摘要:

摘要:

摘要:The early evolutionary history of the Macrocerinae subfamily (Diptera: Keroplatidae) is poorly understood. However, new material from the Cretaceous, particularly in amber, provides a better understanding of this subject. We reassign the oldest known species of Macrocerinae, Hegalari minor Blagoderov & Arillo, 2002, from the amber of álava (~105 Mya), to the genus Macrocera (M. minor comb. nov.). Furthermore, we reassess the systematic position of the problematic genus Burmacrocera Cockerell, 1917 from Cenomanian Burmese amber (~99 Mya), providing evidence that it should be classified within this subfamily. Most significantly, we describe five new species from Burmese amber.

摘要:The origins of peloidal micrites in reefal limestone are not yet well understood. Moscovian microbial reefs with abundant peloidal micrites from Guizhou, South China, provide an opportunity to study the peloids and their geological significance for this time interval. Three types of peloids are differentiated: microbial, lithic, and bioclastic peloids. Microbial peloids that are well-sorted and may form in situ by microbial activities. The poorly sorted lithic peloids are derived from erosion and redeposition of the micrite matrix caused by the bottom turbulence induced by periodic storms. Bioclastic peloids are completely micritized fragments of hard parts and shells. Microbial boring and encrustations promote the processes of micritization. Microbial peloids commonly develop in zones with low or normal energy levels, and contribute to the construction and stabilization of the framework. In contrast, the occurrence of lithic peloids reflects that the reefs are destroyed by bottom turbulence during growth. It is suggested that the microbial reefs were deposited under a dynamic balance between constructional versus destructive processes. By comparative analysis, the peloids as microbial in origin play a key role in the growth and stabilization of bioconstructions during Carboniferous, which should be paid more attention in the studies of Carboniferous buildups.

摘要:Detrital zircon and apatite U-Pb-Hf isotope and trace element analyses of the late Mesoproterozoic to early Neoproterozoic strata in southern Jilin provide detailed information on the sediment provenance and tectonic setting of the northeastern margin of the North China Craton (NCC). Here, we present U-Pb and Lu-Hf analyses of 712 detrital zircons, and U-Pb analyses of 347 detrital apatites from the Baifangzi, Diaoyutai and Qiaotou formations. The Baifangzi and Diaoyutai formations are dominated by Neoarchean (2.5–2.6 Ga) and Paleoproterozoic (1.8–1.9 Ga) zircons, indicating a predominant NCC provenance. The Qiaotou Formation is dominated by Mesoproterozoic (1.5–1.7 Ga and 1.1–1.3 Ga) zircons with mainly positive εHf(t) values, which are similar to those from eastern Laurentia, implying a significant provenance transition. The detrital apatite age spectra of the Baifangzi and Diaoyutai Formations show major populations at 1.8–1.9 Ga and 1.1–1.3 Ga. Based on their trace element compositions, the Mesoproterozoic apatites were mainly sourced from metamorphic rocks, indicating regional metamorphism occurred in the NCC during 1.1–1.3 Ga. Combining these data with regional studies, we propose that the NCC was adjacent to eastern Laurentia during the assembly of the Rodinia supercontinent.

摘要:Geodynamic processes following the Indo–Eurasian plate collision remain a key research focus, and the Jinshajiang–Red River tectonic zone (JRTZ), situated along this collision boundary, provides critical insights into post-collision tectonic evolution. In this study, we identify a lithological assemblage in the JRTZ, including amphibolite, granite gneiss, and migmatite. These rocks exhibit contrasting geochemical signatures, reflecting multiple source regions: asthenospheric mantle, lithospheric mantle, mafic lower and upper crust. Specifically, amphibolite (28.5 Ma) formed through the partial melting of OIB-like mantle source, whereas S-type granite gneiss (28.2 Ma) originated from the dehydration melting of metamorphosed sedimentary rocks. Amphibole monzonite (28.9 Ma) records the mixing of ancient crustal material with mantle-derived components, while migmatite (37.9 Ma) resulted from deep melting processes of metasedimentary rocks under shear conditions. We propose that the ongoing Indo–Eurasian convergence progressively thickened the crust, ultimately driving large-scale lithospheric delamination between the Eocene and Oligocene. This delamination triggered asthenospheric upwelling, which provided the thermal input required for widespread melting. This lithospheric delamination event started around 38–37 Ma and lasted at least until 28 Ma.

摘要:The Precambrian Homrit–Waggat granite is a post-orogenic batholithic intrusion located in the northern region of the Nubian Shield, characterized by a typical annular morphology and significant secondary alteration. This study aims to elucidate the processes that have shaped the intrusion in both macroscopic and microscopic perspectives, employing a combination of field observation and petrographic analysis alongside major and trace element compositions of minerals. Within the central region of the pluton, biotite and amphibole are observed sporadically, while the predominant crystallization of anhydrous oligoclase in the outer regions has led to a progressive increase in volatile components within the residual melt, ultimately resulting in a volatile-saturated aluminosilicate melt. The exsolved fluids subsequently interacted with the previously crystallized mineral assemblage, producing metasomatic overprinting. As the cooling and crystallization continued, the water pressure within the magma chamber gradually escalated until it equaled or surpassed the confining pressure, leading to the formation of fractures and veins filled with minerals that crystallized from the residual aqueous fluids. The ongoing degassing and expulsion of aqueous fluids from the magma chamber’s interior ultimately contributed to the collapse of the chamber’s roof, resulting in the annular ring-dike morphology observed in the Homrit Waggat pluton.

摘要:A systematic study of early Paleozoic S-type granites in Pinghe enhances our understanding of the tectonic evolution of proto-Tethys and provides a foundation for exploring rare metal deposits in the region. The Pinghe granites consist of monzogranite and leucogranite. Zircon U-Pb dating shows that the emplacement ages of the monzogranite and leucogranite are 502.0 Ma and 500.9 Ma, respectively. All samples have high SiO2 content and a weakly to strongly peraluminous character (A/CNK = 1.08–1.23), consistent with S-type granites. The monzogranite has relatively high CaO, Sr, Ba, and CaO/Na2O ratios but lower Rb. In contrast, the leucogranite has lower CaO, Sr, Ba, and CaO/Na2O ratios but higher Rb. The similar εNd(t) values (?9.3 to ?8.4) and Pb isotopic compositions ((206Pb/204Pb)t = 18.03–19.36, (207Pb/204Pb)t = 15.66–15.76, (208Pb/204Pb)t = 37.97–38.55) suggest that the monzogranite formed through partial melting of crustal greywacke, while the leucogranite originated from partial melting of crustal pelite. Regional geological studies suggest that these S-type granites in Pinghe were emplaced in an active continental margin setting, associated with the westward subduction of the proto-Tethys oceanic slab. The geochemical characteristics of leucogranite are consistent with those of tungsten-tin-related granites, indicating significant metallogenic potential for W and Sn deposits.

摘要:Better understanding of shoshonitic rocks is vital to unravel the formation process and spatial distribution of their associated ore deposits. Here, we conducted analyses on the shoshonitic granodiorite and its mafic microgranular enclaves (MMEs) from the Chadi Cu-Pb-Zn polymetallic deposit (South China), with the aim to investigate their petrogenesis and tectonic setting. Zircon U-Pb age of the MMEs (165.0 ± 1.2 Ma) is coeval with that of the host granodiorite (164.8 ± 0.63 Ma). The Chadi granitoids are enriched in large ion lithophile elements and light rare earth elements, but depleted in high-field-strength elements. The granodiorite displays low (87Sr/86Sr)i (0.7069–0.7072), and negative εNd(t) (?5.8 to ?5.5) and zircon εHf(t) (?3.6 to ?0.4) values. These isotopic characteristics of the granodiorite and MMEs indicate the mixing of a mafic magma (formed from the subduction-related, metasomatically-enriched lithospheric mantle) and a felsic magma (formed from the partial melting of crustal materials), which is closely related to the Paleo-Pacific subduction. The Chadi granodioritic magma has likely low oxygen fugacity (<ΔFMQ + 1), low whole-rock Sr/Y ratio (mostly < 30), and low S (0.04 ± 0.02 wt%) and Cl (0.23 ± 0.04 wt%) contents, suggesting that the potential of forming large-scale Cu mineralization is low.

摘要:Weijia Guyot, located in the western Pacific Ocean, has become a research focus due to its abundant cobalt-rich ferromanganese (Fe-Mn) crusts. While most studies on Fe-Mn crusts on seamounts have focused on the exposed variety, less attention has been paid to potential buried crusts. This study presents a preliminary geochemical and chronological study of buried Fe-Mn crusts at Weijia Guyot. The findings suggest that these buried crusts began to form around 57.5 Ma and ceased growing at approximately 46.3 Ma. Following the formation of Weijia Guyot through volcanic eruption, it did not experience continuous and steady subsidence to its current depth. Instead, an exhumation process took place from deep to shallow depths between 46.3 and 11.6 Ma. This process brought the Fe-Mn crusts into shallow water environments, halting their growth. During this time, Weijia Guyot was located near the equatorial Pacific Ocean and was exposed to an extended period of phosphatization. This exposure led to a depletion of key metallogenic elements, such as Co, Ni and Cu, within the Fe-Mn crusts, while P2O5 and CaO levels increased significantly. Since the Middle Miocene, the crusts have been progressively buried by pelagic sediments.

摘要:The Duanfengshan deposit is a newly discovered large pegmatitic-type Nb-Ta deposit in the central section of the Jiangnan orogenic belt, South China. There are three types of pegmatite in the Duanfengshan area: microcline pegmatite, microcline-albite pegmatite and albite pegmatite. Although several geological, geochronological and geochemical studies of this deposit have been carried out, the relationships between the evolution degree of different types of pegmatites and mineralization are still unclear. We address this problem through systematic petrographic and geochemical studies of muscovite and feldspars from two representative pegmatite veins, the No. 328 microcline-albite pegmatite vein, and the No. 610 albite pegmatite vein. The results of electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of muscovite and K-feldspar reveal that K/Rb ratios decrease with increasing Rb, Cs, Ga, Nb and Ta contents alongside decreasing Ba and Sr contents, suggesting that magmatic differentiation played a dominant role in rare metal mineralization. A comparison of the analytical results of this study with those from rare metal pegmatites globally suggests that the No. 610 vein has a high mineralization potential, whereas the No. 328 vein has relatively low mineralization potential. The results from this study may be applied to the evaluation of mineralization potential for other pegmatite veins in the Duanfengshan area and other rare metal pegmatite fields with similar geological settings.

摘要:The Xingyuan large fluorite deposit in Fengning, Hebei Province, China, is a significant deposit in the North Hebei–West Liaoning fluorite mineralization belt. The ore bodies are structurally controlled and occur in fault zones near granitic porphyry veins. Previous studies have focused on the geology and ore-controlling factors, whereas the general features of the hydrothermal systems that contributed to the formation of the deposit remain unclear. This study investigated the nature, origin, and evolution of mineralizing fluids in the Fengning deposit, based on fluid inclusion and H-O isotope data. The fluid inclusions in fluorite are mostly H2O-rich, gas–liquid, two-phase inclusions, along with a few three-phase inclusions containing halite daughter crystals and CO2 gas. The ore-forming fluid was variable in homogenization temperature (108–388°C), salinity (0.2–47.4 wt% NaCl equivalent), and density (0.58–1.11 g/cm3), which indicate it was a H2O-NaCl-CO2 system of moderate–low temperature, low salinity, and low density. Fluorite H-O isotopes (δDV-SMOW = ?123.5‰ to ?111.8‰; δ18OV-SMOW = ?10.3‰ to ?6.5‰), temperature data, and fluid compositions indicate the mineralizing fluid was initially dominated by magmatic waters, but then experienced a large influx of meteoric waters. The fluid temperature and salinity decreased and the density increased from the early to late stages of mineralization. The main mechanisms of fluorite precipitation were water–rock reactions and fluid cooling. The Xingyuan fluorite deposit is a post-magmatic hydrothermal deposit.

摘要:The Disuga Cu deposit, located in the eastern porphyry belt of the Zhongdian arc, southwest China, provides a window into magmatic–hydrothermal processes controlling porphyry Cu mineralization. Based on zircon U-Pb geochronology, hydrothermal mineral chemistry, short-wave infrared spectroscopy, and mass balance modeling, this study investigated the alteration zonation and element mobility in the Disuga Cu deposit. Zircon U-Pb ages of the ore-hosting quartz dioritic porphyries (222.4 ± 3.1 and 219.3 ± 2.4 Ma) are similar to those of Late Triassic subduction-related magmatism. High zircon-crystallization temperatures (727 ± 26°C) and elevated oxygen fugacity (ΔFMQ + 2.0) confirm these porphyries were favorable for mineralization. Hydrothermal sericite (Si = 6.49 atoms per formula unit [apfu]; AlVI = 3.39 apfu) and chlorite (Fe/(Fe + Mg) = 0.59–0.63) compositions indicate an acidic reduced fluid. Three distinct hydrothermal stages were identified: (1) phyllic alteration (370°C); (2) propylitic alteration (315°C); and (3) low-temperature hydrothermal alteration (242°C). Mass balance calculations show that the Cu migration rate (155.6%/114.4%) in the propylitic/phyllic alteration zones was higher than that of Mo (14.3%; limited to the propylitic alteration zone). The alteration mineralization assemblages indicate the occurrence of deep potassic alteration zones and porphyry Cu-(Mo) mineralization in the Disuga area.

摘要:The Shuangwang Au deposit in the western Qinling Orogen is hosted by a WNW–ESE-trending breccia belt that is structurally controlled by the northern limb of the Yindonggou fold. Igneous rocks area in the deposit are part of the Xiba pluton, which comprises granodiorite and monzogranite that contains mafic microgranular envlaves (MMEs), and later mineralized granitic porphyry dikes. The mineralized granitic porphyry dikes were controlled by the same structures that controlled the ore bodies. Zircon LA-ICP-MS U-Pb dating yields ages of 220.0 ± 1.9 Ma for the granodiorite, and 217.9 ± 1.9 Ma for the granitic porphyry, which is consistent with the mineralization ages reported in previous studies (220–218 Ma). Together with the similarity of alteration mineral assemblages?between ore and mineralized granitic porphyry, we suggest that the mineralization was controlled by structure and Xiba pluton. The geochemical data show?that the granodiorite and granitic porphyry are subalkaline and the MMEs are alkaline in composition. All samples have similar chondrite-normalized rare earth element patterns with enrichment of light rare earth elements. The granodiorite and MMEs are depleted in Nb, Ta, Sr, P, and Ti and enriched in U, K, Pb, Zr, and Hf. The granitic porphyry is enriched in large-ion lithophile elements but depleted in high-field-strength elements. The granodiorite and MMEs have low whole-rock εNd(t) values (?10.90 to ?2.32) and (87Sr/86Sr)i ratios (0.7000–0.7285), similar to coeval Triassic granites in the western Qinling Orogen. The (87Sr/86Sr)i ratios of the granitic porphyry have been affected by fluid metasomatism that results in higher (87Sr/86Sr)i values. The geochronological, geochemical, and isotopic evidence suggest that the Xiba pluton formed by partial melting of thickened lower crust that had been intruded by alkaline mafic magma, as documented by the MMEs, which were derived from a source metasomatized by subduction-related fluids. The granodioritic and granitic porphyry magmas were relatively oxidized (fayalite–magnetite–quartz [FMQ] to magnetite–hematite (MH) buffer conditions; zircon Ce4+/Ce3+ = 72–813; log(fO2) = ?22 to ?8). We propose that magma mixing between lower crust and mantle-derived mafic magma was triggered by the tectonic transition from a collisional to post-collision setting, which provided the metals, S, fluids, and increase in magma oxygen fugacity that enabled the formation of the Shuangwang Au deposit. Since the Late Triassic, the western Qinling Orogen evolved from a syn-collisional compressional to post-collisional extensional environment. The mineralization of the Shuangwang Au deposit involved early formation of a tectonic breccia in the compressional stage. Subsequently, hydrothermal fluids derived from a magma ascended, migrated, mixed, and precipitated ores in the tectonic breccia during the later extensional stage to form the Shuangwang Au deposit.

摘要:Research on the distribution and development of black shales in the Lianggaoshan Formation has been deficient, which has hindered exploration for lacustrine shale oil in the Sichuan Basin. Our study characterized the well logging data, core samples, outcrops, and geochemistry of black shales in the Lianggaoshan Formation in the Sichuan Basin. Our analysis focused on the lake basin evolution and the migration characteristics, paleoenvironmental features, formation mechanisms, and developmental model of the black shales. The results indicated that black shales in the Lianggaoshan Formation exhibited significant lateral migration, with an overall thickening trend from east to west. Within the 1st Member of the formation, black shale occurred as a single thick layer in the eastern region that gradually thinned toward the central region. Multiple sets of shale developed within the 2nd and 3rd members, and these had lower thicknesses than the 1st Member and migrated toward central Sichuan. Paleoproductivity and terrigenous input were the main factors controlling the deposition of black shales. A semi-humid climate influenced the deposition of black shales, bringing abundant freshwater, terrigenous debris, and nutrients into the basin. Decomposition of organic matter consumed oxygen in sediment and bottom water, causing localized oxygen deficiency in the strata.

摘要:The Shanan sag in the central–western Bohai Bay Basin hosts high-quality Paleogene source rocks within the Shahejie Formation’s third member (E2s3). Despite hydrocarbon indications in Cenozoic strata, no commercial accumulations have been discovered. An integrated approach combining geochemical analysis, fluid inclusion thermometry, apatite fission-track (AFT) thermochronology, and basin modeling was employed to unravel the paleo-geothermal regime and hydrocarbon generation history of E2s3 source rocks. AFT data from the Shahejie Formation’s second member (E2s2) reveal a tectonothermal event at 25 Ma that accelerated E2s3 maturation. Outside three sub-sag depocenters, current E2s2 reservoir temperatures remain below the 25 Ma paleo-geothermal maxima despite subsequent Neogene burial. Hydrocarbon-bearing brine inclusions in E2s2 reservoirs exhibit peak homogenization temperatures (Th) at 25 Ma, with minimal high-temperature signals, indicating that E2s3 hydrocarbon generation peaked during the Paleogene thermal event, with limited late-stage accumulation. The regional effects of the Dongying Movement necessitate thick Neogene sedimentation to compensate for the 25 Ma paleo-geothermal anomaly. Our findings emphasize targeting Neogene depocenters in petroleum exploration to mitigate the inhibitory effects of high paleo-heat flow on late hydrocarbon generation, thereby enhancing current accumulation potential.

摘要:10Be surface exposure dating is one of the methods most used in the dating of glacial landforms due to its well-understood dating mechanism, readily accessible materials. However, numerous dating studies have shown that nuclide inheritance may overestimate the age as a result of the nuclide concentrations accumulating in glacial deposits prior to their eventual exposure. As the concentration is challenging to measure directly, it is typically assumed to be zero. This study investigated the potential nuclide inheritance in the Hailuogou Glacier by measuring 10Be concentrations in modern moraines. The results showed that (1) in the glacier foreland, the exposure ages of two sub-angular boulders aligned with the timing of glacier retreat suggested minimal or potentially negligible nuclide inheritance, whereas two amalgamated samples exhibited 10Be exposure ages of 820 ± 278 yr and 570 ± 168 yr, indicating that multiple cobbles may contain inherited nuclides; and (2) the exposure ages of the angular boulder samples from the modern glacier surface ranged from 366 ± 151 yr to 221 ± 85 yr, the coarse-grained (CG) sand samples ranged from 470 ± 129 yr to 178 ± 103 yr in age, and the ages of the amalgamated samples ranged from 1,114 ± 197 yr to 97 ± 37 yr, which may reflecting the upper limits of inherited ages.

摘要:The subduction and closure history of the Paleo-Tethyan Ocean is of significant importance to the formation of the Alpine–Himalayan orogenic belt. However, in West Qinling, China, the evolution of the subducted Paleo-Tethyan oceanic slab in the mantle remains unclear. In this work, we determine high-resolution P-wave azimuthal anisotropic tomography of the crust and upper mantle beneath west Qinling by inverting newly collected local and teleseismic data. The local earthquakes are relocated by jointly using permanent and portable stations and weighted by their hypocentral errors during the inversion. Our model reveals a slab-like high P-wave velocity (Vp) anomaly below 300 km depth and significant depth variations of anisotropy in the upper mantle beneath the West Qinling orogen. By comparing with previous geophysical results and integrating with geological and geochemical findings, we interpret that this high-Vp anomaly is most likely the subducted Mianlue oceanic slab preserved in the upper mantle and the mantle transition zone since the early Mesozoic. Beneath the Songpan–Ganzi block and the Longzhong basin, low-V anomalies with weak azimuthal anisotropy suggest a vertical mantle upwelling at a depth of 120 to 200 km, providing positive buoyancy to the subducted oceanic slab and extends its stagnation duration in the upper mantle.

摘要:The lower Yarlung Tsangpo River basin of the Qinghai–Tibet Plateau frequently experiences geo-hazardous occurrences such as landslides, ice/rock avalanches and debris flows, causing loss of human lives and damage to infrastructure. However, a comprehensive inventory map of geohazards is lacking for this region, due to the extreme challenges of the geomorphological and environmental conditions (i.e., steep terrain, dense vegetation cover, and the presence of ice and snow). To this end, we propose a novel approach for mapping active geohazards in complex mountainous regions through InSAR phase gradient measurements based on a deep learning algorithm, which is then applied to the lower Yarlung Tsangpo River basin for the first time, in order to prepare an inventory map of active geohazards using ascending and descending Sentinel-1 SAR images acquired between March 2017 and July 2023. First, the InSAR phase gradient stacking method was introduced to estimate ground deformation, which offers significant advantages in minimizing the influence of InSAR decorrelation and effectively suppressing topographic residuals and atmospheric delays. InSAR phase gradient rates effectively retrieve patterns of localized ground deformation associated with geohazard activity. Then, a DeepLabv3 deep learning model was established and trained with phase gradient rate maps of manually labeled geohazards, in order to achieve the automatic identification of active geohazards. Our results show that there are 277 active geohazards within the lower Yarlung Tsangpo River basin, encompassing an area of ~25600 km2. The DeepLabv3 model achieved good precision, recall rate and F1 scores at 92, 86 and 90%, respectively. The distribution of detected geohazards is closely correlated with the topographic factors, faults and river system. Compared to the results derived from Small Baseline Subset InSAR (SBAS-InSAR) and optical images, the proposed approach can obtain high density pixels of InSAR measurement in low-coherence scenarios, thus enabling high-accuracy mapping of active geohazards in complex mountainous areas.

摘要:Mineral exploration under exotic overburden has been a great challenge in exploration geochemistry. Gas geochemical measurement is a potential method for mineral exploration due to the characteristics of strong penetrability and vertical migration. The previous rapid gas analyzer cannot determine low concentrations of soil gases because of inadequate sensitivity, therefore, it is necessary to develop a more sensitive analytical technique. In this paper, the pilot studies on CO2 and SO2 geochemical measurements were performed at the Zhuxi W-(Cu) deposit, Jiapigou gold ore-concentrated area, and Tukuzbay gold deposit. This study employed rapid gas analyzer based on Infrared Absorption Spectroscopy and Electrochemical Analysis, which can detect low concentrations of CO2 and SO2 and greatly improve the reliability of test data. The results show that CO2 and SO2 show clear anomalies over deeply concealed ore bodies and faults, demonstrating that CO2 and SO2 anomalies can reveal indicative information about concealed mineralization and faults. Moreover, CO2 and SO2 anomalies can identify mineralization information exceeding 1,000 m in depth, suggesting that this method has large detection depth. Therefore, CO2 and SO2 geochemical measurement method is a feasible tool to discern deeply concealed mineralization and faults, and can provide a new idea in prospecting for concealed ore deposits in covered areas.

摘要:Geochemical surveys are essential for understanding the spatial distribution of ore-forming elements. However, these surveys often involve compositional data, the weight concentrations, which do not meet the requirements of statistical methods due to the closure effect. In this study, we applied an integrated approach combining compositional data, multifractal, and multivariate statistical analyses to identify the nonlinear complexity of the spatial distributions of elemental concentrations in the Er’renshan ore field. Initially, the raw concentrations were transformed into log-ratios following the principles of composition data theory to alleviate the impact of the closure effect. Multifractal analysis was then conducted to characterise the nonlinear complexity of the concentration distributions. Furthermore, principal component analysis (PCA) and factor analysis (FA) were applied to identify spurious correlations and the potential factors controlling the distribution patterns. The results demonstrate that: a) the raw data are biased, while the log-ratio data are unbiased and more reliable; b) the spatial distributions of elemental concentrations exhibit nonlinear complexity; and c) the elemental distribution in the study area is largely controlled by structural factors.