Northeastern Segment Research Articles

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

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

Structural Variation Along the Southern Hikurangi Subduction Zone, Aotearoa New Zealand, From Seismic Reflection and Retro‐Deformation Analysis

AbstractThe southern Hikurangi subduction zone exhibits significant along‐strike variation in convergence rate and obliquity, sediment thickness and, uniquely, the increasing proximity of southern Hikurangi to, and impingement on, the incoming continental Chatham Rise, an ancient Gondwana accretionary complex. There are corresponding changes in the morphology and structure of the Hikurangi accretionary prism. We combine widely spaced multichannel seismic reflection profiles with high resolution bathymetry and previous interpretations to characterize the structure and the history of the accretionary prism since 2 Ma. The southern Hikurangi margin can be divided into three segments. A northeastern segment (A) characterized by a moderately wide (∼70 km), low taper (∼5°) prism recording uninhibited outward growth in the last ∼1 Myr. Deformation resolvable in seismic reflection data accounts for ∼20 % of plate convergence, comparable with the central Hikurangi margin further North. A central segment (B) characterized by a narrow (∼30 km), moderate taper (∼8°) prism, with earlier (∼2‐∼1 Ma) shortening than segment A. Outward prism growth ceased coincidentally with development of major strike‐slip faults in the prism interior, reduced margin‐normal convergence rate, and the onset of impingement on the incoming Chatham Rise to the south. A southwestern segment (C) marks the approximate southern termination of subduction but widens to ∼50 km due to rapid outward migration of the deformation front via fault reactivation within the now‐underthrusting corner of the Chatham Rise. Segment C exhibits minimal shortening as margin‐normal subduction velocity decreases and plate motion is increasingly taken up by interior thrusts and strike‐slip faults.

Detection of potential reservoirs of the Mezen syneclise of the Eastern European platform

The possibility of discovering new hydrocarbon deposits within the north-eastern segment of the European part of Russia will reduce the cost of transporting hydrocarbons to major industrial centres. And access to Russia’s most important transport artery, the Northern Sea Route, in the context of the growing importance of the tanker fleet and reorientation of sales markets proves the need to build up the region’s resource base. However, it is necessary to take into account the environmental and climatic risks associated with hydrocarbon production in the Arctic conditions, as well as their transport. This paper presents the data of paleoreconstructions of sedimentation settings of Precambrian sedimentary strata in the light of updating the history of development of the Mezen-Belomr region and studying the reservoir properties of the Riphean-Wendian part of the sedimentary cover section. As a result, formations with enhanced filtration-capacity properties were identified. The Vendian part of the section is characterised by good values of open porosity (up to 20.89%).

Contrasting structures of the Southern Benue trough and the contiguous crystalline basement as observed from high-resolution aeromagnetic data

The present study investigated crustal structures and geological bodies within selected areas of the southern Benue trough and the adjacent crystalline basement. It utilized high-resolution aeromagnetic data to provide original insights into the contrasting structures and geological bodies within the area, while also identifying promising areas for further mineral and hydrocarbon investigations. The aeromagnetic anomaly data were analyzed using various techniques, including total gradient magnitude, pseudo-gravity transformation, tilt derivative, and source parameter imaging. The total gradient magnitude anomalies revealed a considerable component of the basin affected by block faulting which may have resulted from severe tectonic and structural deformation of the metamorphic basement and the subsequent injection into the sedimentary sequence, a few intrusions. The pseudo-gravity transformation identified a large igneous body in the sedimentary basin which is characterized by positive pseudo-gravity anomalies and surrounded on both sides by linear negative anomalies that signify a rift zone. The positive amplitude of the tilt derivative identified subtle linear magnetic minerals associated with the geologic structure and igneous bodies that suggest considerable mineral exploration prospects. A two-dimensional model of the source parameter imaging reveals the basement below the sedimentary basin to be intensely fragmented and variably subsided with the floor of the basin forming irregular upward and downward folds. In conclusion, the findings suggest promising prospects for mineral exploration along the margin of the sedimentary basin and potential hydrocarbon resources in the northeastern segment of the basin, which is characterized by fewer intrusions.

Source Parameters of Strong Turkish Earthquakes on February 6, 2023 (<i>M<sub>w</sub></i> = 7.8 and <i>M<sub>w</sub></i> = 7.7) from Surface Wave Data

Abstract—Based on the amplitude spectra of surface waves, the source parameters of the strong Turkish earthquakes of February 6, 2023 (Mw = 7.8 and Mw = 7.7) were calculated in two approximations: an instantaneous point source and an elliptical shear dislocation. As a result, rupture planes were identified, data were obtained on the scalar seismic moment, moment magnitude, focal mechanism, and source depth of the considered seismic events, and the integral parameters characterizing the rupture geometry and its development in time were estimated. It is shown that the sources of the earthquakes under study were formed under the influence of the regional stress field and their focal mechanisms were left lateral faults with a strike direction close to the strike of the East Anatolian fault zone for the first event and close to the strike of the Sürgü-Çardak fault system for the second. For the first earthquake, our estimates of the rupture duration and its length (t = 52.5 s, L = 180 km) probably refer not to the entire rupture, but only to its main phase, confined to the northeastern segments of the East Anatolian fault and characterized by maximum displacements and values of the released seismic moment. The values of t = 30 s and L = 180 km that we obtained for the second earthquake fully characterize the entire rupture.

U-Pb and Re-Os geochronology and geochemistry of the Ulgen hidden porphyry Mo deposit in the Derbugan metallogenic belt (NE China): Insights into petrogenesis and tectonic setting

The Ulgen porphyry Mo deposit, recently discovered in the northeastern segment of the Derbugan metallogenic belt, NE China, is a large and hidden ore deposit. Investigation of this deposit provides insights into the geodynamic background and metallogenic mechanism of Mesozoic porphyry Mo deposits that are exposed elsewhere in NE China. The host rocks consist of muscovite monzonitic granite (MMG) and biotite granitic porphyry (BGP), which are intruded into Lower and/or Middle Jurassic intermediate-felsic volcanic-sedimentary rocks and pre-ore monzogranitic porphyry (MP). Zircon laser ablation−inductively coupled plasma−mass spectrometric (LA-ICP-MS) U-Pb age dating indicates that the MMG and BGP were emplaced at 144.9 Ma and 144.7 Ma, ca. 14 m.y. younger than the intrusion age of MP (159.3 Ma). Molybdenite Re-Os isotopic dating indicates that Mo mineralization occurred at 144.9 Ma, almost simultaneously with the 145 Ma magmatic activity. Geochemically, all of the Ulgen granitoids are enriched in large ion lithophile elements (e.g., Rb, Th, U, and K) and light rare earth elements, and are depleted in high field strength elements (e.g., Nb, Ta, and Ti). The pre-ore MPs belong to I-type granites with moderately negative Eu anomalies (Eu/Eu* = 0.62−0.65), whereas the syn-ore MMGs exhibit S-type affinity with pronounced negative Eu anomalies (Eu/Eu* = 0.29−0.39). The ore-forming BGPs display adakite-like geochemical features in terms of high-Sr, low-Y, and low-Yb contents, and slightly negative Eu anomalies (Eu/Eu* = 0.72−0.74). All intrusive rocks have relatively low initial (87Sr/86Sr)i ratios (0.7044−0.7055) and positive εNd(t) values (+1.15 to +2.65), positive εHf(t) values (+4.0 to +9.4), young two-stage Nd and Hf model ages (tDM2(Nd) = 841−731 Ma, tDM2(Hf) = 943−604 Ma), and moderate (206Pb/204Pb)i (18.300−18.402), (207Pb/204Pb)i (15.557−15.564), and (208Pb/204Pb)i (38.180−38.307) ratios. Therefore, it is most likely that these intrusive rocks originated from a mixture of two sources of magma derived from the mantle and juvenile lower crust, in which there were variable degrees of the fractional crystallization of ilmenite, apatite, and plagioclase. Rather than the partial melting of oceanic slabs, the fractional crystallization of hornblende and accessory minerals (e.g., ilmenite and apatite) induces the adakitic geochemical signature of BGPs. Compared with the BGPs, the MPs had a relatively deeper magma source region, whereas the MMGs had a relatively shallower magma source region. The BGPs and the Mo-bearing fluids of the Ulgen deposit were most probably derived simultaneously from magma that was generated at an extensional setting following the closure of the Mongol-Okhotsk Ocean during the latest Jurassic. Enrichment of Mo by late-stage fractional crystallization most likely played an important role in concentrating Mo during the formation of the Ulgen hidden Mo deposit.

Prediction of forest fire susceptibility applying machine and deep learning algorithms for conservation priorities of forest resources

Periodic forest fires occur in sub-tropical deciduous forest of Ayodhya hill region which is extended part of Eastern Ghats Mountain Range (India). This forest provides diverse ecosystem services (mostly non timber forest products)to tribal and non-tribal people throughout the year. The main objective of this study is to demarcate the accurate forest fire susceptibility zones applying three relevant machine learning models i.e., Random Forest (RF), Multivariate Adaptive Regression Splines (MARS) and Deep Learning Neural Network (DLNN). In this research, more than 300 hundreds historical forest fire events along with 14 forest fire predictors have been considered. DLNN model has the highest efficacy (AUC = 0.925). Features of DLNN are instinctively presumed and optimally tuned for required outcomes. Applied models explicitly examined that the north western and eastern segments of Ayodhya hill are highly susceptible for forest fire due to its physical and social complexity. DLNN model investigates that total 18% areas of Ayodhya hill have come under very high susceptible zone. The forest fire incidents are taken place during March to May because of the effect of high temperature, poor moisture content and existence of high fuel woods. Both the machine and deep learning techniques have been applied first time in this dry deciduous forest belt and models indicated high accuracy and precision which is harmonized with ground reality. This study will definitely help the local government to take proper management and conservation strategies for sustainable forest resources conservation along with improvement of livelihood of forest and forest fringe dwellers.

ПОСТРОЕНИЕ СКОРОСТНОЙ МОДЕЛИ ВЕРХНЕЙ ЧАСТИ ЗЕМНОЙ КОРЫ ЗОНЫ СОЧЛЕНЕНИЯ ЕВРАЗИЙСКОЙ И ОХОТОМОРСКОЙ ПЛИТ ВДОЛЬ СЕВЕРО-ВОСТОЧНОГО УЧАСТКА ПРОФИЛЯ 3-ДВ ПО РЕЗУЛЬТАТАМ ЦИФРОВОЙ ОБРАБОТКИ ДАННЫХ ПРОДОЛЬНЫХ И ПОПЕРЕЧНЫХ ПРЕЛОМЛЕННЫХ ВОЛН

An automated algorithm for monitoring the areas of refraction event tracking along the profile based on the dynamic conversion method is developed. Time sections of compressional - and shear-wave refractions recorded by the CDP shooting geometry on the North-Eastern segment of the 3DV survey base line are constructed. A high-speed model of the upper part of the Earth’s crust is constructed to depths of ≈2 km in the conjunction zone of the Okhotsk and Eurasian lithospheric plates. According to increased values of the velocity ratio of P- and S- waves, it is found that refracting boundaries in the Ayan-Yuryakh block are sections of rocks with various lithological composition in sedimentary cover. The zone of reduced values of P-wave velocity and the VP /Vs ratio associated with a high fragmentation of rocks is identified on the high-velocity profile of the Chay-Yurya fault zone, both above and below the refracting boundary. The velocity values of P- and S-waves (6.0–6.1 km/s and 3.6–3.7 km/s, respectively,) and reduced values of the Vp /Vs ratio (≈1.65) concerned with intrusions of acid rocks were recorded in the southern part of the Inyali-Debin block within t he depth range of 1–1.5 km.

GEOMETRY OF RECENT RUPTURE ZONE AT СAPE RYTYI BASED ON GROUND PENETRATING RADAR (NORTHWESTERN COAST OF LAKE BAIKAL)

In here, we present the results of the GPR study of the modern rupture zone discovered earlier in the periphery of the Rita River delta flowing into Lake Baikal. The research was aimed at subsurface imaging of dislocation geometry using the Logis-Geotech OKO-2 radar equipped with the ABDL Triton antenna. As a result, the characterizations have been obtained for six 73 to 197 m long profiles across the rupture zone. All disturbances visible on the aerial photography materials are highlighted on the radargrams by the oblique reflection event due to a decrease in the signal amplitude. The rupture zone has two large segments – northeastern and submeridional, – which differ in zone width, number of discontinuities, dip angles, and displacement amounts. The deformation features can be attributed to different amounts of a plastic loamy aggregate of coarse deposits in different parts of the Rita River delta that is indirectly confirmed by weaker signal amplitudes on the northeastern segment. Based on present and previous studies, we proposed that the M=5.2 earthquake occurred on August 13, 1962, in Lake Baikal initiated the gravitational sinking in the Rita river delta edge by subsidence along gently sloped rupture surfaces on one segment and along steeply sloped ones on the other. It is necessary to identify and monitor such phenomena to prevent the development of emergencies associated with the collapse of the coasts of large water reservoirs.

Reply to the discussion of Moustafa (2021) on Sayed et al. (2020) (Marine and Petroleum Geology, 17, 2020-104401)

Moustafa (2021) addressed four main comments in his discussion “On the structures of Abu Roash area and inverted basins of northern Egypt - Comments on “Surface expression of the Syrian Arc Kattaniya inverted basin in the Abu Roash area, northeast Western Desert, Egypt: Structural style and tectonic history” by Sayed et al. (2020)”. Two of these comments criticized the new structural mapping of Abu Roash outcrops and the proposed model for El Ghigiga-El-Hassana Folds based on the early geologic mapping of the Abu Roash area by Moustafa (1988). His other comments were concerning the NE-orientation and end of tectonic inversion of the extensional Jurassic -Lower Cretaceous basins in North Egypt including the Kattaniya basin. Except for two constructive memos on drafting errors in the regional geologic map of Abu Roash, the registered comments were inaccurate and can be refuted with the results of the comprehensive regional and integrated subsurface geologic mapping on the North Western Desert basins, the previous works of Moustafa and his collaborators and the figures included in his discussion as we will present in this reply. It was documented that the inversion time, intensity, and type (orthogonal versus oblique or compressional versus transpressional/transtensional) differ from one basin to another in the northern part of Egypt. The geologic structures of Abu Roash helped to define a transpressional (oblique) inversion tectonic model that started at the Santonian and ended by the Latest Senonian. This tectonic model represents the northeastern segment of the Kattaniya basin and does not generalize to the whole basin or other basins in North Egypt.

Age and genesis of the Jinshan gold deposit in the Chinese North Tianshan: A link to large-scale strike–slip shearing events

Large-scale transcrustal strike–slip shearing, orogenic gold deposits, and magmatic Ni–Cu sulfide deposits are prominent features in the Chinese North Tianshan in the northeastern segment of the Tianshan Orogenic Belt. Therelationshipbetween the shearing events and the different styles of mineralization, however, remains ambiguous. Here, structural data, zircon U–Pb–Hf isotopes, bulk-rock geochemistry, muscovite 40Ar/39Ar age dating, and S–Pb isotopes of pyrite from the Jinshan gold deposit are utilized in conjunction with the Pb isotope composition of mineralized mafic–ultramafic rocks of the Huangshandong Ni–Cu sulfide deposit to characterize thelinkbetweenstrike–slipshearing events, andorogenicAuandmagmaticNi–Cu sulfidemineralization. The new zircon U–Pb age results indicate that the host diorite of the gold orebodies formed at ca. 335 Ma. These diorites are enriched in light rare earth elements and large ion lithophile elements (e.g., Ba, U, K, and Pb), but depleted in high field strength elements (e.g., Nb, Ta, and Ti), and have low MgO (4.45–5.17 wt%) contents, Mg# (0.32–0.36), and (La/Yb)CN ratios (4.81–6.90). Based on the lack of ancient crustal basement rocks in the Qoltag Arc, the depleted Nd–Hf isotope composition (εHf(t) = 10.82–15.38; εNd(t) = 6.17–6.67), the juvenile Hf depleted-mantle model ages (350–530 Ma), and the enrichment in Na2O (4.45–5.17 wt%) relative to K2O (1.05–2.20 wt%) of the diorite, it is inferred that the primary magma from which the diorite crystallized was derived from partial melting of metasomatized mantle wedge in an oceanic arc environment. Two muscovite samples separated from an auriferous quartz lode yield 40Ar/39Ar plateau ages of 248.6 ± 0.8 Ma and 249.6 ± 0.9 Ma, representing the age of the gold mineralization event. The similarity in S–Pb isotope composition of pyrite in the Jinshan gold deposit and pyroxenite in the Huangshandong Ni–Cu sulfide deposit suggests that the auriferous fluids required for the formation of the Jinshan gold deposit could represent a mixture of deuteric fluids with limited upper crustal metamorphic fluids from the Kanggur–Huangshan Shear Zone.

Hydrocarbon gas seepage along the Gydratny Fault (Lake Baikal)

The Gydratny Fault, extending in SW-NE over 60 km, is situated in the central basin of Lake Baikal. This fault governs a distribution of hydrocarbon gas discharge zones on the lake bottom, many of them are hydrate-bearing. During the Class@Baikal-2019 expedition gas samples were obtained from bottom sediments along the fault zone, molecular and isotopic properties of the gases were studied. It is concluded that the fault zone is permeable for hydrocarbons and serves as an important fluid flow conduit from deep sources to the surface. The most intensive gas seepage was determined along the central and north-eastern segments of the fault zone where it is associated with the MSU hydrate-bearing structure and the Novosibirsk and Ukhan mud volcanoes. Within these structures the highest concentrations of methane and C2+ components were detected, the heaviest isotopic composition of methane carbon (–57‰ VPDB) were identified and near-surface gas hydrate accumulations were observed. The south-western segment of the fault is characterized by the lowest concentrations of gases in sediments with light carbon isotopic composition of methane (–76‰ VPDB).A dominant gas migration mechanism (advection or diffusion) in the upper part of the basin sedimentary section conditions the registered concentrations of methane and its homologues in sediments and their carbon isotopic composition. Diffusion and dispersion of migrated thermogenic gases and significant portion of microbial methane in seeping gases are characteristic for the areas where the fault is buried under relatively thick modern sediments. Focused gas migration followed by its focused discharge are specific for the areas where the fault propagates to the lake floor and is well-expressed in a bottom relief. Two models of hydrocarbon gases migration to the surface explaining the observed gas-geochemical characteristics of bottom sediments are described and discussed. Obtained results can help in enhancing interpretation of data of gas geochemical prospecting for offshore oil and gas.

Contemporary background stress field in the eastern Tibetan Plateau: Insights from 3D geomechanical modeling

Knowledge of the crustal stress state is important for understanding tectonic processes and seismic hazard assessment as well as for various practical applications. In this study, we present a model describing the contemporary 3D crustal background stress field of the eastern Tibetan Plateau. The model incorporates a complex fault system and an appropriate initial stress state that matches both model-independent stress observations and kinematic data well. Our results show that the modeled maximum horizontal stress SH is generally oriented in NW-SE direction. The Bayan Har Block and the Chuan-Dian Block are dominated by a strike-slip faulting stress regime. However, in some local areas, the crust is governed by a normal faulting regime. We infer that the local normal faulting stress regime in the Bamei-Kangding area is caused by the clockwise rotation of the strike of the Xianshuihe fault at Kangding. This normal faulting stress regime would promote the ascent of intrusions and provide the space necessary for the emplacement of the Zheduoshan granite. The stress state on the Longmen Shan fault zone is rather inhomogeneous. For the Yingxiu-Beichuan fault, the northeastern segment has a lower normal stress but a higher shear stress than the southwestern segment. This inhomogeneous stress state on the Yingxiu-Beichuan fault could provide an explanation for the northeastward propagation of the ultra-long unilateral rupture in the Wenchuan Ms8.0 earthquake. According to the stress state on the Xianshuihe fault, we conclude that the Kangding-Shimian segment has a high potential to produce a strong earthquake due to its high normal stress and a fast slip rate and should be carefully monitored. On the Bamei-Kangding segment, which is governed by a normal faulting stress regime and may be lubricated by fluids, slip seems to be facilitated favoring more frequent small to moderate magnitude earthquakes to occur on this segment.

Drought and flood characteristics in the farming-pastoral ecotone of northern China based on the Standardized Precipitation Index

The farming-pastoral ecotone of northern China (FPENC) provides an important ecological barrier which restrains the invasion of desert into Northwest China. Studying drought and flood characteristics in the FPENC can provide scientific support and practical basis for the protection of the FPENC. Based on monthly precipitation data from 115 meteorological stations, we determined the changes in climate and the temporal and spatial variations of drought and flood occurrence in the FPENC during 1960–2020 using the Standardized Precipitation Index (SPI), Morlet wavelet transform, and inverse distance weighted interpolation method. Annual precipitation in the FPENC showed a slightly increasing trend from 1960 to 2020, with an increasing rate of about 1.15 mm/a. The interannual SPI exhibited obvious fluctuations, showing an overall non-significant upward trend (increasing rate of 0.02/a). Therefore, the study area showed a wetting trend in recent years. Drought and flood disasters mainly occurred on an interannual change cycle of 2–6 and 9–17 a, respectively. In the future, a tendency towards drought can be expected in the FPENC. The temporal and spatial distribution of drought and flood differed in the northwestern, northern, and northeastern segments of the FPENC, and most of the drought and flood disasters occurred in local areas. Severe and extreme drought disasters were concentrated in the northwestern and northeastern segments, and severe and extreme flood disasters were mainly in the northeastern segment. Drought was most frequent in the northwestern segment, the central part of the northeastern segment, and the northern part of the northern segment. Flood was most frequent in the western part of the northwestern segment, the eastern part of the northeastern segment, and the eastern and western parts of the northern segment. The accurate evaluation of the degrees of drought and flood disasters in the FPENC will provide scientific basis for the regional climate study and critical information on which to base decisions regarding environmental protection and socio-economic development in this region.

Contemporary kinematics in the eastern Tibetan Plateau: Insights from 3D geomechanical modeling

The slip rates on the faults in the eastern Tibetan Plateau play an important role in understanding the plateau's evolution and assessing its seismic hazard. In order to obtain a quantitative picture of the continuous slip rate along and slip partitioning between the faults, we establish a comprehensive 3D geomechanical-numerical model of the eastern Tibetan Plateau. Our results show that the NW-SE-trending faults usually slip faster than the faults striking in NE-SW direction. A substantial variation of the slip rate gradient along the Xianshuihe fault is revealed. The southeastern segment (Moxi fault) has a higher slip rate gradient than the northwestern segment, which is inferred to be caused by a clockwise rotation of the strike of the Xianshuihe fault from NW-SE to NNW-SSE near Kangding. This rotation combined with the accommodated southeastward movement of the Chuan-Dian Block further promotes normal faulting on the southwestern-most section of the Longmen Shan fault. According to the relatively higher slip rate of the Huya fault and the geometric distortion of the Yingxiu-Beichuan fault, we suggest that the Huya fault may have penetrated into the Longmen Shan fault zone and partially transmitted deformation of the Minshan Uplift into the sedimentary cover of the Sichuan basin. Based on the analysis of contemporary kinematics in the eastern Tibetan Plateau, we suggest that the Moxi fault has a high seismic hazard with the potential of an Ms7.4 earthquake, while the northeastern segment and the southwestern-most section of the Longmen Shan fault zone tend to produce more frequent but lower magnitude earthquakes.

Late Quaternary activity of the Qingchuan Fault, eastern Tibetan Plateau margin: Insights from stream channel offsets and catchment erosion

The Qingchuan Fault (QCF) is the main fault of the northeastern segment of the Longmenshan Fault zone (LMSFZ) on the eastern Tibetan Plateau boundary. The QCF accommodates ongoing deformation in the eastern Tibetan Plateau; however, its fault motion and potential seismic risk are still debated. This study combines a systematic analysis of deflected stream channels along the fault using 10-m digital elevation models with field investigations and measurements of the cosmogenic 10Be-derived erosion rates. The degree of channel deflection due to the interaction between strike-slip motion and channel growth processes is analyzed, followed by a quantitative extraction of the actual tectonic offsets and a calculation of the erosion rates. The long-term average strike-slip rates calculated from channel offsets range from 0.4 ± 0.1 to 1.7 ± 0.1 mm/a along the fault, with those in the southwestern section lower than those in the central section. Such differences may be attributed to slip partitioning of the northeastern extension of the Yingxiu–Beichuan Fault. In addition, analysis of stream longitudinal profiles and along-fault topographic variations illustrate that the small thrust component of the QCF decreases to the northeast, and a minor normal component exists at its northeastern end. The distributions of strike-slip and vertical-slip motions of the QCF indicate that fault slip of the central LMSFZ propagates to the northeast across the Minshan uplift and continues to slip along the QCF. Moreover, thrusting of the southern-central segment of the LMSFZ and dextral strike-slip faulting of the QCF may both accommodate complex deformation related to eastward expansion of the Tibetan Plateau. These findings have implications for constraining potential seismic hazards and understanding characteristics of the regional tectonic deformation.

Comparative tectonics of the White Sea paleorift system and other continental rifting systems

Research subject. The Riphean paleorift system of the White Sea, most of which is overlain by the waters of the White and Barents Seas and the platform cover of the East European Platform. This allowed numerous researchers to classify it as an aulacogen. The system was revealed by geophysical methods in the relief of the crystalline basement of the platform in the form of a frame of deep extended trenches of northwestern strike, subparallel to the edge of the East European platform.Materials and methods. Personal observations of the authors within the Onega-Kandalakcha paleorift, Baikal rift zone; a detailed study of seismostratigraphic sections of these zones; extensive literature data on the structure of modern rift zones. A comparative analysis of the structure of the most studied and currently active Baikal and East African rift systems, as well as the Karoo rift system of the Late Paleozoic origin with the paleorift system of the White Sea.Results. The following types of structural parageneses, which are characteristic of both modern rift systems and ancient paleorift systems, were identified. 1. Genetic relationship (inheritance?) of riftogenic structures with more ancient basement structures. 2. Structural paragenesis of concentric complexes in rift propagation zones. 3. Comparability of the area of horizontal extension of the lithosphere of the White Sea paleorift system with extension zones of modern continental rifts. 4. The fundamental similarity of the structure: the complex of paleorifts of the White Sea with modern continental rift systems: the presence of long deep trough segmentation of grabens and semi-grabens separated by bridges, which were accommodation zones with polarity reversal along the strike of the rift zone, displacement of the rift relative to the mantle ledge, the existence of a gently dipping normal fault (detachment), etc.Conclusion. The riftogenic nature of the aulacogens in the northeastern segment of the East European Platform has been confirmed.

PETROGENETIC MODELING OF THE GRANITIC ROCKS IN AND AROUND LODHMA, DIST RANCHI, JHARKHAND, INDIA

The Lodhma area, in the Ranchi district, constitutes the central segment of Chotanagpur Granite Gneissic Complex ( CGGC) and falls in the northeastern segment of Survey of India toposheet number 73E/4. The CGGC is mainly composed of variants of granitic rocks, amphibolites and metasedimentaries. The granitic rocks find good exposure in the area. They comprise predominantly of granite gneisses, crystalline massive granites and migmatites showing noticeable variations in mineralogy, texture, structure and associations. The regional strike of the lithounits of the area show almost E-W trend. However ambient structural controls have brought about local changes in the strike direction. The area has witnessed at least three phases of deformations which is reflected by three generations of folds, which are generally isoclinals. Petrogenetic characterization of granitic rocks and its variants in the area has been attempted using various geochemical tools involving major/ trace element studies and Niggli values. S –type parentage of these Granites have been established on the basis of distribution behavior of various chemical components present in it, thereby indicating role of pelitic schists in the generation of anatectic melt, which ultimately crystallized into granites. S-type lineage of these granites has also been further cemented with the help of several well established binary and ternary variation diagrams

Cenozoic tectono-geomorphic evolution of Yabrai Mountain and the Badain Jaran Desert (NE Tibetan Plateau margin)

Cenozoic tectono-geomorphic growth processes of the Yabrai Fault (YBF) along Yabrai Mountain (YM) and their impacts on the landscape formation of Badain Jaran Desert (BJD) during the late Quaternary are still unsolved, and yet are crucial to exploring the tectonic evolution of the boundary between the northeastern Tibetan Plateau and southern Gobi Alxa block. This study addresses these issues using information extraction-based interpretations of multiple satellite images coupled with field observations. The 138 km-long NE-NEE striking YBF can be divided into 3 segments: southwestern, central, and northeastern segments all characterized by left-lateral faulting with normal faulting components. Apatite (U-Th)/He thermochronology and calcite (U-Th) dating integrated with regional tectonic evolution history provides new geochronological evidence for understanding the multi-stage evolution of the YM and YBF. (1) Before the late Cretaceous (135–72 Ma), the mountain experienced rapid cooling and uplift. (2) During the late Cretaceous to Eocene (ca. 70–33.9), the YM is likely to have experienced denudation and flattening. (3) From the Oligocene to early Pliocene (33.9–5 Ma), the YBF underwent ~47 km of left-lateral displacement that accommodated the slip of Altyn Tagh Fault (ATF). (4) Since the Pliocene (5 ± 1 Ma), the YBF is characterized by left-lateral strike-slip faulting with a normal faulting component. The normal faulting resulted in uplift and the creation of topography along the central segment of the YBF. This has impeded the southeastward migration of sand dunes, building the world's highest megadune within the BJD. The tectono-geomorphic growth of the YM and YBF plays a key role in formation of the unique megadune-lake pattern and in preventing the merging of the BJD and Tengger Desert (TD).

Stress changes associated with the significant first subevent of the 2008 Wenchuan earthquake and implications for the rupture behavior transition

The rupture process of the Wenchuan earthquake demonstrated a transition from thrust-dominated slip to northeastward strike-slip motion along the Longmen Shan Fault Zone. The initial stress has been reported as playing a critical role in this process; however, the stress changes, especially those caused by the significant first subevent of the Wenchuan earthquake are not well understood. Here, we employ a three-dimensional finite element model of the Sichuan-Yunnan region to analyze the stress change caused by the significant first subevent and explore the possible influence on the following ruptures. The results indicate that the auxiliary maximum principal compressive stress (SH) associated with the significant first subevent was horizontal and that the auxiliary stress regime was SH>Sh>Sv, supporting the ongoing regional thrust motion near the southwestern segment of the rupture plane. However, in the northeastern segment, the auxiliary stress regime transitioned to SH>Sv>Sh, demonstrating that the stress changes promoted the transition of the rupture behavior from predominantly thrust motion in the southwest to right-lateral strike-slip motion in the northeastern segment, which was also supported by the dominant shear stress change and the subtle normal stress change along the fault plane in the northeastern segment. In addition, our modeled results also indicate that the orientation of the maximum principal compressive stress changed from SEE to northeastward NEE along the strike of Longmen Shan Fault Zone. This anticlockwise rotation hastened the rupture behavior transition, suggesting that both the initial stress and the stress changes associated with the first subevent jointly controlled the following northeastward rupture of the Mw7.9 Wenchuan earthquake.