Search Results (120)

In the northern Sichuan Basin, distant from the main body of the Emeishan Large Igneous Province (ELIP), marine deposits of the Wujiaping Formation from the Permian period contain widely distributed tuffs of varying thicknesses. To clarify the genesis of these tuffs and their relationship with the ELIP, this study conducted field measurements and sample collection at the Daliang Section, Wangcang County, and the Qiaoting Section, Nanjiang County, of the northern Sichuan Basin and compared them with basalts and tuffs from Well DY1 in a minor basaltic eruption zone in the northern Sichuan Basin. The results indicate that tuffs from the Daliang and Qiaoting Sections of the northern Sichuan Basin exhibit high Al₂O₃/TiO₂ ratios (23.65–39.55) and significant depletion of Eu, Ba, and Sr elements. These characteristics suggest that their origin is linked to multiphase felsic volcanic activity within the ELIP and formation in an intraplate extensional setting. The basalts and tuffs developed at Well DY1 share the same low Al₂O₃/TiO₂ ratios (4.02–4.97), similar to the Emeishan basalts. In the Zr-Ti, Zr/Sc-Th/Sc, Nb/Y-Zr/TiO₂, and Zr/TiO₂-SiO₂ diagram plots, they fall within the basalt range, indicating that the tuffs at Well DY1 originated from the mid-ELIP eruption of basic basalt. In contrast to the felsic nature of the tuffs at Well DY1, the northern Sichuan Basin lacks records of such basic–alkaline igneous eruptions, suggesting that the influence of basalt eruptions in the northeastern Sichuan Basin is limited and does not affect the Wujiaping Formation in the northern Sichuan Basin. There is a positive correlation between volcanic activity and the total organic carbon (TOC) content of black siliceous rocks and siliceous shales in the Wujiaping Formation of northern Sichuan. The acid volcanic eruptions from Emeishan likely also played a key role in the formation of high-quality hydrocarbon source rocks in the deep-water continental shelf areas of the Wujiaping Formation in the northern Sichuan Basin. Full article

Supercontinent cycles are fundamental processes driving the tectonic evolution of Earth, and the periodic assembly and breakup of supercontinents may exert significant influence on global plume heat flux. Large igneous province (LIP) events provide a geological record of mantle plume activity, and their periodicity shows a striking correspondence with the periodicity of supercontinent cycles, suggesting a potential coupling between supercontinent cycles and plume activity. In this study, we employ two-dimensional spherical shell simulations using ASPECT to model the evolution of global plume heat flux, with a focus on its periodicity and phase, which are then compared with the observed periodicity and phase of LIP events. Given the uncertainties in the mode and period of supercontinent cycles, and the potentially important role of the compositionally anomalous and intrinsically dense (CAID) layer, we incorporate all three factors into our models. We then explore the conditions under which the periodicity of global plume heat flux matches the periodicity of supercontinent cycles. We find that the cycle period is the dominant control on the periodicity of global plume heat flux, while the cycle mode significantly modulates its phase. These results suggest that supercontinent cycles regulate not only the periodicity of mantle plume activity but also the timing of heat flux variations. Full article

Permian A-type granites and associated rare-metal mineralization are widespread in the Halajun area, southwestern Tianshan; however, petrogenetic controls on rare-metal enrichment and mineralization remain under-constrained. Here, we integrate zircon and monazite geochronology, whole-rock geochemistry, and zircon Hf-O isotopes from Halajun I and II plutons to constrain the origin of these granites and their metallogenic significance. Zircon U–Pb and monazite ages indicate emplacement at 274–273 Ma, coeval with regional magmatism associated with the Tarim large igneous province. Geochemical signatures—high SiO₂, alkali, and rare-earth element (REE) contents, enrichment of HFSE (e.g., Nb, Zr, and Hf), coupled with LILE (e.g., Ba and Sr) depletion—classify these granites as highly differentiated alkaline A-type rocks. Positive εHf(t) values and intermediate δ¹⁸O compositions of zircons suggest derivation from partial melting of Neoproterozoic lower crust with input from mantle-derived melts, reflecting significant crust–mantle mixing. Magmatic differentiation, in concert with regional crustal reworking driven by mantle plume activity, produced granites enriched in Nb, Ta, Zr, and REEs, which host the rare-metal mineralization in the region. These results indicate that Permian crustal reworking in the southwestern Tianshan was a driver of high-differentiation magmatism and rare-metal enrichment, highlighting the potential of similar A-type granitic systems in Central Asia for rare-metal exploration. Full article

Coarse-grained clastic systems in rift basins are often considered unfavorable for preserving continuous astronomical records. This study investigates the thick conglomeratic succession in the upper Member 4 (43.90–44.73 Ma) of the Wenchang Formation in the Enping 21 sub-sag, Yangjiang East Sag, Zhu III Depression, Pearl River Mouth Basin. Integrating cyclostratigraphy, petrography, and seismic-logging analyses, we established a high-resolution astronomical timescale (43.90–44.73 Ma) covering approximately 828 kyr. Cyclostratigraphic results indicate a highly continuous depositional record with an optimal sedimentation rate of 19.55 cm/kyr. Petrographic and geochemical evidence—including low structural maturity, dominant igneous lithic fragments, and high detrital zircon Th/U ratios—reveals a proximal volcaniclastic source, characterizing the studied interval as tephroid successions. Anomalously high GR responses and chaotic seismic facies further distinguish this succession from conventional terrigenous deposits, linked to a nearby identified magmatic body. Our results suggest that rapid accumulation of volcaniclastic flows and ash fallout, driven by proximal magmatic activity, reduced hydrodynamic reworking and facilitated the preservation of astronomical signals. This study highlights that in active lacustrine rift basins, magmatic activity significantly dictates sedimentary infill patterns by providing rapid volcaniclastic input, thereby enabling the establishment of precise chronostratigraphic frameworks even within complex, coarse-grained depositional systems. Full article

The Late Jurassic–Early Cretaceous Oloy complex was formed in the setting of convergence between the Chukotka microcontinent and the Kolyma–Omolon margin. Its evolution reflects the closure of the South Anyui Ocean, with controversial timing estimates. This study emphasizes the integration of lithological data with magmatic and metallogenic information to reconstruct geodynamic processes. The article presents the results of detailed petrographic and geochemical studies, Sm-Nd isotope analyses, and U-Pb dating of detrital zircons from Kimmeridgian–Lower Hauterivian volcaniclastic and epiclastic sandstones. Petrographic studies and U-Pb dating of detrital zircons identified the main sources at different stages and the amount of synchronous pyroclastic material. Isotope-geochemical investigations suggest a young undifferentiated arc provenance for Kimmeridgian deposits, whereas Tithonian–Valanginian sediments accumulated due to the erosion of more differentiated igneous rocks and input of clastic material from the continent. New data on changes in sedimentation environments and provenance enabled the tracing of the evolution of the Oloy arc. In the Kimmeridgian, the Oloy island arc existed on a heterogeneous basement, with south-dipping subduction towards the Kolyma–Omolon margin. During the Late Tithonian, the arc accreted and magmatic activity continued in the active margin setting. Collision initiated in the latter half of the Berriasian, reaching its active phase in the Valanginian time. Full article

Late Early Jurassic continental arc magmatism in the northern Greater Khingan Range enables the investigation of complicated tectonic processes associated with the subduction and closure of the Mongol–Okhotsk Ocean. To further clarify the timing, genesis, and geodynamic mechanisms driving the magmatic activity during this period, the present study addresses these critical questions by integrating zircon U–Pb geochronological, geochemical, and isotopic analyses of a wide variety of igneous rocks, including gabbro, gabbro-diorite, granodiorite, porphyritic monzogranite, and biotite-bearing monzogranite from the Fushan region. Zircon U–Pb geochronology constrains the timing of magmatic activity to 184–179 Ma, coinciding with active subduction phases. Geochemical data reveal arc-like signatures characterized by enrichment in light rare-earth elements (LREEs) and large-ion lithophile elements (LILEs), together with pronounced depletion in high field strength elements (HFSEs). A comprehensive analysis of geochemical and Sr–Nd–Hf isotopic signatures suggests that the mafic rocks originated from an enriched lithospheric mantle modified by subduction-related fluids and sediment-derived melts. By contrast, the granodiorite and porphyritic monzonite exhibit adakitic characteristics, indicating partial melting of the thickened Mesoproterozoic lower crust with contributions from mantle-derived or newly formed crustal material. The biotite-bearing monzogranite, with its pronounced Eu anomaly and lower zircon saturation temperatures, reflects advanced magmatic differentiation from a shallower source. These findings indicate extensive crust–mantle interactions during the southward subduction of the Mongol–Okhotsk Ocean, driven by high-angle subduction and slab rollback. Full article

This study investigates the rare-earth element (REE) geochemistry of twenty-nine clastic rock samples from the Paleogene Liushagang Formation in the Weixi’nan Sag. The primary objectives were to quantitatively evaluate the depositional paleoenvironment, determine the provenance lithology, and constrain the tectonic setting of the source area. Results reveal distinct chondrite-normalized REE distribution patterns characterized by light REE (LREE) enrichment, relatively flat heavy REE (HREE) segments, and pronounced negative Eu anomalies. The cerium anomaly index (Ce_anom, normalized to the North American Shale Composite) ranges from −0.06 to 0.00, implying broadly suboxic to anoxic-reducing conditions in the water column during deposition. The chondrite-normalized (La/Yb)_N ratio, utilized as a proxy for relative depositional residence time, decreases stratigraphically from member 3 to member 1, reflecting a transition to shorter residence times and higher relative sedimentation rates. Laterally, (La/Yb)_N increases toward the basin center, accurately recording progressively lower sedimentation rates basinward. Provenance analysis indicates that the sediments were predominantly derived from felsic igneous rocks of the upper continental crust. Spatially, the northern steep-slope belt reflects a uniform source, whereas the southern gentle-slope belt and the Weixi’nan low-uplift periphery record multisource mixed inputs. Finally, tectonic discrimination reveals an “active continental margin” affinity. This geochemical signature represents the inherited tectonic environment of the Mesozoic parent rocks in the surrounding source uplifts, rather than the Cenozoic extensional rift setting of the Weixi’nan Sag itself. Full article

The Permian Qixia dolostone in the Central Sichuan Basin is a significant hydrocarbon reservoir of hydrothermal origin, linked to the Emeishan Large Igneous Province and structurally controlled by E–W strike–slip faults. However, how this process controls reservoir quality remains poorly understood. To address this, we integrate core observation, thin-section petrography, XRD analysis, thickness mapping, MICP, and μ-CT to characterize the lithofacies and pore structures of the Qixia Formation in the study area. Six lithofacies are recognized, including mudstone (F1), wackestone (F2), packstone (F3), grainstone (F4), rudstone (F5), and dolostone (F6), and F6 is further divided into three subtypes (F6-1, F6-2, F6-3). Dolostones exhibit superior reservoir quality relative to limestones, and among the dolostone, reservoir quality improves progressively from F6-1 to F6-3 with increasing crystal size and dolomite content. Dolostone distribution is spatially tied to E–W strike–slip faults, and its formation age coincides with documented fault activity, implicating these faults as the primary fluid conduits. Quantitative pore structure analyses further indicates that dolomitization enhanced permeability by enlarging pore–throat radii and improving macropore connectivity, with associated dissolution contributing additional secondary porosity. Full article

As a convergent zone of multiple plates, the Caribbean Sea and its adjacent areas have experienced a complex tectonic evolution process and are characterized by prominent microplate development. This region provides a natural laboratory for studying the formation mechanism of continental margins, the evolution process of ocean basins, and the tectonics of microplates. However, the crustal structure and microplate tectonics in this region remain unclear due to limitations of conventional planar gravity inversion methods, which neglect the Earth’s curvature in large-scale areas, as well as the uneven coverage of regional seismic networks. To precisely delineate the crustal structure and microplate boundaries in the Caribbean Sea region, this study employs a nonlinear gravity inversion method based on a spherical coordinate system. By utilizing GOCO06s satellite gravity data, ETOPO1 topographic data, and the CRUST1.0 crustal model, we performed inversion calculations for the Moho depth in the Caribbean Sea and its adjacent regions and systematically analyzed the crustal structure and microplate tectonic characteristics of the region. The results indicate that the gravity inversion method in the spherical coordinate system has good applicability in complex tectonic regions. The inversion results show that the Moho depth in the study area generally presents a spatial distribution pattern of “shallow in the central part and deep in the surrounding areas”. Among them, the Moho depth is the largest (>39 km) at the junction of the Northern Andes and the South American Plate, while it is relatively shallow (<6 km) in regions such as the Cayman Trough, the Colombian Basin, and the Venezuelan Basin. Based on the Moho undulation, gravity anomalies, and topographic features, this study divides the Caribbean Sea and its adjacent areas into 22 microplates and identifies three types of microplates, including oceanic, continental, and accretionary. Among them, there are 10 microplates with oceanic crust, 6 with continental crust, and 5 with accretionary crust, while the Northern Andes Microplate exhibits a mixed type. The crustal structure characteristics revealed in this study support the Pacific origin model of the Caribbean Plate, indicating that most of the plate is a component of the ancient Pacific Plate with standard oceanic crust properties. Locally, the Caribbean Large Igneous Province developed due to hotspot activity, and the subsequent eastward drift and tectonic wedging processes collectively shaped the complex modern microplate tectonic framework of this region. This study not only reveals the variation pattern of crustal thickness in the Caribbean Sea region but also provides new geophysical evidence for understanding the lithospheric structure and microplate evolution mechanism in the area. Full article

The basement of the Rattlesnake Creek terrane (RCT) in the Klamath Mountains is a mélange of metamorphosed sedimentary and igneous blocks. Recent work shows that the overlying RCT cover sequence has a North American provenance but formed after accretion to the continental margin, so it is unclear if the basement mélange formed exotic or endemic to North America. This study presents petrography and zircon geochronology from RCT metasedimentary blocks and crosscutting intrusions. The southernmost RCT preserves both Early Jurassic and Middle-Late Jurassic cover sequence deposits and records continental clasts and 33% pre-Mesozoic zircons at ~201 Ma, effectively none at ~191 Ma, and 79–90% from 168 to 163 Ma. During active magmatism 207–193 Ma, the RCT was receiving continental sediment, inconsistent with a distant intraoceanic arc. We interpret that the RCT subduction zone formed proximal to North America in the Late Triassic and that there was a sediment pathway to the RCT at ~201 Ma. During Middle to Late Jurassic rifting and subsequent Nevadan compression, the cover sequences were dismembered and incorporated into the mélange by tectonic and sedimentary processes. The age and provenance of metasedimentary deposits in the RCT is inconsistent with west-dipping subduction models in the Klamath Mountains region. Full article

The Qingshan lead–zinc (Pb–Zn) deposit in northwestern Guizhou Province is a structurally controlled, carbonate-hosted system formed from basin-derived hydrothermal processes. Geology, fluid inclusion, and isotopic data reveal a multi-stage hydrothermal circulation after Emeishan Large Igneous Province (ELIP, ~260 Ma) tectono-thermal reactivation within the Sichuan–Yunnan–Guizhu triangle (SYGT) area. Fluid inclusion microthermometry indicates that ore-forming fluids were derived from deep sources influenced by enhanced crustal heat flow linked with possible thermal input from Indo-Caledonian tectonic activity after ELIP. Ore-stage calcite records mixed carbon derived from marine carbonates with additional inputs from organic matter and deep-sourced fluids, reflecting carbonate dissolution and fluid–rock interaction. Sulfide, together with fluid inclusion temperatures > 120 °C, indicates sulfur derived from evaporitic sulfate reduced by thermochemical sulfate reduction (TSR); the heavy sulfur signature and partial isotopic disequilibrium among coexisting sulfides reflect dynamic fluid mixing during ore deposition. Lead isotopes indicate metallogenic metals were leached mainly from Devonian–Permian carbonates with subordinate basement input. Ore precipitated by cooling, depressurization, and mixing of metal-rich, H₂S-bearing fluids in structurally confined zones where the carbonate–clastic interface effectively trapped ore-forming fluids, producing high-grade sphalerite–galena mineralization. Collectively, these data support a Huize-type (HZT) carbonate-hosted Pb–Zn genetic model for the Qingshan deposit. Full article

The Cretaceous marks the peak of magmatic activity in southeastern (SE) China, which is attributed to the subduction of the paleo-Pacific plate beneath the South China Block. This region constitutes a significant igneous belt along the active continental margin of the western Pacific. Despite extensive research, the origin and evolution of Cretaceous felsic volcanic rocks are still debated. This study investigates the characteristics of zircon U-Pb-Hf isotopes and trace elements, and whole-rock geochemistry of Cretaceous volcanic rocks from the Wenzhou–Taizhou region in SE Zhejiang, and discusses their spatio-temporal patterns and petrogenesis. The results indicate that rhyolitic volcanic rocks formed during the period ca. 114 Ma and 95 Ma, representing two distinct magmatic episodes spanning the transition from the late Early to early Late Cretaceous. The late Early Cretaceous and early Late Cretaceous volcanic rocks are of a hybrid crust–mantle origin, as evidenced by their distinct Nb/Ta ratios, zircon ε_Hf(t) values, and variable trace element enrichments (Ti, Hf, U, Nb, and Yb). These compositional signatures suggest partial melting of late Paleoproterozoic to early Mesoproterozoic basement materials, with increasing mantle contributions over time. Both volcanic phases exhibit elevated Nb/Yb, Th/Nb, and U/Yb ratios, indicating a subduction-modified source akin to arc magmas. Together with calculated initial melt temperatures (<800 °C for Early Cretaceous, >800 °C for Late Cretaceous) and whole-rock rare-earth elements (REEs) distribution patterns (U-shaped with δEu = 0.37–0.65, seagull-shaped with δEu = 0.19–0.62, respectively), it is suggested that both phases of the volcanic magmas were generated through water-assisted (hydrous) melting, whereas the later phase formed at relatively higher temperatures and with a diminished water contribution via dehydration melting under extensional conditions. The generation of voluminous high-silica magmas in the SE China coastal region is probably linked to the rollback and retreat of the paleo-Pacific plate. Full article

Sodalite is a common feldspathoid in alkaline systems, with some varieties exhibiting notable fluorescence due to impurity activators. This study reports the first documented occurrence and characterization of fluorescent sodalite from the classic Ditrău Alkaline Massif, Romania, where its optical properties were previously undescribed. Sodalite-bearing syenite samples from different perimeters of the massif were investigated using macroscopic UV fluorescence, petrographic microscopy, and vibrational spectroscopy (Raman and FT-IR). The sodalite occurs as a late-stage, interstitial and poikilitic mineral, often associated with alteration to cancrinite. Under long-wave UV (365 nm) light, it exhibits spatially variable fluorescence, from absent in parts of the western Prişca perimeter to strong, uniform orange in the eastern Aurora perimeter. Raman and FT-IR spectroscopy confirmed the mineral’s identity and revealed subtle spectral variations, particularly the presence of a minor cancrinite component in some analyses. The vibrant orange fluorescence is consistent with activation by disulfide radical anion ($S_2^{·-}$) activators, formed in the sulfur- and chlorine-rich late-stage fluids characteristic of the massif’s evolution. The geographic variation in fluorescence intensity serves as a potential indicator of the geochemical heterogeneity of these fluids across the massif, linking the strongest fluorescence to the most evolved portions of the igneous complex. This finding opens a new avenue for using fluorescence as a tool for petrogenetic investigation in this classic locality. Full article

A necessary evaluation of freshwater ecosystem pollution levels and radiation risks remains crucial for maintaining environmental health, especially within economically developing areas. This study presents a comprehensive evaluation of the mineralogical, geochemical, and radiological characteristics of sediments in Nasser Lake, Egypt, to determine potential ecological and health risks. Forty sediment samples were collected from multiple locations, including both surface and bottom sediments, for analysis of textural attributes, mineral composition, potentially toxic elements, and natural radionuclides (²³⁸U, ²³²Th, and ⁴⁰K). Results revealed sand-dominated sediments with low organic matter content. The heavy mineral assemblages derived from Nile River inputs, wind-deposited materials, and eroded igneous and metamorphic rocks. Geochemical analysis showed that arsenic, cadmium, chromium, and lead concentrations exceeded upper continental crust background values, with enrichment factors and geo-accumulation indices indicating significant anthropogenic contributions. The pollution indices revealed heavy contamination levels and extreme ecological risks, which were primarily driven by arsenic and cadmium concentrations. Radiological assessments detected activity concentrations of ²³⁸U, ²³²Th, and ⁴⁰K below the world average, with hazard indices indicating minimal radiological risk except where localized hotspots were present. The study emphasizes the need for targeted monitoring and sustainable management practices to mitigate pollution and preserve the crucial freshwater environment of Nasser Lake. Full article

Rare earth elements (REEs) and trace elements, due to their relative stability during sedimentary processes, are effective geochemical proxies for sediment provenance. In the Dongdaohaizi Depression of the eastern Junggar Basin, the provenance of the Middle Jurassic Sangonghe Formation remains contentious. In this study, representative sandstone samples were systematically collected from all three members of the Sangonghe Formation in both the Dongdaohaizi Depression and its western margin. Through comprehensive petrographic and geochemical analyses, we obtained the following results. The Sangonghe Formation is primarily composed of feldspathic lithic sandstones, lithic sandstones, and minor lithic–feldspathic sandstones. The heavy mineral assemblage includes zircon, garnet, chromite, and rutile, suggesting source rocks of intermediate to acidic igneous, metamorphic, and mafic lithologies. The total REE contents range from 101.84 to 192.68 μg/g, with an average of 161.80 μg/g. The ∑LREE/∑HREE ratios vary from 6.59 to 13.25 (average 10.96), and the average δEu values are close to 1. The δCe value ranges from 1.09 to 1.13 (average 1.11). Trace element discrimination diagrams, including La-Th-Sc, Th-Co-Zr/10, Th-Sc-Zr/10, and La/Y-Sc/Cr ternary plots, indicate that most samples fall within the continental island arc domain, with a few plotting in the passive continental margin field. Comparison with potential surrounding source regions reveals dual provenances: an eastern source from the Kalamaili Mountains and a western source from the Zhayier Mountains. During the Early Jurassic, these two orogenic belts acted as distinct sediment sources. The Zhayier Mountains provided stronger input, with fluvial and tidal processes transporting sediments into the basin, establishing the primary subsidence center in the west of the depression. By the Middle Jurassic, continued thrusting of surrounding fold belts caused a migration of the lake center and the main depocenter to the western edge of the Dongdaohaizi Depression, while the former depocenter gradually diminished. Furthermore, sustained erosion and denudation of the Mosowan Uplift during the Early–Middle Jurassic reduced its function as a structural barrier, thereby promoting increased mixing between eastern and western sediment sources. The study not only refines existing paleogeographic models of the Junggar Basin, but also demonstrates the utility of REE–trace geochemistry in deciphering complex provenance systems in tectonically active basins. Full article