Tectonic Implications Research Articles

Granites of the Chazangcuo Copper–Lead–Zinc Mining Area in Tibet, China: Magma Source and Tectonic Implications

Intermediate-acidic granites occur extensively in the Chazangcuo copper-lead-zinc mining area (hereinafter referred to as the Chazangcuo mining area) in Tibet, China. Exploring their rock types, sources, and tectonic settings is essential for understanding the genesis of granites in the region. This study investigated the petrology of the Chazangcuo granites, as well as the geochemical characteristics of their major elements, trace elements, and rare earth elements (REEs). Results indicate that the Chazangcuo granites are high-K calc-alkaline metaluminous rocks. These granites are enriched in large-ion lithophile elements (LILEs; e.g., Rb and Ba), depleted in high-field-strength elements (HFSEs; e.g., Nb, Ta, Zr, and Hf), with a relative enrichment in light rare earth elements (LREEs), and relatively depleted in heavy rare earth elements (HREEs), exhibiting a V-shaped distribution pattern and weak negative Eu anomalies. The granites are classified as typical I-type granites, displaying characteristics of crust-derived magmas with contributions from mantle sources and exhibiting significant fractional crystallization. The Chazangcuo granites were derived from the partial melting of mafic rocks, with protoliths formed in a moderate temperature environment. Influenced by the subduction of the Neotethys Ocean, the Chazangcuo granites were formed in an arc caused by the collision between the Indian and Eurasian plates (also referred to as the Indo–Eurasian collision) during the Late Triassic. Under the effect of geological activities such as upwelling of the asthenosphere and fluid intrusion and differentiation, metal mineralization was prompted to be distributed in the granite fissures, forming the Cu-Pb-Zn polymetallic deposits of Chazangcou in Tibet, suggesting that the granites are closely associated with mineralization.

Seismogenic model of the 2023 MW5.5 Pingyuan earthquake in North China Plain and its tectonic implications

The 6 August 2023 MW5.5 Pingyuan earthquake is the largest earthquake in the central North China Plain (NCP) over the past two decades. Due to the thick sedimentary cover, no corresponding active faults have been reported yet in the epicenter area. Thus, this earthquake presents a unique opportunity to delve into the buried active faults beneath the NCP. By integrating strong ground motion records, high-precision aftershock sequence relocation, and focal mechanism solutions, we gain insights into the seismotectonics of the Pingyuan earthquake. The aftershocks are clustered at depths ranging from 15 to 20 km and delineate a NE-SW trend, consistent with the distribution of ground motion records. A NE-SW nodal plane (226°) of the focal mechanism solutions is also derived from regional waveform inversion, suggesting that the mainshock was dominated by strike-slip motion with minor normal faulting component. Integrating regional geological data, we propose that an unrecognized fault between the NE-SW trending Gaotang and Lingxian-Yangxin faults is the seismogenic fault of this event. Based on the S-wave velocity structure beneath the NCP, this fault probably extends into the lower crust with a high angle. Considering the tectonic regime and stress state, we speculate that the interplay of shear strain between the Amurian and South China blocks and the hot upwelling magma from the subducted paleo Pacific flat slab significantly contributed to the generation of the Pingyuan earthquake.

Tectonic implications of a rare metamorphic event in eastern China during the Earth's ‘middle age’

The Mesoproterozoic Era has long been considered a relatively stable, silent and even ‘boring' period in Earth history, during which the lithosphere was tectonically inactive. However, an increasing amount of evidence suggests that metamorphism and magmatism were much more widespread and intense than previously thought, implying that this period was dynamic. Here, we report metamorphism at c. 1.4 Ga along the southeastern margin of the North China Craton in eastern China. We conducted analyses using a TESCAN Integrated Mineral Analyser (TIMA) combined with electron microprobe analysis (EMPA) and zircon sensitive high-resolution ion microprobe (SHRIMP) and laser ablation inductively coupled plasma mass spectrometry U–Pb dating on garnet amphibolites and their country rocks. The detailed mineral composition of a representative garnet amphibolite sample was identified and determined by TIMA. Phase equilibria modelling using pseudo-sections combined with the EMPA data indicated the peak metamorphism stage (M 2 ) of the garnet amphibolites at a P – T condition of 10.6–11.2 kbar and 820°C. The SHRIMP zircon U–Pb analysis yielded an age of 1366 ± 17 Ma for the garnet amphibolites, which is slightly younger than that of the country rock schist (1376 ± 22 Ma). Integrating the metamorphic event with geochemical signatures, magmatic records and sedimentation patterns in analogous geological settings on other continents, our findings collectively demonstrate a protracted and pervasive orogenic process along the periphery of the Columbia supercontinent.

Greenstone belt-hosted Mesoarchaean Mbarga BIF prospect, NW Congo Craton (southern Cameroon): Petrography, geochemistry, Sr-Nd isotopes, zircon u-pb geochronology, petrogenetic, and tectonic implications

Banded Iron Formations (BIFs) interbedded with schists characterize the Mbarga prospect in the Ntem Complex at the northwest edge of the Congo Craton. This study presents new whole-rock geochemical, Sr-Nd, and zircon U-Pb isotopic data for the BIFs and schists to constrain the timing and geodynamic setting of the deposit. The abundances of SiO2 (52.81 to 79.14 wt%) and Na2O+K2O (4.24 to 8.54 wt%) in the schists indicate andesitic, dacitic, to rhyolitic protoliths. Trace element signatures, such as high Ba and depleted Nb-Ta concentrations, suggest a volcanic arc affinity. A well-defined U-Pb zircon age of 2890 ± 4 Ma implies a Mesoarchaean protolith age, while an imprecise Rb-Sr whole-rock age of ca. 2.65 Ga is consistent with known tectonothermal events (∼2.75 and 2.65 Ga) in the Ntem Complex. Initial εNd(2.89) values of + 0.8 to + 2.0 for the schists indicate an unevolved, mantle-like source for the protoliths. The BIFs show partial to extensive alterations of magnetite to hematite-martite and are of the Algoma type. They are characterized by high Fe2O3 (∼54.06 wt%) and SiO2 (∼45.40 wt%) but low Al2O3 (∼0.14 wt%), TiO2 (∼0.1 wt%), Zr (∼4.92 ppm), Th (∼0.11 ppm), and REE-Y contents. Rare earth patterns marked by LREE depletion, positive Eu anomalies (∼2), mild Ce depletion (Ce/Ce* 0.67 to 1.16), and super-chondritic Y/Ho ratios (∼34) suggest formation under anoxic to suboxic Archaean marine conditions, possibly involving mixing of Archaean seawater with minor (0.1–1 %) contributions from medium- to high-T hydrothermal fluids. Sparse 2951 ± 24 Ma zircons, presumably of detrital origin, establish a depositional link to the associated schists, redefining the age of BIF deposition within the Ntem Complex to ca. 2.95–2.89 Ga. However, whole-rock Sm-Nd isotope data for five BIF samples define a scattered array with an imprecise slope equivalent to an age near 1004 ± 78 Ma, which may reflect a previously unrecognized recrystallization event in the BIFs. The initial εNd of this array (−11.1 ± 2.0) suggests a crustal source. The mineralogical, geochemical, and isotopic datasets reconcile the Mbarga BIF prospect with arc magmatism in the Late Archaean, suggesting their formation in a back-arc basin setting.

Coseismic geodetic and geophysical variations detected for the January 19th, 2021 San Juan earthquake. Tectonic implications

The coseismic surface variations and crustal deformation in the Central Precordillera region of San Juan (Argentina) as a consequence of the Mw 6.5 earthquake of January 19th, 2021 (2:46 UTC) were characterized by a multidisciplinary team, integrating information from Gravity, Seismology, GNSS and DInSAR (Synthetic Aperture Radar Differential Interferometry) techniques.Prior to the occurrence of the event, several periodic measures were taken at fixed reference points throughout San Juan province. The results of the data analysis show significant changes in height corresponding to the uplifting of a few centimeters of the hanging wall block in accordance with the estimated deformation obtained by the focal mechanism. In addition, the transcurrent component is evident in the GNSS vectors calculated after the earthquake. These results are consistent with the Gravity variations measured at the control points. This indicates the uplifting of the basement of Central Precordillera while the elastic Andean compressional deformation migrates N-E related to the Tulum lineament. The joint analysis of 4D gravity with GNSS heights shows an accumulation of deformation involving the lower crust prior to the earthquake, and the release of stresses with permanent deformation, which partially complies with the laws of isostasy in the Precordillera, after the earthquake.

Genesis and Tectonic Implications of Early Cretaceous Granites in the Haobugao Area, Southern Great Xing’an Range: Insights from Zircon U–Pb Geochronology, Hf Isotopic Composition, and Petrochemistry

In the Huanggangliang–Ganzhuermiao metallogenic belt in the southern Great Xing’an Range, the Haobugao Pb–Zn deposit is the most widespread skarn-type polymetallic deposit. The observed mineralization processes in this area are closely associated with both magmatic and tectonic activity. The zircon U–Pb ages of two granitoid phases are 134.0 ± 0.6 Ma and 133.4 ± 0.9 Ma (Early Cretaceous). High SiO2 content (average mass fractions of 77.98 wt.% and 73.25 wt.%), high alkalinity (average mass fractions of 6.19 wt.% and 8.78 wt.%), and low CaO levels (average mass fractions of 0.16 wt.% and 0.12 wt.%) are characteristic of these rocks. They are also enriched in high-field-strength elements (HFSEs) (Th, U, Ta, Zr, Hf, etc.) and depleted in large ion lithophile elements (LILEs) (Ba, Sr, etc.). Furthermore, the Nb/Ta ratios (7.80~8.82, 10.00~10.83) point to a crustal origin of the magma. The zircon Hf isotopic compositions suggest that the melting of young crust derived from Meso-Neoproterozoic and Neoproterozoic depleted mantle gave rise to the magma in these granite porphyries. These rocks formed in an extensional environment driven by the subduction and retreat of the Paleo-Pacific plate during the Early Cretaceous.

Tectonic Implications of Early Permian Arc Rocks and Their Cretaceous to Early Cenozoic Reworking in Southern Lhasa Terrane, Tibet

AbstractThe Lhasa terrane in southern Tibet occupies a central position in Asian tectonics, yet its pre‐Mesozoic petrologic and tectonic evolution is poorly constrained, especially the Southern Lhasa subterrane (SLS). Here, new zircon U–Pb ages, zircon trace element and Hf isotopic compositions, and whole‐rock geochemical data for mafic meta‐igneous rocks from the SLS distinguish three tectono‐thermal events at ∼290 Ma, ∼126 Ma and ∼49 Ma. Whole‐rocks and zircons with ages of the two older events have arc magma geochemistry, but Hf isotopes are distinct from Mesozoic Gangdese arc magmas. Zircon cores and, arguably, whole rocks instead derive from ∼290 Ma magma formed during southward subduction of Paleo‐Tethys beneath the SLS. These rocks later underwent Early Cretaceous (∼126 Ma) remelting and early Cenozoic (∼49 Ma) metamorphism with P–T conditions of ~800°C and 15.3 kbar, and record a retrograde P–T path characterized by exhumation with cooling, consistent with a collisional origin. These data suggest Permian igneous rocks underwent reworking during both the Early Cretaceous and the early Cenozoic, reaching crustal thicknesses of at least ~50 km during the early Eocene. Combined with regional data, Paleo‐Tethys evidently experienced early Permian double‐sided subduction within the Lhasa terrane, with back arc basins forming between the SLS and the Indian margin to the south. These back arc basins ultimately widened to form the Neo‐Tethys Ocean, which then subducted during the Mesozoic, leading to Cretaceous arc magmatism and overprinting, followed by early Cenozoic metamorphism and final reworking during collision with India.

Geochemistry, zircon U–Pb chronology and Hf isotope of the Weideshan high Ba–Sr granites in Jiaodong Peninsula of the North China Craton: Constraints on their petrogenesis and tectonic implications

Geochemistry, zircon U–Pb chronology and Hf isotope of the Weideshan high Ba–Sr granites in Jiaodong Peninsula of the North China Craton: Constraints on their petrogenesis and tectonic implications

Lifecycle of an Isolated Seismic Swarm in Continental Southern Norway from Nucleation, Acceleration, and Yielding to the Demise of Fault Slip

Abstract An intraplate earthquake swarm started near the Bitdal valley in the seismically inactive mountains of Southern Norway in summer 2020 and continued for more than two years. We detected 1600 earthquakes through template matching and obtained high-resolution relative magnitudes and locations for the events to resolve the swarm’s spatiotemporal evolution and tectonic implications. The detection results reveal that no earthquakes occurred at the swarm site for at least 22 yr prior to the current activity. In July 2020, six months before the swarm’s initially recognized onset, weak precursory events appeared. Hypocenter relocation shows that the swarm develops along a single 1.5 km patch on a northwest–southeast-striking fault with oblique-normal sense containing a left-lateral component. The seismicity follows a dual-velocity migration for which the slow, general migration reverses sense twice, and 30 short bursts show internal migration both with and against the general migration direction. Changes in the distribution of events let us divide the swarm into four phases: precursory activity, accelerating growth, main slip, and slow decline. The observed seismicity bursts, pauses, and dual migration velocities are consistent with a rupture-driven mechanism for which slip initiates spontaneously and keeps going in slow and quick failure cascades due to stress transfer and slip weakening.

The effective elastic thickness along the Emperor Seamount Chain and its tectonic implications

SUMMARY The Hawaiian–Emperor Seamount Chain, a pre-eminent example of a hotspot-generated intraplate seamount chain, provides key constraints not only on the kinematics of plates but also on their rigidity. Previous studies have shown that the effective elastic thickness, Te, a proxy for the long-term strength of the lithosphere, changes abruptly at the Hawaiian–Emperor ‘bend’ from low values (∼16 km) at the Emperor Seamounts to high values (∼27 km) at the Hawaiian Ridge. To better constrain Te along the poorly explored Emperor Seamounts we have used a free-air gravity anomaly and bathymetry gridded data set, together with fully 3-D elastic plate (flexure) models, to estimate the continuity of Te and volcano load and infill densities along 1000 profiles spaced 2 km apart of the chain. Results show that Te generally decreases northwards along the chain. The decrease is most systematic between Ojin and Jimmu guyots where Te depends on the age of the lithosphere at the time of volcano loading and is controlled by the 340 and 400 °C oceanic isotherms. The largest variation from these isotherms occurs at the northern and southern ends of the chain where Te is smaller than expected suggesting the influence of pre-existing, older, loads. We use these results to constrain the subsidence, flexural tilt, rheological properties and tectonic setting along the seamount chain. We found an excess subsidence in the range 1.2–2.4 km, a tilt as large as 2–3°, oceanic lithosphere that is weaker than it is seawards of the weak zone at subduction zones, and a tectonic setting at Detroit and Koko seamounts that, despite their forming an integral part of the hotspot generated seamount chain, retains a memory of their proximity to earlier loads associated with plume influenced mid-oceanic ridges.

Origin and metamorphism of ophiolitic serpentinites from the Yuli belt, eastern Taiwan: new findings and tectonic implications

ABSTRACT Serpentinites associated with metamafic and metaplagiogranitic rocks occur sporadically within metasedimentary schists in the Yuli belt. Such metaigneous rocks are considered to represent ophiolitic protoliths and some contain high-pressure (HP) metamorphic minerals or assemblages. However, the origin and metamorphism of these serpentinites have long been a mystery. This study systematically investigates the four major serpentinite-bearing exposures at the Fengtien, Wanjung, Tsunkuanshan, and Chinshuichi. The results reveal that the serpentinites are of two different protoliths on the basis of relict chromian spinel composition. Cr-spinel compositions of the Fengtien and Tsunkuanshan samples are characterised by moderate Cr# [Cr/(Cr + Al)] (0.45–0.57), relatively high Mg# [Mg/(Mg+Fe2+)] (0.59–0.79), but low Fe3+# [Fe3+/(Fe3++Cr+Al)] (0.02–0.06), reflecting an abyssal peridotite type protolith. By contrast, Cr-spinel compositions of the Wanjung and Chinshuichi samples show high Cr# (up to 0.74) and Fe3+# (0.03–0.08), but low Mg# (<0.6), indicating a forearc mantle peridotite origin. Peak metamorphic conditions of the serpentinites are represented by the assemblage of antigorite + magnetite + chlorite + olivine + diopside, which is estimated as up to 550°C but the pressure cannot be constrained quantitatively. Based on field relations, it is inferred that the serpentinites, associated HP metaigneous rocks, and garnet-bearing metasedimentary schists were metamorphosed isofacially. Despite two origins, the peridotitic protoliths were all subjected to hydration and subduction processes. We suggest that precursors of the serpentinites, metaigneous rocks, and metasedimentary schists were juxtaposed and metamorphosed at intermediate to great depths (~35–55 km) of a subduction zone. Therefore, the Yuli belt serpentinites and associated rocks likely represent exhumed materials from a palaeo-subduction interface.

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.

Precise Relocation and Source Characterization of Two Earthquake Sequences in Yellow Sea Using Regional Lg-Wave Observations

ABSTRACT Two significant earthquakes of magnitude ML 4.6 and 4.5 occurred on 18 January and 3 December 2021 in the central region of the Yellow Sea, respectively. The earthquakes occurred beneath the Gunsan sedimentary basin at about 10 km depth with a strike-slip faulting mechanism on nodal planes striking northwest–southeast (NW–SE) and north-northeast–south-southwest (NNE–SSW). Despite a lack of close-by seismographic stations, we successfully utilized regional Lg-wave observations on both coasts of the sea—the Korean peninsula on the east and eastern China on the west. For nine earthquakes in two event sequences, the Lg-wave differential travel times of the nearby event pairs at the common station are carefully measured using the waveform cross-correlation technique. The double-difference earthquake relocation method is employed to obtain precise relative epicentral locations using the Lg correlation measurements. Relocated epicenters align along the NW–SE direction, indicating that the nodal plane striking the same direction is the likely fault plane on which both sequences occurred. This is the first case reported in the literature in which the causative fault plane has been identified for earthquakes in the central Yellow Sea region. It has an important implication for current regional tectonics; it favors neither old tectonic features trending NE–SW (Qianliyan uplift) nor the north–south alignment of significant earthquakes in the region along the Amur plate boundary. The Lg waves from the earthquake sequences are dominant seismic signals on all three-component records at stations in 160–550 km and allowed us to analyze source properties of the two largest earthquakes using the empirical Green’s function approach. Azimuthal variations of the source corner frequencies suggest that earthquake rupture likely propagated toward southeast (125°) along the fault plane, supporting the aftershock relocation results.

The 3D Density Structure of the South China Sea Based on Wavelet Multi-Scale Analysis of Gravity Data and Its Tectonic Implications

Due to its unique geographical location and complex geological evolution processes, the South China Sea has been a focus of extensive research. Previous studies on the density structure of the South China Sea mostly focused on 2D density structures, with relatively limited research on 3D density structures. A comprehensive study is still needed to refine the expansion mechanism and tectonic evolution of the South China Sea. In this study, we utilized wavelet multi-scale analysis of gravity data to obtain a 3D density model of the South China Sea and discussed its tectonic evolution from the pattern of density anomalies. The inversion results show that (1) the expansion of the South China Sea caused the typical thin oceanic crust and parts of the continent–ocean transition zone may fracture due to the expansion; (2) the low-density anomaly in the upper mantle of Luzon Island may indicate partial melting or the upwelling of asthenosphere materials; and (3) the expansion of the South China Sea is influenced by multiple plate forces and uneven forces affect the distribution of high-density anomalies in the upper mantle.

Geochemistry of Volcanic Rocks in Ponelo Island, North Gorontalo, Indonesia

Ponelo Island is located in the northern part of Sulawesi, which is still an enigma regarding the genesis of the volcanic rocks found on this island. Therefore, the objective of this study is to understand the petrogenesis and tectonic implication of these volcanic rocks. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) to obtain trace and rare earth elements is the method of this study. The volcanic rocks found on Ponelo Island consist of basalt and basaltic andesite rocks with a calc-alkaline affinity. The transition data suggested a highly fractionated cause of low transition element (Ni=17-38 ppm; Cr=13-47) compared to primary magma concentration, anomalies negative of Ba, Sr, and Ti of spider diagrams, and negative anomaly of Eu (Eu/Eu*=0.88-0.99). Relationship between low concentration between Ce/Y (0.74-0.76) and La/Yb vs Sm/Yb ratio indicated ~5% spinel-lherzolite mantle source partial melting. On the other hand, incompatible element ratios, such as Ba/Nb (39.03-45.28), Ba/Th (75.52-82.67), Rb/Nb (3.93-6.22), K/Nb (1772.22-2703.45), Ba/La=13.67-14.57, Th/La (0.17-0.18), La/Nb (2.91-3.16), depleted Nb/U (6-6.74), and also lack of xenolith or enclaves indicate cryptic crustal contamination. The slab-derived fluid indicated by ratios of Rb/Y (0/019-0/05), Nb/Y (0.10-0.11), Th/Yb (0.52-0.61), and Ba/La ratio (13.29-14.57). Ponelo volcanic rocks shows typical calc-alkaline island arc tectonic setting particularly with enrichment in ion lithophile element (LILE) and light rare earth elements (LREE) along with depletion in high field strenght elements (HFSE) and heavy rare earth elemets (HREE), as shown by spider diagrams.

Petrogenesis and tectonic implication of the Triassic monzogranite from the central segment of the East Kunlun Orogen, NW China

The Triassic granitoids in the East Kunlun Orogenic Belt (EKOB) are crucial for understanding the tectonic evolution of the Paleo-Tethys Ocean. This study presents zircon U–Pb ages, Lu–Hf isotopes, whole-rock major and trace elements, and Sr–Nd isotope compositions from monzogranite plutons in the central segment of EKOB to constrain their petrogenesis and tectonic evolution. These monzogranites are dominant composed of mineral assemblages of K-feldspars, plagioclase, minor biotite and accessory minerals. U–Pb dating of zircons from the Xinle South (XLS), Nanshankou (NSK) and Changgou South (CGS) plutons yield ages of 251 Ma, 232 Ma and 221 Ma, respectively. The studied monzogranites have relatively high SiO2 and Al2O3, but have low contents of TiO2, Fe2O3T, MgO relative to the coeval granodiorites. These monzogranites are classified as fractionated I-type granites, ranging from calc-alkaline to high-K calc-alkaline compositions. Their negative εNd(t) values (−4.2 to −6.3) and zircon εHf(t) values (−6.1 to −9.3) suggest that magma generation occurred through partial melting of ancient lower crust, followed by extensive fractional crystallization. Integrating our new data with regional geological evidence, we propose that the Early Triassic XLS monzogranite emplaced in a localized extensional environment linked to the northward subduction of the Paleo-Tethys oceanic plate. In contrast, during the post-collisional extensional phase of the Late Triassic, the formation of the NSK and CGS monzogranite plutons was directly influenced by asthenospheric upwelling, lower crust delamination, and subsequent continental rifting.

Mineralogy and Major Element Geochemistry of the Oligocene Barail Group Sandstones from the Sylhet Trough, Bengal Basin: Provenance and Tectonic Implications

The origin of Oligocene sediments in the Bengal Basin and associated tectonic setting remain poorly understood. This study investigates the framework mineralogy and major element geochemistry of the Barail Group sandstones from the Sylhet Trough within the Bengal Basin to clarify the provenance and tectonic history of the Oligocene. Modal analysis (Q83F7L10) and geochemical data support a classification of sublitharenite to subarkose, some with Fe enrichment. The heavy mineral assemblage is dominated by opaque minerals, followed by ultrastable minerals with zircon &gt; tourmaline &gt; rutile. The sub-angular to sub-rounded sand grains with a compositionally moderate mature nature suggest that the sediments were deposited close to the source area. The mineralogical and geochemical provenance discrimination diagram suggests contributions from felsic igneous, sedimentary/metasedimentary, and low-grade metamorphic sources, with detritus derived from the Indian craton and proto-Himalaya region. Data suggest moderate to intense chemical weathering, indicative of low relief and a sub-humid to humid climate in the source area. The tectonic analyses indicate that the Bengal Basin transitioned from a predominantly passive margin to an active tectonic margin setting during the Oligocene.

Morphometric indices assessment: Implications for active tectonics in the upper Narmada Basin, central India

During the Palaeoproterozoic era, the Northern and Southern cratonic blocks of the Indian Plate came together and amalgamated. Farther, facilitated by the East-West trending central Tectonic Suture Zone, characterized by the Son-Narmada Fault/Lineament (SNF/L) and Central Shear (CIS) Zone, has long intrigued researchers due to its implications for active tectonics, particularly in the Narmada basin. In this study, we employ geomorphic and morphotectonic indices to elucidate the neotectonic activity in the Upper Narmada basin (UNB) of central India. Utilizing SRTM-DEM data, we analyze morphometric and morphotectonic parameters to shed light on the development of drainage patterns and active tectonics within the basin. Our findings reveal a pronounced influence of tectonics on basin evolution, as evidenced by high bifurcation ratios indicative of intense tectonic activity and elevated ruggedness values suggestive of heightened erosion susceptibility. The predominant ENE-WSW orientation of the Son Narmada South Fault (SNSF) and Son Narmada North Fault (SNNF), aligned with major lineament trends, exerts control over the Narmada River drainage network. Additionally, the high value (<50) of the asymmetric factor reveals the significant tectonic influence on the Upper Narmada basin, while the transverse asymmetric factor and stream length index values further corroborate the basin's susceptibility to active tectonics. Notably, the abrupt elevation changes (200–600 m asl) reflected by Dhuandhar, Kapildhara and other falls along the course of Narmada provide compelling evidence of neotectonic activity. Thus, we assert that morphotectonic analyses employing Digital Elevation Maps, satellite imagery, and SRTM-DEM data represent an efficacious approach for investigating complex basin morphotectonics.

Quaternary morpho-stratigraphic evolution of the eastern Campo Imperatore basin (Gran Sasso range, central Italian Apennines) and tectonic implication

ABSTRACT Geological survey and geochronological analyses were conducted in the Campo Imperatore plain to understand its Quaternary morpho-sedimentary and tectonic evolution. In the Late Pliocene-Early Pleistocene, low relief energy and steady and warm climatic conditions promoted a long phase of areal peneplanation, resulting in the formation of gently sloping landscape. With further regional uplift and changes in frequency/amplitude of the glacial-interglacial cycles (Early-Middle Pleistocene transition) and after establishment of the expansion-contraction cycles of the Apennine glaciers (Middle Pleistocene), the morpho-sedimentary processes become highly dynamic. In Middle Pleistocene, more than 100 meters of breccias deposited all along the slopes of the Gran Sasso range, followed by higher frequency processes of sedimentation, erosion and pedogenesis of Middle-Late Pleistocene to Holocene fluvio-glacial deposits. These have been progressively offset by synthetic and antithetic normal faults belonging to the Gran Sasso fault system, a 40-km-long seismogenic structure which released in the past earthquakes of Mw~7.

Coseismic deformation analysis of the 2017 Milin Ms 6.9 earthquake in the Namche Barwa Syntaxis: Implications for regional tectonics

The 2017 Milin earthquake occurred near Namche Barwa on the southeastern Tibetan Plateau. This research employed Sentinel-1 imagery to capture the corresponding coseismic deformation field and adopted a joint inversion approach using geodetic measurements and teleseismic waveform data to assess earthquake mechanics. The coseismic deformation indicated distinct differential movements, indicating a thrust movement of this fault with uplift in northeast side. The calculated seismic moment magnitude was Mw 6.5, with the fault striking of 305° and a dip angle of 72° The earthquake hypocenter was located at a depth of approximately 10 km, and the maximum fault slip was approximately 1.08 m. The event was attributed to the northwestern segment of the Xixingla fault. Numerical simulations indicated a peak ground velocity of approximately 0.3 m/s. The northwestern segment of the Xixingla fault was identified as the seismogenic fault of the event. Furthermore, the Coulomb stress analysis indicates that the earthquake induced stress loading on the Dongju–Milin and Jiali faults. The surface strain analysis reveals a region of high strain adjacent to the fault. The 2017 Milin earthquake occurred because the Xixingla fault underwent predominantly thrust-type sliding due to the continuous tectonic stress induced within the Tibetan Plateau. Notably, the middle segment of the Xixingla fault currently experiences relatively low seismic activity and is in a state of stress and strain accumulation. Thus, strong earthquakes may occur within the middle segment of the Xixingla fault.