Characteristics Of Deposits Research Articles

Sedimentary Processes and Depositional Characteristics of Coarse‐grained Subaqueous Fans along Steep Slopes in a Lacustrine Rift Basin: A Case Study from the Dongying Depression, Bohai Bay Basin, China

AbstractCoarse‐grained subaqueous fans are vital oil and gas exploration targets in the Bohai Bay basin, China. The insufficient understanding of their sedimentary processes, depositional patterns, and controlling factors restricts efficient exploration and development. Coarse‐grained subaqueous fans in the Yong'an area, Dongying Depression, are investigated in this study. These fans include nearshore subaqueous fans, and sublacustrine fans, and their sedimentary processes, depositional patterns and distribution characteristics are mainly controlled by tectonic activity and paleogeomorphology. Nearshore subaqueous fans developed near the boundary fault during the early–middle deposition stage due to strong tectonic activity and large topographic subsidence. Early sublacustrine fans developed at the front of the nearshore subaqueous fans in the area where the topography changed from gentle to steep along the source direction. While the topography was gentle, sublacustrine fans did not develop. During the late weak tectonic activity stage, late sublacustrine fans developed with multiple stages superimposed. Frequent fault activity and related earthquakes steepened the basin margin, and the boundary fault slopes were 25.9°–34°. During the early–middle deposition stage, hyperpycnal flows triggered by outburst floods developed. During the late deposition stage, with weak tectonic activity, seasonal floods triggered hyperpycnal flows, and hybrid event beds developed distally.

Stratigraphical, microfacies, and ichnological characteristics and depositional environments of the Permo‒Carboniferous Aheimer Formation, western side of the Gulf of Suez, Egypt

The palaeoenvironments of the upper Palaeozoic succession in the eastern foot slopes of the Northern Galala Plateau, west of the Gulf of Suez, Egypt, are interpreted based on a detailed study of the sequence-stratigraphic framework, sedimentary facies and trace fossils. The upper Carboniferous–lower Permian Aheimer Formation has been studied in its type section exposed in Wadi Aheimer. Three unconformities bound four 3rd-order depositional sequences, including the upper Carboniferous DS NG 1, and the lower Permian DS NG 2‒4. These sequences are correlated with their counterparts on the North African and Arabian plates. The sedimentary facies characteristics indicate palaeoenvironments ranging from fluvial, estuarine, intertidal, shallow subtidal, shoreface to offshore transitional settings. The abundant and diverse ichno-assemblages are composed of horizontal, vertical and sub-vertical traces. At least 26 ichnotaxa have been identified, representing suites of the Glossifungites, proximal Cruziana, and proximal-archetypal Cruziana ichnofacies. Ichnofabric analysis revealed three distinct ichnofabrics: Tisoa, Schaubcylindrichnus and Zoophycos ichnofabrics. The trace and body fossil distribution and trophic structure of some of the recorded faunal assemblages confirm relatively stable and low-stress shallow-marine environments. In contrast, the trophic structure of some other assemblages indicates the influence of particular environmental parameters, including substrate consistency, bathymetry, water energy, productivity, rate of sedimentation, salinity and oxygen availability. The integrated results indicate that the sequences were formed during an interval dominated by different perturbations that resulted in a wide spectrum of depositional features. Moreover, evidence for Carboniferous–Permian glaciation is tentatively established in North Egypt but require further investigations.

Sedimentary Facies, Architectural Elements, and Depositional Environments of the Maastrichtian Pab Formation in the Rakhi Gorge, Eastern Sulaiman Ranges, Pakistan

An integrated study of sediments was conducted to examine the facies architecture and depositional environment of the Cretaceous Pab Formation, Rakhi Gorge, and Suleiman Ranges, Pakistan. This research focused on analyzing architectural elements and facies, which are not commonly studied in sedimentary basins in Pakistan. To identify lithofacies, outcrop analysis and section measurement were performed. The identified lithofacies were then categorized based on their depositional characteristics and facies associations, with a total of nine types identified within a stratigraphic thickness of approximately 480 m. These facies were mainly indicative of high-energy environments, although the specifics varied by location. Sedimentary structures such as planar and trough crossbedding, lamination, nodularity, load-casts, and fossil traces were found within these facies, indicating high-energy environments with a few exceptions in calm environments. The identified facies were grouped into seven architectural elements according to their depositional environments: delta-dominated elements, including laminated shale sheet elements (LS), fine sandstone elements (SF), planar cross-bedded sandstone elements (SCp), trace sandstone elements (ST), and paleosol elements (Pa); and river-dominated elements, including trough cross-bedded sandstone elements (SCt), channel deposit elements (CH), and paleosol elements (Pa). These architectural elements, along with their vertical and lateral relationships, indicate a transitional fluvio-deltaic environment within the Pab Formation. In conclusion, by interpreting facies and architectural elements, it is possible to gain a better understanding of the depositional history of the formation and the distribution of reservoir units.

Compressibility characteristics of clays in the Red River Delta

The Red River Delta (RRD) is the second largest delta in Vietnam and is a significant economic zone in the country, encompassing important cities and economic zones. Geologically, the delta consists of clay layers distributed all over its area, which strongly impact the foundation designs of the infrastructure system (e.g., highways, industrial parks, harbors). However, up to date, there were no comprehensive studies on the compressibility characteristics of the clays in the delta. This study presents a primary study on some compressibility characteristics of clays in the whole delta with an emphasis on the use of CPTu data in the interpretation. For this, high-quality field and laboratory test results obtained from four research test sites and eight project sites were analyzed to depict the characteristics. The results indicate that the clays in the delta are typically soft to medium stiff and normally consolidated to slightly overconsolidated, which represent typical characteristics of young Holocene deposits. The compression index (Cc) of the clays was found to have good correlations with natural water content (Wn) or in-situ void ratio (e0). The ratio of radial coefficient of consolidation from a consolidation test with a central drain (CD) to the vertical coefficient of consolidation from the standard consolidation test (i.e., cr,CD/cv) from the 4 research test sites is on average 2.76 (log t method) and 2.32 (root t method) and these average ratios are found typical for deltaic soil deposits. The correlations for the remolded samples indicate that the drainage type has a strong influence to the induced coefficients of homogeneously remolded soils. Results from this study help geotechnical engineers have a general view on the compressibility characteristics of the clays in the delta, which in turn helps secure optimal foundation design solutions.

Numerical and Experimental Investigations of CoNiCrAlY Particle Suspension Dynamics in Kerosene-Oxygen High Velocity Oxygen Fuel Spraying

Three-dimensional computational fluid dynamics (CFD) modelling is employed to simulate a typical high velocity oxygen fuel process (HVOF) under laboratory operating conditions. Two different modelling approaches, viz., the continuum and discrete models, are engaged to model the liquid fuel kerosene, and their influence on the resulting primary gas dynamics is investigated. Numerical results of the primary gas dynamics are validated against the available measurements and found to be in good agreement. It is observed that the fuel droplets less than 5 μm react completely inside the combustion chamber, whereas the larger droplets do not. With increasing fuel droplet size, the chemical reaction gets extended to the downstream of the combustion chamber, resulting in decreased flame temperature. Thus, it is inferred that a fuel droplet size of up to 5 μm yields better combustion characteristics. Discrete solid CoNiCrAlY particles are then injected into the high velocity primary gas stream, and their inflight dynamics are simulated. Results reveal that a maximum mean particle velocity of 700 m/s and a maximum particle temperature of 1350 K may be achieved under the given operating conditions. Particle deposit shape and size are determined both numerically and experimentally and found to be in good agreement. The influence of substrate stand-off distance on the particle deposit characteristics is investigated and reported in detail.

The Hydraulic Connection Analysis of Dongying Geothermal Fluid Using Hydrochemical Information and Isotope Data in Tianjin Coastal Regions

Dongying’s Paleogene geothermal resources are an important part of the geothermal resources of the Tianjin coastal region. The extent of the geothermal fluid resources and the supply relationship have become increasingly important, and will determine whether demand targets can be met. Dongying’s Paleogene formation in the Tianjin coastal regions is widely distributed to the east of the Cangdong fracture, but it is absent west of the Cangdong fracture. On the basis of introducing the geological characteristics and depositional characteristics of the Dongying formation, we analyzed the hydraulic conductivity of the Cangdong fracture to the Dongying formation geothermal reservoir from the aspects of geological condition, dynamic of groundwater level and hydrologic geochemistry. Based on the hydrochemical information and the isotope data gained during the water quality evaluation and isotope data analysis process, we discovered the main chemical composition, hydrogen and oxygen isotope data and geothermal fluid age are significantly different between the Dongying formation geothermal reservoir and the overlying and underlying geothermal reservoirs. It is inferred that the hydraulic conductivity of the Cangdong fracture to the Dongying formation geothermal reservoir in this area is weak, and along the Haihe fracture, where the Haihe fracture intersects with the Cangdong fracture, there is a certain hydraulic conductivity. In addition, there is no obvious hydraulic connection between the Dongying formation and the upper and lower geothermal reservoirs.

Prediction of deposit characteristics based on the discrete coaxial nozzle during laser direct metal deposition

The variation in powder mass concentration distribution caused by the nozzle structure influence the deposit profiles and quality to a considerable extent in laser direct metal deposition (DMD) process. For symmetrical discrete nozzles, the powder mass concentration distribution was described, and the results were utilized in a molten pool model without powder feeding simulations. The evolution of the molten pool dimensions, and the temperature and velocity fields of single-track deposit were explored. The influences of specific energy (E) and mass per unit length (MUL) on the characteristics of single-track deposits were investigated. The correlation between the powder stream position and the concentration distribution was clearly expressed. The results indicated that the width/height ratio of single-track deposits decreased significantly, and the contact angle first increased and then decreased with higher specific energy intensity. Besides, the variation in the spatial position of the powder stream led to different mass concentration distributions, resulting in the tilt of deposit cross-sections towards the side with a higher mass concentration. The model exhibited a capacity for predicting the profiles of the deposits formed by symmetrical discrete nozzles.

Seismic bearing capacity of shallow foundations subjected to inclined and eccentric loading using modified pseudo-dynamic method

In this paper, a comprehensive parametric study is conducted to evaluate the seismic bearing capacity of shallow strip foundations overlying dry and cohesionless granular soil under the actions of inclined and eccentric loadings. For this purpose, a systematic combination of the lower-bound theorems of the limit analysis, the finite element method, and the nonlinear programming is implemented. The seismic loading condition is simulated by the well-established modified pseudo-dynamic (MPD) approach by accounting for the significant influence of phase difference as well as the primary and shear waves propagation through applying non-uniform inertia forces along the vertical and horizontal directions, respectively. Unlike the pseudo-static approach, in the so-called modified pseudo-dynamic loading, a more realistic dynamic nature of the seismic excitation is taken into account using various soil dynamic properties and spectral parameters of the problem under study. In this way, a more viable response of the shallow foundation subjected to seismic loading could be captured by simulating a visco-elastic material through the well-defined Kelvin-Voigt model. The modified pseudo-dynamic (MPD) method considers the influences of shear and primary wave velocities, amplification of earthquake loading, and period of lateral shaking. The current MPD approach is capable of considering the local site effects and damping characteristics of the soil deposit underneath shallow footing by adopting a non-uniform and nonlinear acceleration field inside the soil medium. The results of the seismic bearing capacity are presented in the forms of spectral responses and failure envelopes for the eccentric and inclined loadings. The results show that the failure envelopes of the shallow foundation subjected to either inclined or eccentric loading significantly shrink with the increase in the earthquake accelerations and decrease in the material damping of the underlying soil mass. The amount of changes in the size of failure envelopes in the normalized V-H and V-M spaces due to the variation of seismic intensity and material damping depends directly on the non-dimensional frequency of the earthquake excitation.

Spectral signatures for iron ore deposits in Tirthamalai area, Dharmapuri District, Tamil Nadu, India

The demand for iron ore has increased recently and employing geochemical and hyperspectral remote sensing techniques for discovering new ore and mineral resources have primarily been concentrated on the economic phases. The present study aimed to characterize the hyperspectral spectral signatures of iron ores of field samples to map the deposits that occurred in the Tirthamalai hill region, which lies in the parts of Harur Taluk, Dharmapuri district of Tamil Nadu state, India The measurement and study of spectral signatures of the different samples of the deposits showed strong spectral absorptions near 500 nm, 900 nm and 2400 nm wavelength regions and were confirmed with the Fourier Transform Infrared (FTIR) spectroscopy method. The spectral absorption characteristics of the samples were evaluated by the study of the physical, optical, and chemical characteristics of the samples. The study of hyperspectral and FTIR spectral signatures with petrographic and major chemical elements revealed the best absorption characteristics of the iron ore deposits of the study region and can be used elsewhere in the world. This report presents preliminary findings on the use of hyperspectral imaging to characterize iron ore. The mineralogical products produced from hyperspectral images may improve in situ grade control on an iron ore mine face. It will be extremely useful for businesses in measuring large numbers of commodities quickly and objectively.

Geologic and Geochemical Features of the World-Class Archean Windfall Intrusion-Related Au Deposit, Abitibi Subprovince, Canada

Abstract The Neoarchean Windfall gold deposit, hosted in the Urban-Barry greenstone belt of the Abitibi subprovince (Quebec, Canada), represents an emerging and significant Au deposit with a resource of 7.4 Moz of Au. It is hosted in 2717 Ma bimodal volcanic rocks that are cut by several generations of calc-alkaline quartz-feldspar porphyry dikes separated into (1) a 2697.6 ± 2.6 Ma group spatially related to Au mineralization and (2) a 2697.6 ± 0.4 Ma group that truncates the earlier dikes and the Au mineralization. The Au zones are structurally controlled and localized to faults and fractures proximal to the contacts of the early quartz-feldspar porphyry dikes; these zones form thin, subvertical, and elongate lenses plunging 35° east-northeast. Gold mineralization, present as both free gold and inclusions in pyrite, occurs (1) in gray quartz veins and stockworks with pyrite and subordinate carbonate and tourmaline and (2) in pervasive to patchy sericite-silica-pyrite-carbonate ± tourmaline ± fuchsite alteration zones. The Au mineralization and associated hydrothermal alteration, along with all the host rocks that include postmineralization intrusions, are overprinted by D2 deformational features that include a penetrative fabric, shear zones, and associated folds. The spatial and temporal association of the quartz-feldspar porphyry intrusions with the Au mineralizing event at the Windfall gold deposit, along with its elemental association (Ag, As, Sb, S, Se, Bi, Te, ± Zn, Cu, Pb, Mo, W), suggests an intrusion-related model and contrasts with the more abundant orogenic gold deposits in the Abitibi greenstone belt. This interpretation has important implications both locally and regionally for Au exploration in Archean greenstone terranes.

Geology and geochemistry of Zn-Pb(-Ge-Ag) deposits in the Sichuan-Yunnan-Guizhou Triangle area, China: A review and a new type

Mississippi Valley Type (MVT)1 deposits represent the majority of carbonate-hosted Zn–Pb deposits globally. They typically form in an extensional tectonic setting along passive margins. However, studies on carbonate-hosted Zn–Pb deposits in the Sichuan–Yunnan–Guizhou Triangle area (SYGT) reveal differences in terms of the essential features of typical MVT deposits. We discuss the main features of these deposits, controlled by folds and faults, high-grade Zn–Pb ores and symbiotic or associated elements (i.e., abundant Ag and dispersed amounts of Ge, Ga, and Cd) of significant economic value. Based on a comparison of Pb-Zn deposits in SYGT and classical MVT deposits formed in an extensional tectonic setting, as well as a subsequent discussion on deposit classification, we propose that the Huize-style Zn–Pb deposits are a new deposit style, whose basic features can guide future ore exploration. We define the Huize-style deposits based on four factors: i) Hierarchical ore-controlling system of strike-slip fault-fold structures, ii) litho-facies associated with typical alternation and mineralisation, iii) ore-forming geochemical features revealed by typical mineral assemblages, mineralisation alteration zoning, fluid-inclusion, isotope geochemistry and metallogenic acid–alkali geochemical barriers, and iv) different prospecting methods to those typically used for MVT deposits. The Huize-style and typical MVT deposits constitute the carbonate-hosted non-magmatic epigenetic hydrothermal-type (CNHT) Zn–Pb deposits.

Combination model-based numerical simulation of the mineralizing processes within iron oxide-apatite systems

Iron oxide-apatite (IOA) deposits are high grade iron magmatic-hydrothermal mineral deposits having significant economic values and extremely complex and coupled forming processes. The combination model of ore deposits is a model integrating characteristics of several deposits with the same genetic type or sharing close temporal-spatial correlations. This research highlights the usage of numerical simulation method and combination model of deposits in quantitatively analyzing ore-forming processes during the formation of IOA systems and views the future developments of numerical modeling in ore geology research. Our numerical model couples heat transfer, pressure, fluid-flow, chemical reactions and migration of ore-forming materials. Results match the fact that temperature reduction and pressure variation are two key factors controlling the temporal-spatial distribution of iron mineralization, and results of cooling process indicates that a single period of ore formation of IOA deposits may last no more than 12,200 years, a timespan much shorter than previously estimated. These results are obtained based on the concept of combination model of IOA systems, providing quantitative information reflecting the generation of IOA deposits. However, the methods in our research are stills limitations remained, such as uncertainty of pre-metallogenic conditions and restriction from elementary reactions. Future advances in analytical methods and mathematical models will definitely improve the practicality of combination model of deposits and numerical modeling of ore formation, and provide quantitative answers for existing problems related to mineral deposits.

О проблеме границы среднего и верхнего девона на Восточно-Европейской платформе

A brief overview of the history of the identification of the Frasnian Stage (Upper Devonian) and the determination of its lower boundary in the stratotype region is presented. The characteristics of the Givetian-Frasnian boundary deposits in the East European platform and the stratigraphic significance of the regional event levels are considered. Debatable issues on the age definition of the boundary deposits are discussed; tasks for the further investigations are set.

Prospecting for ophiolite-type chromite deposit in Sartohay, West Junggar (NW China): Constraints from geological and geophysical data

Chromite is a critical mineral that is of great significance for the development of metallurgical, chemical, and other industries. In order to study the deep ore prospecting methods of ophiolite-type chromitite, we have carried out plane-profile geological and mineral surveys, as well as high-precision gravity, magnetic, and controlled source audio-frequency magnetotelluric (CSAMT) measurements in the Sartohay, West Junggar. Based on the analysis, interpretation, and inference of multi-source geological information, a three-dimensional (3D) geological model of the typical mining area in Sartohay District was established. The results show that Sartohay ophiolite was occurred in the form of rootless tectonic blocks and generally displayed deformation and metamorphism (e.g., oblique thrust, transverse extrusion, and lateral strike slip). Sartohay ophiolite is in tectonic contact with surrounding strata. Several northwest dipping high-angle thrust faults are developed at the contact sites and inside the ophiolite rock mass, showing a thrust imbricated structure. Meanwhile, ophiolite in the modeling area is a NW-trending monoclinic rock mass. The base surface of the ophiolite is obliquely distributed in an “N-like” shape, and the chromitite bearing lithofacies zones also have a NW-trending distribution. Geophysical data reveal that the studied mining area is characterized by a layered electrical structure in the vertical direction. The upper layer displays a high-resistivity agglomerate and a low-resistivity band distributed alternately, while the lower layer is a complete high-resistivity block. Combined with the deposit characteristics in Sartohay, it is considered that the morphological occurrence, geological structure, lithology, and lithofacies of ophiolite control the spatial distribution of related chromitites. The dunite-harzburgite lithofacies belts, highly strain zones, and strong tectonic alteration belts of the ophiolite rock mass are significant sites for the chromite ore bodies/groups occurrence. This study provides approaches for researching on the production laws of ophiolite-type chromitite and supplys a prospecting pattern for deep concealed orebodies.

Spatial-temporal distribution, metallogenic mechanisms and genetic types of nephrite jade deposits in China

The nephrite jade deposits of different tectonic units in China exert significant commercial quality, which have attracted wide attention. However, these deposits have not been systematically summarized to date. Here, we investigate the major nephrite jade deposits in China to decipher their gemological and mineralogical characteristics, spatial-temporal distribution, and mineralization processes as well as to identify their geological settings and gemological properties, via integrating published geochronology, major and trace elements as well as H-O isotopes. The compiled data suggest that the major nephrite jade deposits in China can also be generally divided into green jade-type (GJ-type) and white jade-type (WJ-type) which covers different species, but most of them belong to the latter. The GJ-type nephrite deposits predominantly occur in ophiolite/ophiolitic mélange suites or are embedded into ultramafic serpentine jade orebodies. This type of nephrite jade mainly formed through the late auto-metamorphic metasomatism of serpentine or the spontaneous crystallization/precipitation along suture/shear zones that acted as pathways to migrate Ca-rich fluids during orogeny. In contrast, the orebodies of WJ-type nephrite jade are usually hosted at the contact zones between the dolomitic marbles and intermediate-felsic or mafic intrusive rocks, which were produced through metamorphism-metasomatism during post continent-continent collision, such as the Kunlun orogenic belt with about ∼1,300 km Hetian nephrite belt, and the eastern nephrite jade deposits along the Pacific Ocean. Our study highlights that the nephrite jade deposits in China originally formed during multiple tectonic stages related to the interactions between hydrothermal fluids and metamorphism under subduction accretion- and collision orogenesis-related settings. In addition, this study also provides insights into the genetic discrimination, mineral exploration, and occurrence characteristics of nephrite jade deposits as well as the evaluation and identification of nephrite jade quality.

Case Histories of Orogenic Gold Deposits

This review compares genetic parameters of 12 orogenic gold deposits. The set of examples is considered to represent largely the variability of orogenic gold deposit (OGD) characteristics. The data are presented in tables and include following definitive parameters: regional geologic settings, nature of hosts rocks and mineralization, ore controlling structures, ages of host rocks and mineralization and timing of mineralization relative to metamorphism, hydrothermal alteration mineralogy and ore mineral assemblages, isotopic signatures, physical conditions of ore formation and proposed origin of ore fluids aa well as gold reserves, production, and grades. This allows comparison of deposits from different geologic terrains having different ages and formed under different P-T conditions. The data are further discussed before the background of the orogenic gold system and the crustal metamorphic models that provide different scenarios to explain the source of ore fluids. The orogenic gold system model advocates a metal and fluid source external to the terrain in which mineralization occurred, but the model applies only for 3 of the 12 deposits studied. All other deposits formed most likely from a crustal source, which would favor the crustal metamorphic model. However, the formation of hypozonal OGDs cannot be accounted for by the crustal metamorphic model or by the metamorphic devolatilization model. The data identify a set of coherent signatures in OGDs, but there seem to be no unified model for all possible environmental conditions and facets of ore formation and fluid sources, tectonic and lithologic setting, and scale of gold endowment.

Modal analysis and extraction method for the frame structure considering soil-structure interaction effect

For a soil-structure interaction (SSI) system, the direct method can analyze the dynamic characteristics of the arbitrary complicated soil deposits. However, to determine the radiation damping effect on the structural dynamic characteristics, the complex modal analysis using the direct method needs to calculate many complex modes for obtaining the few exact structural modes due to a large number of soil degrees of freedom. The needed structural modes among a large amount of soil modes are difficult to be extracted. In this paper, a new complex modal analysis method using sequential eigenvalue-shift is developed for the calculation of the modal parameters of the frame structure under SSI effect. Accordingly, a new index of the local modal mass ratio is proposed to quickly and accurately extract the structural modes from many combinations of modes from structures and soil. Several comprehensive examples are presented to validate the proposed method, and the influence of artificial boundary on the natural frequency, mode and modal damping ratio of the structure is investigated.

Depositional and structural characteristics of the Chashm Sub-basin; implications for the late Cenozoic tectonic evolution of the east-central Alborz Mountains, northern Iran

Depositional and structural characteristics of the Chashm Sub-basin; implications for the late Cenozoic tectonic evolution of the east-central Alborz Mountains, northern Iran

Channel morphology as a key factor to hydrological and sedimentological patterns in the largest fluvial ria lake of Amazonia

Amazon ria lakes are geomorphological features still poorly known despite their great magnitude and uniqueness. The Tapajós ria comprises one of the largest natural channels in the world, measuring impressive 20 km in width in its lower reach. Important data on longitudinal distribution of matter and energy has been collected in the last decades, but far less attention has been given to its transversal variation. In this paper we analyze grain size and major element concentration of bottom sediment on Tapajós ria lake, sampled along transversal profiles, in order to investigate the importance of channel morphology on data interpretation and to better describe fluvial dynamics. Geomorphological analyses of the channel Digital Elevation Model (DEM) coupled with remote sensing products allowed us to describe depositional features along the ria. We observed that novel patterns might emerge when transversal distribution is considered. Our results also support that local drainages and processes such as marginal scarp retreat may have an important role on the ria infilling. This approach has the potential to be applied to other large fluvial systems in the world helping to increase our understanding of the processes that shape their morphology.

Tectonic Background of Carboniferous to Early Permian Sedimentary Rocks in the East Kunlun Orogen: Constraints from Geochemistry and Geochronology

The formation of the East Kunlun Orogen (EKO) was related to the tectonic evolution of the Proto-Tethys and Paleo-Tethys Oceans. However, how the Paleo-Tethys Ocean transited from the Proto-Tethys Ocean, and whether the Paleo-Tethys Ocean subducted northward beneath the East Kunlun–Qaidam Terrane in Carboniferous to Permian times, is still highly debated. Early Carboniferous Halaguole and Late Carboniferous to Early Permian Haoteluowa formations are extensively outcropped in the EKO, north Tibetan Plateau, and have thus recorded key information about the tectonic processes of the Paleo-Tethys Ocean that have implications for the reconstruction of the Northern Paleo-Tethys Ocean (Buqingshan Ocean). Siliciclastic rocks within these formations are collected for petrogeological, geochemical, and detrital zircon U–Pb dating research. Our results show that sandstones from Halaguole and Haoteluowa formations have an average total quartz–feldspar–lithic fragment ratio of Q67F12L21 and Q50F20L30, respectively, indicating relatively high compositional maturity. The geochemical results suggest that the average values of the Chemical Index of Alteration (CIA) are 57.83 and 64.66; together with their angular to subangular morphology, this indicates that their source rocks suffered from weak weathering and the sandstones are the result of proximal deposition. Geochemical features such as the low La/Th, TiO2, and Ni values suggest that the parental rocks in the provenance area are mainly acidic igneous rocks with minor intermediate igneous and old sedimentary components. The detrital zircon U–Pb age spectrum of these samples is dominated by age peaks at ~405–503 Ma and ~781–999 Ma, with subordinate age peaks at ~1610–2997 Ma and ~1002–1529 Ma, which show tectono–thermal events similar to those of the North Qimatag Belt (NQB), North Kunlun Terrane (NKT), and South Kunlun Terrane (SKT). These features suggest a contribution from the Early Paleozoic magmatic arc and Proterozoic basements in the NQB, NKT, and SKT to the Halaguole and Haoteluowa formations in these areas. In addition, the youngest zircon age of ~440 Ma from these sandstones is greater than the depositional age of Halaguole and Haoteluowa formations, which is a typical basin depositional feature in a passive continental margin. Geochemical tectonic discrimination diagrams, based on a major and trace element Ti/Zr–La/Sc plot, in combination with a detrital zircon age distribution pattern, all suggest a passive continental margin setting. Considering this together with the previous data, we argue that the Paleo-Tethys Ocean did not begin to subduct northward and that there was no oceanic subduction zone in the south EKO during Carboniferous to Early Permian times. Combining this information with that from previous studies suggests that the initial opening of the Paleo-Tethyan Ocean may have occurred before the Early Carboniferous time, and all the branches of the Paleo-Tethys Ocean constituted a complex ocean–continent configuration across parts of what is now Asia during the Early Carboniferous to Early Permian.