Continental Blocks Research Articles

On the crustal composition of the Sardinia–Corsica continental block inferred from receiver functions

Abstract. Subduction-related geodynamic processes significantly influence plate tectonics and Earth's evolution, yet their impact on the continental crust remains poorly understood. We investigated the Sardinia–Corsica continental block, situated in the Mediterranean Sea, which has experienced intense subduction-driven geodynamic events. By analyzing P-wave receiver functions from our LiSard (Lithosphere of Sardinia) seismic network and publicly available stations, we aimed to understand crustal structure and composition. We inferred the Moho depth and examined the P-wave to S-wave velocity ratio (VP/VS). We interpret our findings considering petrological data, heat flux measurements, and other geophysical information. We found that the Variscan granitoid batholith has the greatest Moho depths in both Sardinia and Corsica. VP/VS ratios (ranging from 1.65 to 1.70) are consistent with average crustal values of SiO2 between 65 % and 70 %. However, in central Corsica, two stations have exceptionally high VP/VS values (> 1.80), suggesting the possible presence of serpentinite throughout the crust. In Alpine Corsica, a station exhibited similar high VP/VS values but a shallower Moho depth of 21 km. The western part of Sardinia, where Cenozoic volcanism occurred, also showed a shallower Moho depth (20–25 km) and high VP/VS values. The highest VP/VS value (1.91) is recorded in an area where surface-wave dispersion curves from ambient noise identified the lowest average S-wave velocity and where the highest heat flux has been reported. This suggests elevated crustal temperatures, although these values may also reflect the influence of thick Plio-Quaternary sedimentary deposits. Overall, our results indicate that recent geodynamic processes have left the granitoid batholith almost intact, with minimal alteration to its composition.

The Triassic tectonic transition of the Northwestern margin of Ordos Basin, North China Craton

ABSTRACT The Northwestern margin of Ordos Basin (NWOB), which contains the Helanshan Tectonic Belt (HTB) and Northwestern margin of Ordos Basin Thrust Belt (NWOBTB), is situated in the northwest of the North China Craton (NCC). The Triassic sedimentary-tectonic transition of the NWOB provides crucial insights for revealing the tectonic evolution of the NCC. In this study, we have utilized a comprehensive dataset including the palaeocurrent orientations, sandstone modal composition, U-Pb age analysis of detrital zircons, and balanced cross-sections restorations, to clarify the Triassic sedimentary-tectonic evolution of NWOB. The southeast-directed palaeocurrent indicates the sediments were primarily derived from northwest. The composition of clastic material suggests diverse sources, including magmatic arc and continental blocks. Detrital zircons extracted from four sandstones yield five major LA-ICP-MS U-Pb age groups: 2600–2500 Ma, 2300–2200 Ma, 2000–1800 Ma, 500–400 Ma and 390–230 Ma. A comparison of these U-Pb age groups from the Triassic strata in the NWOBTB with the magmatic records in the Alxa Massif, the Qilian Orogenic Belt, and detrital zircons from pre-Triassic strata in the HTB reveals that the Triassic detritus in the NWOBTB was predominantly originated from the Alxa Massif. Furthermore, the absence of detrital zircons in NWOBTB that originated from the HTB suggests the HTB had not been uplifted until the Mid-Late Triassic and remained in a steady sedimentary environment with NWOBTB during this period. In addition, the E-W treading shortening structures, along with the angular unconformity between the Jurassic and the Upper Triassic in the HTB, indicate a phase of extensive N-S shortening occurred in the HTB in the end of the Triassic. Balanced cross-section restorations demonstrate the southern HTB experienced 27% shortening, while the middle HTB underwent 15% shortening. In contrast, the Jurassic strata are in parallel-unconformity with the Triassic strata in the NWOBTB. This suggests the NWOBTB was not significantly effected by the end Triassic N-S shortening deformation. These distinct deformations between the HTB and NWOBTB imply that there was a phase of dextral strike-slip displacement between the two regions in the end of the Triassic, which is related to the closure of Paleo Tethys Ocean.

The Lithosphere‐Asthenosphere System Beneath the North Atlantic and Surroundings: Results From Multi‐Observable Probabilistic Inversions

AbstractThe North Atlantic region is a complex geodynamic setting that comprises multiple continental blocks, sedimentary basins, mid‐ocean ridge systems and prominent hotspots. Recent geophysical surveys of the near‐surface have enhanced our understanding of crustal elements and the shallow lithosphere. However, our knowledge of the deep lithospheric structure and the physical state and dynamics of the upper mantle is still limited. Here, we exploit the combined sensitivity of surface‐wave data, geoid anomalies, absolute topography and surface heat flow to obtain full thermochemical models of the region from the surface down to 350 km. We jointly invert these data sets using a simulation‐based, multi‐observable probabilistic framework. We validate our results with independent thermobarometric and chemical information from mantle xenoliths and test the effects of using different seismic models on the inversion results. Our model reveals an intricate sublithospheric flow system, driven by the interaction of deep upwellings with the highly irregular lithospheric structure. We corroborate that the main thermal anomaly in the sublithospheric mantle shows a tilted geometry, moving toward Greenland with depth. We reveal that this large‐scale anomaly transition into a more complex pattern once it reaches depths of 150 km beneath the North Atlantic. Small‐scale downwellings originate from the margins of continental domains, resulting in a complex circulation pattern that limits the radial spread of the deep upwellings and preferentially focuses them within regions of thin lithosphere along a N–S direction. Distinct compositional anomalies in the Greenland lithosphere delineate the North Atlantic Craton, the Nagssugtoqidian mobile belt, and the covered remnants of the Disko Craton. In continental Europe, the East European Craton shows clear indications of depletion in incompatible elements, with the Kola‐Karelian cratonic region showing the highest levels of depletion. Our model serves as a base to make interpretations on the enigmatic paleotectonic history of the North‐Atlantic region.

Review and updates of the lithosphere structure and geodynamics evolution of the Neogene Transcarpathian Basin and its substratum (Ukraine)

Geological and geophysical data on the structure of Mukachevo and Solotvyno sub-basins of Transcarpathian Basin (TB), located in the hinterland of Outer Carpathians, are integrated and adapted to modern ideas about the Carpathian realm geodynamics. Analysis of published data and newly compiled geological map and cross-sections suggests: the Mukachevo sub-basin substratum can be attributed to the Alcapa terrane, and a significant portion of the Solotvyno sub-basin basement may belong to the Pieniny Klippen Belt. A model of the lithospheric structure, supported by deep seismic (PANnonian-CArpathians-Cratonic Europe or DOBRE-3 transect) PANCAKE and P-17 profiles, and density modelling identify the crustal domain beneath the Mukachevo sub-basin as a rootless fragment of the Alcapa terrane. The substratum of the Solotvyno sub-basin is interpreted as thrust-sheets of the Pieniny Klippen Belt, Czorsztyn continental block, Monastyrets nappe and Tisza–Dacia terrane at their base. Paleostress reconstruction identified four evolutionary phases: (1) opening of the TB as dextral shear pull-apart (earliest Middle Miocene), (2) rapid subsidence of the TB (Badenian), (3) inversion of Solotvyno and slow subsidence in the Mukachevo sub-basins (Sarmatian–Pliocene) and (4) inversion of the TB (Quaternary). The lithosphere of the TB is significantly thermally reworked and is characterized by (1) a thinned crust with zones of reduced velocity and density, (2) astenospheric uplift, (3) absence of residual slab and (4) presence of a reflector in the upper mantle descending under the Carpathians.

Tectonic history of the Mesoproterozoic Coal Creek serpentinite, Llano Uplift, central Texas, USA

The Llano Uplift Coal Creek serpentinite is one of few exposed Grenville-age ultramafic rocks and is an important element in reconstructing the tectonic history of the Grenville orogeny in Texas, USA. During Grenville-age collisional orogenesis, the ultramafic harzburgite protolith underwent dynamothermal prograde metamorphism, which resulted in partial to complete serpentinization during emplacement, deserpentinization during subsequent regional high-temperature, medium-pressure metamorphism, and continued post-kinematic metamorphism. An unrelated late (post-Grenville) serpentinization occurred when the ultramafic rocks were exposed near or at the surface. Disequilibrium assemblages and structural fabrics allow the pressure−temperature−time path to be estimated with peak conditions ranging between 685 °C and 810 °C and pressures of 0.8−1 GPa. Although most of the serpentinite has been replaced by lizardite, layers of incompletely replaced olivine and enstatite have metamorphic chemistries and are truncated by randomly oriented anthophyllite. Foliated metasomatic blackwall zones of tremolite, Mg chlorite, talc, and magnetite have a continuous foliation with the adjacent serpentinite. Tectonic emplacement of the serpentinite with a northward vergence occurred early in the deformational history of the Llano Uplift. The serpentinite was structurally imbricated with an exotic ensimatic arc and most likely represents the mantle portion of an obducted ophiolite. The serpentinite and ensimatic arc underwent deformation and regional amphibolite facies metamorphism together as a package, necessitating the overriding of some southern continental block. This polyphase deformational and metamorphic history is similar to the rest of the southeastern uplift and consistent with continent-arc-continent collision. The Texas Grenville-aged tectonic history provides an unambiguous record of Mesoproterozoic orogenic events not obscured by any older or younger orogeny.

East-Siberian Sea–Chukchi Sea Prograded Margin Tectono-Sedimentary Element and Makarov Oceanic Basin Composite Tectono-Sedimentary Element, Siberian and Central Arctic

The East Siberian Sea–Chukchi Sea Prograded Margin (ESCPM) and Makarov Oceanic Basin (MOB) include interconnected sedimentary accumulations with gradual facies transitions that occupy a significant part of the Amerasia Basin and the adjacent Siberian Arctic continental margin. The ESCPM contains a succession of Cenozoic clinothem featuring shelf-margin progradation caused by a rapid influx of siliciclastic material from NE Asia into the adjacent Amerasia Basin and represents a single tectono-sedimentary element (TSE) as per the volume's terminology. The MOB is a most distant and isolated from continental depositional systems part of the Arctic Ocean. It consists of two first-order sedimentary accumulations with distinct depositional styles and provenances. The lower, Passive margin TSE is composed of a fragment of the presumably Paleozoic-Mesozoic Barents and North Kara passive continental margin. The upper, Synoceanic TSE was formed following the separation of continental block of the Lomonosov Ridge from the Eurasian continental margin at ∼ 56 Ma and during the opening of the Eurasian Basin. It includes mostly Eocene to Holocene hemipelagic and pelagic deposits and ice-rafted sediments. Each of these accumulations is characterised as a TSE, and the MOB itself is considered as a composite TSE (CTSE). Assessments of petroleum potential in both elements rely on regional geological constraints, sedimentary architecture, and modelling. Direct hydrocarbon indicators have been detected in seismic profiles in both ESCPM and MOB. In the latter, petroleum generation likely began in the Jurassic or Late Cretaceous, peaking in the Paleocene and possibly extending into the Miocene. Reservoir rocks are inferred in Cretaceous and Cenozoic strata. In ESCPM TSE, Paleocene-middle Eocene sedimentary successions are considered to include potential source rocks, associated with main flooding surfaces and clinothem bottomset deposits.

Generalized <i>Р—Т</i> path and fluid regime of exhumation of metapelites of the central zone of the Limpopo complex, south Africa

The P–T paths of exhumation of Precambrian granulite complexes at the craton boundaries usually include two stages: sub-isothermal decompression and a decompression–cooling stage with a more gentle P–T path. Our goal is to understand the possible causes of the change in the slope of the P–T path of exhumation of the Central Zone (CZ) of the Limpopo granulite complex (South Africa), located between the Kaapvaal and Zimbabwe cratons. For this purpose, rocks (mainly, metapelites) from various structural positions within the Central Zone, i.e. dome structures, regional crossfolds, local and regional shear-zones, were studied. Metapelites are gneisses of similar bulk composition. Relics of leucosomes composed of quartz-feldspar aggregates with garnet and biotite are variously manifested in rocks, and melanocratic areas enriched in cordierite usually mark micro-shear-zones that envelope and/or break garnet porphyroblasts. Study of polymineral (crystallized melt and fluid) inclusions in garnet, its zoning with respect to the major (Mg, Fe, Ca) and some trace (P, Cr, Sc) elements, fluid inclusions in quartz, as well as phase equilibria modeling (PERPLE_X) showed that rocks coexisted with granite melts and aqueous-carbonic-salt fluids (aH2O = 0.74–0.58) at the peak of metamorphism at 800–850°C and 10–11 kbar. Partial melting initiated sub-isothermal exhumation of rocks to 7.5–8 kbar during diapirism of granitic magmas in the Neoarchean (2.65–2.62 Ga). This is reflected in the specific zoning of garnet grains in terms of the grossular content. A change in the rheology of rocks as a result of partial removal and crystallization of the melt activated shear-zones during further exhumation to 6–5.5 kbar along the P–T decompression–cooling path of 95–100°/kbar, reflecting a slower uplift of rocks in the middle crust. This process was resumed due to thermal effects and interaction of rocks with aqueous fluids (aH2O 0.85) in the Paleoproterozoic (~2.01 Ga). Such a scenario of metamorphic evolution implies that the Limpopo granulite complex, in general, and its Central Zone, in particular, are the result of the evolution of an ultra-hot orogen, where vertical tectonic movements associated with diapirism were conjugate with horizontal tectonic processes caused by the convergence of continental blocks.

Shaka Ridge (South Atlantic)—a Remnant of Continental Crust?

As a result of a study of igneous rocks of the basalt - andesite series, dredged on the Shaka Ridge in the South Atlantic, it was found that they differ from the basalts of mid-ocean ridges and ocean islands, and have an age of 183.8 ± 2.2 Ma, comparable to the time of manifestation of the Karoo-Maud mantle plume in central Gondwana. Geochemical and Sr–Nd–Pb isotopic features of the studied igneous rocks show their similarity with the Jurassic mafic complexes of the Ferrar province in Antarctica and the Falkland Islands, formed during the intrusion of the Karoo-Maud plume and under the influence of paleo-Pacific subduction. However the supply of ice rafted debris into the study area due to ice transportation is considered unlikely. Based on the all data obtained, it was concluded that the Shaka Ridge is a continental block that was moved during the opening of the South Atlantic in the Early Cretaceous-Early Miocene from the continental margin of Africa along an extended transform fault into the present Bouvet triple junction area.

Palaeozoic and Cenozoic reef formation. An attempt in comparative analysis

An article contains a comparative analysis of the Palaeozoic and Cenozoic reef formation, mainly in terms of the position of reefs in the basins of continental and oceanic blocks. It is shown that in the Cenozoic the main formation of reefs took place directly in the oceans, including at the boundaries between oceans and continents, and, to an extremely limited extent, in the basins of the continental segment. In the Palaeozoic, along with oceanic reef formation, there was intensive development in extensive basins of the continental block. This is one of the manifestations of the general evolution of carbonate accumulation, when the Palaeozoic carbonate sediments were formed in similar shallow water bodies that covered very significant surfaces of the continents.

Long-lived topography of the Oaxacan Complex (southern Mexico) after the assembly of Pangea: Evidence from apatite fission-track dating

Long-lived topography of the Oaxacan Complex (southern Mexico) after the assembly of Pangea: Evidence from apatite fission-track dating

Integrated detrital rutile and detrital zircon ages: a new perspective on the tectonic evolution of South China.

Paleogeographic reconstructions are of key importance for understanding the history of continental breakups and amalgamations during Earth's history. A special case is the history of the Asian continent, which, compared to other continents, consists of several large cratons and numerous smaller continental blocks. The history of the assembly of South China remains controversial in terms of the timing, Late Neoproterozoic or Early Paleozoic, and the participating continental blocks, e.g. Yangtze, Cathaysia, India and Australia. Detrital rutile U-Pb dating has significant potential with regard to deciphering tectonic settings as rutile frequently crystallizes during orogenic events associated with the processes of collision and subduction. Detrital zircon U-Pb dating is a perfect instrument for identifying the provenance characteristics and age characteristics of sedimentary sources. An integration of these two methods of dating offers better opportunities for reconstructing tectonic settings. This paper presents a first attempt to reconstruct the Neoproterozoic to Early Paleozoic tectonic history and paleogeography of the whole South China based on U-Pb geochronology of rutile and zircon and Hf-in-zircon isotopes from Lower Jurassic Baitianba Formation sedimentary rocks of the western margin of the Yangtze Block, a major part of South China. Our obtained integrated U-Pb rutile and zircon age data show three main age populations of 960-940 Ma, 630-610 Ma and 530-520 Ma. The new U-Pb detrital rutile and zircon ages, compared with former data from Gondwana and Australia, suggest that Yangtze amalgamated with Cathaysia to form South China during the Sibao orogeny at 960-940 Ma. The detrital rutile and zircons of the new 630-610 Ma age group could have been delivered from western Australia during the Late Neoproterozoic to Cambrian Paterson-Petermann orogeny. The abundant 530-520 Ma detrital rutile and zircon ages fit well with the coeval zircon age populations recorded in Gondwana-derived terranes, like India and Indochina.

Neoproterozoic arc-magmatism of the Silet Terrane, Western Hoggar (Algeria), new constraints from zircon U-Pb-Hf isotope analyses and whole rock geochemistry

Neoproterozoic arc-magmatism of the Silet Terrane, Western Hoggar (Algeria), new constraints from zircon U-Pb-Hf isotope analyses and whole rock geochemistry

Dynamic evolution of competing same-dip double subduction: New perspectives of the Neo-Tethyan plate tectonics

Dynamic evolution of competing same-dip double subduction: New perspectives of the Neo-Tethyan plate tectonics

Crustal structures and anisotropy in southeastern China: Continental collision and intraplate earthquakes

Crustal structures and anisotropy in southeastern China: Continental collision and intraplate earthquakes

Occurrence of Mafic Rocks within Ediacaran Strata in the Aksu Region, NW Tarim Craton, and its Geological Implications

AbstractThe Tarim Craton is an ancient Precambrian continental block, and detailed knowledge of its thermo‐tectonic history is crucial for understanding the early history of continental evolution. Abundant layered mafic rocks, which have commonly been regarded as basalts, occur within the Ediacaran Sugetbrak Formation (Fm.) in the Aksu region of the northwestern Tarim Craton. Clear intrusive features have now been discovered, including mafic rocks truncating Ediacaran sedimentary layers, exhibiting an intrusion‐baked margin where they interact with both the overlying and bottom wall rocks, and displaying a fine‐grained transition zone from their interior to their margins. The new findings demonstrate that these mafic rocks within the Aksu Ediacaran strata were not erupted basalts but instead are intrusive diabase dykes. Therefore, these mafic rocks cannot be used to constrain the timing of the Sugetbrak Fm. in the Aksu area, nor as marker layers for regional stratigraphic correlation. Furthermore, the Ediacaran thermo‐tectonic evolution in this region, deduced from the assumption that the mafic rocks are lavas, needs to be revised.

How and when did Paleozoic Maizuru back-arc basin close? Implications on the East Asian continental margin tectonics

How and when did Paleozoic Maizuru back-arc basin close? Implications on the East Asian continental margin tectonics

Pristine helium from the Karoo mantle plume within the shallow asthenosphere beneath Patagonia

Mantle xenoliths usually represent fragments derived from the depleted and degassed lithospheric mantle with 3He/4He isotope ratios (6 ± 1 RA) lower than those of mid-ocean ridge basalts (8 ± 1 RA). Otherwise, basalts from oceanic islands related to hotspots often have high 3He/4He ratios (>10 RA), suggesting a deep and pristine undegassed mantle source. Here we present a striking high-3He/4He component (up to 27.68 RA) recorded by spinel-facies mantle xenoliths from Patagonia. Remarkably, the highest ratios were found in a long-lived trans-lithospheric suture zone related to the Carboniferous-Permian collision of two continental blocks: the Deseado and the North Patagonian massifs. The mantle xenoliths with notably high-3He/4He ratios are inferred to be fragments of the shallow asthenosphere rising through the eroded and rejuvenated thin lithosphere. The pristine helium component is derived from the western margin of the Karoo mantle plume, related to the initial stages of the Gondwana fragmentation.

Maximum depositional ages and provenance analysis of the Precambrian Manyovu redbeds, Tanzania: Implications for Neoproterozoic tectonics

Abstract The Manyovu redbeds are an up to 600 m succession of fine-grained, siliciclastic strata in northwestern Tanzania and are part of the Neoproterozoic Bukoban Supergroup. Previous authors estimated the age of the Manyovu redbeds to be Neoproterozoic or older based on the K-Ar dates of underlying volcanic rocks (ca. 800 Ma). However, no other age constraints exist for these Neoproterozoic units. U-Pb detrital zircon results from six stratigraphic intervals of the Manyovu units, including both sandstone and siltstone samples, indicate maximum depositional ages as young as 614 ± 6 Ma, almost 200 m.y. younger than the underlying volcanics, with primary detrital contributions from Pan-African orogens, which indicates that these units are syn-tectonic accumulations associated with the assembly of Greater Gondwana/Pannotia. Detrital zircon spectra and modal compositions reveal that the sediment that formed these strata was sourced from a range of terranes, including continental blocks (i.e., Tanzania Craton), magmatic arcs (i.e., Mozambique Belt and Arabian-Nubian Shield), and recycled orogens (e.g., Ubendian-Usagaran belts). Together, these data indicate that the Manyovu redbeds accumulated following the Marinoan Snowball Earth event (ca. 635 Ma) and record the initiation of collision along the Mozambique Belt during Pan-African orogenesis and the formation of greater Gondwana.

Recent Holocene activity and regional tectonic significance of the northern segment of the red river fault zone

Recent Holocene activity and regional tectonic significance of the northern segment of the red river fault zone

Permian tectonic evolution of the proto-Japan and East Asia: Insights from detrital zircon geochronology and crystal morphology

Permian tectonic evolution of the proto-Japan and East Asia: Insights from detrital zircon geochronology and crystal morphology