Tectonic Framework Research Articles

El Zorro: early Jurassic intrusion-related gold (IRG) mineralization in the oldest, western-most segment of the Andean Cordillera of Northern Chile

AbstractThe El Zorro gold district is the most recent gold discovery in the Coastal Cordillera of northern Chile. Ternera is the largest deposit in the district with total resources currently estimated at 1.282 Moz. New geology, geochemistry and geochronology data indicate that hydrothermal mineralization is mostly hosted within felsic to intermediate, ilmenite-bearing calc-alkaline dikes and stocks of the Upper Triassic to Lower Jurassic Relincho Pluton, and some of the adjacent Devonian to Carboniferous metasediments of the Chañaral Epimetamorphic Complex. Sheeted veins, veinlets, and fault zones with quartz, low amounts of pyrite, pyrrhotite and arsenopyrite, and local calcite are surrounded by narrow haloes of albite-biotite-quartz ± sulfides-K-feldspar-sericite-chlorite. Gold (mostly in the veins) is associated with elevated W-Bi and also As-Te-Sn, and not with iron enrichment or base metals, even though this system is proximal (~ 20 km) to IOCG and IOA deposits of the Coastal Cordillera. The main phase of gold mineralization occurred soon after emplacement of tonalitic dikes and granodiorite from the Relincho and Cuevitas plutons (U–Pb zircon between ~ 205 and 190 Ma), about 80 m.y. later than the development of orogenic fabrics. An absolute upper age limit is provided by compositionally distinct ore-cutting mafic dikes dated at 175–170 Ma (U–Pb apatite). The deposit falls into the intrusion-related gold category, as indicated by the cutting of earlier orogenic fabrics, the metal and alteration associations, and the spatial and temporal connection to reduced ilmenite-series intrusions, which are also very similar geochemically to the ‘type-locality’ IRG intrusions of the Tintina Belt in Yukon/Alaska. The El Zorro gold district represents the oldest and geologically western-most mineralizing event in the Central Andes of northern Chile, consistent with its time–space placement within the tectonic framework of easterly-younging mineralization and igneous activity in the Chilean Cordillera.

Teleseismic virtual-source reverse time migration of upper crustal structures in the Three Gorges region, China

Summary The Three Gorges (TG) in central China is an earthquake prone region that lacks active-source seismic surveys, hence requiring high-resolution passive seismic imaging to reveal crustal structures in detail. While teleseismic virtual-source reflection (TVR) profiling is effective for imaging gently dipping upper crustal structures, it is unsuitable for mapping steep structures beneath rugged topography in the TG region. Here we develop a teleseismic virtual-source reverse time migration (TV-RTM) to improve the imaging of steep structures. Synthetic tests are conducted to demonstrate the validity and resolution of the TV-RTM method. To mitigate the imaging inaccuracy due to sparse station spacing, we interpolate direct-arrival waveforms to achieve a doubling of the minimally required station spacing from 2 km to 4 km. The TV-RTM images of the upper crustal structure beneath a 2D array in the TG region reveal significant fold and thrust structures that correlate well with the surface geology and tectonic framework. The resolution of the images is assessed using 2D and 3D synthetic models with the station and source geometry of field data. The TV-RTM method provides a new passive seismic solution for studying upper crustal structures in regions that lack active-source seismic data.

U-Pb ages of pre- to post-salt carbonates, Santos and Campos basins, SE Brazil: Implications for the evolution of the South Atlantic

The exploration campaigns and independent studies conducted in the central South Atlantic basins after the discovery of giant oil accumulations in the Lower Cretaceous lacustrine carbonates sealed by the salt layer resulted in a new panorama of the tectonic framework, stratigraphic architecture, and petroleum systems of the investigated basins and passive margins in general. Despite these remarkable advances, the ages of the carbonate reservoirs and the sealing evaporites remain uncertain. Aiming to fill this gap, we present here the results of 30 U-Pb LA-ICP-MS calcite and dolomite age determinations representative of the depositional/eo-diagenetic processes and subsequent phases of carbonate cementation recorded by pre-to post-salt units of the Santos and Campos basins of southeastern Brazil. Microcrystalline calcite of a mudstone of the Itapema Formation (Santos Basin) yielded a minimum age of 126.8 ± 4.7 Ma. 19 depositional/eo-diagenetic ages obtained in mudstones, grainstones, shrubstones, spherulitestones, and travertines of the correlative Barra Velha and Macabu pre-salt lacustrine carbonates cluster around 124.1 ± 2.2 and 122.1 ± 2.3 Ma. Considering the errors, these results limit the deposition/eo-diagenesis of these units to the 126.2–120.0 Ma interval. Two determinations carried out in calcite laminae of a nodular anhydrite sample extracted from the lower portion of the Retiro Evaporite (Campos Basin) returned the ages of 119.2 ± 1.6 Ma and 119.18 ± 0.79 Ma, which we interpreted as the best approximation of the timing of the salt deposition. Analyses performed in 3 samples from the post-salt Quissamã carbonates (Campos Basin) provide a minimum age of 114.2 ± 2.8 Ma yielded by interparticle dolomite cement. Other phases of calcite and dolomite cements present in the investigated units were dated at ca. 119.4, 116.5, and 110.7 Ma. The stratigraphically coherent spectrum of ages obtained differs significantly from most available data, providing a new perspective for the ongoing discussions on the tectonic evolution of the South Atlantic and probably impacting the current views of the burial history and petroleum system of the Santos and Campos basins.

Provenance and tectonic evolution of the forearc basin along the northwestern Central Qilian belt, northeastern Tibet

The age and properties of detrital zircon grains in a forearc basin provide crucial information on the history of convergent plate margins. These data can be used to constrain provenance dispersal patterns, establish source-to-sink relationships, and reveal the tectonic framework and subduction history. The Qilian orogen in the northeastern margin of the Tibetan Plateau records the tectonic history of the Proto-Tethys Ocean from its initial spreading and subduction to final closure. However, the timing of subduction initiation and the subduction polarity of the Proto-Tethys Ocean remain controversial. The Qilian orogen includes the North Qilian, Central Qilian, and South Qilian belts. A succession of sedimentary rocks along the northwestern margin of the Central Qilian belt, previously considered to be Precambrian in age, has been redefined based on detailed field investigation and geochronology. U-Pb analysis of detrital zircon grains from metasedimentary rocks of the Gongcha Group of the northwestern Central Qilian belt yielded Paleozoic ages between 530 and 470 Ma, with prominent Mesoproterozoic and Paleoproterozoic ages between 1800 and 1000 Ma. In contrast, the overlying Duoruonuoer Group yielded predominantly early Paleozoic ages between 465 and 434 Ma, with a few older age populations. This change in source is reflected in a substantial increase in volcanic detritus within the Duoruonuoer Group as compared to the Gongcha Group. The detrital zircon age spectra and lithologic characteristics indicate the Gongcha and Duoruonuoer Groups constitute the lower and upper volcanic-sedimentary strata in the forearc basin. Based on resemblances of statistical ages and εHf(t) values of zircon, we interpret that the early Paleozoic intrusive and volcanic units and Precambrian basement rocks of the Central Qilian belt were the main source of the Gongcha and Duoruonuoer Groups, verifying the southward subduction of the North Qilian Ocean, a portion of the larger Proto-Tethys Ocean, beneath the Central Qilian belt. The detrital zircon ages reveal that the initial subduction of the Proto-Tethys Ocean in the Qilian orogen occurred ca. 530 Ma and closed ca. 435 Ma. These forearc sedimentary units constitute the tectonic boundaries between the Central Qilian belt and North Qilian belt.

Kernel Density Estimation for the Interpretation of Seismic Big Data in Tectonics Using QGIS: The Türkiye–Syria Earthquakes (2023)

Numerous studies have utilized remote sensing techniques to analyze seismic data in active areas. Point density techniques, widely used in remote sensing, examine the spatial distribution of point clouds related to specific variables. Applying these techniques to complex tectonic settings, such as the East Anatolian Fault Zone, helps identify major active fractures using both surface and deep information. This study employed kernel density estimation (KDE) to compare two distinct point-cloud populations from the seismic event along the Türkiye–Syria border on 6 February 2023, providing insights into the main active orientations supporting the Global Tectonics framework. This study considered two populations of seismic foci point clouds containing over 40,000 events, recorded by the Turkish Disaster and Emergency Management Authority (AFAD) and Kandilli Observatory and Earthquake Research Institute (KOERI). These populations were divided into two datasets: crude and relocated-filtered. Kernel density analysis demonstrated that both datasets yielded similar geological interpretations. The high-density cores of both datasets perfectly matched, exhibiting identical structures consistent with geological knowledge. Areas with a minimal concentration of earthquakes at depth were also identified, separating different crustal strength levels.

Tectonics of the Mw 6.8 Al Haouz earthquake (Morocco) reveals minor role of asthenospheric upwelling

A reliable identification of the fault responsible for the magnitude 6.8 Al Haouz earthquake that struck Morocco on 8 September 2023 has so far been hampered by a lack of accurate tectonic analyses. Here we provide the first updated tectonic framework of the earthquake epicentral area based on original field data. We cast our results into the context of available geomorphological, thermochronological and geophysical constraints, and discuss the earthquake characteristics within the framework of competing tectonic models either based on asthenospheric upwelling or transpressional tectonics. We found that the Al Haouz earthquake was likely generated by rupture along a north-dipping high-angle fault, linking former fault planes belonging to an orogen-scale WSW-ESE transpressional shear zone. The geological evolution and seismotectonic structure of the region are largely governed by the oblique convergence of tectonic plates. The impact of asthenospheric upwelling, if any, remains limited and may only influence the geomorphological evolution of the Western High Atlas, but cannot explain the seismotectonic and geological features observed today at the surface, which are instead effects of transpressional tectonics.

Deep Tectonic Environment Analysis of the Lingshan Conjugate Earthquake within the Qinzhou Fold Belt, South China: Insights Derived from 3D Resistivity Structure Model

The Qinzhou fold belt, situated at the contact zone between the Yangtze and Cathaysia blocks in South China, was affected by the 1936 Lingshan M6¾ earthquake and the 1958 Lingshan M5¾ earthquake, both of which occurred within the conjugate structure. Understanding the deep seismogenic setting and causal mechanism of the Lingshan conjugate earthquake is of great significance for assessing the seismic disaster risk in the region. In this study, we utilized 237 magnetotelluric datasets and employed three-dimensional electromagnetic inversion to characterize the deep-seated three-dimensional resistivity structure of the Qinzhou fold belt and the Lingshan seismic zone. The results reveal that: (1) The NE-trending faults within the Qinzhou fold belt and adjacent areas are classified as trans-crustal faults. The faults exhibit crust-mantle ductile shear zones in their deeper sections, which are essential in governing regional tectonic deformation and seismic activity; (2) The electrical structure of the Qinzhou fold belt is in line with the tectonic characteristics of a composite orogenic belt, having experienced several phases of tectonic modification. The southeastern region is being influenced by mantle-derived magmatic activities originating from the Leiqiong area over a significant distance; (3) In the Lingshan seismic zone, the NE-trending Fangcheng-Lingshan fault is a trans-crustal fault and the NW-trending Zhaixu fault is an intra-crustal fault. The electrical structure pattern “two low, one high” in the zone has a significant impact on the deep tectonic framework of the area and influences the deformation behavior of shallow faults; and (4) The seismogenic structure of the 1936 Lingshan M6¾ earthquake was the Fangcheng-Lingshan fault. The earthquake’s genesis was influenced by the coupling effect of tectonic stress and deep thermal dynamics. The seismogenic structure of the 1958 Lingshan M5¾ earthquake was the Zhaixu fault. The earthquake’s genesis was influenced by tectonic stress and static stress triggering from the 1936 Lingshan M6¾ earthquake. The conjugate rupture mode in the Lingshan seismic zone is influenced by various factors, including differences in physical properties, rheology of deep materials, and the scale and depth of fault development.

Variscan basement tectonics and Alpine shear zones in the external Balkanides: Structural data from the Vezhen Massif, Central Stara Planina Mts., Bulgaria

The Alpine Balkanides in Bulgaria are developed over Variscan orogenic fragments, which are variously affected by late-stage thick-skinned thrust tectonics. Often, these fragments hold both Variscan and Alpine structural records. А key area to shed light on important aspects of the tectonic evolution of the external parts of the Alpine Balkanide orogen is the Vezhen Massif in the Central Stara Planina Mountains. Although it is built exclusively of Paleozoic crystalline rocks, its structure was long considered as an example of intense mid Eocene to early Oligocene (Late Alpine) shortening. Detailed fieldwork in the area shows a more complicated tectonic framework and provides evidence of a polyphase structural evolution, involving an important stage of Variscan metamorphism and deformation and two stages of north-vergent Alpine shortening. The Stargel-Boluvanya Tectonic Zone that affects the western Vezhen Massif is one of the most important Variscan structures in the Balkan fold-and-thrust belt. Structural data indicate that the metamorphic basement records initial top-to-north thrusting, followed by further shortening, which led to folding and localized strike-slip deformation. The Variscan syn-metamorphic fabric is cross-cut by several post-kinematic igneous bodies of late Carboniferous to Permian ages. The tectonic history continues with a development of a network of greenschist facies north-vergent mylonitic zones for which an Early Alpine (post-late Permian but pre-Late Cretaceous) age is assumed. Late Alpine north-vergent thrusting is evident only on the eastern and northern flanks of the Vezhen Massif. In a broad structural context, the documented record in the basement rocks of the Vezhen Massif is comparable with those of the external massifs of the Alps and Iberia.

Mineralogy and geochemical controls on the distribution of REY-Ga-Se-Nb enrichment in the No. 6 Coal Seam, Soutpansberg Coalfield, South Africa

Coal is being explored as a potential alternative source for rare earth elements (REY + Sc), which are critical for advancing modern technology. Previous research has mainly focused on assessing the concentration and distribution of REY + Sc in coals from South Africa. However, the modes occurrence of these elements in coal is yet to be investigated. This study offers new insights on the mineralogy and inorganic geochemistry of the No. 6 Seam coal from the Soutpansberg Coalfield (South Africa). The objective is to investigate the distribution, enrichment, and modes of occurrence of critical elements such as Ga, Se, Nb, and REY + Sc within this coal. The No. 6 Seam is a medium rank-B, moderate vitrinite (avg. 41.5 vol%) coal, and contains major minerals such as kaolinite, quartz, and minor minerals including muscovite, siderite, dolomite, pyrite, and calcite. The total REY + Sc concentrations in the coal samples range from 79.9 to 332.1 mg/kg (avg. 213.2 mg/kg; whole-coal/rock basis), higher than global averages for hard coal. The upper continental crust (UCC) normalized concentration coefficients (CC) of the coal shows enrichment of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, and Y. Distinct REY + Sc enrichment patterns are observed across different coal horizons, divided into two categories: light-REY (LREY) and medium-REY (MREY) in the bottom horizon coal [bottom-upper (BU) and bottom-lower (BL)], whereas the middle horizon coal [middle-upper (MU) and middle-lower (ML)] are enriched in medium-REY (MREY) and heavy-REY (HREY). The BU and BL samples show greater REY + Sc enrichment relative to the MU and ML samples. The samples also contain elevated concentrations of Ga (max. 106.1 mg/kg), Se (max. 50.9 mg/kg), and Nb (max. 14.8 mg/kg), exceeding the average values reported for Chinese coals.When considering the correlations between REY + Sc and major oxide elements, minerals, and organic petrographic assemblages, REY + Sc appears to be more closely associated with inorganic fraction, particularly aluminosilicate (such as kaolinite) and carbonate minerals (like dolomite), rather than with the organic fraction. The kaolinite and dolomite represent mostly detrital input and epigenesis, respectively. Gallium in the coal is primarily associated with aluminium oxide-hydroxide, Nb with minerals such as clay, rutile/anatase, and zircon; and Se with pyrite. Redox-sensitive elemental ratios of Al2O3/TiO2 andTiO2/Zr suggest that the detrital components of the No. 6 Seam coals were predominantly derived from a source consisting of felsic-intermediate rocks. These materials likely represent the weathering products of magmatic rocks from the passive-continental margin tectonic framework of the Limpopo Mobile Belt. Paleoclimatic conditions are inferred to be warm-humid to hot, with the peat deposited under suboxic-to-oxic environments. High values of critical REY percentage (REYdef,rel%: 29.85 to 39.75 %) and an outlook coefficient ≥ 0.7 suggest these Soutpansberg coal samples to be promising for REY + Sc recovery along with Ga.

Paleogeographic implication of a titanosaur eggshell from the Neogene of the Entre Ríos Province, Argentina

The Lower Member of the Ituzaingó Formation (LMIF), fluvial in origin and assigned to the Upper Miocene, contains a conglomerate level known as “Mesopotamiense” or “Conglomerado osífero” that has yielded a rich fauna of vertebrates. The aim of this contribution is to describe a titanosaurian dinosaur eggshell fragment recovered from the LMIF at the locality of Toma Vieja (western Entre Ríos Province), discussing its paleogeographic history and implications. Fragments of eggshells referred to Titanosauria are frequent from litostratigraphic units of the Upper Cretaceous of western Uruguay (e.g., Guichón, Mercedes, and Queguay Formations). Besides, a fragment of eggshell recovered from the Puerto Yeruá Formation (Upper Cretaceous) at eastern Entre Ríos Province was described. Geophysical data from the Entre Ríos Province allow to propose the presence of a Lower Cretaceous field of extensional tectonic stresses that generated structural lineaments with a E-W and ENE-WSW trend. This ancient penetrative Cretaceous tectonic framework would have exerted control on the shape of the basin and sediment flow patterns and subsequent sedimentation, by promoting the generation of accommodation space over the late Paleogene and the Neogene. The phenomenon would have conditioned the deposition of the Fray Bentos Formation, the subsequent marine Paraná Formation, and the sedimentation of the LMIF, with source materials coming from the east. Thus, it is hypothesized that the fragment of eggshell of Titanosauria would come from the eastern area of the basin (western Uruguay) as a consequence of the existence of a paleohydric system with predominantly E-W and ENE-WSW directions. This late Neogene system would have been controlled by inherited Cretaceous structural lineaments with orientations similar to those that also govern the current fluvial systems of western Uruguay, developed on the Mesozoic substrate.

Tectonic framework of Iraq. A critical review and discussion

The Iraqi territory forms the northeastern part of the Arabian Plate, which is in collision with the Eurasian Plate. The collision of the plates has formed the Zagros Foreland Basin, which includes the Zagros Fold–Thrust Belt. The belt covers the majority of the northern part of Iraq (Kurdistan Region of Iraq) and parts of the central part of Iraq. South of the belt, the Mesopotamian Foredeep is developed. All these parts of Iraq are considered tectonically unstable. To the west and south of the Mesopotamian Foredeep, the tectonically stable part is developed that has been affected by a lesser amount of deformation as compared to the remaining unstable parts by the exerted forces related to the collision of both plates. All researchers have divided tectonically Iraq into two main tectonic domains; called Stable and Unstable shelves, which are further divided into zones and sub-zones. However, different terms and names were used by different researchers, which has confused readers and workers who have dealt with the tectonics of the Iraqi territory. We have reviewed and discussed all existing divisions by different researchers and have suggested new terminology using the existing maps, reports, scientific published articles, and interpreting satellite images, besides field observations. Moreover, we presented a tectonic map with the suggested new terminology.

The geodynamics of plume-influenced mid-ocean ridges: insights from the Foundation Segment of the Pacific-Antarctic Ridge

The intersection of the Foundation Plume with the Pacific-Antarctic Ridge is a key location in global geodynamics where a mantle plume is approached by and interacting with a fast-spreading mid-ocean ridge. Here, we discuss a comprehensive major and trace element and Sr-Nd-Pb isotope dataset of new and existing samples from the young Foundation Seamount Chain (<5 Ma) and adjacent section of the Pacific-Antarctic Ridge. We use the geochemistry of axial, off-axis and intraplate lavas to map the spatial extent of plume dispersal underneath the ridge as well as the internal zonation of the upwelling plume. We show that the unusual length, increased crustal thickness and occurrence of silicic rocks on the axis of the Foundation Segment are the direct result of plume being tapped by the axial melting zone. We demonstrate that the plume is not homogeneous but shows a HIMU-like (high time-integrated 238U/204Pb) OIB (Ocean Island Basalt) component characterized by 206Pb/204Pb of up to 20.5 in its center and a more EM1-like (Enriched Mantle one) OIB component characterized by low U/Pb and 206Pb/204Pb but high Rb/Nb and 87Sr/86Sr towards its edges. Plume entrainment leads to a high magma supply rate that fosters the formation of silicic rocks and triggers the lengthening of the segment over time. However, plume dispersal is not symmetric as the geochemical tracers for the OIB component are extending <100 km northwards but >300 km southwards. We relate this to the current plate tectonic framework in which the obliquity between the migrating ridge and the absolute plate motions induces a sub-axial asthenospheric flow that preferentially channels plume material southwards.

Geodynamic Evolution of the Proto-Tethys Ocean in the West Kunlun Orogenic Belt, northwest Tibetan Plateau: Implications from the Subarc Crust and Lithospheric Mantle Modification

Abstract Radiogenic isotopes serve as a crucial tool for investigating crustal evolution, playing a pivotal role in revealing magma sources and petrogenesis. However, they can be ineffective in distinguishing between distinct magmatic sources with similar radiogenic isotopic compositions, a common occurrence in nature. Here we addresse this challenge in the Ordovician igneous rocks from the West Kunlun orogenic belt (WKOB), aiming to distinguish between two potential magmatic sources (i.e. the Tarim Craton and the Tianshuihai terrane) with similar isotopic compositions using appropriate thermodynamic and geochemical modeling based on mineral and whole-rock geochemistry. Zircon U–Pb dating yields ages of 483 ± 3 Ma for the Pushou gabbros and 469 ± 2 Ma and 461 ± 2 Ma for the Datong monzogranites and syenites, respectively. The Pushou gabbros exhibit low SiO2 (47.4–49.1 wt %), high MgO (5.5–6.9 wt %), high large-ion lithophile elements (LILEs, e.g. Rb, Ba, Th, and K), and low high field-strength elements (HFSEs, e.g. Nb, Ta, Zr, Hf, P, and Ti), suggesting an origin in subduction-modified mantle. They display high whole-rock (87Sr/86Sr)i ratios (0.7156 to 0.7192), negative whole-rock εNd(t) values (−7.1 to −7.8), as well as high zircon δ18O values (7.6–7.9‰) and enriched zircon Hf isotopic compositions (εHf(t) = −5.3 to −7.7), which are consistent with 1–5% subducted sediments in an enriched mantle source. Trace element models further confirm that the gabbros are most likely derived from low-degree (~15%) partial melting of subduction-modified Tarim mantle in the spinel–garnet facies rather than from the Tianshuihai mantle. The Datong syenites belong to the shoshonitic series and are characterized by medium SiO2 (59.5–61.4 wt %), relatively low MgO (0.9–1.2 wt %) and Mg# (37–42), enrichment in LILEs and depletion in HFSEs. They have high whole-rock (87Sr/86Sr)i ratios (0.7103 to 0.7105) and negative whole-rock εNd(t) values (−3.8 to −4.3), along with negative to slightly positive zircon εHf(t) values (−3.8 to +2.6), similar to coeval mafic rocks. Thermodynamic and geochemical modeling suggest that the Datong shoshonitic rocks likely originated via crystal fractionation of shoshonitic basaltic magmas in the SW Tarim Craton. The Datong monzogranites have high SiO2 (69.7–72.6 wt %), low MgO (0.6–0.7 wt %), and a typical enrichment in alkalis, Zr, and Nb, with depletion in Sr, P, and Ti, consistent with A-type granites. They are characterized by high whole-rock (87Sr/86Sr)i ratios (0.7321 to 0.7323), negative whole-rock εNd(t) values (−11.3 to −11.8), negative zircon εHf(t) values (−11.0 to −16.5), and high zircon δ18O values (7.2–8.0‰), indicating derivation from the remelting of an ancient crustal source. Thermodynamic, major, and trace element modeling indicate that their parent magma may have been generated by water-deficient (~2 wt %) partial melting of ancient crustal material beneath the SW Tarim Craton rather than that of the Tianshuihai terrane, under high-temperature (T > ~950°C) and low-pressure (P = 5–8 kbar) conditions. Based on the tectonic framework of the WKOB, we propose that the original mantle and crust beneath the southern Kunlun terrane may have been modified or partially replaced by that beneath the SW Tarim Craton during the Ordovician. Therefore, this evidence for Tarim-derived magmatism, when combined with regional sedimentary and structural records, indicates that Ordovician magmatism in the southern Kunlun terrane is most consistent with episodic northward subduction of the Proto-Tethys Ocean, commencing at ~485 Ma. Middle Ordovician slab break-off can explain the formation of the A-type granites, but reinstated northward subduction is required for the generation of late Ordovician Datong syenites.

Gravity and magnetism of southern Africa in relation to Craton structures and belts

The general tectonic structural architecture of southern Africa is an ensemble comprised of Kalahari Craton, a vast range of mosaics of the best-preserved geological Belts, and exposed crustal blocks. In the region, demarcation of geological boundaries, tracing of magnetic and gravitational bodies, and detrending lineaments are essential to understanding the structural limits. The study presents the prevalent gravitational and magnetic investigation of major geological Belts, enhancing edges of Cratons, and evaluation of surface invariants to improve the geological understanding and evaluate the correlation of structures with the general structural tectonic framework. The utilized filter methods in the gravity maps are the Directional derivatives along x, y, and z-directions, the Modulus tensor, the Total horizontal derivative, and the Tilt angle techniques.The phase-based filters used in the magnetic section include the Total horizontal derivative, Analytical signal, Tilt angle method, Tilt of total horizontal derivative, Theta method, Horizontal tilt angle method, Enhanced tilt filter, and Enhanced total derivative of the tilt angle. The Directional derivatives of the gravity field and the Modulus of the gravity gradient tensor demarcate the boundaries of geological structures. The Total horizontal derivative method gives an immediate and easy-to-read image of the linear structures and fault systems. The signal cluster on the Analytical signal and Tilt angle maps delineate the boundaries of causative geological sources. The Theta map is comparable with the enhanced total derivative of the tilt angle. The Tilt of the total horizontal derivative, Theta map, and Enhanced tilt filter accentuate the traces of magnetic bodies, including the Cratons. The study finds regional lineaments surrounding the Cratons and concentrated along the geological Belts. The approach of using joint elegant filters is effective and increases the certainty of the interpretation.

Paleoenvironmental factors controlling organic-rich formations deposition in the Babouri-Figuil Basin (Northern Cameroon)

The Babouri-Figuil Basin is an intracratonic basin (half-graben) in northern Cameroon that is genetically connected to the Benue Trough from Nigeria, and is an area of interest in terms of petroleum prospectivity. Recent studies highlighted the presence of organic-rich formations in the basin. However, none of these works have identified factors that governed the accumulation of organic matter (OM) in the sediments. The main objective of this work is the characterization of these formations through palynofacies and organic geochemical techniques (total organic carbon - TOC, total sulfur, insoluble residue and biomarkers), in order to determine the organic facies, their depositional environments and the main drivers for organic enrichment in the basin. The current study reveals that black shale and massive claystone lithologies constitute the main organic-rich formations in the basin, with TOC reaching up to 26.08 wt%, being characterized by a dominance of bacterially-derived amorphous OM. Palynofacies and biomarker data revealed that these formations are positively associated with anoxic conditions and a partly highly saline and stratified lake water column. The deposition of organic-rich formations in the Babouri-Figuil Basin was mainly controlled by restriction conditions which developed in connection with the regional tectonic framework. The Lower Cretaceous rifting episode in the West and Central African Rift System (WCARS) basins led to the formation of accommodation space, a reduction in water levels, and the development of anoxic conditions within the basin, facilitating the deposition of organic-rich formations. Therefore, the organic enrichment of the Babouri-Figuil Basin has been predominantly controlled by its tectonic evolution, particularly during the syn-rift phase. This phase created favorable conditions for the deposition and preservation of OM, including the establishment of anoxic conditions. Additionally, the paleoclimate (arid conditions), the development of bacterial biomass, and the basin's paleogeography all played a significant role in this process. The organic-rich formations of the Babouri-Figuil Basin show characteristics of prospective petroleum source rocks (high organic content, high proportion of oil-prone kerogen, significant thickness and lateral extension). The combination of organic-rich formations with sandstone deposits above and extensive claystone/shale deposits on top can indicate the presence of an oil play in the basin. A detailed study with broader sampling is needed to investigate thoroughly the variation of organic facies and the influence of paleoenvironmental factors that control the deposition of thick source rock intervals.

Conjugate extrusion with dextral oblique-slip faulting in SE Tibet: new insights into Oligo-Miocene deformation

SE Tibet experienced significant deformation during the Late Cenozoic, characterized by clockwise rotation of blocks separated by left-lateral strike-slip faults. Through field surveys, structural analyses and microstructural observations, we identified an early phase of ductile shear zones along three major faults: the Anninghe, Jinhe–Jinghe and Jinpingshan faults. New geochronological and thermochronological data collected from these fault zones and from carbonatites associated with a tear fault between two right-lateral oblique faults provide evidence that this slip occurred before c. 30 Ma. These findings lead to a new conceptual model suggesting that these north–south-trending right-lateral oblique-slip faults, together with the NW-trending left-lateral strike-slip faults in SE Tibet, form a network of large conjugate fractures. The conjugate fracture system, as a result of north- to NE-trending contraction, had a crucial role in controlling the overall tectonic framework of SE Tibet during the Oligocene. By integrating previous research and combining this with our latest findings, we propose a two-phases evolution model of Cenozoic tectonics in the region of SE Tibet, in which a drastic change in kinematics took place from an early phase (before ∼30 Ma) oblique dextral shearing to a late phase sinistral strike-slip faulting since the Miocene.

Kinematics Along the Qingchuan Fault and Deformation Pattern in the Eastern Tibetan Plateau

AbstractThe accommodation of the substantial eastward crustal motion of the Bayan Har block characterizes the dynamics of faults located at the eastern Tibetan Plateau. However, uncertainties persist concerning the manner and amount of deformation distributed on these faults, with slip senses and rates constituting critical factors. In the northeastern segment of the Longmenshan thrust zone, the contentious activity and the unknown geologic slip rate present challenges. This study, focusing on the Qingchuan fault, the predominant fault within the northeastern Longmenshan, employed satellite imagery interpretation, displaced fluvial terraces surveying, displacement measurements, and chronological analysis to comprehensively characterize its fault activity. Our investigation robustly demonstrates the Qingchuan fault has been active since the late Quaternary, and is primarily marked with a pronounced dextral slip at a rate of 0.6–1.0 mm/year. By quantitatively assessing the deformation rates of the faults at the eastern Tibetan Plateau, we propose that they sufficiently accommodate the entire eastward crustal movement of the Bayan Har block; thereby no additional deformation propagates beyond the Qingchuan fault. Furthermore, we introduce a subblock model to elucidate the regional crustal deformation pattern, wherein the eastward movement of the Bayan Har block transfers to the northeastward movement of the Bikou subblock. This movement results in reverse slip patterns for the Minjiang and Huya faults, while the Beichuan and Qingchuan faults predominantly experience dextral displacements. The complex strain partitioning within the northern Longmenshan range underscores the observed variations in slip patterns across different segments of the Longmenshan thrust zone, advancing our understanding of fault behavior and the orchestration of crustal deformation in this intricate tectonic framework.

Petrogenetic implications, geochemistry and tectonic framework of albitite hosted magnetite in North Delhi Fold Belt: Application of geochemistry and apatite chemistry

The iron ore bodies in the form of lensoidal and pocket type deposits occur within the Meso to Neo-Proterozoic meta-sedimentary rocks and albitites of Ajabgarh Group of Delhi Supergroup in Khetri basin, Western India. These are exposed as detached and linear ore bodies at the southern (western flank) and south-eastern (eastern flank) part of the Khetri copper deposit which follows the regional trend of the host rocks. The detailed field and petrographic studies reveal that the magnetite and hematite are associated with major silicates like quartz, actinolite, muscovite, biotite, albite and, K-feldspar. Some minor occurrences of apatite, sphene, ilmenite and monazite are also found. This work is focused on understanding the evolution of albitite-hosted magnetite with respect to tectonic signatures, the source of mineralizing fluid, and its spatial relationship with the regional albitites and meta-sediments. To interpret the above, whole rock geochemistry of albitite rocks, magnetite ore and mineral chemistry of fluorapatite, were adopted.The whole rock geochemistry of albitite suggests that the parent rocks are of calc-alkaline magma series that are originated from the subduction-related rift zone of volcanic arc environment. The apatite chemistry signifies that these are evolved from the highly fractionated granitic rocks (granitoid) at moderate to high oxidizing conditions. Some deformed apatite grains are also encountered having small distorted monazite inclusions. Thus, it has an indication of high-temperature metasomatic/hydrothermal fluids that may be responsible for the removal of REEs from apatite and re-nucleate as monazite inclusions within it. Therefore, the overall evidence and associations of albitite with apatite-magnetite is demonstrating that the source rock of the study area could have evolved from the arc system of active continental margin which was abundant with Fe, U, REEs, etc. Hence, the sources rocks were suitably metasomatized by hydrothermal fluids channelized through the regional shear zone and simultaneous precipitation of the magnetite in the study area. The dominance of magnetite, associated REEs, apatite, and non-association of sulfide minerals with the magnetite in the area of study has close similarities with the IOA type deposits.

Characteristics of Metamorphic Rocks and the Deformation and Metamorphism Period in Northern Lhasa,Tibet

The study of metamorphic rocks and deformation and metamorphic features in Gangdise-Lhasa metamorphic zone is helpful for the establishment of regional tectonic framework and the discussion of the evolution history of the region, which will provide new basic data for the study of geological structure evolution in the Qinghai-Tibet Plateau. There are few studies on metamorphic rocks in the northern area of Lhasa, Tibet. This paper summarizes and studies them from the perspective of petrography, and briefly discusses the stages of deformation and metamorphism. The area is divided into two metamorphic belts, which are divided into Yebagou-Gandansi metamorphic belt and Shexing-Binjiaolin metamorphic belt from south to north. The types of metamorphic rocks are slate, kyanite and schist. The dynamic metamorphism is manifested as brittle deformation and ductile deformation. The dynamic metamorphic rock belt developed in the area is several kilometers long, which basically belongs to the low green schist facies belt. The metamorphism in the area occurs under the geological background of the northward subduction, subduction and collision of the Neotethys oceanic crust plate. And with the change of tectonic environment and heat flow, different metamorphisms are produced in different geological development stages.

Low-Temperature Thermochronology Records the Convergence between the Anatolide–Tauride Block and the Arabian Platform along the Southeast Anatolian Orogenic Belt

SE Anatolia is witnessing the final stage of the Wilson Cycle, where a continental collision between the Tauride–Anatolide block and Arabian platform occurred, and a 1.5 km Eastern Tauride mountain chain formed. We present new low-temperature thermochronology (LTT) ages, including eight apatite fission track (AFT) and seven apatite and zircon U-Th-Sm/He (AHe, ZHe) ages, for the metamorphic rocks from the Nappe Zone of the Southeast Anatolian Orogenic Belt. The ZHe ages vary from 51.2 ± 0.7 Ma to 30.4 ± 0.6 Ma, the AFT ages range from 33.1 ± 1.6 Ma to 18.1 ± 0.9 Ma, and the AHe ages range from 23.6 ± 2.5 Ma to 6 ± 1.9 Ma. The LTT data show a continuous slow uplift of the region. However, the thermal modeling results suggest an Eocene and middle–late Miocene fast uplift of the region. Similar to our results, the LTT studies along the SAOB show that the vertical movements initiated during the Eocene period have continued in a steady-state regime to recent times. The Eocene epoch is identified by arc–back-arc setting in the region, whereas the Miocene epoch is marked by the continental collision. Within this tectonic framework, vertical movements on the overriding plate are controlled by both extensional and compressional tectonics. The LTT data obtained along the SAOB show fingerprints of thrust propagation from north to south.