Southern Margin Research Articles

Paleoenvironments and Sedimentation in the Southeastern Margin of Lake Pannon (Western Smederevsko Podunavlje Area, Serbia)

The Late Miocene - Pliocene Lake Pannon gradually diminished as sediments sourced from the Alps and Carpathians filled its basin and pushed its northern shoreline southward. Sedimentary successions from the southern margin of the lake SE of Belgrade (Smederevsko Podunavlje area) were studied in several outcrops and interpreted together with literature data referring to the area. Three facies associations were distinguished: offshore lacustrine clays, delta front sands, and delta plain sands with paludal huminitic clays. The facies associations are organized into at least four delta-scale (10-50 m thick) transgressive-regressive cycles. Age of the succession spans from the Sarmatian-Pannonian boundary (11.6 Ma) to the Prosodacnomya dainellii Zone (older than 7.2 Ma), and most of the littoral and sublittoral mollusc biozones of that interval are represented by their characteristic fossils in the succession. These patterns suggest very low subsidence rate, low accommodation rate, and low rate of sedimentation. Although the investigated sections do not display any obvious stratigraphic gap, erosion must have been a major factor determining the apparently low average sedimentation rate. Persistent aggradation of lacustrine-deltaic sediments at the southern margin of the Pannonian Basin aligns with the general aggradational architecture of the basin fill in the high-supply endorheic Lake Pannon.

South-central Laurentide Ice Sheet dynamics and the formation of proglacial Lake Vita during MIS 3

Abstract An understanding of the growth and demise of ice sheets over North America is essential to inform future climate models. One poorly studied subject is the glacial dynamics during interstadial Marine Isotope Stage (MIS) 3 (57–29 ka). To better constrain the southern margin of the Laurentide Ice Sheet during this time period, we re-examined a stratigraphic sequence in southeast Manitoba, Canada, and provide robust evidence for advance and retreat of ice. Around 46.6 ± 5.1 ka (1σ error), fluvial sands were deposited under similar precipitation and significantly cooler summer temperatures than present-day. Ice then advanced south over the area, before retreating once again and a return to boreal forest and grassland conditions. The area was then covered by proglacial Lake Vita, dammed by ice to the north. Geochronology constraints indicate Lake Vita existed from ca. 44.3 ± 3.6 to 30.4 ± 2.3 ka (1σ error), although gaps in the optical and finite radiocarbon ages suggest either a lack of data or plausible temporary ice-margin advances during this time period. Ice covering most of Manitoba during MIS 3 is in line with global δ18O records, and glacially influenced sediment deposition in the Mississippi River basin.

Geochemical characteristics and depositional conditions of the Lower-Middle Jurassic source rocks in the Southern margin of the Junggar Basin, NW China

The Lower-Middle Jurassic source rocks are identified as the primary contributors along the southern margin of the Junggar Basin. To elucidate their geochemical characteristics, a comprehensive and unprecedented collection of deep Basin (>4500 m) source rock samples was undertaken in the region. A systematic analysis of 124 samples was performed, including studies on organic carbon, Rock-Eval, and organic petrology. Additionally, Gas Chromatography-Mass Spectrometry (GC-MS) analysis was conducted on 21 selected samples. The findings reveal that the Lower-Middle Jurassic source rocks were deposited in a weakly oxidizing to reducing freshwater environment, predominantly comprising liptinite, and vitrinite organic macerals, with a high abundance of Types III and II organic matter. Maturity assessments indicate a varied reservoir formation potential along the southern margin of the Junggar Basin, with the western part generally exhibiting lower maturity levels compared to the central and eastern regions. This suggests that condensate gas reservoirs are more likely to form in the central and eastern areas, while the western part is more favorable for oil reservoir formation. These results underscore the “source control” characteristics of the southern margin of the Junggar Basin.

Sedimentary response of the superposition of two major tectonic systems on the southern margin of the South China Block during the Late Triassic

Sedimentary response of the superposition of two major tectonic systems on the southern margin of the South China Block during the Late Triassic

Polyphase deformation history and its structural controls on auriferous quartz vein stockwork in the Xiaoqinling district, southern margin of the North China Craton

“Structural control” is a crucial point in revealing the genesis mechanism and distribution patterns of vein-type gold deposits. Being the second largest gold producer in China, the Xiaoqinling region has experienced complex and polyphase structural deformations. However, the persistent absence of research on the regional structural deformation sequences and superimposed relationships have posed significant challenges to understanding the ore-controlling structural model, timing of gold mineralization, and dynamic mechanisms. In this contribution, we established an Early Paleoproterozoic to Late Mesozoic structural deformational-event framework (D1–D5) and proposed an ore-controlling structural model by integrating an analysis of the geometry, kinematics, overprinting, and crosscutting relationships of structures at different deformation events, the spatial coupling relationship between gold veins and structures with various orientations, and prior geochronological data. The D1–D4 deformation structures initially established the EW–NW, NE and NS-oriented pre-existing ore-controlling structures framework. The reactivation of pre-existing structures (D1–D4) during the D5 deformation event (gold mineralization period), concurrently giving rise to new NE-trending extensional structures accompanying the tectonic evolution of the metamorphic core complex (MCC), collectively created a multi-directional structural network connecting mineralizing fluids to structural traps, within which auriferous quartz veins emplaced, and displaying a phenomenon of multi-directional intertwining. Combined with previous studies, new structural analysis showing that gold mineralization in the Xiaoqinling area falls within the Early Cretaceous, peaking at 126 Ma, aligning with the timing of rapid crustal uplift, generated in a backarc extension setting induced by the roll-back following the flat subduction of the Paleo-Pacific slab. Our study highlights the crucial role of reactivated pre-existing structures in controlling gold mineralization, demonstrating that structural deformation analysis is essential for understanding the genesis and mechanisms of complex gold district, and suggests that the ductile–brittle shear zones trending in both E–W and NE directions within the middle part of the Xiaoqinling district are crucial positioning areas for exploration of deep-seated gold deposits.

The relative effects of climatic drivers and phenotypic integration on phenotypic plasticity of a globally invasive plant.

Understanding the constraints of phenotypic plasticity can provide insights into the factors that limit or influence the capacity of an organism to respond to changing environments. However, the relative effects of external and internal factors on phenotypic plasticity remain largely unexplored. Phenotypic integration, the pattern of correlations among traits, is recognized as an important internal constraint to plasticity. Phenotypic plasticity is critical in facilitating the acclimation of invasive species to the diverse environments within their introduced ranges. Consequently, these species serve as ideal models for investigating phenotypic plasticity and its underlying determinants. Here, we collected seeds of a global salt marsh invader Spartina alterniflora from seven invasive populations covering the entire latitudinal range in China. These populations were cultivated in two common gardens located at the southern and northern range margins, respectively. We quantified plasticity and variation therein for plant height, shoot density, first flowering day and inflorescence biomass (on a per capita basis). These traits have direct or indirect effects on invasiveness. We examined the relationships between traits plasticity with climatic conditions at site of origin (external factor) and phenotypic integration (internal factor). We found that plasticity differed according to the trait being measured, and was higher for a trait affecting fitness. Phenotypic variance increased with latitude and temperature at the site of origin was the primary factor affecting phenotypic variation. These results indicated that external abiotic factors directly affected the selection on phenotypic plasticity of S. alterniflora. Our study provides a unique viewpoint on assessing the importance of identifying influential factors and mechanisms underlying phenotypic plasticity. Understanding these factors and mechanisms is a critical indicator for invasive and other cosmopolitan species' responses, establishment, persistence, and distribution under climate change.

Tectonic Evolution of Tuvinian Trough (Northern Part of Central Asian Orogenic Belt): Synthesis of Geological Data and Results of Feldspar Ar‒Ar Dating

The Tuvinian rift trough, located in the northern part of the Central Asian orogenic belt (CAOB), was formed in the Early Devonian on late Proterozoic (?)‒Early Paleozoic terranes as a result of the activity of the Altai-Sayan mantle plume. The sedimentary record from the middle Paleozoic to the middle Mesozoic, preserved in the Tuvinian trough, and the middle Paleozoic igneous complexes confined to the structures of the trough, reflect the stages of evolution of the Earth’s crust in the Tuva segment, that necessary for understanding the history of the geological development of the CAOB as a whole. Dating of accessory and rock-forming minerals from igneous rocks using low-temperature geochronology methods allows us to obtain additional information about post-magmatic processes and thereby update the model of tectonic evolution of the region. In this study, we have reconstructed the stages of tectonic development of the Tuvinian trough in the northern part of the CAOB based on the analysis of geological data and new Ar‒Ar dating data on feldspars from mafic intrusions. As a result of this study, the chronology of the previously known stages of post-magmatic processes manifested in the Tuvinian trough was clarified, and new stages were identified according to the tectonic evolution of the CAOB. Ar‒Ar dating of feldspars carried out on eight samples showed four age groups: (i) Late Devonian, (ii) middle Carboniferous, (iii) early Permian and (iv) Early Jurassic. Late Devonian (~377 and 375 Ma) ages record an impulse of mafic magmatism, widely manifested in the northern segments of the CAOB (~380‒365 Ma). Middle Carboniferous (~320 and 319 Ma) dates may be associated with the closure of the Ob-Zaisan branch of the Paleo-Asian ocean as a result of the Kazakhstan-Siberian collision. Early Permian (~290–279 Ma) ages are consistent with the formation of late Carboniferous–Early Permian (~305–275 Ma) large igneous provinces in connection with rifting processes in the northern segments of the CAOB. Finally, a single Early Jurassic (~188 Ma) age marks tectonic reorganization of the CAOB in Late Triassic‒Early Jurassic in response to (i) closure of the Paleotethys ocean with subsequent collision of the Cimmerian blocks and the southern margin of the Eurasian continent and/or (ii) activity of the Mongolian mantle plume.

METAL AND MINERAL MICROINCLUSIONS IN ADAKITES FROM THE FRAMING OF THE UTANAK MASSIF (STANOVOI SUPERTERRANE, RUSSIAN FAR EAST) AS EVIDENCE FOR METAL ENRICHMENT IN ADAKITIC MAGMAS

Porphyritic amphibole–plagioclase andesites at the southern margin of the Utanak ultramafic massif (Stanovoi superterrane, Russian Far East) show low yttrium and ytterbium contents and high Sr/Y and La/Yb ratios typical of adakites. Microinclusions in these volcanic rocks are Cu–Ag–Au alloys, native silver, composites of gold and silver with Cu, Zn, In, Mn, Ni, and Mo minerals, as well as microparticles of platinum, silver sulfides and chlorides, pyrrothite, chalcopyrite, barite, tungsten oxide, crocoite, and cassiterite. The structural features of some microinclusions and their association with primary amphibole and plagioclase suggest their magmatic origin, while other microinclusions hosted in the quartz–chlorite–K-feldspar groundmass formed during later metasomatism. The Utanak adakites are characterized by elevated gold contents (up to 134 ppb) and, together with other manifestations of Mesozoic adakitic magmatism within the Stanovoi superterrane (Il’deus, Lucha, and Gabbrovyi massifs), are classified as ore–bearing (fertile) adakites according to geochemical criteria. We suggest that common association of adakitic magmatism with large porphyry, epithermal, and skarn deposits at convergent plate boundaries is related not only to the high water content and the oxidation state of adakitic magmas but also to the initial enrichment of the latter in various ore components.

Paleolatitudinal movements of the eastern Sakarya Zone from Jurassic to Eocene

The study area covers a region oriented north-south from the Black Sea coastline in the north to the Kelkit Basin in the south within the eastern Sakarya Zone in northern Türkiye. The objective of this study is to investigate the paleolatitudinal movements of the eastern Sakarya Zone during the Jurassic-Eocene time interval through paleomagnetism. Various volcanic and sedimentary units (e.g., the Şenköy, Berdiga, Mescitli, Çatak, Kızılkaya, and Çağlayan Formations) spanning the time interval from the Early Jurassic to Middle Eocene were identified. A total of 98 locations belonging to Early/Middle Jurassic to Eocene volcanic and sedimentary units were selected for paleomagnetic core sample collection. The samples were subjected to demagnetization through thermal and alternating field methods. Characteristic remanent magnetization directions (ChRM) were obtained. Isothermal remanent magnetization (IRM) and high temperature susceptibility (HTS) measurements were made to identify the minerals responsible for magnetization. To ascertain whether magnetization was acquired through rock formation or as a consequence of subsequent tectonic processes, conglomerate and fold tests were performed. The results showed that magnetization was acquired before folding, i.e., the rocks have primary magnetization. Polarity tests were also conducted using coeval normal and reverse polarity sites. The results indicate that the mean magnetization direction for the Early-Middle Jurassic is 18.1°/55.2° (D/I) and 3.3°/51.5° (D/I) for sedimentary and volcanic rocks, respectively, and 348.7°/46.7° (D/I) for Late Jurassic/Early Cretaceous sedimentary rocks. In the Late Cretaceous period, the mean magnetization direction is 8.0°/49.3° (D/I) and 9.1°/47.0° (D/I) for sedimentary and volcanic rocks, respectively. In the case of the Early/Middle Eocene, the mean magnetization direction is 348.6°/52.7° (D/I) and 5.9°/48.8° (D/I) for sedimentary and volcanic rocks, respectively. In this study, the E/I correction was applied to the Late Jurassic/Early Cretaceous sedimentary rocks, and paleolatitude data obtained from sedimentary rocks were also utilized. Our paleomagnetic results indicate that the eastern Sakarya Zone was situated at latitudes spanning from 27.9° to 35.7° during the Early Jurassic - Middle Eocene time interval. In consequence, the eastern Sakarya Zone constituted a portion of the southern margin of the Eurasian continent during the Late Jurassic and Middle Eocene periods.

The geology of the Greenstone orogenic gold deposit, Geraldton, Ontario, Canada: Structural controls, mineralogy, geochemistry, and geochronology

The Greenstone orogenic gold deposit is located in the Beardmore-Geraldton belt (BGB) along the boundary between the granite-greenstone Wabigoon subprovince and the metasedimentary Quetico subprovince of the Archean Superior craton, Canada. The deposit is hosted by ca. 2700–2694 Ma turbiditic sandstone, banded iron formation, and ca. 2694 Ma feldspar-quartz porphyry, which underwent strong deformation within the 1 km-wide Bankfield-Tombill deformation zone along the southern margin of the BGB. The deformation zone includes folds and cleavage that formed during early D1 thrust imbrication of the BGB, S-shaped folds and fabrics that formed during D2 sinistral transpression, and Z-shaped folds, fabrics, and localized shear zones that formed during D3 dextral reactivation of the deformation zone. Gold mineralization is associated with folded, early-D1, quartz-carbonate veins (V1) and with NE- to E-striking, syn-D2, tourmaline-quartz veins (V2) as well as quartz-carbonate veins (V3). The V1 and V3 veins are surrounded by sericite-carbonate-pyrite ± albite–rutile alteration halos, and the V2 veins are surrounded by carbonate-tourmaline-pyrite ± pyrrhotite-chalcopyrite alteration halos. Gold was deposited during fluid-rock sulfidation reactions that resulted in the formation of inclusion-poor pyrite with Ni-Co-As primary crystallographic zoning and inclusion-rich pyrite enriched in Au and other metals (Ag-As-Bi-Co-Ni-Pb-Sb-Te). Hydrothermal alteration associated with the deposition of the veins produced a broad, up to 250 m wide, sericite-carbonate alteration envelope, with S, Te, As, W, and Bi as the best pathfinder indicators to gold mineralization. Contrary to previous studies, which attributed the formation of gold deposits in the BGB to late-D3, our results suggest that gold was emplaced during early-D1 and D2 and involved multiple hydrothermal fluid pulses during several deformation events, as suggested for other major Archean orogenic gold camps associated with major fault zones such as the Timmins and Kirkland Lake camps in the Abitibi subprovince of the Superior craton.

Titanite as an indicator of granite fertility and gold mineralization in the Xiaoqinling gold province, North China Craton

The Xiaoqinling gold province, located in the southern margin of the North China Craton (NCC), is the second largest gold-enriched region in China. In this region, the Mesozoic Huashan (HS) and Wenyu (WY) plutons are the major magmatic intrusions coeval with gold mineralization, although they show contrasting characteristics in the distribution of gold. In this study, we use geochemical features of titanite determined by LA-ICP-MS and EPMA analyses and elemental mapping to decipher the mechanisms that led to the difference in gold enrichment related to the two plutons. Titanite from the Wenyu granitic pluton exhibits significantly higher (La/Sm)N, (La/Yb)N, ΣLREE/ΣHREE ratios, and ΣREE concentration and slightly higher (Gd/Yb)N values than those of the Huashan Pluton, suggesting that the Wenyu pluton might have experienced more complex magmatic evolution, widespread hydrothermal alteration, and higher silica activity in the melt than the Huashan pluton. The titanite grains from the Huashan pluton show higher (Nb/Ta)N and (Lu/Hf)N values and significantly lower Zr concentration than those of the Wenyu pluton. The titanite grains from the Wenyu pluton show higher vanadium and gallium concentrations and Fe/Al ratio than those of the Huashan pluton, indicating comparatively higher fo2. Furthermore, the titanite grains from Wenyu pluton indicate higher water content in the magma. In addition, magma mingling and magmatic hydrothermal fluids derived from the crust/mantle are critical sources for ore-forming materials. These results suggest that the Wenyu pluton is more conducive to gold migration and enrichment than the Huashan pluton.

The Seismic Surface Rupture Zone in the Western Segment of the Northern Margin Fault of the Hami Basin and Its Causal Interpretation, Eastern Tianshan

The Eastern Tianshan region, influenced by the far-field effect of northward compression and expansion of the Qinghai-Xizang block, features highly developed Late Quaternary active faults that exhibit significant neotectonic activity. Historically, the Barkol-Yiwu Basin, located to the north of the Eastern Tianshan, experienced two major earthquakes in 1842 and 1914, each with a magnitude of M71/2. In contrast, the Hami Basin on the southern margin of the Eastern Tianshan has no historical records of any major earthquakes, and its seismic potential, mechanisms, and future earthquake hazards remain unclear. Based on satellite image interpretation and field surveys, this study identified a relatively recent and well-preserved seismic surface rupture zone with good continuity in the Liushugou area of the western segment of the Northern Margin Fault of the Hami Basin (HMNF), which is the seismogenic structure responsible for the rupture. The surface rupture zone originates at Kekejin in the east, extends intermittently westward through Daipuseke Bulake and Liushugou, and terminates at Wuzun Bulake, with a total length of approximately 21 km. The rupture zone traverses the youngest geomorphic surface units, such as river beds or floodplains and first-order terraces (platforms), and is characterized by a series of single or multiple reverse fault scarps. The morphology of fault scarps is clear, presenting a light soil color with heights ranging from 0.15 m to 2.13 m and an average displacement of 0.56 m, suggesting that this surface rupture zone likely represents the most recent seismic event. Comparison with historical earthquake records in the Eastern Tianshan region suggests that the rupture zone may have been formed simultaneously with the Xiongkuer rupture zone by the 1842 M71/2 earthquake along the boundary faults on both sides of the Barkol Mountains, exhibiting a flower-like structural pattern. Alternatively, it might represent a separate, unrecorded seismic event occurring shortly after the 1842 earthquake. The estimated magnitude of the associated earthquake is about 6.6~6.9. Given that surface-rupturing earthquakes have already occurred in the western segment, the study indicates that the Erdaogou–Nanshankou section of the HMNF has surpassed the average recurrence interval for major earthquakes, indicating a potential future earthquake hazard.

Rapid topographic growth of Diancang Shan, southeastern margin of the Tibetan Plateau, since 5.0–3.5 Ma

Abstract. As a crucial geological, climatic, and ecological boundary in the southeastern margin of the Tibetan Plateau (SEMTP), the topographic evolution of Diancang Shan (DCS) remains unclear due to the lack of direct constraints on its paleoelevation. Here, we quantitatively reconstructed changes in annual mean temperature (ANNT) based on palynological data from the terrestrial Dasongping section (∼7.6–1.8 Ma) in the Dali Basin, located at the northeastern margin of DCS in Yunnan, China. Integrating the thermochronological data from the eastern and southern margins of DCS, we have clarified the paleotopographic evolution of DCS during this period: the paleoelevation of DCS likely exceeded 2000 m a.s.l. (above sea level) due to initial normal faulting at ∼7.6 Ma, possibly comparable to the current average elevation (∼2200 m a.s.l.) of the surrounding Dali Basin region. Significant growth occurred between ∼5.0 and ∼3.5 Ma, with at least ∼1000 m uplift gain in the northern segment and up to ∼2000 m in the southern segment of DCS, caused by the intensification of normal faulting activities. Finally, the northern segment of DCS reached the elevation of ∼3500 m a.s.l. after ∼1.8 Ma. Our findings suggest that the quantitative ANNT reconstruction, combined with thermochronological and sedimentary data, can significantly improve constraint on the paleotopographic evolution of DCS.

Glabrobournonia Morris and Skelton (Rudist, Bivalvia) from the Campanian–Maastrichtian of Türkiye: Taxonomy, palaeoecology and palaeobiogeography

A re-examination of the specimens described as Bournonia anatolica Özer and Bournonia sp. from central and southeastern Anatolia, Türkiye reveals that they have diagnostic characteristics of the genus Glabrobournonia Morris and Skelton. New rudist material from the middle Campanian to late Maastrichtian mixed siliciclastic-carbonate sequences in the Sakarya Zone (Eastern and Central Pontides), in the east of the Anatolid–Tauride Block and in southeastern Anatolia (north of the Arabian Platform) in Türkiye also showed the occurrence of Glabrobournonia anatolica (Özer) and Glabrobournonia arabica Morris and Skelton. Glabrobournonia anatolica is characterised by a large, rectangular right valve with pronounced growth lamellae, a salient ventral carina and interband, a less salient dorsal carina, a concave indentation anterior band, a slightly concave posterior band and broad and smooth anterior surface as well as the absence of radial ribbing and ligamentary infolding. Glabrobournonia arabica has the diagnostic features of the species, such as small valves, conical right valves with a smooth surface, ventral and dorsal carinae and two concave indentations of anterior and posterior bands separated by an interband. The palaeoecological characteristics of these lateral clinger morphotypes are presented according to growth geometries. For the cosmopolitan genus Glabrobournonia, two main migration routes have been proposed for the Campanian–Maastrichtian time: one along the southern margin of the Tethys from the United Arab Emirates–Oman border region to the Zagros (Iran) and southeastern Anatolia, connecting to the northern margin of the Tethys to the Anatolid–Tauride Block and the Sakarya Zone in Türkiye, and another from the United Arab Emirates–Oman border region to the Zagros Zone (Iran) and the Tarim Basin, connecting the northern and southern margins of the eastern Tethys.

Timing of S-saturation in the formation of the Oubulage porphyry Cu-Au deposit, Inner Mongolia, Northern China

The Oubulage porphyry Cu-Au deposit, Inner Mongolia, North China, is located in the Langshan Tectonic Belt on the southern margin of the Central Asian Orogenic Belt (CAOB). The ore-forming quartz porphyry intrusion was formed during the Middle Permian (268.4 ± 1.6 Ma). Randomly and directionally distributed sulfide blebs are observed in some porphyry rocks. These blebs are spherical or ellipsoidal in shape. There are two groups of such blebs: polymetallic sulfide blebs and silicate-carbonate-sulfide blebs. Sulfide minerals in these blebs include pyrite, chalcopyrite, and pyrrhotite. Silicate-carbonate-sulfide blebs also contain calcite, epidote, plagioclase, chlorite, fluorite, and bastnaesite. Pyrite of sulfide blebs has δ56Fe ranging from −0.38 ‰ to 1.19 ‰. Calcite in sulfide blebs has C-O-Sr isotopic compositions (δ13CVPDB = −7.35 – −5.35 ‰, δ18OVSMOW = 8.35 – 9.92 ‰, 87Sr/86Sr = 0.7032 – 0.7064) indicative of a magmatic origin. We propose a new possible genetic model in which sulfide saturation occurred in a magma chamber, leading to the formation of sulfide droplets. Assimilation added sulphur (S) into the magma chamber and caused S-saturation. The sulfide melts are transported to the shallow crust attached by fluids.

Deep thermal state on the southern margin of the Zhangzhou Basin based on the electrical conductivity model

Exploring the internal spatial and thermal structure of the Zhangzhou Basin is of great scientific significance in understanding the properties of the deep heat sources and the heating mechanism of hot springs in this region. This study estimates the temperature distribution within the upper mantle of the Basin's southern margin using the Arrhenius equation and Hashin-Shtrikman bounds based on a two-dimensional crust-mantle electrical resistivity model. We also employ a layered simulation technique to calculate the crustal temperature distribution using a one-dimensional steady-state heat conduction equation, constrained by the upper mantle's top and ground surface temperatures. This approach displays the characteristics of the longitudinal variations and horizontal inhomogeneities in crust-mantle temperature. Additionally, we estimate the heat flow values within the study area. Our findings reveal that: (i) the upper mantle (at depths of 30 - 50 km) exhibits a temperature range of 700 - 1100 °C, with the presence of local Moho and upper mantle uplifts; (ii) the crustal temperature spans from 21 - 900 °C, with a diminishing influence of the upper mantle uplift area on crustal temperature at shallower depths; (iii) the surface heat flow values derived from our simulations range between 87 and 100 mW/m2, averaging at 93.23 mW/m2; (iv) the exploration of dry heat rock in this region is likely to reach a depth of at least 6 km. These results suggest that the genesis of hot springs in the study area is not solely influenced by the heat energy extracted from large-area granitic surrounding rocks during a long transport process, but is also considerably affected by local deep thermal anomalous bodies and deep-large faults.

The Jurassic through Early Cretaceous Magmatic Belt of the Southern Margin of the Chukotka Terrane, Northeast Russia: New Results of U–Pb Dating of Zircon

The Jurassic through Early Cretaceous Magmatic Belt of the Southern Margin of the Chukotka Terrane, Northeast Russia: New Results of U–Pb Dating of Zircon

Indosinian magmatism in NE Vietnam: Petrogenesis and geodynamic implications of Triassic mafic suites from the Song Hien region

The Song Hien region is located at the southern margin of the South China Block and includes Early–Middle Triassic mafic suites. The petrogenesis and tectonic context of these rocks are important to comprehending one of the most challenging periods in the tectonic evolution of northern Vietnam related to the South China–Indochina collision. In the present study, we provide the first systematic examination of whole-rock geochemical and SrNd isotopic compositions of mafic suites from the NE Vietnam. The studied Early–Middle Triassic suites are dominated by basalts. The rocks are enriched in LILEs, U, and Th and depleted in Nb and Ta and show a wide range of geochemical and SrNd isotopic compositions ((La/Yb)CN = 0.4–4.6; Dy/Dy⁎ = 0.7–1.3; (87Sr/86Sr)i = 0.7053–0.7125; εNd(t) = (+3.7)–(−8.0)). They all originated from shallow melting of a subduction-modified lithospheric mantle, and the compositional diversity of these basalts is attributed mainly to geochemical and Nd-isotopic heterogeneity in the mantle source. The geochemical and SrNd isotopic features of the studied mafic suites indicate a negligible contribution of the asthenospheric mantle to magma generation and differ significantly from those of the Emeishan plume-related basalts. A model in which Early–Middle Triassic mafic magmatic activity in the NE Vietnam region is the result of decompression melting driven by convective thinning of the South China mantle lithosphere during the 250–240 Ma period is discussed in the study. This period corresponds to the South China–Indochina continental collision. In the NE Vietman region, the Early–Middle Triassic syn-collisional magmatism has an important metallogenic context, controlling NiCu sulfide and Sn(Cu) mineralizations.

Genesis of the Haopinggou breccia-hosted Au deposit, western Henan Province, China

Breccia-hosted Au deposits within the North China Craton (NCC) exhibit a complex genesis, with some breccias being genetically linked to Au mineralization and others unrelated. Understanding the origin of these breccias is crucial for elucidating the genesis of associated ore deposits and guiding exploration strategies. The Haopinggou deposit in the Xiong’ershan district, on the southern margin of the NCC, comprises quartz-carbonate vein-hosted Ag–Pb–Zn–Au deposits and related breccia pipe in metamorphic rocks of the late Archean to early Paleoproterozoic Taihua Group. The origin of the Haopinggou breccia is crucial to understand the Xiayu Ag-Pb-Zn-Au mineralization (5640 t Ag). In this study, we examine the genetic relationship between breccia and Ag‒Pb‒Zn‒Au mineralization, drawing on new insights from the characteristics of the Haopinggou deposit, breccia features, breccia‒hosted Au mineralization, and isotopic data. These findings enhance our understanding of the Haopinggou Ag‒Pb‒Zn‒Au hydrothermal systems and refine exploration models for discordant breccia pipes. Recent underground tunnel surveys and drill-core logging reveal a close spatial link between the breccia and hidden granite porphyry. Juvenile magmatic clasts (granite porphyry) and cement (K-feldspar and quartz crystallized from granite porphyry) are present in the breccia pipe above a granite porphyry apophysis, indicating that the breccia was formed by phreatomagmatic brecciation caused by emplacement of the granite porphyry. Fluidization at the cm- to 100-m-scale reveals that the movement direction of clasts inside the breccia pipe was from northwest to southeast after crypto-explosion, creating a northwest-trending breccia zone. Anhedral monazite (131.2 ± 7.6 Ma) encapsulated in pyrite from the breccia constrains the upper limit of brecciation. The δ34S values of pyrite in rock flour and hydrothermal cements range from 3.8 ‰ to 5.3 ‰ (mean: 4.8 ‰) and 2.7 ‰ to 7.5 ‰ (mean: 5.2 ‰), respectively, with δ34S-sphalerite in hydrothermal cement ranging from 5.7 ‰ to 6.1 ‰ (mean: 5.9 ‰) and δ34S-chalcopyrite ranging from − 0.9 ‰ to 5.6 ‰ (mean: 2.9 ‰). The S isotope characteristics of vein-hosted and breccia-hosted mineralization zones are consistent, with complete alignment of the sulfide assemblages and alteration features. These pieces of evidence collectively indicate that both vein- and breccia-hosted mineralization zones are products of magmatic activity. The metallogenic model for the Haopinggou breccia pipe underscores its unique formation mechanism, driven by pre-existing northwest-striking structural weaknesses and fluidization. This model implies a predominant northwest‒to‒southeast transport of clasts and raises the hypothesis of an underlying porphyry‒type Au mineralization system at depth.

Basin–Orogen Coupling‐Driven Meso‐Cenozoic Deformation Along the Southern Margin of the Junggar Basin, NW China: Insights From Integrated Multidisciplinary Analysis

ABSTRACTThe southern margin of the Junggar Basin (SMJB) represents the typical intra‐continental basin–orogen coupling structure of the Central Asian Orogenic Belt and is a key area to study the deformation mechanisms and the geodynamic evolution processes of the North Tianshan Orogen. Herein, we compiled data from boreholes, gravity and magnetism, seismicity‐ and magnetotellurics‐derived geological profiles and field data to recover the sedimentary history of the SMJB and discuss the intra‐continental deformation driven by the basin–orogen coupling mechanism. The results show that the sedimentary and tectonic evolution of the SMJB were both profoundly controlled by the intra‐continental orogeny of the North Tianshan Orogen and its coupling with the Junggar Basin during the Meso‐Cenozoic period. Consequently, the SMJB is dominated by thick‐skinned thrust nappes accompanied with strike‐slip faulting and thrusting. The foreland thrust belt of the SMJB is characterised by three structural belts, from south to north, including the basement‐involved thrust belt, the cover‐detached foreland thrust‐fold belt and the thrusted foreland basement uplifts, respectively. Meanwhile, as indicated by the geometry of the basement thrusts, the thickness of décollements and the structure of the foreland basement, the stress field in the SMJB is obviously stronger in the west and weaker in the east. The sedimentation and deformation migrated northwards into the basin area in a stepwise process, that corresponded to the pace of the overthrusting of the North Tianshan Orogen onto the Junggar Block. Intense regional compression induced the rapid uplifting of the North Tianshan and the significant crustal shortening of the Junggar Block, driving the three structural belts to form accordingly during the Late Jurassic to the Neogene. There are at least one or two décollements within the SMJB, representing one of the main features of basin–orogen coupling structure in most cases. The décollement of some layers represents the decoupling of the sedimentary cover with the basement, which helps to accommodate the lateral crustal shortening of the SMJB by a translation into vertical uplift. As a result, the detached foreland thrust‐fold belts in the shallow level of the upper crust overthrusted upon the basement‐involved nappes of the mountain's side, forming the opposite thrust system. Coevally, the basement of the basin, in the deep level of the upper crust keeps underthrusting beneath the North Tianshan Orogen, forming a typical crocodile mouth‐like structure. In general, both the shallow and deep deformation in the SMJB have been formed by the intense intra‐continental compression during the Meso‐Cenozoic, which were driven by the basin–orogen coupling mechanism.