninsula, Gawler Craton in 2008 to enhance the prospectivity of this region for uranium and geothermal energy, by establishing the crustal architecture and regional geodynamic framework. The seismic line crossed several tectonic domain boundaries, including the Kalinjala Mylonite Zone, which is a key structure in the southern and central Gawler Craton. In the vicinity of the seismic section, this mylonite zone dips moderately to the east and appears to be a major crustal-scale fault which cuts through to the Moho; it separates middle to lower crust of differing seismic reflectivity. The changes in seismic character correspond with the boundary between the Olympic Fe-oxide Cu- Au-U Province (host of Olympic Dam and Prominent Hill deposits) in the east, and the Central Gawler Au Province in the west, and also are suggested to limit the extent of the South Australian Heat Flow Anomaly.

Acquisition and processing of seismic reflection, refraction and magnetotelluric data, northern Eyre Peninsula, Gawler Craton

SUMMARY In 2008 Geoscience Australia acquired regional seismic reflection, wide-angle refraction/reflection, gravity, and magnetotelluric (MT) data along a 253km east-west transect across northern Eyre Peninsula, Gawler Craton in South Australia as part of the Australian Government’s Onshore Energy Security Program (OESP). These datasets provide complementary information on the crustal architecture and evolution of this part of the Gawler Craton. Twenty three Earth Data recorders were deployed along the reflection transect as a fixed, wide-angle recording array, with 5 and 10 km interval spacing, using threecomponent seismometers. The high quality data of up to 60-70 km offsets were collected using vibroseis sources. MT data were acquired at 40 broadband and 12 long period sites along the reflection transect. This paper presents acquisition parameters and processing steps for these datasets, to highlight their advantages and limitations, and improve the quality of the geological interpretation over the Gawler Craton.

Devonian continental arc intermediate-felsic magmatism in the Gorny Altai terrane, northwestern Central Asian Orogenic Belt: Heterogenous crustal melting and input of mantle melts

Devonian intermediate-felsic igneous rocks are widespread in the Gorny Altai terrane and they were suggested to form in a continental arc setting that was built on the late Neoproterozoic to early Ordovician Kuznetsk-Altaiintra-oceanicsubduction-accretion system (KAIOSS).11KAIOSS, Kuznetsk-Altaiintra-oceanicsubduction-accretion system Petrogenesis of these rocks will not only provide information on geodynamic mechanisms for continental arc magmatism but also shed light on how accretionary orogens can be differentiated and matured, both of which are pivotal in understanding the continental generation and evolution. This study is focused on igneous suites from the early Devonian Ongudai and middle Devonian Kuratin complexes. The former complex is dominated by andesites and basaltic andesites. Zoning patterns of clinopyroxene phenocrysts and whole-rock geochemical modeling suggest that these volcanic rocks formed mainly by magma mixing with substantial input of mantle-derived mafic melts, signifying significant crustal growth. The latter complex comprises a volcanic suite (ca. 383–382 Ma) ranging from andesites to rhyolites and minor granitic intrusions (ca. 385–382 Ma). The rhyolitic endmembers of the volcanic suite were probably sourced from the late Neoproterozoic to early Ordovician meta-sedimentary sequences of the KAIOSS. In contrast, the andesitic endmembers possibly formed by partial melting of mixed crustal components comprising the late Neoproterozoic magnesian andesites (or their geochemical equivalents) and more depleted basaltic rocks of the KAIOSS. Geochemical data demonstrate that the granitic intrusions were most likely products of melts from the late Neoproterozoic to Cambrian arc-type basaltic rocks of the KAIOSS. Taken together, the whole igneous suite of the Kuratin complex documents strong crustal differentiation. Of particular importance is that the highly heterogenous crustal components involved likely mirror the pre-Devonian crustal architecture that was induced by prolonged subduction-accretion of the KAIOSS. Our study suggests that heterogeneous crustal melting by underplating of hydrous basaltic melts in continental arcs is a plausible way to transform previous immature oceanic materials in accretionary orogens into differentiated and mature continental crust. This process contributes significantly to the magmatic diversity in subduction zones and crustal growth and differentiation in accretionary orogens.

Unravelling the Crustal Architecture of Cape Verde from the Seamount Xenolith Record

The Cape Verde oceanic plateau hosts 10 islands and 11 seamounts and provides an extensive suite of alkaline lavas and pyroclastic rocks. The volcanic rocks host a range of crustal and mantle xenoliths. These xenoliths provide a spectrum of lithologies available to interact with magma during transport through the lithospheric mantle and crust. We explore the origin and depth of formation of crustal xenoliths to develop a framework of magma-crust interaction and a model for the crustal architecture beneath the Cape Verde oceanic plateau. The host lavas are phononephelinites to phonolites and the crustal xenoliths are mostly mafic plutonic assemblages with one sedimentary xenolith. REE profiles of clinopyroxene in the host lavas are light rare-earth element (LREE) enriched whereas clinopyoxene from the plutonic xenoliths are LREE depleted. Modelling of REE melt compositions indicates the plutonic xenoliths are derived from mid-ocean ridge basalt (MORB)-type ocean crust. Thermobarometry indicates that clinopyroxene in the host lavas formed at depths of 17 to 46 km, whereas those in the xenoliths formed at 5 to 20 km. This places the depth of origin of the plutonic xenoliths in the oceanic crust. Therefore, the xenoliths trace magma-crust interaction to the MORB oceanic crust and overlying sediments located beneath the Cape Verde oceanic plateau.

The 3D Geophysical Investigation of a Middle Cretaceous to Paleocene Regional Décollement in the Cordillera of Northern Canada and Alaska

AbstractA new approach to the 3D inversion and interpretation of gravity data is applied to the crustal architecture of the northern Cordillera of Canada and Alaska. The technique models the distribution and depth extent of rocks with systematic density contrasts, such as sedimentary or intrusive rocks. In the northern Cordillera, the geometry of low‐density zones, primarily associated with middle to Late Cretaceous granitic intrusions, and Neoproterozoic and Cretaceous sedimentary rocks, is defined. Variation in the depth extent of these zones delimits a surface, interpreted herein as a regional décollement syntectonic with, or postdating, middle Cretaceous intrusions, but predating and displaced ~430 km by the Eocene‐aged Tintina fault. The décollement trends N35°E and shallows from a depth of ~15–20 km beneath Selwyn basin to ~11 km beneath the Mackenzie Mountains. Here surface faults echo the décollement geometry, linked to fold and thrust belt development between the middle Cretaceous and Paleocene. The décollement continues southward for an unknown distance into northern British Columbia, but the Liard line represents a structural discontinuity between the fold and thrust belts of the Mackenzie Mountains and northern Rocky Mountains. The décollement's northwestern extent is broadly defined by surface faults in the northern Ogilvie Mountains. However, prior to Tintina fault displacement, the décollement was likely connected to a fold and thrust belt and related décollement in east‐central Alaska. Estimates of post‐middle Cretaceous exhumation suggest regional tectonic modification of the décollement, possibly including the presently active detachment inferred for the weak lower crust.

The Calc-Alkaline Hidden Bay and Kagalaska Plutons and the Construction of the Central Aleutian Oceanic Arc Crust

Abstract Calc-alkaline plutons are the major crustal building blocks of continental margins, but are rarely exposed in oceanic island arcs. Two of the best examples are the ∼10 km wide Hidden Bay and Kagalaska plutons that intrude Eocene mafic volcanic–sedimentary rocks on Adak and Kagalaska islands in the central Aleutian arc. Twenty new Ar/Ar and U/Pb ages, coupled with published ages, show that the Hidden Bay pluton was intruded in multiple stages from ∼34·6 to 30·9 Ma, whereas the Kagalaska pluton was intruded at ∼14 Ma. The plutons largely consist of medium- to high-K2O hornblende-bearing cumulate diorite (53–55 wt % SiO2) and hornblende–biotite granodiorite (57–64 wt %), with lesser amounts of gabbro (50–52 wt % SiO2), leucogranodiorite (67–69 wt % SiO2) and aplite (76–77 wt % SiO2) that can generally be linked to each other by crystal fractionation. The compositions of these plutons are generally similar to those of continental plutons, except for more oceanic-like large ion lithophile element and isotopic signatures (87Sr/86Sr = 0·703–0·7033; ɛNd = 9·4–7·7) that reflect oceanic- rather than continental-type crustal contaminants. Chemical similarities between the Hidden Bay homogeneous gabbros and high-Al basalts in Adak Pleistocene-Holocene volcanoes indicate little temporal evolution in the general character of the mantle-derived basalts. Rather than a unique arc setting and distinctive magmas, formation of the Aleutian calc-alkaline plutons seems to require a sufficient crustal thickness (∼37 km) and a high enough water content to stabilize pargasitic hornblende amphibole in a relatively closed magma system that favors increasing K, Ti and H2O at the end of a magmatic cycle. This termination of magmatism coincides with a northward migration of the magmatic front that is inferred to be associated with fore-arc subduction erosion. In accord with Adak region crustal architecture based on seismic data, crystallization models for the plutons suggest that mantle-generated hydrous arc basalts fractionated olivine and clinopyroxene in the lower crust to form high-Al basaltic composition magmas that rose into the mid-crust, where gabbro and diorite crystallized to form the magmas that buoyantly rose into the upper crust and crystallized to form the volumetrically dominant granodiorite (58–63 wt % SiO2). The most important temporal changes in chemistry can be explained by fore-arc crust incorporated into the mantle wedge by fore-arc subduction erosion creating ‘adakitic’ signatures at times of northward arc migration and a change to a more continental subducted sediment component at the time of Plio-Pleistocene glaciation.

Depth-to-basement for the East European Craton and Teisseyre-Tornquist Zone in Poland based on potential field data

Results of a depth-to-basement study are presented for the East European Craton and the Teisseyre-Tornquist Zone (TTZ) in Poland. The terrestrial gravity data are inverted for the top of the Paleoproterozoic basement and, independently, for the top of the Ediacaran using seismic horizons from the PolandSPAN™ seismic survey and well tops as input depth measurements. The depth to the Ediacaran modelling was additionally extended to cover the Łysogóry Block and northern Małopolska Block. The results are visualised as isobath maps for the top of the Paleoproterozoic basement and top of the Ediacaran and an isopach map for the Ediacaran, supplemented with qualitative structural interpretation based on gravity and magnetic data. The results of modelling show a smooth crystalline basement slope within the TTZ with the top of the Paleoproterozoic basement uniformly descending south-westwards by 10–14 km. The thickness of the Ediacaran in SE Poland increases in the same direction to more than 10 km within the TTZ. Such a crustal architecture, in combination with the earlier documented Moho elevation of 4–6 km, reveals significant thinning of the Paleoproterozoic crust within the TTZ to form a crustal necking zone due to the Ediacaran rifting. A smooth geometry of the top of basement along with the lack of basement-rooted faults suggests a ductile mode of crustal thinning during rifting of Rodinia. Moreover, the development of the NW–SE-oriented rift, a precursor of the Tornquist Ocean, was associated with rifting in a NE–SW direction parallel to the Orsha-Volyn Rift.

Imaging the Moho and the Main Himalayan Thrust in Western Nepal With Receiver Functions

AbstractThe crustal structure of Western Nepal is studied for the first time by performing receiver function analysis on teleseismic waveforms recorded at 16 seismic stations. The Moho geometry is imaged as it deepens from ~40‐km depth beneath the foothills and the Lesser Himalaya to ~58‐km depth beneath the Higher Himalayan range. A midcrustal low‐velocity zone is detected at ~15‐km depth along ~55‐km horizontal distance and is interpreted as the signature of fluids expelled from rocks descending in the footwall of the Main Himalayan Thrust. Our new image allows structural comparison of the Moho and of the Main Himalayan Thrust geometry along‐strike of the Himalayas and documents long‐wavelength lateral variations. The general crustal architecture observed on our images resembles that of Central Nepal; therefore, Western Nepal is also expected to be able to host large (MW > 8) megathrust earthquakes, as the 1505 CE event.

Geology, geophysics, geochemistry of a hidden Palaeoproterozoic ocean-continent transition in the northern Gawler Craton

Craton margins are known to host many major deposit styles across the globe, and constraining the spatial and temporal relation between permissive geometries and thermal drivers for alteration processes are key for identifying prospective terranes. Orthogonal deep crustal reflection seismic profiles provide insight into the three-dimensional crustal architecture of the north-western Gawler Craton, South Australia. Correlating between north-south seismic line 08GA-OM1 and east-west seismic line 13GA-EG1, has enabled the interpretation of a major crustal boundary separating the core of the Gawler Craton from re-worked crustal provinces to the west and north. We use seismic character, potential fields and magnetotellurics to locate and constrain the geometry of this major boundary, and isotopic signatures from sparse drillholes to characterize the crustal age and composition either side of the interpreted boundary.In recent years, isotopic evidence has been used to infer the presence of early Palaeoproterozoic oceanic crust having existed between the Gawler and Yilgarn Cratons. We present a new model for the north-western Gawler Craton, locating a transitional region between a cratonic core and this oceanic crust, and suggest that the craton margin was ~100 km inboard of current interpretations.

Composite basement along the southern margin of the North Australian Craton: Evidence from in-situ zircon U-Pb-O-Hf and whole-rock Nd isotopic compositions

Hafnium-isotope compositions of emplacement-age zircon grains are integrated with zircon δ18O and whole-rock Nd-isotope data in order to characterise the age and composition of the sources of Paleoproterozoic granites along the southern margin of the North Australian Craton. The petrogenesis of the granitic rocks is interpreted in terms of partial melting of distinct crustal components with variable crustal residence ages, at different crustal levels, reflecting the local Paleoproterozoic crustal architecture. This finding implies a composite nature of the unexposed deep crust, which comprises Paleoproterozoic supracrustals and subordinate, discontinuous and local Neoarchean meta-igneous components. The limited lateral extension of Neoarchean deep crust does not support tectonic models for the Paleoproterozoic amalgamation of the craton that consider intracratonic and/or continent-continent collision settings. The composite nature of the basement and the presence of cryptic boundaries are consistent with the accretion of Paleoproterozoic supracrustal elements, as back-arc and island-arc, to a Neoarchean proto-craton. The dominant Paleoproterozoic reworking of Archean-derived supracrustal materials indicates that accretionary orogenesis was an important setting for crustal reworking and craton stabilisation in the Paleoproterozoic.

The You Yangs batholith in Southeastern Australia, the sources of its magmas and inferences for local crustal architecture

The 365-Ma You Yangs batholith is a mainly I-type monzogranitic body, containing rocks with both clinopyroxene and hornblende, but with a 2–2.5 km-wide rim of S-type rocks. In places, the margins of the intrusion wedge out laterally. A laccolithic shape may explain there being only low-grade contact metamorphism of the Ordovician metasedimentary wall rocks. The chemical and isotopic characteristics of the granitic rocks suggest that the magmas formed by partial melting of a source that contained some meta-igneous rocks but was dominated by chemically immature metasedimentary types, to impart an evolved Sr isotope signature (87Sr/86Srt = 0.70877–0.71066 for the main monzogranitic rocks), combined with relatively non-radiogenic εNd t (–2.4 to –1.9). Crystal fractionation played little role in shaping the compositions of the granitic magmas, with the main variations interpreted to be source-inherited. Igneous-textured microgranular enclaves (IMEs) are prominent in the monzogranitic rocks. The IMEs probably had an ultimate enriched-mantle source, and their magmas did not mix significantly with the crustally derived granitic host magmas. The characteristics of the monzogranitic rocks hosting the enclaves suggest the possibility that an unrecognised metasediment-dominated terrane of ancient arc crust may be present beneath the Bendigo Zone.

Devonian Crustal Stretching in the Northern Tasmanides (Australia) and Implications for Oroclinal Bending

AbstractThe Tasmanides in eastern Australia exhibit a number of orogenic curvatures (oroclines), and possibly, a continental‐scale bend that defines the continuation of the Delamerian Orogen with the Thomson Orogen. We provide an insight into the geodynamic processes associated with the origin of this orocline. We present interpretations of seismic reflection profiles and potential field data from the Thomson Orogen, which provide information on the crustal architecture and unravel major structures and kinematic relationships. Results show that a large area in the northern Tasmanides is underlain by thinned crust, bounded in the north and south by ~E‐W trending geophysical features with apparent sinistral and dextral sense of kinematics, respectively. Within the highly extended crust of the Thomson Orogen, there is evidence for widespread Devonian basins bounded by normal faults. In stark contrast to the southern Tasmanides, where rocks show evidence for an earlier (Silurian) episode of extension and Devonian contractional deformation, no evidence for Silurian synrift sedimentation is observed in the Thomson Orogen. Evidence for ~E‐W trending sinistral and dextral crustal‐scale shear zones in the northern and southern boundaries of the Thomson Orogen, respectively, may represent tear faults, which were active during the Early Devonian and were possibly accompanied by tear‐related magmatism. We suggest that crustal stretching in the northern Tasmanides was associated with Devonian back‐arc extension in response to trench retreat, bounded by zones of slab‐tearing and crustal segmentation that ultimately led to the development of the Delamerian‐Thomson Orocline.

New Magnetic Anomaly Map of the Antarctic

AbstractThe second generation Antarctic magnetic anomaly compilation for the region south of 60°S includes some 3.5 million line‐km of aeromagnetic and marine magnetic data that more than doubles the initial map's near‐surface database. For the new compilation, the magnetic data sets were corrected for the International Geomagnetic Reference Field, diurnal effects, and high‐frequency errors and leveled, gridded, and stitched together. The new magnetic data further constrain the crustal architecture and geological evolution of the Antarctic Peninsula and the West Antarctic Rift System in West Antarctica, as well as Dronning Maud Land, the Gamburtsev Subglacial Mountains, the Prince Charles Mountains, Princess Elizabeth Land, and Wilkes Land in East Antarctica and the circumjacent oceanic margins. Overall, the magnetic anomaly compilation helps unify disparate regional geologic and geophysical studies by providing new constraints on major tectonic and magmatic processes that affected the Antarctic from Precambrian to Cenozoic times.

The non-cylindrical crustal architecture of the Pyrenees

We exploit the data from five seismic transects deployed across the Pyrenees to characterize the deep architecture of this collisional orogen. We map the main seismic interfaces beneath each transect by depth migration of P-to-S converted phases. The migrated sections, combined with the results of recent tomographic studies and with maps of Bouguer and isostatic anomalies, provide a coherent crustal-scale picture of the belt. In the Western Pyrenees, beneath the North Pyrenean Zone, a continuous band of high density/velocity material is found at a very shallow level (~10 km) beneath the Mauleon basin and near Saint-Gaudens. In the Western Pyrenees, we also find evidence for northward continental subduction of Iberian crust, down to 50–70 km depth. In the Eastern Pyrenees, these main structural features are not observed. The boundary between these two domains is near longitude 1.3 °E, where geological field studies document a major change in the structure of the Cretaceous rift system, and possibly a shift of its polarity, suggesting that the deep orogenic architecture of the Pyrenees is largely controlled by structural inheritance.