Orogenic Research Articles

Age and origin of Bereinsky complex Granitoids of Kamensky Terrane of the Monghol-Okhotsk orogenic belt: results of U-Pb (ID tims) geochronological and Sm-Nd isotope-geochemical research

Dating of magmatic rocks from paleo-island arcs of orogenic belts helps to define the precise timing of subduction processes that took place during the formation of the orogen. Within the central (East Trans-Baikal) part of the Mongol-Okhotsk orogenic belt, the Kamensk island-arc terrane is an example of such paleo-island-arc complex. Its intrusive part is included into the Bereinsky complex, represented by a gabbro-diorite-tonalite-plagiogranite series of rocks demonstrating subduction geochemical characteristics. The dating of zircons from acidic rocks of this complex by the U–Pb classical method showed that they were produced in a narrow time interval – 203±1–205±1 Ma, which corresponds to Norian/Rhaetian boundary of the Late Triassic. Taking into account the previously obtained age of the diorites (254±5 Ma), the timing of formation of the entire series of intrusive rocks is about 50 Ma, thus indicating in the Late Permian – Late Triassic the subduction along the northern (in modern coordinates) margin of the Mongol-Okhotsk Paleocean beneath the Siberian paleocontinent. Diorites of the first phase have positive values ɛND(254MA) = 3.2–3.6 (TNd(DM) = 879–994 Ma), and plagiogranites – ɛND(205MA) = 2.3–3.5 (TNd(DM) = 859–1028 Ma), which points to the connection of these rocks with the substance of the depleted mantle source and is consistent with the Sm-Nd isotope characteristics of the juvenile crust of the Central Asian orogenic belt. This study was supported by Russian Science Foundation, grant no. 22-27-00775. The resources of the Shared Use Center for Isotope-Geochemical Research (Vinogradov Institute of Geochemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk) were used in this work.

Exploring the Gravitational Impact of Spring Tides on Earthquake Occurrence in Central Asia

Abstract In this study, we analyzed variations in seismic activity in relation to the syzygy of the Sun, Moon, and Earth, corresponding to the semilunar or spring tide (ST) cycle. We focused on two regions within the Central Asian Orogenic Belt: the North Tien Shan region (NTSR) and the Xinjiang Uygur tectonic province (XUTP), using data from two regional earthquake catalogs. For the NTSR, we used data from the Seismological Experimental and Methodical Expedition in Almaty, Kazakhstan, covering 1 January 1970 to 31 July 2022. For the XUTP, we utilized data from the Data Management Centre of China National Seismic Network at the Institute of Geophysics China Earthquake Administration, spanning 1 January 1987 to 30 June 2019. We applied the nonparametric Kuiper’s test to evaluate cyclic variations in seismic activity, focusing on different magnitude thresholds in the regional catalog. For both regions, the original catalog as well as the catalogs of mainshocks and aftershocks were analyzed. The nearest-neighbor declustering method was employed to decompose the seismic catalogs. Kuiper’s test statistics revealed varying trends in the occurrence times for mainshocks and aftershocks during ST cycles. The test showed “the good-to-fit” to a uniform distribution for the timing of mainshocks within the ST cycle. Kuiper’s test revealed notably consistent trends in aftershock occurrence times during ST cycles with a significance level α of 0.001 or less in both regions analyzed. These results suggest a potential correlation between aftershock activity and the gravitational effects of the ST cycle. The most substantial decrease in aftershocks occurs during the micromoon ST cycle, when the distance between the Moon and the Earth exceeds 400,000 km.

Late Mesozoic intracontinental reactivation of the southern Altai, Central Asia

The Altai orogenic belt is a main constituent of the Central Asian Orogenic Belt, and serves as a crucial site for studying strain propagation from the Meso-Cenozoic plate margins to the Eurasian interior. The ranges of the Altai Mountains have undergone multiple reactivation events during the Mesozoic and Cenozoic, but the full extent of these events is not yet fully understood. To constrain the thermo-tectonic history of the southern Altai orogenic belt of Northwest China, apatite fission-track (AFT) and apatite (U-Th)/He (AHe) thermochronological methods were used to study 29 pre-Mesozoic basement rocks from several key localities, including the Altay, Xibodu, Fuyun, and Qinghe regions. Late Jurassic to Early Cretaceous AFT and AHe ages were found in the low-elevation Xibodu region, which has been characterized by slow-to-moderate rock cooling since the Jurassic. However, rock samples from all other regions investigated are characterized by comparable Late Cretaceous AFT and AHe ages. Inverse thermal history modeling results reveal moderate-to-rapid upper crustal cooling in the mid- to Late Cretaceous (ca. 110−70 Ma), which is interpreted to be related to distant plate-margin processes (e.g., the Cimmerian collisions). These findings, combined with previously published data, indicate that Late Cretaceous exhumation was widespread in the western Altai orogenic belt, including in the Chinese and Siberian (Russian) parts of the Altai region. As in many other areas of Central Asia, no Cenozoic low-temperature thermochronological signal was detected in this study. We propose that Cenozoic deformation indeed occurred in the southern Altai, but the magnitude of associated denudation was insufficient to have replaced the Cretaceous cooling signals.

Petrology of gabbroic rocks from the lower crust of a back-arc basin: an example from the ophiolitic Liuyuan Complex, northwestern China

Abstract The 290-282 Ma ophiolitic Liuyuan Complex in northwestern China preserves a section of oceanic crust formed in a back-arc basin during the final stages of the evolution of the Central Asian Orogenic Belt. We present results of detailed field work, petrography, whole rock, and mineral chemistry of the plutonic rocks of the Liuyuan Complex. These include: troctolite, melatroctolite, olivine gabbro, podiform olivine gabbro, podiform hornblende gabbro and intrusive hornblende gabbro. Major element data, petrography, low incompatible trace element concentrations, and positive Eu-Sr anomalies suggest that basal troctolite and melatroctolite are accumulations of olivine + plagioclase primocrysts, with varying proportions of interstitial, ophitic, and poikilitic clinopyroxene forming from trapped melt. Olivine gabbro dominates the plutonic crust between the troctolites and sheeted dykes. Troctolites and olivine gabbros have weak paleo-horizontal foliations and show systematic upward cryptic mineral-chemical trends of decreasing clinopyroxene Mg#, plagioclase An, and olivine Fo and NiO contents. Trace element modelling suggests low trapped melt fractions in the cumulates (5-15%) and implies clinopyroxene was a minor cumulus phase in the olivine gabbros. The cryptic mineral-chemical evolution and textures imply most troctolites and olivine gabbros formed as sequential accumulations from an evolving melt. Melatroctolite layers (~5m thick) in troctolite may represent fossil replenishment events. Immediately below the sheeted dyke unit, there are meter-scale pods of cumulate olivine gabbro containing abundant hornblende (25-45%), as well as decimeter- to meter-scale pods of quasi-liquid olivine gabbro with compositions similar to overlying dykes and lavas. Isolated intra-plutonic dykes of hornblende gabbro also have basaltic compositions. In the podiform hornblende gabbro, high-temperature magnesio-hornblende likely formed as a reaction product between clinopyroxene and a hydrous pore melt. Trace element inversion models indicate that these diverse plutonic rock units formed from a tholeiitic parental melt cogenetic with the overlying basalts. The Liuyuan ophiolitic complex represents a coherent slice of oceanic crust formed in a back-arc basin.

Neoproterozoic-early Paleozoic tectonic evolution of Oman revisited: implications for the consolidation of Gondwana

Implications of a new tectonic evolution model that puts Oman at the eastern margin of the Mozambique Ocean during the Neoproterozoic are wide and regionally significant. This model helps understanding the Neoproterozoic tectonics and paleogeography of Gondwana, the closure of the Mozambique Ocean, the paleogeography of the world-renowned Cryogenian and Ediacaran successions of Oman, and the petroleum systems of Oman and the rest of Arabia. The proposed evolution model implies that the basement of Oman formed at the margin of Neoproterozoic India, and that the Cryogenian-Ediacaran sedimentary succession of Oman, and its early tectonic evolution, whose structural trends influenced tectonics through its geological history, were separate from those of the Arabian-Nubian Shield to the west*, as they were on opposite sides of the Mozambique Ocean up to the early Cambrian. It also implies that the final Gondwanan suture lies somewhere along, or just west of, the Western Deformation Front, an early Cambrian orogenic belt now found in the subsurface of Oman and in outcrops of north and south Oman. Its development is related to Malagasy-Angudan Orogeny, and it separates two realms: the juvenile Ediacaran basement and active margin sedimentary successions of the Arabian-Nubian Shield, and the Tonian igneous and metamorphic basement, Cryogenian rift deposits and Ediacaran passive margin deposits of Oman/Neoproterozoic India. The Precambrian hydrocarbon systems of Oman do therefore not extend to western Arabia, but to India and Pakistan instead. Sediment provenance studies using zircon geochronology and facies maps of the Neoproterozoic successions help to understand the tectonic setting during deposition and the distribution of reservoir rocks in shallow water settings in northeast Oman, and source rocks in deep basinal settings in south and west Oman.

The occurrences, characteristics, and implications of chaotic rocks (accretionary rocks) within the Trans-Saharan orogenic belt in Nigeria

The present research paper reveals the occurrences of metachaotic rocks/accretionary sediments (mélange) in Igarra, southwest Nigeria. These metachaotic rocks are associated with schistose, marble, pegmatite, granitoid, and gneissose units. The mineral assemblage of the surrounding rocks shows garnet, biotite, staurolite, quartz, and chlorite assemblage, which suggest that the rocks were metamorphosed to the epidote–amphibolite facies grade. The chaotic rocks were classified into four groups based on major differences in color, grain size distribution, and stratigraphic and structural characteristics of observed blocks and matrices surrounding them. Group I metachaotic rocks are melanocratic in color, and form pockets of coarse lineation. They are highly deformed with mullions, rodding structures, and burrow-like cavities and show quartzite veins. Group II occurs as a leucocratic to melanocratic mixture of meta-siltstone and metapelite with greenish rock fragments trapped within the meta-siltstone layers. This unit has a cover of meta-siltstone layers occurring in pockets as striations forming mullion and rodding structures as well as ripple-like lineation. Group III metachaotic rocks occur as multiple benches of different strata tilted between 70 and 80º, with mild folding and burrow-like cavities at the base and well-preserved sedimentary structures. In Group IV, there are evidences of pre-metamorphic soft sediment deformational structures that are well-preserved in the metachaotic rocks, with discontinuous blocks of different units trapped within mixtures of metapelite and meta-siltstone. In this group, micro-faults and quartzite veins are scattered within the rocks. Meta-siltstone occurs as horizontal and vertical layers and web-like structures showing dendritic patterns. Overall, the field and petrographic characteristics suggest the Igarra metachaotic rocks are tectonic in origin and may have been formed within the trench basin of an outer accretionary complex.

Zircon U-Pb geochronology and Sr-Nd-Pb-Hf-O isotope signatures of Middle Eocene high-K plutons from the Eastern Pontides Orogenic Belt, NE Turkey: implications for parental magma sources and magmatic processes

ABSTRACT The Eastern Pontides Orogenic Belt (EPOB) in northeastern Turkey is a well-preserved continental magmatic arc in the Alpine-Himalayan Orogenic Belt and contains many Eocene I-type high-K plutons. Employing LA-ICP-MS U-Pb zircon geochronology, the crystallization ages of the investigated Yaylalıköy and Taşbaşı plutons were established to be Lutetian (Middle Eocene), ranging from 47 Ma to 46 Ma. These plutons exhibit a compositional spectrum ranging from diorite to granodiorite, characterized by I-type, metaluminous, and high-K geochemical signatures. Notably, they are enriched in large-ion lithophile elements (LILEs) and light rare earth elements (LREEs), displaying pronounced negative Eu anomalies (EuN/Eu* = 0.58–0.96). Isotopic signatures reveal homogeneous and moderately low initial 87 Sr/86 Sr(i) ratios (0.704643–0.705034) and positive εNd(i) values (0.24 to 1.67) for the investigated plutons. These isotopic signatures are consistent with mantle origin, as evidenced by their position within the mantle array on isotope ratio diagrams. Lead isotope compositions exhibit limited variations, with initial ratios of 206 Pb/204 Pb(i) (18.55–18.64), 207 Pb/204 Pb(i) (15.61–15.64), and 208 Pb/204 Pb(i) (38.46–38.75). Zircon εHf(i) values are positive (2.32–6.20), plotting between the depleted mantle and chondritic evolution lines. Additionally, these rocks display low zircon δ18 O values (+4.54 to + 6.53‰), comparable to mantle composition. The petrographic characteristics of the investigated plutons suggest that fractional crystallization with minimal assimilation and/or magma mixing played a dominant role during their solidification. The integration of geochemical and isotopic data, alongside regional geological constraints, advocates for enriched lithospheric mantle as the source for the parental magmas of the studied plutons. These magmas subsequently underwent differentiation within a deep-seated magma chamber, followed by emplacement into the crust.

Air Temperature Variations Analysis of the Hualian M6.9 Earthquake

This study examines the three-dimensional layered air temperature variations associated with the Hualian M6.9 earthquake, which occurred on 18 September 2022, using data from the National Center for Environmental Prediction (NCEP) and extracting background information for air temperature through tidal forces. Changes in air temperature stratification revealed that near the epicenter, temperature anomalies began on 12 September and peaked on 13 September, with pronounced increases in magnitude and area. These anomalies followed a seismic thermal anomaly pattern, i.e., one with greater amplitude and a wider range near the land surface, decreasing with altitude until they dissipated, while the other exhibited high atmospheric temperature anomalies, i.e., the upper atmospheric warming exceeded that near the land surface, likely due to meteorological factors. Stable weather conditions and a low geomagnetic Kp index and Dst index during the research period supported the reliability of these findings. The deformation field recorded by InSAR reflects crustal deformation directly caused by fault slip and stress accumulation; moreover, the area with significantly higher air temperature coincides with the areas with the most concentrated deformation.

Crustal deformation in East of Cairo, Egypt, induced by rapid urbanization, as seen from remote sensing and GNSS data

Abstract The area located East to Cairo, the Capital of Egypt, represents an obvious example for the rapid urban expansion, as it contains many new housing cities. Beside its socio-economic importance, it’s located in the Cairo-Suez seismic zone. We utilized Persistent Scatterer Interferometry (PSI) of 2015–2021 Sentinel-1 SAR scenes along with two GNSS stations (KATA and PHLW) to assess the distribution and rates of crustal deformation of this region. The PSI analysis is applied to 140 Sentinel-1 SAR images collected from the ascending track number (58) and the descending track number (167). The Bernese software V. 5.0 is used for the processing of the GNSS data. A good agreement between the rates estimated from the PSI analysis and GNSS data is observed. Based on results, most of the new cities showing land subsidence with variable rates. The rates at Obour, New Cairo, Shorouk, Madinty, and Capital Gardens are 0.54 ± 0.30 mm/year, 0.58 ± 0.30 mm/year, 1.01 ± 0.30 mm/year, 0.58 ± 0.30 mm/year, and 0.99 ± 0.30 mm/year, respectively. The highest recorded subsidence rates are at Asher, Administrative Capital, and Badr with 2.18 ± 0.30 mm/year, 1.89 ± 0.30 mm/year, and 1.69 ± 0.30 mm/year, respectively. Nasr city is the only city with an uplift of 0.82 ± 0.30 mm/year. Our new findings introduce the probable use of integrated techniques such as GNSS and InSAR to evaluate the extent of crustal deformation connected to rapid urbanization in arid areas. Beside tectonic setting, it should be considered while executing mega-projects for sustainable development especially within Egypt’s Vision 2030.

Tectonic anabranching of Brahmaputra River system: implications on survival of world’s largest inhabited river island Majuli

Brahmaputra is a large, tropical, trans-boundary river with high sediment load and has the unique distinction of possessing both largest and smallest inhabited river islands. Majuli is the largest inhabited river island situated in the Indian state of Assam and bounded by Brahmaputra on the south, Subansiri River on the northwest, and the Kherkatia River (anabranch of Brahmaputra) on the northeast. The island was formed during a flooding event in 1750 with a sudden change in the course of the Brahmaputra from a low energy meandering to a high energy braided river and subsequent capture of one of its tributaries. The island is a part of the Brahmaputra alluvium squeezed between active Himalayan and Indo-Burmese orogenic belts in an intricate tectonic regime. The dominant flow path of Brahmaputra is controlled by the crustal scale reorganization in this part of the world. The tectonic factors that controlled the anabranching process and created the island, is at present acting as the destroyer of the same by the means of unabated erosion. The erosion pattern of the two rivers viz. Brahmaputra and Subansiri were studied and areas with marked selective erosion have been found. From a combined study of satellite imaging, bathymetric survey and mapping, it is found that the lobate shaped erosions in the study areas are restricted to traces of the tectonic elements related to the Himalayan thrust system through which the rivers are trying to anabranch.

A volcanic and gravity flow controlled fine-grained organic rich deposits of the lower Jurassic Beipiao formation in the Western Liaoning, northeast China

IntroductionThe Lower Jurassic Beipiao Formation in the western Liaoning of northeast China represents a significant case study for understanding the interplay between volcanic activity, sedimentary processes, and organic matter enrichment.MethodsThis study aims to investigate the lithofacies, depositional environments, and hydrocarbon potential of the Beipiao Formation, using core, outcrop, thin-section, and geochemical data.ResultsThirteen lithofacies types were identified, which reflect a complex depositional history influenced by volcanic processes and gravity flows. The sedimentary facies analysis revealed three key depositional environments: shallow lake, semi-deep to deep lacustrine, and fan delta. The basin evolution suggests a transition from fan delta deposits to deep lake deposits and then back to fan delta, with volcanic and gravity flow deposits interbedded. Volcanic activity not only provided nutrient-rich environments conducive to biological productivity but also helped create conditions favorable for organic matter preservation. The earthquake, flooding or stormed events induced gravity flow, which favored plant fragments dispersal to the deep-lake and formed type III kerogen in the deep-lake developed area.DiscussionThese findings suggest that the Jurassic Beipiao Formation in western Liaoning Province, exhibit significant hydrocarbon potential. This challenges previous assumptions regarding the dominance of shallow water environments and limited exploration prospects within the Yanshan Orogenic Belt. Furthermore, this study highlights the crucial role of volcanic activity and gravity flow in organic matter enrichment, transportation, and preservation within a volcanic-rift basin, with potential applicability to similar basins worldwide.

Advances in Magmatic Ni–Cu–(PGE) Sulphide Deposits and Their Constraints on Neoproterozoic Tectonic Settings of China

ABSTRACTMagmatic Ni–Cu–(PGE) sulphide deposits are the primary global sources of nickel, copper and platinum group elements (PGE). The study of these deposits is critical for mineral exploration and holds important economic implications. This paper reviews recent advances in understanding magmatic Ni–Cu–(PGE) sulphide deposits and their related magmatism. Findings reveal that these deposits have an uneven global distribution and a wide range of classifications. The Proterozoic era represents the main period of mineralisation, and the mineralisation setting is closely related to continental rifts, mantle plumes and collision orogenic belts. An ongoing debate exists between the ‘magma conduit’ and ‘deep‐multiple magma chamber segregation’ models, which differ in mineralisation location, magma intrusion mechanisms and the role of external sulphur addition. The primary mechanisms of sulphide segregation include rapid cooling, crystal differentiation and crustal contamination. Furthermore, this paper examines the spatial–temporal distribution and mineralisation dynamic settings of Neoproterozoic magmatic Ni–Cu–(PGE) sulphide deposits in China and their relationship to the convergence and breakup of the Rodinia supercontinent. These Neoproterozoic deposits are located along the margins of the Yangtze, North China and Tarim blocks. They formed in five different stages, 1000–960, 900–850, 830–800, 760–740 and 650–620 Ma, corresponding to the following tectonic settings, respectively: (1) a back‐arc extensional setting before the convergence of the Yangtze and Cathaysia blocks; (2) a post‐orogenic extensional setting following the convergence between the Yangtze and North China blocks; (3) a rift setting related to the first Neoproterozoic mantle plume event (830–795 Ma) within the Yangtze Block or North China Block; (4) a rift setting related to the second Neoproterozoic mantle plume event (780–745 Ma) within the Tarim Block and (5) an intraplate rift setting within the Yangtze Block. The evolving mineralisation dynamic settings of these deposits indicate that their mineralisation is directly related to large‐scale mafic–ultramafic magmatism during the Neoproterozoic and the convergence and breakup of the Rodinia supercontinent.

Ophiolites in the Central Asian Orogenic Belt record Cambrian subduction initiation processes

Subduction initiation remains elusive because no present example exists. Ophiolites formed over nascent subduction zones in the past provide the key to constraining the processes of subduction initiation. Here we document three Cambrian ophiolites with supra-subduction zone affinity, which likely reflect the inception of a plate-boundary scale subduction zone within the Paleo-Asian Ocean. Our findings, together with a compilation of Cambrian ophiolites in the Central Asian Orogenic Belt, indicate diachronous subduction initiation(s) along a > 6000 kilometer zone within the Paleo-Asian Ocean between 536 and 528 million years ago. The subduction initiation of the Paleo-Asian Ocean coincides with the closure of the Mirovoi Ocean following the collision of a series of microcontinents with the Siberian craton, likely representing a typical record of collision-induced subduction jump. Our observations and numerical modeling provide a new scenario that subduction initiations would locate at oceanic weak zones rather than passive margins of accreted microcontinents during collision-induced subduction process.

Silurian–Devonian boundary in Northern Xinjiang, NW China

During the Silurian–Devonian Boundary (SDB) interval, in contrast to the predominantly carbonate facies observed in Europe and North America, China was composed of several plates/terranes dominated by clastic and pyroclastic rocks. Continuous sections across the SDB have been only sporadically reported from the orogenic belts and southwestern margin of South China. In many regions or sections in China, the identification of the SDB is based solely on fossil assemblages or non-index fossils, which results in only a rough approximation of the position of the boundary. This study focuses on the Junggar area in the Central Asian Orogenic Belt, characterized by pyroclastic rocks and scarcity of fossils compared to regions with carbonate dominated successions. This paper summarizes previous research findings and discusses the SDB in northern Xinjiang, China, integrating new data on Devonian conodont Caudicriodus hesperius, the presence of benthic organisms represented by encrinurid trilobites and crinoids, and the occurrence of late Silurian graptolites, along with the first organic carbon isotope curve around the SDB for the Central Asian Orogenic Belt, and provided crucial evidence for the recognition of the SDB in the orogenic belt area of China, consindering the SDB in Northern Xinjiang is located within the Utubulag Formation in the western Junggar and the presence of the SDB in the Kaokesaiergai Formation of the eastern Junggar has also been confirmed. The age of the corresponding strata: Utubulag, Manger, Kaokesaiergai formations are revised, and a more detailed description of the classic sections of the SDB in northern Xinjiang is provided. The new fossil and geochemical data serve as basis for recognition of the Silurian–Devonian boundary in northern Xinjiang, and also contribute to a more comprehensive understanding of paleoenvironmental events at the Silurian–Devonian transition in the northern hemisphere and the orogenic belt areas.

Final subduction-closure process of the Paleo-Asian Ocean in the middle segments of the southern Central Asian Orogenic Belt: Constraints from Permian volcanic rocks and late Triassic mafic dike swarms

The final subduction-closure process of the Paleo-Asian Ocean (PAO) in the middle segments of the southern Central Asian Orogenic Belt (CAOB) is widely debated. Linear arc-related pyroclastic sedimentary rocks and subsequent mafic-alkaline intrusive rocks parallel to the orogenic belt provide valuable constraints on ocean closure. Linearly distributed volcanic samples from the northern margin of the Alxa Block have zircon UPb ages ranging from 272 to 271 Ma, displaying arc geochemical signatures and large ranges of variation (−14.4 to +6.4) of zircon Hf isotopic composition. The Honggueryulin mafic dikes in the Nuoergong–Langshan Belt (NLB) with zircon and apatite UPb dating of 232–231 Ma show a clear geochemical imprint of subduction components with enrichment of light rare earth elements and large-ion lithophile elements (e.g., K, Rb, and Ba) and depletion of high-field-strength elements (e.g., Nb, Ta). The whole-rock major and trace elements and Sr–Nd–Hf isotopic compositions suggest that the Late Triassic mafic dikes mainly originated from a lithospheric mantle that had been metasomatized by subduction-related fluids. Coupled with published data, our geochronological and geochemical data support an east–west-trending Late Triassic alkaline–mafic intrusive rock belt distributed along the northern margin of the Alxa Block–North China Craton, which was formed in a post-orogenic intraplate extensional setting. These pyroclastic sediments and mafic dikes in the NLB document the tectonic transition from the Permian subduction to the Late Triassic post-orogenic extension. Therefore, the final closure of the PAO in the middle segments of the southern CAOB is constrained to between the Early and Middle Triassic.

Fluid evolution and halogen fractionation in orogenic belts: A comparative fluid inclusion appraisal in the Eastern Pyrenees

Fluid evolution and halogen fractionation in orogenic belts: A comparative fluid inclusion appraisal in the Eastern Pyrenees

Lithium pegmatite formation in Kelumute-Jideke pegmatite field, Chinese Altai: Insight from geochronology, petrology and lithium isotope geochemistry

The Kelumute-Jideke pegmatite field is an important lithium (Li)-rich pegmatite mineralization area within the Chinese Altai orogenic belt. There have been four large (Kalu’an No.803, No. 805, No.806, No.807 veins), one medium (Kelumute No.112 vein), nine small deposits (such as Jiamukai, Qunkuer, Azubai) with totally 130,000 tons Li2O found in this area. However, it remains enigmatic whether Li-rich pegmatite formed through fractional crystallization of coeval granite or direct anatexis of metasedimentary rocks. Here we selected pegmatites and their surrounding rocks of metasedimentary rocks and granitic batholith in this pegmatite field to conduct geochronology, whole major and trace element, and Li isotope analyses. The granite intrusions in this field exhibits multiple-stage emplacement ages, including 447.7 ± 4.2 Ma, 405.8 ± 0.0 – 397.4 ± 4.1 Ma, 358.4 ± 3.1–308.4 ± 4.6 Ma, 239.5 ± 1.6 – 213.7 ± 1.5 Ma. The youngest magmatism is coeval with the formation age of rare metal pegmatites. Geochemistry analyses of granites show a peraluminous S-type granite signature with high SiO2 (71.21–75.01 wt%) contents and A/CNK (> 1) ratios. The metasedimentary rocks of Kulumuti Group in this field have experienced weak weathering and exhibit extremely high Li content (maximum of 1193 ppm), which is much higher than that of the Traissic granite (96.1 ppm). The average composition of metasedimentary rocks is used to calculate the partition coefficient of different mineral proportions during the modelled equilibrium melting of the metamorphic phase. This approach determines the mineral proportions and partition coefficients under various conditions. Subsequently, Rayleigh dehydration melting simulations were performed on the Li-rich and Li-poor metasedimentary rocks. The Rayleigh dehydration melting simulations show that melts produced from partial melting of Kulumuti Group display Li content of 80–3435 ppm and δ7Li values of 1.0–8.3 ‰, consistent with natural pegmatites. The low-degree partial melting of claystone-rich metasedimentary rocks (Li-rich) in the Kulumuti Group can produce a preliminary Li-rich melt. However, through Rayleigh fractional crystallization simulation of coeval granite, it is found that the calculated δ7Li value (+6‰) of pegmatites is much higher than that of natural Li-rich pegmatite (average + 3.0 ‰). Therefore, the formation of Li-rich pegmatites in the Kelumute-Jideke pegmatite field is predominantly attributed to the partial melting of Li-rich protoliths with low δ7Li values, rather than high differentiation of Halong granite. The study highlights the importance of anatexis of metasedimentary rocks in formation of Li-rich pegmatite, which is key to mineral exploration for Li pegmatite in Altai orogenic belt.

Comparative mineralogical characterization of REEs ore samples from the Mushgai Khudag and Lugiin Gol deposits, Mongolia

Mongolia, situated in the Central Asian orogenic belt, is characterized by geology that is highly conducive to the abundance of mineral resources, including significant rare earth elements (REEs) reserves. However, limited knowledge of the mineralogy of its deposits has hindered the development of efficient REEs extraction methods. This study presents a detailed investigation of the mineralogical characteristics of Mongolian ores and analyzes their compositions, mineral associations, liberation, and REEs concentrations via advanced analytical techniques, including the TESCAN Integrated Mineral Analyzer (TIMA). Additionally, the BCR sequential extraction method was employed to determine the binding and leaching properties of REEs. Our results revealed that the two ore samples were predominantly rich in light rare earth elements (LREEs), with REE-bearing minerals closely associated with gangue minerals such as calcite, albite, and quartz, leading to poor liberation. The extraction data indicated that >85 % of the REEs in the Mushgai Khudag deposit were retained in the residual fraction, whereas in the Lugiin Gol deposit, the majority of the REEs were associated with the reducible fraction. These findings underscore the challenges associated with extracting REEs from Mongolian deposits, which demand stringent conditions for effective recovery. This research contributes valuable insights into the complex mineralogy of Mongolian REEs deposits, offering a foundation for future advancements in REE extraction technologies.

New U-Pb zircon ages from Cadomian basement of the Balkan fold-and-thrust belt of northern Bulgaria

New U-Pb zircon ages are preliminarily reported here from various high-grade units within the overall low-grade Balkan fold-and-thrust belt of northern Bulgaria. The Stakevtsi gneisses yielded Cadomian ages interpreted as magma crystallization ages ranging from 651±8 Ma to 601±3 Ma, some of the samples exhibited a significant proportion of Mesoproterozoic ages with peaks at 1.6 and 1.5 Ga. Paragneisses in the Barzyia Massif exhibit complex U-Pb zircon age patterns, with age peaks typically at 580 Ma and 540 Ma, but also Paleo- and Mesoproterozoic and younger at 430 Ma to 310 Ma. The Divchovoto gneisses yielded age spectra with a minor contribution of Archean, Paleo- and Mesoproterozoic grains and a dominant population of Cadomian ages at 610 Ma. In summary, most of the samples point to the north African provenance, however, some of the Stakevtsi gneisses indicate rather a Baltican provenance. This suggests that the pre-Variscan tectonics and juxtaposition of different terranes was complex in this segment the former Cadomian orogenic belt, but also the possible proximity of Baltica to Gondwana at the end of Neoproterozoic.

Did Along-Strike Changes in Continental Subduction Styles Occur in the Dabie-Sulu Orogenic Belt?

The Triassic collision between the North China Block (NCB) and the South China Block (SCB) formed the Dabie-Sulu orogenic belt, renowned for its extensive ultra-high-pressure metamorphic rocks and the prominent Tan-Lu Fault. Geological and geophysical data reveal significant along-strike differences in both shallow and deep structures within the belt, raising a critical question: What tectonic processes drive these structural variations? Considering that the Triassic collision involved pre-collisional accreted microcontinents and along-strike variations in convergence velocities, this study investigates the influence of microcontinental width, convergence rate, and initial Moho temperature on continental subduction styles using numerical modeling. The models incorporate pre-collisional accreted microcontinent(s) and reveal a two-stage subduction evolution: an initial transition from one-sided to two-sided continental subduction, followed by subduction polarity reversal. High initial Moho temperatures, rapid convergence rates, and wide accreted microcontinents promote the development of two-sided subduction, characterized by an initially vertical interface that gradually inclines towards the pro-plate as convergence progresses. These subduction styles significantly influence crustal suture migration. One-sided subduction results in minimal horizontal displacement, whereas two-sided subduction and polarity reversal lead to substantial horizontal shifts. Based on the modeling results, this study proposes a new evolutionary model for the Dabie-Sulu orogenic belt during the NCB-SCB collision. The model effectively explains along-strike structural differences, such as the inconsistent tectonic trends on either side of the Tan-Lu Fault and the opposite dipping directions of high-velocity mantle anomalies observed in geophysical profiles. Furthermore, the proposed model sheds light on the formation and evolution of the Tan-Lu Fault.