Thrust Zone Research Articles

Structural control on a Ypresian karstic aquifer revealed by an integrated geophysical and geological approach: the Mateur imbricated thrust zone (northern Tunisia)

We present a characterization of a poorly studied karstic aquifer, documenting the geometry, resistivity properties and the control of structural discontinuities that affect the Ypresian limestone cropping out in the Mateur imbricated thrust zone in northern Tunisia. The karst system was produced by meteoric diagenesis. Geophysical methods and field investigations were useful in extracting geological features. First, our findings suggest that N110–N140 directions are the preferred dissolution paths orientated parallel to strike-slip and extensional faults. Second, the gravity data analysis (regional–residual separation, horizontal gravity gradient and Euler deconvolution) show a particular tectonic node as a junction of the NE–SW and NW–SE directions. Third, 2D electrical resistivity models display various karstification typologies with high (>1000 Ω m), medium (between 200 and 1000 Ω m) and low (<100 Ω m) electrical resistivity zones. These electrical resistivity models have contributed to the establishment of a conceptual structural model of the global karst features. Finally, 2D electrical resistivity tomography (ERT) and 1D time-domain electromagnetic analysis highlighted the presence of potential water zones integrated into the aquifer. Thematic collection: This article is part of the Karst: Characterization, Hazards & Hydrogeology collection available at: https://www.lyellcollection.org/topic/collections/karst

Mineral resources of the Gandaki Province of Nepal: present status and prospect

Mineral resources serve as the foundation of prosperity for any country or community. However, the process of prospecting and exploring these resources is time-consuming and involves financial risks. It requires the combined expertise of both geoscientists and mining engineers, encompassing academic knowledge and professional skills. In this research, we provide an overview of the mineral resources within the Gandaki province of Nepal and evaluate their present status. The main objective is to examine the current status and potential of mineral resources in the province. To achieve this, we extensively utilize available reports, journal articles, and online sources. We gather both primary and secondary data on mineralization. Additionally, we systematically list the potential locations of all documented mineral resources within the Gandaki province, along with their GPS coordinates. Based on the current geological and mineralogical investigations, as well as our understanding of the province’s mineral resources, we identify ten minerals or mineral groups with potential economic value: iron, copper, uranium, tourmaline, syenite, thermal springs, limestone, dolomite, slate, and meta-basic rocks like amphibolite. We strive to provide geological evidence and context for supporting the presence of these minerals.
 In general, iron mineralization is observed as sedimentary deposits, exhibiting a syngenetic nature. Many copper ores are hydrothermally deposited originating from the underlying meta-basic rocks like amphibolite. The region is also known for its abundance of gemstones, including quartz crystals, garnet, kyanite, and tourmaline. These minerals are concentrated in the vicinity of the Main Central Thrust zone and its surrounding areas. Moreover, the province has significant potential for high-quality dimension stones for flooring, roofing, and pavements such as quartzite, slate, phyllite, schist, granite, and gneisses. Additionally, there are ample opportunities for the extraction of construction materials like sand and gravel from the river terraces and natural rock outcrops. Nevertheless, a systematic study focused on prospecting, exploration, and utilization of these potential and possible mineral resources is imperative for an accurate economic evaluation. To achieve this, the provincial government must develop plans and policies to facilitate the development of its own mineral resources. Furthermore, establishing strong collaboration between professionals and academia is crucial to make well-informed investments in the mineral sector. Considering the present status of minerals, the Gandaki province of Nepal holds promising prospects for harnessing its mineral resources for sustainable development.

Structure of the Assynt window, Moine Thrust Zone and relationship of thrusts to alkaline igneous complexes, Caledonian orogeny, NW Scotland

AbstractThe Moine Thrust Zone forms the Caledonian orogenic thrust front where the Moine Supergroup metamorphic rocks have been thrust westward across the Laurentia plate stable foreland, comprising Archean-Proterozoic granulite and amphibolite facies rocks (Lewisian gneisses), with unconformably overlying Mesoproterozoic and Neoproterozoic Torridonian clastic sediments and Cambrian-Ordovician passive margin sedimentary rocks. Four major thrusts beneath the Moine thrust in the Assynt window include the (i) Ben More Thrust, which places the Loch Ailsh syenite intruded into Lewisian basement and Cambrian-Ordovician sedimentary rocks over the Sole thrust sheet, (ii) Glencoul thrust, which places Lewisian basement and folded cover rocks over Cambrian-Ordovician sedimentary rocks, (iii) Borralan thrust, which carries a large alkaline syenite intrusion beneath the Ben More roof thrust and (iv) the Sole thrust sheet, which carries imbricated Cambrian-Ordovician sedimentary rocks and lamprophyre sills over the stable foreland. Three further thrust sheets within the Lewisian basement gneisses are now recognised through restoration of balanced cross-sections, which were responsible for doming of the Assynt window. Although the Moine thrust is mapped as a single line on the map it encompasses, (a) deep ductile shear zone formed of mylonites derived from hangingwall Moine schists, footwall Cambrian quartzites and Ordovician limestones, and basement Lewisian gneisses, (b) roof thrust of the Glencoul and Ben More Thrust sheets and (c) brittle out-of-sequence motion where the Moine schists have been thrust over mylonites, which directly overlie the stable foreland (Knockan Crag).

Decoding the Late Pleistocene-Holocene Terrace Evolution along the Main Frontal Thrust Zone, Northeastern Himalayas, India: Insights from Tectonic Geomorphology, Sedimentology, and Optical Dating

Abstract Fluvial archives are the best preserved and provide valuable means of obtaining information pertaining to climate and tectonic deformation of an area. The present study is an attempt to reconstruct the landform evolution history in the northeastern Himalayan region of India. Based on field investigation, tectonogeomorphic mapping, and OSL dating, strath and various levels of cut-and-fill terraces were investigated along the mountain front. Optically stimulated luminescence ages of the terrace sequences suggest that the valley incision occurred in three phases, at ~23 ka, ~14 ka and ~9 – 3 ka and one phase of aggradation was also identified at ~ 7 ka. The strath terraces suggest two major episodes of tectonic uplift in the region around ~ 8 ka and ~ 6 ka. This yields an uplift rate of 0.4 and 0.9 mm/yr. The result from the study suggested that the rapid rejuvenation along the mountain front led to the formation of the strath terraces with enhanced incision of the fluvial terrace and influenced the sedimentary architecture of valley fill sequences.

Structural architecture and late Cenozoic tectonic evolution of the Ulsan Fault Zone, SE Korea: New insights from integration of geological and geophysical data

Integration of geological and geophysical data is essential to elucidate the configuration and geometry of surface and subsurface structures, as well as their long-term evolution. The NNW–SSE-striking incised valley and parallel mountain range in the southeastern margin of the Korean Peninsula, extending 50 km from Gyeongju to Ulsan cities, are together regarded as one of the most prominent geographical features in South Korea. This paper presents an investigation into the structural architecture and deformation history of the valley and mountain range during the late Cenozoic based on combined data from field observations and gravity and electrical resistivity surveys. Our results based on integrated and reconciled geological, structural, and geophysical data are as follows. First, the incised fault valley can be divided into 1) the northern part, which comprises several distributed buried or exposed fault strands; and 2) the southern part, which comprises a concentrated deformation zone along the eastern margin of the valley. Different deformation features between the two parts are controlled by the lithology of host rocks and by the location and geometry of the neighboring major structures, that is, the Yeonil Tectonic Line (YTL) and the Yangsan Fault. Second, we defined the Ulsan Fault Zone as a NNW–SSE-to N–S-striking fault within the incised valley and along the eastern margin of the valley. In particular, the constituent strands located along the eastern margin of the valley have acted mainly as an imbricate thrust zone, characterized by an east-side-up geometry with moderate to low dip angles and reverse-dominant kinematics in the shallow subsurface during the Quaternary. Third, reactivated strands within the Ulsan Fault Zone during the Quaternary are interpreted as shortcut faults developed in the footwall of Miocene subvertical structures, predominantly the YTL. In addition, movements on the Ulsan Fault Zone and the YTL during the Miocene to Quaternary were arrested by the NNE–SSW-striking Yangsan Fault, which was a prominent and mature pre-existing structure. Our results highlight the spatiotemporal structural variation in SE Korea and emphasize the strong control of the configuration and geometry of pre-existing structures on the distribution and characteristics (i.e., geometry and kinematics) of the subsequent deformation under changing tectonic environments through the late Cenozoic.

Structural Styles of Thrust Zones of the Urals and Pay-Khoi Foredeep

Structural Styles of Thrust Zones of the Urals and Pay-Khoi Foredeep

Structural and geochronological constraints for the Mesozoic nappe structures of the Taqian–Fuchun thrust zone, eastern Jiangnan orogenic belt, South China

The NE‐trending Jiangnan orogenic belt has experienced multi‐tectonic episodes since the Mesozoic separates the Yangtze Block in the north‐west from the Cathaysia Block in the south‐east. The Taqian–Fuchun thrust zone in north‐east Jiangxi Province is located in the eastern Jiangnan orogenic belt. It is considered as an essential unit to understand the geometry, kinematics and dynamics of the Mesozoic nappe structures in the eastern Jiangnan orogenic belt and an ideal region to reveal the Mesozoic tectonic evolution in South China. Here, we present new detailed structural data coupled with zircon U–Pb and apatite fission‐track dating studies, establishing a four‐stage deformation history and describing the geometry, kinematics, ages and dynamic background. The Middle–Late Triassic NW–SE compression event (D1, 243–226 Ma) is mainly characterized by regional angular unconformity between the Lower and Upper Triassic and asymmetric folding of the underlying strata. The associated regional NW–SE shortening was related to the intercontinental collision. The Middle–Late Jurassic NW–SE compression event (D2, 175–160 Ma) is characterized by the angular unconformity between the Middle Jurassic and Cretaceous and the SE‐vergent imbricate nappe structures. The shortening has been associated with the NW‐ward subduction of the Paleo‐Pacific Plate. The Late Jurassic–Cretaceous NW–SE extension event (D3, 160–67 Ma) includes the transition stage from compression to extension (160–145 Ma) and the intensive extension stage (145–67 Ma). The former is characterized by the development of the extensional detachment structures and intermediate‐acid magmatism, while the latter is characterized by the development of Cretaceous extensional sedimentary basins and A‐type granites. This extension was correlated to the slab roll‐back of the Paleo‐Pacific Plate. The Paleocene–Eocene compression event (D4, 67–35 Ma) is manifested by the thrusting of metamorphic rocks in the Shuangqiaoshan Group to the Cretaceous red beds. This shortening possibly originated from the collision between the India and Eurasian Plates. This study provides new constraints on the Mesozoic structural style and establish a reliable geochronological framework of the Mesozoic tectonic evolutions of the eastern Jiangnan orogenic belt.

Structural Styles of Thrust Zones of the Urals and Pay-Khoi Foredeep

The article presents an interpretation of geophysical data characterizing the structure of the frontal fold and thrust zones of the Urals and Pay-Khoi, which show the diversity of structural styles of deformations in the study region. The following structural styles of deformations are considered: classical-style thrust zones, which are in-sequence thin-skinned imbrication systems (i); areas of distribution of wedge-shaped allochthons, composed of duplex tectonic plates that are not reflected in the sub-surface layers (ii); inversion zones where faults associated with Ural rifting are transformed into thrust faults (iii); areas whose structure is determined by the deformation of salt diapirs and extrusion of salt (iv); zone, tectonic thickening of the Precambrian complexes overlain by the Paleozoic cover (v). Interpretation of historical and new data on the structure of fold belts makes it possible to significantly update understanding of the structure and development of areas such as zones of wedge-shaped thrusts, areas of development of squeezed salt diapirs, and areas where reactivation and tectonic thickening of Precambrian complexes occurred due to the reactivation of pre-existing faults. New seismic data provided constraints on the magnitude of horizontal displacements in the thrust zones as well as timing of shortening. For the first time they have revealed the development of arrays of small-scale protothrusts.

Landsat 8 and Alos DEM geological mapping reveals the architecture of the giant Mesoproterozoic Kunene Complex anorthosite suite (Angola/Namibia)

The quasi-monomineralic composition and huge spatial extent of massif-type anorthosites make detecting lithological regions and boundaries challenging. We use processed Landsat 8 OLI multispectral images and ALOS digital elevation models integrated with field and petrographic observations to characterize the architecture of the ≥17,000 km2 Mesoproterozoic Kunene Complex (KC) anorthosite suite in Angola and Namibia. Images of false colour composite bands 6, 4 and 1 and band ratios 4/2 (ferric minerals), 6/5 (ferrous minerals) and 6/7 (OH-bearing minerals), as well as assessment of the PCA and MNF matrices of eigenvectors and eigenvalues from Landsat 8 data using available spectral libraries, have substantially improved the interpretation of the Kunene Complex rock types and structures. The dataset shows that the reflectance signature of KC anorthositic rocks is primarily a function of the degree of metasomatism, which is most significant in olivine-poor rock types. The weathering intensity of the olivine-bearing anorthosite substrate is another control on the remote sensing signal.Our remote sensing and field-based approach has enabled us to divide the KC anorthosite suite into six distinct spectral and architecture domains and at least four distinct magmatic plutons when considering available high-precision geochronological data. The northernmost pluton (ca. 1380 Ma) of massive, olivine-bearing anorthosite shows distinct remote sensing signatures in the band ratio and MNF images marked by the dominance of OH-bearing and subordinate ferric minerals. The central pluton (1412–1400 Ma) is composed of NNE- to N-striking steeply dipping interlayered olivine-bearing and olivine-poor anorthosite, which correspond to ridges of dark-coloured, low albedo rocks with subordinate slightly oxidised ferrous mineral spectral signatures, and valleys of low albedo and OH-bearing mineral spectral signatures. A NNE-striking tectonic zone along a linear belt of KC granite gneiss separates the northern and central plutons. To the south is a NNW- to NNE-striking layered pluton (ca. 1390 Ma), marked by olivine-bearing anorthosite that forms ridges and metasomatized olivine-poor and pyroxene-bearing anorthosite that forms valleys. This domain is separated from the similarly layered and E–W-striking Zebra Lobe–Oryeheke anorthosite by a top-to-the north thrust zone. A small domain of ca. 1438 Ma olivine-bearing anorthosite sensu lato is situated to the SE of the main Kunene Complex.This work highlights the variability in layered and massive textures, the extent of metasomatism, and the importance of internal tectonic boundaries in the architecture of the Kunene Complex anorthosite suite. Our approach can be applied in other anorthositic terrains and large igneous bodies elsewhere on Earth, especially those where outcrop is poor, or access is inhibited.

Lithofacies and Depositional Environments of the Garubathan Alluvial Fan, North Bengal, India

Abstract The sedimentology of the Garubathan alluvial fan of north Bengal foothills is a product of Himalayan neotectonics and monsoon climate. The active neo-tectonics of the Main Central Thrust (MCT), Ramgarh Thrust (RT) and Ghis Transverse Fault (GTF) produce a huge amount of angular clasts in the upper reaches of the river Chel and Mal. During the wet season, either sediment flow by gravity or turbulent stream flow or both, move the clasts to the downhill. The tectonic zone of Main Boundary Thrust (MBT) and Main Frontal Thrust (MFT) are relative passive thrusts than the MCT, RT and GTF in the study area. A very low angle slope is observed in the area of MBT and MFT of the study area. So, the downhill deposition occurred in MBT and MFT zones of the study area. The river Chel and Mal are perinial rivers. During dry periods (pre-monsoon and post-monsoon), in the absence of sediment flow by gravity or turbulent stream flow, the low stream competency deposit the fine sediments. To identify the depositional environments three, seven and six lithofacies varieties were identified in the upper, middle and lower fan surfaces, respectively. The non-cohesive sediment flows by gravity deposited large angular boulders, cobbles and pebbles in the upper fan area. These deposits are either chaotic, unsorted, un-imbricated or graded and imbricated. Deposition of sand is scanty. Both, sediment flow by gravity and fluvial processes deposited angular to round clasts with matrix in the middle fan area. In this area the deposits are reverse graded, reverse to normally graded, laminated and cross-bedded. The high facies diversity of this area indicates highly variable nature of the depositional environments. In the lower fan area, presence of both clast-supported chaotic and matrix-supported laminated or cross-bedded layers suggests a complex nature of the depositional environment of sediment flow by gravity and fluvial processes.

Architecture and permeability structure of the Sibillini Mts. Thrust and influence upon recent, extension-related seismicity in the central Apennines (Italy) through fault-valve behavior

The central Apennines are a fold-thrust belt currently affected by post-orogenic extensional seismicity. To constrain the influence that the inherited thrust-related structures exert on the present seismic behavior of the belt, we provide the high-resolution structural and hydraulic characterization of one of the most external exposed thrust fault systems of the central Apennines, the Sibillini Mts. Thrust Front (STF). We integrate structural mapping, multiscale structural analysis, and in situ air permeability on the brittle structural facies of the thrust zone. We also performed K-Ar dating of selected fault rocks to better constrain structural inheritance. The STF is defined by a complex, ∼300-m-thick deformation zone involving Meso-Cenozoic marl and limestone that results from the accommodation of both seismic and aseismic slip during shortening. Permeability measurements indicate that the low permeability (10−2 ÷ 10−3 D) of the marly rich host rock diminishes within the thrust zone, where the principal slip surfaces and associated S-C structures represent efficient hydraulic barriers (permeability down to ∼3 × 10−10 D) to sub-vertical fluid flow. Field data and K-Ar dating indicate that the STF began its evolution ca. 7 Ma (early Messinian). We suggest that the studied thrust zone may represent a barrier for the upward migration of deep fluids at the hypocentral depth of present-day extensional earthquakes. We also speculate on the influence that similar deformation zones may have at depth on the overall regional seismotectonic pattern by causing transient fluid overpressures and, possibly, triggering cyclic extensional earthquakes on normal faults prone to slip while crosscutting the earlier thrust zones (as per a classic fault valve behavior). This mechanism may have controlled the origin of the 2016−2017 central Apennines devastating earthquakes.

Schistes Lustrés in a hyper-extended continental margin setting and reinterpretation of the limit between the Mont Fort and Tsaté nappes (Middle and Upper Penninics, Western Swiss Alps)

The Schistes Lustrés form a large and complex unit at the top of the Penninic nappe stack of the Alpine belt. Calcschists, partly of Late Cretaceous age, constitute the dominant lithology. They are closely associated both with blueschist facies Piemont-Ligurian ophiolites and continent-derived Mesozoic metasediments. The question of whether the Schistes Lustrés originated on continental or oceanic crust has been extensively debated among Alpine geologists and is locally still controversial. We present here new structural and stratigraphic observations, as well as Raman graphite thermometry (RSCM) data, for the Schistes Lustrés complex of the Combin zone in the Hérens, Dix and Bagnes valleys. Our observations indicate that the basal part of this Schistes Lustrés complex (defined as the Série Rousse) is systematically devoid of ophiolitic material, and rests in stratigraphic contact on the underlying Triassic - Lower Cretaceous metasediments and Paleozoic basement of the Mont Fort nappe (Prepiemont paleogeographic domain). The unconformity at the base of the Schistes Lustrés complex is interpreted as resulting from the sedimentation of the Série Rousse on a paleorelief formed by remnants of Jurassic normal fault scarps, and not as an Alpine tectonic contact, as previously proposed. The lithostratigraphic comparison with the Breccia nappe in the Prealps, as well as a foraminifer discovery, allows us to better constrain the age of the Série Rousse. It extends from the middle of the Early Cretaceous (Aptian?) to the Late Cretaceous (Campanian to earliest Maastrichtian?). In contrast, the upper contact of the Série Rousse with the ophiolite-bearing Schistes Lustrés clearly corresponds to an Alpine thrust. The thrust zone is underlined by thin and discontinuous slices of highly strained continental-margin derived Mesozoic metasediments (Frilihorn slices). RSCM data show that the recrystallization of the organic matter progressively increases on both sides towards this contact. This contact, internal to the Schistes Lustrés complex, is reinterpreted as the major tectonic contact separating the Middle Penninic Mont Fort nappe from the Upper Penninic Tsaté nappe (defined here as including only the ophiolite-bearing Schistes Lustrés and associated meta(ultra-)basites). This study clearly documents that the Schistes Lustrés consist of sediments either deposited on oceanic crust, showing locally preserved stratigraphic contacts with ophiolitic or serpentinized sub-continental mantle slivers, or sediments still resting stratigraphically on a former hyper-extended continental margin.

Magnetostratigraphy of palaeolake sequence from Kumaun Lesser Himalaya, India: Implications on young geomagnetic excursions

Geomagnetic excursions are short‐lived episodes when Earth's magnetic field deviates into an intermediate polarity state. Understanding the origin, frequency, amplitude, duration, and field behaviour associated with excursions is a forefront research area within solid Earth geophysics. Excursion events typically last a few thousand to tens of thousands of years; unlike full reversals, excursions are generally not recorded around the globe. We present here a new palaeomagnetic record (Geomagnetic excursions) from a lacustrine sediment sequence (at times, punctuated by undersized horizons of the gravels) with extraordinarily stable signals. Palaeomagnetic and rock magnetic investigations were performed on a 17‐m‐thick profile of unconsolidated sediments from Bagwalipokar palaeolake (Lat. 29°43′18″; Long. 79°28′42″; altitude 4167 ft), Binta Basin in the Kumaun Lesser Himalaya, situated in the zone of the active North Almora Thrust (NAT). A total of 540 oriented palaeomagnetic samples from 108 horizons (five samples per horizon) were collected from the section. The extrapolation of the optically stimulated luminescence (OSL) date indicates that the whole section was deposited between 45 and 2.5 ka. Magnetic remanence is predominantly carried by magnetite alone. Virtual Geomagnetic Pole (VGP) latitudes were determined using mean declinations and inclinations. Two geomagnetic excursions were observed at younger levels [11.6–10.5 m (15.5–14.7 ka) and 15–11.7 m (8.0–2.85 ka)]. These geomagnetic excursions correlate with the recently reported younger Hawaiian lava flow excursions. The youngest excursion from 8 ka may be attributed to the climatic event beginning at 8.2 ka cooling event of an oxygen isotope record of biogenic carbonate from palaeolake Riwasa in north‐western India that provides a history of the Indian Summer Monsoon (ISM) from ∼11 to 6 ka BP and also the North Atlantic glacial outburst flood and the slowdown of Atlantic meridional overturning circulation. However, further work is needed to verify this interpretation.

The Lower Silurian (Hot Shale) Source Rocks of Western Iraq: Depositional Model and Stratigraphic Distribution

The Hoseiba Member, an Early Silurian basal mature hot shale of the Akkas Formation (Silurian) consists of about 80% of the Paleozoic hydrocarbon potential system, it is organic-rich with total organic carbon up to 16% as the main source for the Paleozoic gas resources in Iraq. The hot shale is the main source of rocks that are penetrated in deep wells in the western Iraqi desert such as Akkas-1, Qaim-1, and Khleisia -1, which are distributed due to paleo uplift in the restricted regional basin in the west, south, and northwest Iraqi desert and wedged to north thrust zone in Ora area of extreme northern Iraq, Ora subbasin to Aljezira NW and in the west where the approved source rocks of ‘Hot shale” Akkas -Widyian subbasin (Rephrase). The Hoseiba Member, basal hot shale in the Akkas Formation in Iraq and their correlative units are extended within neighboring countries Jordan, Syria, Saudi Arabia, Iran, Oman, and south Turkey. Qualitative and quantity of Hot Shales source rocks Silurian are Excellent in Akkas well -1 (0.95-16.62%) TOC in Akk-1 Akkas sub-basin west Iraq and an average thickness (30 m.) with 1-9.94% TOC in Kh-1 Al-Jezira sub-basin NW Iraq. The hot shale distribution was controlled by the Caledonian uplift that created paleo-high in northern Iraq and moderately deep to the northwest, and deep depression deposition in west and south desert Iraq. The hot shale expulsion and migration of hydrocarbon are controlled by the underlying main reservoir of the Khabour Formation K1 sandstone ember by block faulting

Three-dimensional magnetotelluric signatures and rheology of subducting continental crust: Insights from Sikkim Himalaya, India

3D inversion of broad band MT data present variation of electrical signatures across the subducting Indian crust in Sikkim Himalaya. The vertical and horizontal geoelectric cross-sections are dominated by north-east dipping conductive zones. Two high conductivity zones (4–8 Ω m) at a depth of 5–18 km in Lesser Himalayan Domain (LHD) are explained by conductive mineral assemblage associated with abundant low saline and entrapped fluids. Another conductive feature (6–16 Ω m) in Main Himalayan Thrust Zone close to Main Himalayan Thrust ramp could have arisen from entrapment of CO2-H2O fluids and fluids released by metamorphic reactions. The high conductive anomaly (4–10 Ω m) at a depth of 5–16 km in Greater Himalayan Sequence (GHS) is caused by the presence of partial melts/aqueous fluids derived by present day fluid-absent melting of leucogranite source rocks. A combination of leucogranite intrusion, shear heating, and radiogenic heat production (4–17 μW/m3) are the heat sources for inferred partial melting. Though, the constrained melt fractions of 1.4–3.8% in GHS are lower than the estimation in south Tibet that might be due to the less intrusion of leucogranites. The obtained moderate viscosities of (104.19-105.49 Pa.s) from empirical relation with low melt and fluid fractions of 5–6 wt% in high conductive zone suggest viscous/ductile deformation and weakening mid-crust beneath northern Sikkim Himalaya. However, the estimated values of melt fractions and viscosities at mid-crustal depth of GHS are insufficient to develop a melt channel to flow southward between Main Central Thrust-1(MCT-1) and South Tibet Detachment (STD) envisaged by channel flow model.

Tectono-metamorphic transitions in the higher Himalayan sequence: A clue for Main Central Thrust (MCT) localization in Darjeeling-Sikkim Himalaya

This study recognizes a transition in the modes of ductile deformation across the Himalayan Crystalline Complex (HCC) from field and microstructural evidence. This transition leads to the Main Central Thrust (MCT) zone localization in the Darjeeling-Sikkim Himalaya. In the initial stage of crustal shortening (prior to ∼16 Ma), the HCC experienced temporally varying distributed ductile strains that produced regionally occurring planar fabrics and folds of three generations. Thereafter, the tectonic transition (from distributed to localized deformation) at ∼16 Ma occurred, forming the MCT zone in the HCC. This MCT zone (∼4–6 km thick) marks a diffuse metamorphic/rheological boundary between the hot HCC and the relatively colder Lesser Himalayan terrane to the south. The field data suggests that the base of compressed reverse paleo-isograds at the bottom of the MCT zone coincides with the transition of quartz creep mechanisms, from sub-grain rotation (SGR) to grain boundary migration (GBM). The present study documents the prograde metamorphic imprints to establish the P-T conditions of these multiple deformation episodes. Finally, this study presents a conceptual tectonic model, based on previous laboratory findings, to propose a two-stage tectono-thermal evolution of the Higher Himalaya.

СТРОЕНИЕ КЫЛЛАХСКОЙ ЗОНЫ (ЮЖНЫЙ СЕКТОР ВЕРХОЯНСКОГО СКЛАДЧАТО-НАДВИГОВОГО ПОЯСА) ПО МАТЕРИАЛАМ СЕЙСМИЧЕСКОГО ПРОФИЛИРОВАНИЯ

The structure of the Kyllakh thrust zone of the Verkhoyansk fold and thrust belt has been studied by seismic profiling. The construction of geoseismic sections refined the thickness of individual sedimentary complexes and the total thickness of the sedimentary cover, the structure of thrust sheets, and the position of detachments. Also, geoseismic sections were used to estimate the amount of the minimum slip of allochthons and to calculate compression coefficients for individual parts of the Kyllakh zone. The seismic and geological data were compared. A brief description is given of the sequence of geodynamic events that resulted in thrust folding in the region.

Mapping of Destructive Tectonic Earthquakes in the West Nusa Tenggara (NTB) Region Based on the Zhao Attenuation Function

NTB is a group of small islands located between the earthquake zone, namely in the south there is a subduction zone of the Eurasian and Indo-Australian plates and in the north, there is a back-arc fault or Flores Thrust. Earthquakes in this area are very active in the form of shallow tectonic earthquakes of large magnitude, so the risk of disaster is very high. Based on this, our research aims to map the distribution of destructive earthquakes using the attenuation function Zhao, released in 2006. The Zhao attenuation function has been applied to earthquake sources in subduction zones which are inputs for seismic hazards in various parts of the world, because the distance uncertainty factor used has better accuracy. The distribution of earthquake epicenter points in the West Nusa Tenggara region is clustered in four places, namely the Eurasian and Indo-Australian plate subduction zones in the sea south of the West Nusa Tenggara islands, the non-volcanic zone to the south of the West Nusa Tenggara islands, the volcanic zone to the east, and the Back Arc Thrust zone in the waters north of the NTB islands. Meanwhile, the hypocenter distribution is spread majorly on the Eurasian plate. Most of the islands of West Nusa Tenggara are characterized on the MMI VII-VIII intensity scale, and only a small part is characterized on the V-VI MMI intensity scale. The implications of the results of this research are useful in disaster mitigation, so it is hoped that there will be a reduction in disaster risk.

Earthquake on August 6, 2022 in the zone of the West Timan overthrust

On August 6, 2022, an earthquake was registered in Komi Republic, in the Udora district. Data from 17 seismic stations with epicentral distances from 227 to 1142 km were involved in processing the seismic event on August 6. The azimuth environment is uneven, the maximum azimuth gap is GAP=111.8°. As a result of instrumental processing, the following parameters were obtained: coordinates 64.023°N, 50.091°E, time at the source t0 =10:21:32 (UTC), depth h=14 km, energy class according to T.G. Rautian KR=10.2, local magnitude ML=3.6, error ellipse Azmajor=40°, Rminor=6.2 km, Rmajor=10.5 km. According to our calculations, the seismic event occurred in the middle reaches of the river Mezen, on the territory of the state natural reserve of regional significance “Udorsky”. The nearest settlements to the epicenter are located only 50 km away and the residents did not feel the earthquake. This area is not mining, so the seismic event is classified by us as a “tectonic earthquake”. The earthquake is confined to the West Timan thrust zone, which is a collision suture of the Russian and Pechora plates. The source at a depth of 14 km is located in the region of pericratonic subsidence covering the northeastern margin of the Russian Plate and the Kanino-Timan belt; on the boundary of the basement of the Mezen syneclise and the Timanid complex thrust over it. The earthquake may have been caused by tectonic pressure from the Pechora plate. This is the first earthquake in the West Timan thrust zone. Earthquakes occur mainly in the northeast of the Russian Plate, within the Volga-Ural anteclise, Mezen and Moscow syneclise. In addition, although the recorded earthquakes are mostly low-magnitude, they reflect the modern tectonic activation of the earth’s crust.

GIS-BASED HIGH-RESOLUTION GEOLOGICAL MAP (SCALE 1:50,000): A NEW WINDOW INTO STRUCTURAL DOMAINS OF THE QUETTA AND SURROUNDING AREAS

The Quetta and surrounding areas are part of the collision zone between the Indian and Eurasian plates, named as Kirthar and Sulaiman Fold-Thrust belts. The collision is accommodated by folding, thrusting and the Nushki-Chaman Transform Fault System. Detailed high-resolution (scale 1:50,000) mapping and structural analyses were carried out using modern remote-sensing techniques of the ArcGIS to understand mutual relationships of the structural patterns and geometries, and the regional and local stress patterns in the study area. Fieldwork was carried out to acquire the stratigraphic, structural and geomorphological data, using topographic maps and satellite images as base maps in order to plot additional information and further incorporate them in the GIS-based map. Balanced structural cross-sections were also prepared along the selected lines using ArcGIS techniques. Based on new mapping, the understudy area has been subdivided into five distinct structural domains. These domains are classified as; Domain I: broad syncline intervened by a narrow anticline; Domain II: upright folds and thrusts; Domain III: tight, over-turned thrust zone; Domain IV: flysch and molasse successions of Paleocene-Holocene age; and Domain V: suture belt (ophiolites) and associated mélanges and sediments.