Eurasian Plate Research Articles

New insights into the crustal structures of the Arabian Plate and surrounding plates unveiled from the crustal thickness model and its implications for geodynamics

Geodynamics of the Arabian Peninsula is less understood as crustal structures are not well delineated due to uneven distribution and lack of seismic measurements and ground based geophysical data in the Arabian interior. To address this, we delineated crustal structures in the Arabian Peninsula through the creation of a crustal thickness model from the inversion of GOCO60s gravity field model, which revealed details on the underlying crustal structures. Our model revealed strong crustal thickness variations in the Zagros fold belt that indicates high deformational history and crustal reworked, which also reflect directional collisional events between the Arabian and Eurasian Plates, similar to the Himalaya type as the result of mantle processes. The resolved crustal structures also reveal a relatively slow rifting process on the southern end of the Red Sea than at the northern end, which resulted in the bulging of crust in the southern part of Zagros Fold Mountains. Further, folding and bulging of crustal structures is more intense near the Arabian Platform and slower on the Eurasian side, which could indicate a relatively stable Eurasian plate compared to the geodynamically active Arabian Plate. Overall improvement in our high-resolution crustal thickness model yields an improved representation of crustal structures over previously derived models of the Arabian Peninsula and the Surrounding plates that indicates a variation in the Proterozoic crust in Arabian Plate, possibly indicating a secular variation in the crustal structure.

Current tectonic deformation of the Sulaiman range (Pakistan) with InSAR

Summary In Pakistan, the relative displacement between the Indian and Eurasian plates is accommodated by a left lateral transpression zone comprising the Chaman and Ghazaband faults and the Sulaiman Range. The current tectonic deformation of the Sulaiman Range is known only from some focal mechanisms and a few neotectonic studies. In this study, we propose an InSAR quantification of current tectonic deformation using the Sentinel 1 satellite. Velocity maps for the ascending and descending tracks enabled us to locate active faults affected by creep: the Harnaï and Kingri strike-slip faults, and the Gwal-Bagh thrust. We propose a numerical simulation that considers these faults as well as the level of detachment fold-and-thrust belt. Our results suggest the existence of out-of-sequence deformation along the Gwal-Bagh thrust, creep along the Harnaï and Kingri strike-slip faults, and slip along the décollement of the Sulaiman Range. The eastern part of the Sulaiman Range is characterized by a partitioning of the deformation with a left lateral strike-slip along the N170° Kingri fault and an eastward thrust. In contrast, the western part is characterized by north-south compressive deformation associated with right lateral strike-slip on the Harnaï N120° fault. Modelling of the co-seismic deformation of the 21 October 2021 earthquake shows that this earthquake occurred on a fault with a ramp geometry but affected by a strike-slip motion.

Identifying geological structures in the Pamir region using non-subsampled shearlet transform and gravity gradient tensor

Summary The Pamir tectonic zone originates from the intense collision of the Indo-Eurasian plate. Identifying the faults in the Pamir region region is essential for elucidating the collision mechanism and seismic characteristics. This paper compares the effect of the two-dimensional discrete wavelet transform (DWT2D) and the non-subsampled shearlet transform (NSST) on gravity field separation through synthetic model gravity field experiments. The results show that NSST can avoid the Gibbs phenomenon of DWT2D and better maintain the gravity field distribution. The surface gravity disturbances data of the Global Gravity Model Plus (GGMplus) with a high-spatial resolution (7.2 arcsec or approximately 200 m) is employed to separate the region-residual gravity fields in the neighbouring domain of the Pamir region based on the NSST. Furthermore, the gravity gradient tensor (GGT) is computed, and the correspondence between the GGT and the location and strike of the surrounding faults is analyzed. The results show that the GGT component and its various combinations can effectively identify shallow and deep faults, the residual field GGT and its combinations can effectively identify the distribution and direction of shallow faults, and the regional field GGT and its combinations can effectively identify the distribution and direction of deep faults. The existence of north-south trending faults in the Pamir-Hindu Kush region is widely accepted. However, our study has revealed an east-west trending concealed fault in the deep areas of the Hindu Kush (Depth > 200 km). This finding provides significant insights for studying the bidirectional subduction of the Indian and Eurasian plates. This research not only helps us to analyze the tectonic characteristics of the shallow and deep parts of the region separately but also provides complementary information for investigating the distribution of deep underground faults, especially when fault inversion of intermediate to deep source earthquakes is limited by factors such as uncertainty in source depth and complexity of seismic wave velocities.

The 2020 Mw 6.4 Koryak Highlands earthquake illustrates hidden seismic hazards in the northern Pacific Cordillera

Summary On 9th January 2020, a Mw 6.4 earthquake struck the central Koryak Highlands of eastern Siberia, northeast of the diffuse triple junction between the North American, Pacific and Eurasian plates. The largest earthquake recorded in the central Koryak Highlands to date, it provides an excellent opportunity to study the little-known active tectonics of this remote, sparsely instrumented region. We mapped coherent, coseismic surface deformation with Sentinel 1 Interferometric Synthetic Aperture Radar (InSAR), making this one of the highest-latitude earthquakes to be captured successfully with satellite radar, in spite of the rugged, snow-covered terrain. Elastic dislocation modelling, teleseismic back-projections, calibrated hypocentral relocations, and teleseismic moment tensor solutions are used to resolve a left-lateral fault trending northwestwards, proximal but perpendicular to a regional geological suture zone, the Khatyrka-Vyvenka Thrust. The earthquake probably ruptured unilaterally northwestwards along a 20 km long segment that appears indistinct in the local topography, and likely generated no surface rupture. We interpret that these observations are indicative of a structurally immature fault zone and estimate a seismogenic zone thickness of 10–15 km. The Koryak Highlands earthquake illustrates how terrane boundaries within cordilleran belts may continue to accommodate tectonic strain long after accretion, resulting in significant earthquakes even along hidden faults.

Spatiotemporal Growth of Seismic‐Scale Syn‐Flexural Normal Faults in the German Molasse Basin

ABSTRACTFlexure in pro‐foreland basins results from the interplay between (sub)surface loading, foreland plate strength, inherited crustal architecture, and the degree of plate coupling. It is expected that lateral variations in these controlling mechanisms will result in along‐strike variations in the flexural profile of the foreland basin. This will directly influence the position and width of the forebulge, thereby altering the associated extensional stress field in space and time around which syn‐flexural normal faults accommodate deformation. As such, spatiotemporal variations in the growth of the syn‐flexural normal faults in foreland basins may provide valuable information regarding the evolution of an orogen‐foreland basin system. However, the relation between syn‐flexural normal fault growth and the mechanisms controlling foreland basin flexure remains underexplored. Here, we quantify lateral and vertical throw distributions for growth strata of syn‐flexural normal faults in the German Molasse Basin. This allowed us to develop a 4D fault growth model. Our results indicate that the flexure in the German Molasse was associated with both the nucleation of new faults and selective reactivation of pre‐flexural faults, with the latter depending on fault burial depth at the onset of flexure. Furthermore, our results suggest that localisation of the extensional strain and deformation at the top of the European plate during flexure controlled the nucleation site of the syn‐flexural normal faults in the German Molasse. Additionally, the spatiotemporal variation in the onset of syn‐flexural normal fault activity suggests a northward migration rate of 7.8 mm/year of the orogen‐foreland basin system. This is consistent with previous estimates based on other independent methods. Lastly, a west‐to‐east increase in cumulative syn‐flexural offsets down‐dip the normal faults in the German Molasse Basin may have been controlled by orogen‐parallel lithospheric strength variations in the downgoing European plate.

P‐ and S‐Wave Velocity Structures and the Influence of Volcanic Activities in the East Java Area From Seismic Tomography

The tectonic complexity in Indonesia has made it one of the most interesting targets for studies on seismic tomography. The Indian oceanic plate sunk beneath the Eurasian continental plate, forming the subduction zone in Southern Indonesia. This activity led to the formation of volcanoes along the Sunda Arc, including East Java, the research area covered in this study. This research is mainly aimed at identifying the influence of the volcanic activities by tomography analysis. The data of the earthquakes was recorded by 22 seismic stations of the Indonesia Tsunami Early Warning System (InaTEWS) seismic network in the period of 2009–2017. The tomographic image was analysed by exploring the anomalies of primary (P)‐ and secondary (S)‐wave velocities and Vp/Vs ratio. The result shows the presence of a low‐velocity zone with a high Vp/Vs ratio found around the volcanic area, which is correlated with the partial melting zone or magma chamber. The low‐velocity zone was observed at the depth range of 27–155 km, which was also correlated with the subducted slab beneath Java Island. This leads to an assumption that there is an interlinked volcanic system which extends from west to east of Java.

Penerapan Collective Risk Model dalam Penentuan Premi Asuransi Bencana Alam

Indonesia is prone to natural disasters such as volcanic eruptions, earthquakes, and tsunamis due to tectonic activity involving the Indo-Australian and Eurasian plates. Therefore, the government introduced natural disaster insurance in 2018 to mitigate financial losses caused by such events. This study employs the Collective Risk Model (CRM) to determine premium rates. The Poisson process and Gamma distribution are utilized to estimate the frequency and severity of natural disasters. Estimation is performed using Maximum Likelihood Estimation (MLE), while premiums are calculated based on the expected value and variance of aggregate risk using the Expected Value Principle and the Standard Deviation Principle. The results show that the expected value and variance of claim frequency are both . Furthermore, claims for losses follow the Gamma distribution, with an expected value and variance of and . The mean and variance of aggregate claims are Rp and Rp . The Standard Deviation Principle produces lower premiums than the Expected Value Principle under the same loading factor.

Thrust-dominated unilateral rupture of a blind listric fault associated with the 2024 Hualien earthquake

The 2024 Hualien Mw 7.4 earthquake struck the Longitudinal Valley, which accommodates the partial collision between the Eurasian and Philippine Sea plates. As the most significant event in Taiwan since the 1999 Chi-Chi Mw 7.6 earthquake, it presents a distinct opportunity for investigating the current rupture behavior related to the northern Longitudinal Valley. The spatiotemporal rupture process of the Hualien earthquake is reconstructed through the analysis of geodetic and seismic observations. We demonstrate that the Hualien earthquake occurs on a blind listric fault, manifesting as a unilateral rupture primarily extending toward the NNE. The slip distribution exhibits a compact pattern dominated by the thrust faulting. As indicated by the increased Coulomb failure stress, the 2022 Chihshang Mw 6.5 and Mw 6.9 earthquakes cause a triggering effect on the Hualien earthquake. The Hualien earthquake also promotes the occurrence of a seismic swarm at the southernmost tip of its rupture area.

Role of Intraplate Strike-Slip Earthquakes in Accommodating Convergence Across the Eastern Himalayan Plate Boundary System

Abstract North-East India, at the eastern extremity of the Himalaya, is one of the most rapidly deforming intraplate regions. The tectonics of this region is shaped by oblique convergence between two nearly perpendicular plate boundaries of the Eastern Himalaya and the Indo-Burman convergence zone. This region of distributed deformation is associated with intraplate strike-slip and oblique-slip earthquakes. We model the source mechanisms of six recent moderate-to-strong intraplate earthquakes (5.0≤ Mw ≤6.7) using teleseismic P- and SH-waveform inversion and use source directivity and rupture back-projection, for the largest event, to isolate the fault plane. We combine these mechanisms with previous earthquake source studies, GPS-geodetic-velocity vectors, and GPS-derived strain-rate field, to build a kinematic model. Majority of the earthquakes have strike-slip to oblique-slip (thrust) motion and originate in the middle-to-lower crust. These reveal that the entire NE-Indian crust is seismogenic. The oblique-thrust earthquakes occur due to high in-plane compressive stresses in the flexed Indian Plate. The region north of the Dawki Fault, in the vicinity of the Kopili and Dhubri-Chungthang Fault Zones, deforms through dextral strike-slip faulting and anticlockwise rotation of blocks along NW-SE trending transverse structures. The transitional crust of the Bengal Basin has several NE-SW trending paleo-rifts which are reactivated as sinistral strike-slip faults and the intervening blocks undergo clockwise rotation. The oblique convergence between the Indian and Eurasian Plates is partitioned into dextral and sinistral strike-slip motions across NE-India. The GPS velocity vectors and the strain-rate field indicate that the region north of the Dawki Fault has strong coupling between the surface deformation and the earthquake faulting. However, in the region south of the Dawki Fault, the coupling is weaker. The strike-slip earthquakes beneath Indo-Burma probably occur due to a complex interplay between the trench-normal slab-pull forces and lateral-shear forces set up by the strike-parallel components of the interplate-coupling resistance and the mantle-drag forces.

Discovery of Marine Macrozoobenthos Fossils in the River of Wonocolo Geosite, Indonesia

Wonocolo Geosite is a geoheritage known for the existence of the Kawengan Anticlinal Trap, which is the only one in the world, causing oil to be found in shallow locations. This condition has allowed for traditional mining since the Dutch colonial era and continues today. Geological history states that the anticlinal structure was formed when the Indo-Australian plate collided with the Eurasian plate, resulting in folds and uplift of the seafloor above the surface. However, there has not been much research supporting the truth of the theory. Therefore, evidence is needed to support the uniqueness of the Wonocolo Geosite. The fossil collection method was carried out simultaneously with the collection of substrates at the upstream, middle, and downstream riverbeds using 20 cm diameter PVC pipes at a depth of 10 cm.This study found marine macrozoobenthos fossils during substrate sampling in the upstream, middle, and downstream river beds using a PVC pipe with a diameter of 20 cm at a depth of 10 cm. The samples were then identified in the laboratory, revealing fossils from the deep sea. The fossils found include Azooxanthellate (Cnidaria), which lives at depths of up to 2000 m; Dentaliida (Mollusca) which lives at depths of 500-7000 m and Foraminifera which also live in the deep sea. This phenomenon is unusual, considering that the fossils were found in a river far from the sea at an altitude of 250 MASL. Therefore, the discovery of marine macrozoobenthos fossils at the bottom of the Wonocolo River strengthens the theory of the formation of the Wonocolo Formation from a raised seabed which is also an important asset supporting the Wonocolo Geoheritage.

SPECTRAL and SOURCE PARAMETERS of NORTH CAUCASUS EARTHQUAKES in 2020

The spectral parameters of the sources of 38 earthquakes in the North Caucasus were determined from the displacement spectra of S-waves for the period 2020. The calculations used events with an energy classes KR=9.3–12.9 and waveforms from stations with epicentral distances 50–250 km. The values of local magnitudes ML were calculated using a new calibration curve. The calculation of source spectra was carried out in the SEISAN program based on the frequency-dependent quality factor Q(f). The following values were obtained: 0 – spectral density, f0 – corner frequency, M0 – scalar seismic moment, Mw – moment magnitude,  – stress drop, and RMS for each of the parameters. For 30 earthquakes with KR=9.0–12.9 focal mechanisms were calculated, which are represented by reverse faults (including reverse faults with strike-slip components – 73 %), normal faults – 20 % and strike-slip – 7 %, which corresponds to deformation processes in the collision zone of the Arabian and Eurasian plates.

Seasonal variations of permanent stations in close vicinity to tectonic plate boundaries

Abstract With the increasing use and popularity of GNSS, there is a growing emphasis on understanding the characteristics of the signals and the impact on their outputs. This article provides an analysis of the daily solution of Iceland permanent GNSS stations daily time series in near proximity to tectonic plate boundaries, aiming to investigate seasonal changes in coordinate values. As a part of the study, the data are prepared, and a function is fitted using the method of least squares, providing for further analysis coefficients and the quality of fit. The research reveals no unequivocal correlation between location and the height of annual amplitudes, except for the stations situated on the Vatnajökull ice cap. It consistently demonstrates higher seasonal changes compared to others, which indicates the influence of snow and water load. Excluding these results, the annual displacement for horizontal components is approximately 1 mm, while the average yearly amplitude for vertical components is almost 5 mm. The results concerned with the Up generally exhibit larger values compared to the other components. It is observed that the mean station variations are higher for the Eurasian plate. The quality of the fit, with regard to outliers and RMSE, does not demonstrate a correlation between the duration of the time series. Furthermore, the average percentage of detected outlier observations is higher for the North American plate.

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.

Contingency Planning for Tourism Development in Volcanic Disaster-Prone Areas in Indonesia

Abstract Indonesia is geologically recognized as a complex region due to its location at the convergence of the Eurasian, Pacific, and Indo-Australian tectonic plates, making it highly susceptible to geological hazards. Among these hazards, volcanic activity poses a significant threat, with 127 volcanoes identified as potential eruption hazards. Volcanic disasters often result in substantial loss of life and property. The natural beauty and allure of volcanic landscapes attract numerous tourists, leading to heavy concentrations of people in potentially dangerous areas. If tourism in these regions is not managed effectively, the risk of disasters may increase. Catastrophic volcanic eruptions, such as those at Lokon (1991), Semeru (2000), Bromo (2004), and Marapi (2023), have resulted in considerable casualties among tourists. This paper aims to provide essential considerations for tourism stakeholders in active volcanic regions to enhance safety and reduce fatalities associated with volcanic eruption hazards. It will explore the challenges and risks posed by tourism in these areas, emphasizing the need for comprehensive contingency planning. To safeguard tourists, future tourism development in areas prone to volcanic disasters must incorporate disaster risk assessments, early integration of volcanic hazard maps into tourist site designs, adherence to technical guidance from volcanological institutions, implementation of early warning systems, and regular dissemination of volcanic hazard mitigation measures.

Assessment of Geoconservation Potential in Part of Sukabumi Area Using Swot Analysis Based on Regulation by Ministry of Energy and Mineral Resources no 32 of 2016

Abstract Sukabumi located in West Java, Indonesia. The regional structure of the Sukabumi region is influenced by the convergence plate of the Eurasian and East Indies-Australia plates. The geological dynamic creates uniqueness and threat in the area studied. The uniqueness of the Sukabumi Region with the existence of the Cimandiri fault gives rise to the natural beauty that is considered to have potential as a geotourism area. Geotourism needs to be maintained and preserved as Geological Nature Reserve Areas (GNRA). The background of this research is the lack of public attention to the geotourism potential areas in Sukabumi. The study method uses thematic map analysis with the overlapping and the SWOT (scoring)-methods at 3 study areas: Cikundul, Santa Sea, and Karang Para. The potential of GNRA is given weight considering the regulation of the Minister of Energy and Mineral Resources No. 32 of 2016. The results of this study include development directions and the potential maps of Geological Reserves in the Sukabumi Region, West Java Province. The research output is to provide development directions related to the utilization and protection of Sukabumi geological uniqueness as a Geological Nature Reserve Area.

Optimization of disaster management vessel networks in integrated disaster management governance in Indonesia using genetic algorithm

Abstract Indonesia is highly susceptible to natural disasters due to its location at the convergence of three major tectonic plates: the Indo-Australian, Eurasian, and Pacific plates. These disasters significantly impact the nation’s economic development. This study focuses on natural hazards such as earthquakes, tsunamis, volcanic eruptions, landslides, floods, and flash floods. Currently, maritime disaster management primarily involves ships from the Indonesian National Armed Forces (TNI). However, this often leads to mismatches between disaster-prone areas and the locations of available ships, resulting in delayed emergency response times and higher disaster management costs. In addition to TNI ships, the government has vessels from the National Search and Rescue Agency (BASARNAS) and the Indonesian Maritime Security Agency (BAKAMLA) that could be utilized for disaster management. There are also situations where certain response functions cannot be effectively performed by ships, leading to inadequate assistance for disaster victims and potentially increasing fatalities. This research aims to optimize the use of existing ships for disaster management by considering operational costs and coverage areas through the application of the Genetic Algorithm (GA) method. GA is used to identify the optimal combination of ships that minimize costs and maximize coverage areas. The findings of this study provide several ship combinations suitable for responding to natural disasters in Indonesia, which can serve as valuable input for the government in enhancing disaster management efforts.

Himalayan Leucogranites: Rare-metal Resources

Himalayan leucogranites were once overlooked for rare-metal resources because they initially were thought to have formed by in-situ partial melting of underlying high-grade metamorphic rocks. However, recent findings have revealed widespread rare-metal mineralizations of Be, Nb/Ta, Li/Rb/Cs, and W/Sn associated with leucogranites in the area, suggesting these mineralizations resulted from extensive fractionation of leucogranitic magmas during long-distance magma transport along the low-angle South Tibetan Detachment System. When combined with coeval Au-Sb-Pb/Zn mineralizations in the Himalayas of the Indian plate, and porphyry Cu-Mo mineralizations in the Gangdese of the Asian plate, a specific Himalayan-type mineralization is proposed to describe the metallogenesis related to the exhumation of the subducted Indian continent, coinciding with the uplift of the Himalayan mountains.

Earthquake risks assessment and urban vulnerability: Case of Nador city, northeast Morocco

This study introduces an innovative approach to assessing seismic risks and urban vulnerabilities in Nador, a coastal city in northeastern Morocco at the convergence of the African and Eurasian tectonic plates. By integrating advanced spatial datasets, including Landsat 8–9 OLI imagery, Digital Elevation Models (DEM), and seismic intensity metrics, the research develops a robust urban vulnerability index model. This model incorporates urban land cover dynamics, topography, and seismic activity to identify high-risk zones. The application of Landsat 8–9 OLI data enables precise monitoring of urban expansion and environmental changes, while DEM analysis reveals critical topographical factors, such as slope instability, contributing to landslide susceptibility. Seismic intensity metrics further enhance the model by quantifying earthquake risk based on historical event frequency and magnitude. The calculation based on higher density in urban areas, allowing for a more accurate representation of seismic vulnerability in densely populated areas. The modeling of seismic intensity reveals that the most susceptible impact area is located in the southern part of Nador, where approximately 50% of the urban surface covering 1780.5 hectares is at significant risk of earthquake disaster due to vulnerable geological formations, such as unconsolidated sediments. While the findings provide valuable insights into urban vulnerabilities, some uncertainties remain, particularly due to the reliance on historical seismic data and the resolution of spatial datasets, which may limit the precision of risk estimations in less densely populated areas. Additionally, future urban expansion and environmental changes could alter vulnerability patterns, underscoring the need for continuous monitoring and model refinement. Nonetheless, this research offers actionable recommendations for local policymakers to enhance urban planning, enforce earthquake-resistant building codes, and establish early warning systems. The methodology also contributes to the global discourse on urban resilience in seismically active regions, offering a transferable framework for assessing vulnerability in other coastal cities with similar tectonic risks.

Change in the direction of Early Cretaceous tectonic extension in eastern North China Craton as the result of Paleo-Pacific/Eurasian plate interaction

How the subduction direction of the Paleo-Pacific plate beneath the Eurasian plate changes in the Early Cretaceous remains highly controversial due to the disappearance of the subducted oceanic plate. Intraplate deformation structures in the east Asian continent, however, provide excellent opportunities for reconstructing paleostress fields in continental interior in relation to the Paleo-Pacific/Eurasian plate interaction. Anisotropy of magnetic susceptibility (AMS), geological, and geochronological analyses of post-kinematic mafic dykes intruding the detachment fault zone of the Wulian metamorphic core complex (WL MCC) in Jiaodong Peninsula exemplify emplacement of mantle-sourced dykes in a WNW–ESE (301°–121°) oriented tectonic extensional setting at ca. 120 Ma. In combination with the results from our previous kinematic analysis of the MCC, a ca. 21° clockwise change in the direction of intraplate extension is obtained for early (135–122 Ma) extensional exhumation of the MCC to late (122–108 Ma) emplacement of the dykes. Such a change is suggested to be related to the variation in subduction direction of the Paleo-Pacific plate beneath the Eurasian plate, from westward (pre-122 Ma) to west-northwestward (post-122 Ma).

Lithospheric structure beneath Tibet based on gravity data from World Gravity Map 2012

An appreciation of the geodynamics of the Cenozoic great collision between the India and Eurasia plates necessitates an understanding of the lithospheric structure beneath Tibet. Here, we utilise the World Gravity Map 2012 (WGM2012) gravity data to derive the lithospheric density variations and gravity anomaly beneath Tibet, employing the multi-scale inversion and regularised downward continuation methods. The findings indicate that the E-W striking structures persist to a depth of 90 km. The deep lithospheric mantle displays block-like density anomalies that exhibit a distinct N-S trend with increasing depth. The results clearly indicate a decoupling between the lithospheric crust and mantle. It is possible that changes may occur along the Indian plate’s subduction front, which subducts to the south of 32°N along the western portion of the subduction zone, as indicated by the apparent density of the lithospheric mantle. In contrast, in the central and eastern regions, the Indian lithosphere appears to subduct primarily north of the Indus-Tsangbo suture zone (30°N), where it may undergo tearing and delamination beneath the Lhasa block. This phenomenon promotes the convection of soft materials and the upwelling of mantle material, which causes the Tibetan lithosphere to thin and stretch in an E-W direction. At a depth of 150 km beneath central Tibet, alternating lower-density belts trending north–south may be connected at greater depth. These structures likely reflect lithospheric deformation, which plays a crucial role in shaping the geodynamics of the region.