Tectonic Activity Research Articles

Evaluation of the Preservation of Chitinozoans in a Case Study of the Katian?—Hirnantian Succession, Eastern Precordillera of Argentina

The poor preservation state of chitinozoans recovered from samples of the La Pola (Sandbian–Katian) and Don Braulio formations (Hirnantian-Llandovery), after being processed with standard methods, required significant modifications in processing. The sodium hexametaphosphate technique was used to avoid invasive mechanical procedures. Hence, more complete chitinozoans that preserved original features produced by biological, mechanical, and chemical degradation appeared. The processes that affected the good preservation of the chitinozoan exine are associated with factors inherent to the sedimentary environment, and biological and geological taphonomic effects that occurred in different regions of the Precordillera, added to the important associated tectonic activity. The thermal alteration was also an important factor in the fragile and brittle condition of the organic matter recovered. This transcends the preservation-processing technique relationship to be used. The results obtained from non-standard processing contribute to the paleoenvironmental interpretation of the Pola and Don Braulio successions, which are still widely discussed, and the determination of the most accurate age of the La Pola Formation. The latter will allow us to propose a biostratigraphic correlation between chitinozoan zones and graptolite zones, given the presence of both groups in the succession studied here, and to establish correlations with other successions in the Precordillera and elsewhere.

Rapid shear zone weakening during subduction initiation

Subduction zones play a pivotal role in the mechanics of plate tectonics by providing the driving force through slab pull and weak megathrusts that facilitate the relative motion between tectonic plates. The initiation of subduction zones is intricately linked to the accumulation of slab pull and development of weakness at plate boundaries and, by consequence, the largest changes in the energetics of mantle convection. However, the transient nature of subduction initiation accompanied by intense subsequent tectonic activity, leaves critical evidence poorly preserved and making subduction initiation difficult to constrain. We overcome these limitations through a comprehensive analysis focused on Puysegur, a well-constrained extant example of subduction initiation offshore South Island, New Zealand. Through time-dependent, three-dimensional thermo-mechanical computations and quantitative comparison to new geophysical and geological observations, including topography, stratigraphy, and seismicity, we demonstrate that subduction initiation develops with a fast strain weakening described with a small characteristic displacement ([Formula: see text] 4 to 8 km). Potential physical mechanisms contributing to the strain weakening are explored and we find that the observed fast weakening may arise through a combination of grain-size reduction within the lower lithosphere and fluid pressurization at shallower depths. With the shared commonality in the underlying physics of tectonic processes, the rapid strain weakening constrained at Puysegur offers insights into the formation of the first subduction during early Earth and the onset of plate tectonics.

Tectonic activation and the risk of Ilisu Dam collapse to Iraq through modelling and simulation using HEC-RAS

Floods caused by dam failures can cause huge losses of life and property, especially in estuarine areas and valleys. In spite of all the capabilities and great improvements reached by man in the construction of dams and their structures, they will remain helpless before the powerful forces of nature, especially those related to tectonic activation, and the occurrence of earthquakes of different intensities.The region extending from the Ilisu Dam in Turkey to the Mosul Dam in Iraq was chosen as an area for this study, and the HEC-RAS application was used to simulate the collapse of the Ilisu Dam due to a major earthquake, to know the magnitude of the risks and losses that could result from this. The Ilisu Dam was built very close to a highly tectonically active fault system, particularly the East Anatolian Fault (EAF), which is one of the largest tectonically active faults in the world with a length of 500 km. This region has witnessed past and present earthquakes of high magnitude (M > 7), especially in the EAF, so the construction of the Ilisu Dam near the EAF fault system is of great concern, as it was built in a basin with very complex seismic activity and geology.Using the HEC-RAS simulation application, the study found that the flood resulting from the collapse of the Ilisu Dam would reach the edges of the Mosul Dam Lake in just 13 h. With a flow of more than 100,000 m3/s, more than 10 billion m3 of water will flow into the Mosul Dam Lake within four days of the disaster. This will lead to the collapse of the Mosul Dam and direct the flood wave of the collapse of these dams towards Baghdad through Mosul, Tikrit, and Samarra. This could pose risks to all Iraqi cities located within the Iraqi sedimentary plain (Mesopotamia), from south of the Mosul Dam up to Basra, in a scenario similar to Noah’s Flood.

Thallium enrichment mechanism and geological significance of the Xiangquan thallium deposit in Anhui Province, China

The discovery of the independent thallium (Tl) deposit in Xiangquan, Anhui Province, provides an example for the study of the enrichment and mineralization of the highly dispersed rare metal element Tl. In this paper, a range of methods are used to characterize the enrichment, depletion, migration and occurrence state of Tl in different types of rocks and ores: lithogeochemistry; electron microprobe and principal component analysis; and exploring the significance of geochemical anomalies on the geological indication of Tl deposit formation. The results show that Tl is mainly distributed in silicified rocks of the Ordovician Lunshan Formation, and its average content is 307.08 μ g g –1 . The contents of As, Sb, S, Fe 2 O 3 and Tl in wall rocks, altered rocks and ores are significantly correlated, indicating a close relationship with Tl accumulation. The geochemical characteristics confirm that pyrite in the study area originates from submarine hot-water deposition. The main carrier of Tl is pyrite of hydrothermal sedimentary origin, in which Tl occurs as isomorphs in fine grains of pyrite. Tl mineralization may be accompanied by silicification, and the metallogenic environment is in a relative oxidation state. The mineralization process results in the geochemical differentiation of elements. Under the influence of tectonic and low-temperature hydrothermal activities, ore-forming elements migrate to structurally favourable conditions for mineralization to occur. This study provides a basis for further understanding the mechanisms of co-enrichment and separation of Tl and guidance for Tl mineral exploration.

The Indosinian Granitoids of the Songpan–Garze–West Kunlun Orogenic Belt, China: Distribution, Petrochemistry, and Tectonic Insights

During the Indosinian orogeny, the Songpan–Garze–West Kunlun orogenic belt experienced significant tectonic and magmatic activity, leading to the widespread emplacement of granitoid bodies. This study provides a detailed petrochemical and geochemical analysis of these granitoids, offering new insights into their tectonic settings and magmatic evolution. The granitoids of this belt are systematically categorized into arc calc-alkaline and arc tholeiitic granitoids (ACG and ATG), cordierite peraluminous and muscovite peraluminous granitoids (CPG and MPG), potassium calc-alkaline granitoids (KCG), and peralkaline granitoids (PAG) suites. ACG and ATG types dominate early magmatism (230–190 Ma), reflecting a convergent tectonic setting, while KCG and MPG types magmatism, respectively, emerged 10–20 Myr and 15–25 Myr later, during post-collisional extensional phases. Geochemical analyses show that ACG and ATG granitoids follow calcic and calc-alkalic trends, while KCG and MPG display alkalic characteristics. These findings align with the region’s tectonic transition from the closure of the Paleo–Tethys Ocean to Late Triassic transpressional deformation. This study enhances the understanding of granitoid petrogenesis and provides valuable implications for regional tectonic evolution and mineral exploration.

Coupled evolution of basin structure and fluids recorded by microfractures: A case study of deep-buried ordovician in the tarim basin

The fluid activity in the deep strata of sedimentary basins is commonly related to tectonic activity, and the cements filled in fractures are a good carrier for the tectonic-fluid coupling evolution. Compared to macrofractures, microfractures have characteristics of high frequency and easy identifiable periods. Abundant microfractures infilled by carbonate cements (MCCFs) developed in carbonates of the Ordovician Yingshan and Yijianfang formations in the platform basin area of the Tarim Basin. Based on the study of petrology, U-Pb dating, and geochemical characteristics, this study determined the stages of MCCFs and clarified the tectonic-fluid coupling evolution process recorded by MCCFs in the study area. The formation order of these MCCFs is D1, C1, C2, D2, C3, and C4. The precipitation times of MCCFs have a good correspondence with orogeny around the Tarim Basin and active times of strike-slip faults in the platform basin area. The six stages of MCCFs in the Ordovician Yingshan and Yijianfang formations in the SLU recorded the tectonic-fluid coupling evolution process of concentrated seawater in the late Middle Ordovician, meteoric water at late Ordovician, organic acids during the Silurian, Mg-rich hot brine at the end Devonian-early Carboniferous, and magmatic hydrothermal fluids during the Permian. This not only indicates a close connection between fluid activity and tectonic activity in sedimentary basins, but also confirms that the formation of MCCFs in carbonate formations is closely related to regional tectonic-fluid coupling activities. This study provides a good example for studying macro scale tectonic-fluid coupling activities in basins using microfractures.

AGE AND GEODYNAMIC SETTINGS FOR FORMATION OF CARBONATITE COMPLEXES AND ASSOCIATED RARE METAL DEPOSITS OF THE SOUTH URAL

The Ilmen-Vishnevogorsky and Buldym carbonatite complexes occurring in the Southern Urals represent linear deformed carbonatite complexes. Their origin, as well as the age and geodynamic conditions remain the subject of debate. The isochron methods (Rb-Sr, Sm-Nd, TIMS) and local U-Pb-dating of zircons (SHRIMP II and LA-ICP MS) of these carbonatite complexes were employed to determine the age and duration of the stages of alkali-carbonatite magmatism and associated rare-metal ore formation. The Silurian-Devonian U-Pb zircon ages of the early phases of Ilmen-Vishnevogorsky miaskites and carbonatites were determined as 420.7±11 Ma (S2) and 417±2.8 Ma (D1), respectively. In the later phases of miaskites and carbonatites, early zircons are resorbed, they have broken isotope systems, and later zircon generations form a cluster of 386±7.6 Ma (D2). The Lower Permian U-Pb age of zircon 280±8 Ma (P1) was determined in the miaskite-pegmatite and late carbonatite. The isochron dating of late ore-bearing varieties of carbonatites provided the ages from the Lower Permian to the Early Triassic (P1–T1): 254±18 Ma, Sm-Nd and 247±4 Ma, Rb-Sr, IVC; 280±53 Ma, Sm-Nd, Buldym complex. Thus, the generation and intrusion of alkaline magmas in the Urals occurred ~420 Ma (S2–D1), synchronously with the formation of island-arc complexes. They are related to rifting on the emerging continental margins. The tectonic activity and formation of alkaline rocks and carbonatites proceeded in the Middle Devonian (~380 Ma, D2); it correlates with the accretion-collision stage of the Urals development. At the stage of "hard" collision (~280 Ma, P1), the Ilmen-Vishnevogorsky and Buldym complexes were plastically deformed, underwent melting and emplaced conformably with collision-slip tectonic structures. Recrystallization of rocks and minerals, plastic and brittle deformations, processes of pegmatitic, carbonatitic and rare-metal ore formation are associated with palingenic-metasomatic transformation of rifting alkaline complexes of Silurian-Devonian age at the collision and post-collision (~250 Ma, P3–T1) stages of the Urals emplacement.

The role of gas emissions (He, Rn, and CO2) from fault zones in understanding fault and seismic activity

Active fault zones are critical pathways for the migration of deep fluids to the Earth’s surface, carrying gases such as He, Rn, and CO2 that provide evidence for the physical and chemical dynamics of the Earth’s interior. This review examines the geochemical characteristics of fault zone gases and their implications for understanding fault activity and seismic events. Fault zones with high activity levels exhibit significant gas release, and variations in soil and hot spring gas concentrations can serve as indicators of seismic activity. Changes in gas concentrations and isotopic ratios, particularly before and after earthquakes, reflect the dynamic interplay between deep-sourced and shallow-sourced fluids. Seismic-induced stress alterations enhance gas release along fault zones, leading to observable anomalies that can aid in earthquake monitoring and prediction. The study underscores the importance of isotope tracing in deciphering fluid sources, migration pathways, and the evolution of fault zones, providing valuable information for assessing tectonic activity and mitigating seismic risks.

Stratigraphy and microfacies analysis of the Lower–Middle Jurassic platform carbonate succession in the Yeşilovacık (Mersin) area (Central Taurides, S Turkiye)

This study covers the detailed analyses of stratigraphy, microfacies and depositional environments of the Lower-Middle Jurassic carbonate succession in the southern part of Anatolide-Tauride Carbonate Platform in southern Türkiye (south of Central Taurides, around Yeşilovacık). The carbonate succession is composed of the Dibekli and Tokmar formations, and the Işıklıkızıtepe Member which forms the base of the Tokmar Formation. The Dibekli Formation (Upper Sinemurian-Lower Bajocian) is composed of limestones intercalated with intraformational conglomerates in the lower parts, with dolostones in the lower to middle parts and with oncoidal limestones in middle to upper parts. The Işıklıkızıtepe Member (Upper Bajocian) starts with basal conglomerates containing brown-red- iron nodules and consists of sandstone and sandy-clayey limestone alternations. These are overlain by thin limestone layers passing upward to thick-bedded dolostones of the Tokmar Formation (Upper Bajocian–Bathonian). The middle to upper parts of the formation are composed of sandy, oncoidal limestones rich in bivalve shells and end with dolostones-limestone alternations in the upper part. According to microfacies analyzes and litho-bio content; Late Sinemurian-Plesbachian is a period that low-to moderate-energy, restricted inner platform conditions dominated the depositional environments. The presence of comman intraformational conglomerates shows tectonic activity from time to time in this period. The Toarcian to the earliest Bajocian, low-energy intertidal and shallow lagoon conditions dominated the depositional environments, and in the Early Bajocian, the depositional environment changed to a high-energy sand shoal and above wave base environment. The basal conglomerate consisting of brown-red, iron-noduler and bauxite grains at the base of the earliest Late Bajocian indicates a short-term emersion and continued under low energy shallow lagoonal conditions during the Late Bajocian–Bathonian. Environmental changes during the Toarcian to Early Bajocian, and the earliest Late Bajocian short-term emersion, and the environmental changes during the Late Bajocian-Bathonian are interpreted to short-term sea level changes. Yeşilovacık Lower-Middle Jurassic carbonate sequences are correlated with those in peri-Mediterranean platforms. They show close similarities to the other Tauride carbonate sequences in terms of stratigraphy and facies. Paleontological and sedimentological analyses enable us to reconstruct a detailed dating and paleoenvironmental evolution for the Yeşilovacık carbonate deposits during the Lower-Middle Jurassic period.

The crustal juvenile and reworking in eastern Tibet due to tectonism and magmatism

Crustal thickening in Tibet results from the collision of India and Eurasia. The fine structure of the crust is vital information to detect the tectonic genesis of crustal growth and reworking. Here, we constructed the crustal structure of eastern Tibet and its neighboring areas using depth-domain receiver function imaging. The imaging results reveal widespread low-velocity layers in the mid-crust, alternating high- and low-velocity structures in the lower crust, and regional variations in the velocity at the bottom of the lower crust and the thickness of the entire crust. We propose that the lower crust is juvenile crust, formed by multiphase magmatism and tectonic activity during continental collision. The regional variations in crustal structure can be attributed to differences in the tectonic position of subduction-collision system and the distinct crustal-derived materials that contribute to the formation of the juvenile crust. The low-velocity layers in the mid-crust are more likely to be the product of arc magmatism during the assembly of micro-continents. Based on the constraints of the unique crustal structure, we suggest that tectonic compression and magmatism caused the juvenile and reworking of the Tibetan crust.

Precision Seismicity of the San Andreas Fault System in Central California: Insights into Active Tectonics and Earthquake Physics

Since the late 1960s, seismicity of the San Andreas Fault system in central California has been under intense observation by U. S. Geological Survey’s Northern California Seismic Network (NCSN). Designed to provide accurate focal depth control and a low magnitude of catalog completeness, the network maps fault, both large and small across the full breadth of this 400-kilometer-long portion of the plate boundary, including many that are known only from their seismicity. Beginning in 1984, with the advent of routine digital recording, new opportunities were created to significantly enhance the spatial resolution of seismicity. This led to the co-evolution of method that take full advantage of digital waveforms and new insights into the nature of seismicity and faults. Collectively referred to as precision seismicity, discoveries included repeating earthquakes and highly organized and stable distributions of seismicity on major faults. Long term observation of seismicity before and after the six largest earthquakes over the last half-century underscore the outstanding challenges for earthquake predictability and theories of earthquake nucleation.

Characteristics and Tectonic Implications of the Geomorphic Indices of the Watersheds around the Lijiang–Jinpingshan Fault

The Lijiang–Jinpingshan fault (LJF) is an important secondary boundary fault that obliquely cuts the Sichuan–Yunnan rhombic block. It is of great significance for understanding the tectonic evolution of the Sichuan–Yunnan rhombic block and even the southeastern margin of the Tibet Plateau. Based on a digital elevation model (DEM), this work combines ArcGIS with MATLAB script programs to extract geomorphic indices including slope, the relief degree of the land surface (RDLS), hypsometric integral (HI), and channel steepness index (ksn) of 593 sub–watersheds and strip terrain profiles around the LJF. By analyzing the spatial distribution characteristics of the geomorphic indices and combining the regional lithology and precipitation conditions, the spatial distribution of the geomorphic indices around the study area was analyzed to reveal the implications of the LJF’s activity. The results of this work indicate that (1) the distribution of geomorphic indices around the LJF may not be controlled by climate and lithological conditions, and the LJF is the dominant factor controlling the geomorphic evolution of the region. (2) The spatial distribution patterns of geomorphic indices and strip terrain profiles reveal that the vertical movement of the LJF resulted in a pronounced uplift on its northwest side, with tectonic activity gradually diminishing from northeast to southwest. Furthermore, based on the spatial distribution characteristics of these geomorphic indices, the activity intensity of the LJF can be categorized into four distinct segments: Jianchuan–Lijiang, Lijiang–Ninglang, Ninglang–Muli, and Muli–Shimian. (3) The activity of the LJF obtained from tectonic geomorphology is consistent with the conclusions obtained in previous geological and geodesic studies. This work provides evidence of the activity and segmentation of the LJF in tectonic geomorphology. The results provide insight for the discussion of tectonic deformation and earthquake disaster mechanisms in the southeastern margin of the Tibet Plateau.

Constraining timing of Proterozoic fault movement in the Capricorn Orogen, Western Australia

Ancient faults dissect low-grade Mesoproterozoic sedimentary rocks of the 1673–1455 Ma Edmund Basin and the 1455–1075 Ma Collier Basin in the Capricorn Orogen, Western Australia, and reveal a protracted history of basin formation and subsequent deformation. K–Ar dating of illite from fine-grained fault gouge separates (ideally <0.1 µm) provide robust dates of the most recent fault movement. From the Godfrey–Mount Vernon Fault, a sample of siltstone from the Kiangi Creek Formation (1590–1514 Ma) in the Edmund Basin, which was collected adjacent to faulting, provided a whole-rock date of 1506 ± 30.2 Ma. This is interpreted as a mixed age, encompassing modification of the depositional age by subsequent faulting during the extensional opening of the Edmund Basin. A fault gouge sample dated at 1141.4 ± 58.6 Ma, also from the Godfrey–Mount Vernon Fault, is consistent with the tectono-thermal 1321–1171 Ma Mutherbukin Tectonic Event identified in underlying high-grade Gascoyne Province basement rocks. Fault gouge sample dates of 885.5 ± 45.9 Ma from the Godfrey–Mount Vernon Fault and 782.2 ± 40.1 Ma from the Quartzite Well Fault define the younger newly identified crustal shortening during the Kuparr Tectonic Event. Concomitant tectonic activity in eastern Australia and South China has been considered as a possible precursor of the breakup of Rodina. In southern Africa, the Zambezi Supracrustal Sequence has been dated at 880–820 Ma and the Munali Intrusive Complex at 862–857 Ma also identified as rift-related.

Tectonic Activity Analysis of the Laji-Jishi Shan Fault Zone: Insights from Geomorphic Indices and Crustal Deformation Data

Fault segmentation plays a critical role in assessing seismic hazards, particularly in tectonically complex regions. The Laji-Jishi Shan Fault Zone (LJSFZ), located on the northeastern margin of the Tibetan Plateau, is a key structure that accommodates regional tectonic stress. This study integrates geomorphic indices, cross-fault deformation rate profiles, and 3D crustal electrical structure data to analyze the varying levels of tectonic activity across different segments of the LJSFZ. We extracted 160 drainage basins along the strike of the LJSFZ from a 30 m resolution digital elevation model and calculated geomorphic indices, including the hypsometric integral (HI), stream length-gradient index (SL), and channel steepness index (ksn), to assess the variations in tectonic activity intensity along the strike of the LJSFZ. The basins were categorized based on river flow directions to capture potential differences across the fault zone. Our results show that the eastern basins of the LJSFZ exhibit the strongest tectonic activity, demonstrated by significantly higher SL and ksn values compared to other regions. A detailed segmentation analysis along the northern Laji Shan Fault and eastern Jishi Shan Fault identified distinct fault segments characterized by variations in SL and ksn indices. Segments with high SL values (&gt;500) correspond to higher crustal uplift rates (~3 mm/year), while segments with lower SL values exhibit lower uplift rates (~2 mm/year), as confirmed by cross-fault deformation profiles derived from GNSS and InSAR data. This correlation demonstrates that geomorphic indices effectively reflect fault activity intensity. Additionally, 3D crustal electrical structure data further indicate that highly conductive mid- to lower-crustal materials originating from the interior of the Tibetan Plateau are obstructed at segment L3 of the LJSFZ. This obstruction leads to localized intense uplift and enhanced fault activity. These findings suggest that while the regional stress–strain pattern of the northeastern Tibetan Plateau is the primary driver of the segmented activity along the Laji-Jishi Shan belt, the direction of localized crustal flow is a critical factor influencing fault activity segmentation.

INSIGHTS INTO THE MOHO DEPTH VARIATIONS AND CRUSTAL CHARACTERISTICS IN THE GUELMA–CONSTANTINE BASIN, NORTHEASTERN ALGERIA: A SHORT-PERIOD SEISMIC-RECEIVER-FUNCTION PERSPECTIVE

Teleseismic receiver functions (RF) were extracted from data collected at eight short-period, three-component seismic recording stations over the Guelma–Constantine Basin, northeastern Algeria, to improve the understanding of crustal structure and geodynamic processes. The H-κ stacking method was used to determine the Moho depths and average vP/vS ratios at each station. Careful linear inversion of RF was performed to determine the most appropriate average shear-wave and P-wave velocity profiles at each site. Both methods have yielded highly congruent results, with Moho depths showing robust correlations with previous seismological and geophysical studies. The previously observed pattern of the increasing Moho depth from north to south in the Tell Atlas has been confirmed. Furthermore, the identified transitional nature of the Moho in the Constantine Basin is consistent with a recent study. In addition, we identify a low-velocity zone (LVZ) at approximately 20 km depth within the southern Guelma Basin, confirming previous results in the Constantine Basin and suggesting an eastward elongation of the LVZ, at least into the southern periphery of the Guelma Basin. Examination of data from the northern tip of the Hammam Debbagh–Roknia NW–SE fault, the western boundary of the Guelma pull-apart basin, revealed a shallow Moho depth (22 km), less than the basin average depth of 25 km. The LVZ observed in the lower crust (12 km) suggests the presence of partial melts, consistent with gravimetric and chemical analyses of hydrothermal sources in the area. The extensional tectonic activity along this boundary, coupled with the low-viscosity zone and low average vP/vS ratio, is potentially associated with delamination processes. The effectiveness of our approach underscores its potential as a viable alternative or complementary method for investigating variations in the Moho depth.

Mineralogical and geochemical studies of shales from Kopili Formation, Dima Hasao district Assam, North East India: Insights into diagenesis, deposition and provenance

The Eocene Kopili Formation in the Assam foreland basin records sediment sources, tectonic activity and depositional environments following the India-Eurasia collision. Mineralogical and geochemical analysis of these shales exposed near Garampani, Assam, NE India was conducted to study the diagenesis, palaeoweathering, palaeosalinity, redox conditions, tectonic settings and provenance. The Kopili Formation is composed of mainly shale with thin beds of limestone, black shale and sandstone and these units overlie the Upper Sylhet Limestone. The presence of goethite-rich phosphatic nodules, secondary precipitation within the fissile planes of shale and the occurrence of anatase, talc, smectite and chlorite suggest diagenesis. The prevalence of kaolinite and mean Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Al2O3/MgO and Rb/Sr values of 86.73, 97.26, 16.36 and 1.32, respectively indicates extensive source rock weathering in humid tropical climate. The Index of Compositional Variation (ICV) values ranging between 0.47 and 2.38 also signify high weathering and tectonically active basin. The Sr/Ba ratio 0.34 ± 0.27 (mean±2σ) suggest overall freshwater basin. The Ni/Co (2.84 ± 2.29), V/Cr (1.65 ± 0.45) and Ce/Ce∗ (0.97 ± 0.63) suggest fluctuating redox environment. The samples predominantly cluster in continental island arc domain on the Th-Sc-Zr/10, La-Th-Sc and Th-Co-Zr/10 discriminant diagrams. Elemental ratios of Th/Sc, La/Sc, Cr/Th with average 0.91, 3.18, 10.13 respectively and La/Th-Hf plot suggest a felsic source rock. The Kopili shale was deposited in freshwater, continental island arc basin with fluctuating redox conditions, receiving sediments from weathered Himalayan granites and gneisses under a warm and humid climate. Subsequently, they underwent diagenetic alteration by low-pH fluid(s).

Giant landslide, hidden caldera structure, magnetic anomalies and tectonics in southern Tyrrhenian Sea (Italy)

Phlegraean Fields and Ischia Island are large, densely populated, active volcanic structures located in the Campanian Tyrrhenian margin between the onshore and offshore sectors. While the emerged landforms provide significant insights into a series of intense volcano-tectonic events of the last 60 ka, our understanding of the sub-marine portion of these volcanoes remains limited due to its inaccessibility to direct exploration. In the last decades, the use of magnetic methods has proven to be useful in volcanic context, given the presence of large magnetization contrasts, whereas the implementation of a high-resolution Digital Elevation Model (DEM) has allowed the integration of detailed morphological analyses into the geophysical studies. In this work, we present two new high-resolution airborne and shipborne magnetic surveys, carried out by the National Institute of Geophysics and Volcanology (INGV) in the marine sector of the Phlegraean Fields caldera (Pozzuoli Bay) and surrounding sea sectors. Moreover, the new datasets have been integrated with older marine surveys carried out by the National Research Council (CNR) to extend the resulting magnetic anomaly map embracing the whole Campanian offshore volcanic structures, excluding Ischia Island. As a result, we present here three new magnetic anomaly maps used for an integrated interpretation of magnetic, morphological, and tectonic features. The study results provide valuable insights into the relationship between volcanic, magmatic, and tectonic activity, which may be useful for further investigations. Among the most notable findings are: the identification of the magnetic signatures of regional faults, previously unknown caldera structures, and a massive rock avalanche. Consequently, our research provides a significant contribution to seabed exploration aimed at identifying potential hazard factors in the study area.

Recent and active faulting along the exposed front of the Northern Apennines (Italy): New insights from field and geochronological constraints

Establishing genetic links between active shallow faulting and deep seismogenic sources is challenging, especially in areas where seismogenic faults lack clear and readily interpretable geological evidence at the surface. The architecture of the Pedeapenninic margin of the Northern Apennines (Italy) reflects a regional-scale and complex NE-verging blind thrust system, which is dissected by transpressive/transtensive faults resulting from active NE-SW orogenic compression. The local geological framework is defined by allochthonous ocean-derived units resting atop Pliocene-to-present successions exposed along the Northern Apennines margin and to the NE of it, while the innermost chain sector mostly contains Adria-related units. We present results from field structural-geological investigations to identify and characterize potential active faults along the margin. There, the Pliocene-to-present units are faulted and folded, indicating that tectonic activity is still on-going, thus contributing to the local seismic hazard. Top-to-the NE and SW normal faults are common in the area and deform the Pliocene-to-present succession together with NE-SW strike-slip and transpressional/transtensional faults. Based on field evidence, we define four potentially active thrust segments affecting Middle Pleistocene to Holocene deposits exposed along the margin. Calcite U-Th dating on samples from faults extend the most recent datable tectonic activity back to the Middle Pleistocene. Paleostress analysis from inversion of fault-slip data from the most recent identified striated fault planes constrains a NE-SW shortening direction parallel to the Apennines regional migration direction. A distinct but coaxial extensional stress regime, recorded by structures measured within Plio-Pleistocene formations, was also identified. Our results offer a sound starting point for future investigations aimed at improving our understanding of active and seismogenic faulting in the area, so as to create robust Probabilistic Seismic and Fault Displacement Hazard Assessment (PSHA and PFDHA) models that can implement refined seismic hazard maps benefitting from structural-geological deterministic inputs in addition to the classic seismological constraints.

Nd isotope mapping in the Go Home region of Georgian Bay: a misunderstood key to the geology of the Central Gneiss Belt, Grenville Province of Ontario

The Georgian Bay transect forms an important geological section across the deeply exhumed Central Gneiss Belt of the Ontario Grenville Province. Its geological mapping was one of Nick Culshaw’s major research contributions, but the tectonic structure of the southern part of this transect in the Go Home region was never properly established. New Nd isotope data show that the classically recognized Go Home domain should be divided into three structural “decks” with distinct TDM (depleted mantle) Nd model ages. The upper deck consists of the Pine Island and Honey Harbour domains, with TDM ages averaging 1.56 and 1.57 Ga, respectively, which form two isolated units of the Grenvillian allochthonous belt. These are underlain by the newly-recognized Six Mile Lake domain, whose average TDM age of 1.71 Ga is representative of the tectonic duplex entrained elsewhere onto the base of the allochthon. Finally, the lowermost deck yields an average TDM age of 1.87 Ga, which identifies it as part of the Grenvillian parautochthon, exposed here in a tectonic window. The presence of a large retrogressed eclogite body within the allochthonous Honey Harbour domain confirms the exhumation of this unit from the deep crust on a major structural ramp. The coherent boundaries of these domains are consistent with the ramp–flat thrusting model of the Ottawan (Grenvillian) orogeny and limit the action of later extensional tectonics in the southwest Grenville Province.

Shallow subsurface fluid dynamics in the Malvinas Basin (SW Atlantic): A geoacoustic analysis

Using a database consisting of sub-bottom profiles, 2D and 3D seismic data, a series of seep structures and acoustic anomalies associated with a plumbing system in the subsurface of the southern part of the Malvinas Basin off the Argentine coast are presented. The seep morphologies consist of mounds, pockmarks, and a carbonate mound, derived from hydrocarbons migrating from the Early Cretaceous Springhill and Lower Inoceramus formations through extensional faults and overthrusts of the Malvinas Fold-Thrust Belt and accumulating in the gas hydrate stability zone. This configuration is widely observed in the anticlines of the Malvinas Fold-Thrust Belt, which are characterized by a vertical structure highlighting a Bottom Simulating Reflector (BSR) overlain by a blanked-out zone at the seabed, interpreted as a gas hydrate stability zone. The plumbing system is influenced by active transtensional tectonics, as shown by two sets of extensional faults concentrated over some anticlines. These faults lead to displacements that, in many cases, reach the seabed. One nuance of the influence of tectonic activity on fluid escape is most evident in the Malvinas anticline, where all the pockmarks and the carbonate mound are concentrated. In the western part of the Malvinas anticline, five pockmarks are observed in an area characterized by a shallow BSR. In contrast, in the eastern part of the Malvinas Basin, one pockmark and one carbonate mound are derived from a series of extensional faults. The presented data, as well as a comparison between the western and eastern parts of the Malvinas anticline, indicate that the anticlines are the main cause of seepage in this area, as they allow the accumulation of migrating fluids. Likewise, the seepage morphologies outside the anticlines are much less pronounced, as can be observed in the mounds that overlie the bottom vents.