Acta Geochimica最新文献

The Shangdan suture zone preserves critical information about the Paleozoic collision between the North and South Qinling Belts. Although this collision event significantly influenced the tectonic evolution of the Qinling Orogenic Belt, the timing remains a subject of debate. In this study, we comprehensively analyzed the Th/U ratios, elongation ratios, and U–Pb ages of detrital zircons to investigate provenance signatures and tectonic-sedimentary settings. Detailed U–Pb dating of detrital zircons from Ordovician to Devonian strata in the Shanyang and Xunyang area of South Qinling Belt revealed age clusters of 430–450, 710–840, and 910–960 Ma for Devonian and Silurian samples, with peaks at ~ 440, ~ 800, and ~ 940 Ma, respectively. Ordovician samples predominantly exhibited ages of 710–850 Ma, peaking at ~ 735 Ma, but lacked the 910–960Ma age group. Comparison with magmatic events in adjacent terranes and detrital zircon mixing provenance modeling identified 430–450 and 910–960 Ma peaks associated with granitoids in the North Qinling Belt, while the 710–840 Ma age population corresponded to sources from the South China Block and South Qinling Belt. Provenance analysis indicated that Devonian and Silurian samples originated from the northern and southern sides of the Shangdan suture zone, whereas Ordovician samples were derived from the southern side. This shift in provenance suggests a significant change in sedimentary sources in the South Qinling Belt from the Ordovician to the Silurian. The closure of the Shangdan Ocean likely occurred during the Silurian-Devonian period, resulting in a northern provenance for the Silurian and Devonian strata.

The Kuqa Depression, recognized as one of the best hydrocarbon-enriched depressions within the Tarim Basin, has long been debated regarding its principal source intervals, which has restricted petroleum exploration and development in this area. This study focuses on the hydrocarbon source rocks of the Middle-Upper Triassic Karamayi Formation and Upper Triassic Huangshanjie Formation in the northern part of the Kuqa Depression through a comprehensive organic and elemental investigation. The examinations indicate that the source rocks of the Karamayi Formation-Huangshanjie Formation are dark mudstones developed in a lacustrine setting. The organic matter abundance generally ranges from fair to good. The organic matter type is mainly Type II, with a portion being Type III, and the source rocks have reached a mature stage. During the depositional period of the source rocks in the Karamayi Formation, variations in paleoproductivity, characteristics of ancient water bodies and intensity of hydrothermal activity together influenced the organic matter enrichment model of the Misbrac section, which is controlled by preservation conditions and paleoproductivity. In contrast, the Heiyingshan and Kuqa River sections exhibit paleoproductivity-dominated enrichment mechanisms. During the depositional period of the Huangshanjie Formation, the organic matter enrichment model in the study area is controlled by both the preservation conditions and paleoproductivity.

The migration mechanisms of ore-forming fluids have long been a focus in the field of ore deposit studies. Calcite is ubiquitously present in various types of rocks in the lithosphere, and the underlying mechanisms of its influence on fluid migration are of crucial importance. While previous studies have revealed that salinity changes can modulate fluid migration, the underlying mechanisms remain poorly understood. We employ molecular dynamics simulations to elucidate how salinity variations in ore-forming fluids modulate the adsorption onto calcite nanopore walls, thereby revealing the microscopic mechanisms governing ore fluid transport through calcite nano-fractures. The results show that the adsorption energy E_int of the solution on the calcite surface increased from −14,948.84 ± 182.48 kcal/mol to −12,144.08 ± 118.2 kcal/mol as salinity increased, which is conducive to the long-range transport of the fluid in the calcite nanopore.

The Beishan area (BA), located along the southern margin of the Central Asian orogenic belt, represents a key region for studying the opening of the southern Paleo-Asian Ocean (PAO) during the Neoproterozoic Era. Current understanding of BA’s Neoproterozoic tectonic evolution remains limited because of insufficient constraints. This study presents petrological, whole-rock geochemical, Sr–Nd isotopic, zircon U–Pb dating, and Hf isotopic analyses of gabbro (765 Ma), dacitic tuff (756 Ma), syenogranite (764 Ma), and monzogranite (770 Ma) from the BA. The gabbros show high MgO (8.06–8.31 wt%) and low K₂O (0.23–1.09 wt%) contents, depletion of high-field-strength elements (Nb, Ta, and Ti), (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7051–0.7057, and positive ε_Nd(t) values (+ 2.55 to + 3.19). These geochemical signatures suggest derivation from a depleted mantle metasomatized by subducted slab-derived melts, consistent with formation in a back-arc rift setting. The dacitic tuffs display negative ε_Nd(t) values (− 16.38 to − 1.29) and Zr-Hf enrichment, indicating an origin from ancient crustal melting. The syenogranites and monzogranites are characterized by high 10,000 Ga/Al and (Zr+Nb+Ce+Y) values, classifying them as A1-type granites. They yield negative ε_Nd(t) values (− 6.66 to − 2.29) and variable ε_Hf(t) values (− 3.7 to + 4.8), indicating partial melting of Paleoproterozoic crust material. Based on these findings and previous studies, we propose that the initial opening of the southern PAO in the BA occurred no earlier than 770 Ma, likely driven by combined subducted slab rollback and mantle plume upwelling.

Recent studies have confirmed the critical and essential role of elemental hydrolysis in metallogenic processes, such as metal migration and precipitation. However, the kinetic processes, characteristics, and formation mechanisms of hydrolyzed precipitates require further comprehensive investigation. This paper is based on a systematic investigation of the hydrolysis mechanisms of Pb and Zn in various systems under ambient temperature and pressure, the storage conditions of the hydrolyzed precipitates, and the characterization of these precipitates. The results indicate that the hydrolysis behaviors of Pb and Zn exhibit significant differences across various systems. Within the monometallic regime, there is a pronounced disparity in the hydrolysis rates between Pb ions and Zn ions. Pb ions demonstrate a substantially higher degree of hydrolysis, a trend that persists over time and remains largely unaffected by the "fluid retention or isolation" phenomenon in the surrounding environment. Both hydrolytic precipitation rates were observed to decrease in the mixed system, with Zn ions exhibiting less reduction than Pb ions. After hydrolysis, hydrolyzed precipitates can remain in the fluid environment for extended periods of time, which can lead to re-dissolution. Over time, this re-dissolution can increase, eventually leading to significant loss of hydrolyzed precipitates. The hydrolyzed precipitates obtained from the experiments primarily consisted of alkaline carbonates of Pb and Zn. Notably, the crystalline characteristics of the hydrolysis products of Pb and Zn ions exhibited significant differences across various experimental systems; however, the crystallographic characteristics of the primary hydrolysis products are essentially identical to those of their corresponding natural counterparts. Based on the findings from physical phase analysis and previous research, it is concluded that the hydrolysis process consists of three main stages: oxides/hydroxides, carbonates, and alkali carbonates. In the Pb-Zn-NaCl-H₂O system, the proportion of the basic carbonate products of Pb and Zn is 6:2. This research offers an in-depth analysis of the hydrolysis dynamics of lead and zinc under ambient temperature and pressure conditions. Furthermore, it characterizes the crystallization features of the hydrolyzed precipitates and reconstructs the three stages of the formation process. This study holds significant scientific value for understanding the metallogenic mechanisms of Pb and Zn.

Mining activities are often associated with significant environmental degradation, particularly due to the accumulation of mine tailings (MTs). These waste materials are frequently stored in dams or open ponds without adequate treatment, posing serious risk of heavy metals (HMs) contamination to surrounding ecosystems. Given these challenges, restoration of MTs to mitigate their negative impacts has become highly important. This study attempts to compile different types of MTs, their characteristics, and associated issues such as acid mine drainage (AMD) and HMs contamination, along with other environmental impacts. It also explores the fundamentals of phytoremediation, highlighting key processes, recent advancements, benefits, limitations, and strategies for post-harvest management. The findings indicate that MTs are a major source of HM pollution and contribute significantly to environmental deterioration. Phytoremediation has emerged as a promising, cost-effective, and eco-friendly solution for MT restoration. In addition to mitigating contamination, phytoremediation enhances soil quality, prevents erosion, reduces HM leaching into groundwater, and improves the visual appeal of degraded sites. Research suggests that revegetating MT-contaminated soils with specific plant species can effectively remediate these areas, reducing HM leaching risks while improving soil properties. This review serves as a valuable resource for researchers working on MT restoration, offering insights into the latest advancements in phytoremediation technology and its potential to address the environmental challenges posed by MTs.

The Cambrian basin of the Tethyan Himalaya lies along the northern margin of the Indian Plate. For the first time to our knowledge, the clastic sediments of the Kunzam La Formation (Cambrian Series 2–Stage 4) in the Tidong Valley, Kinnaur, have been subjected to a geochemical investigation. Analysis of rare earth elements and trace elements, supported by sandstone petrography and modal analysis, indicates a mixed provenance—primarily felsic (UCC composition) with some basic (HFSE-depleted) input—suggesting derivation from continental crustal melts in an active marginal continental island arc setting, linked to recycled orogens. The Cambrian basin was subsequently obliterated by the Late Cambrian-Early Ordovician Kurgiakh Orogeny, accompanied by extensive acidic magmatism and metamorphism. Elemental ratios of Ce/Ce*, Eu/Eu*, Ni/Co, U/Th, Y/Ho, Sr/Ba, and Sr/Cu, suggesting the formation, were deposited in a shallow marine environment with fluvial influence under highly oxidizing palaeo-redox conditions, low palaeo-salinity, and a warm, humid climate. The present geochemical data complement previous sedimentological studies of the formation in the Tidong Valley and enable a comparative assessment with geochemical data from the Spiti region.

Lithium is a critical strategic metal with significant reserves in pegmatites, serving as the primary source for global Li production. Apatite has attracted increasing attention as an indicator in petrogenesis studies and for the exploration of ore deposits. In this study, we investigated the volatile compositions and major and trace elements of apatite from the Qiongjiagang pegmatite-type lithium deposit in Himalaya. Apatite derived from spodumene pegmatite exhibits relatively constant and high total rare earth element (ΣREE+Y) concentrations, ranging from 5899 to 8540 ppm. In contrast, apatite in barren pegmatite displays evidently lower (ΣREE+Y) concentrations, varying between 1345 and 3095 ppm. The REE patterns of apatite in spodumene pegmatite generally exhibit a flat shape [(La/Yb)_N = 1.55–2.15)], with distinctively negative Eu anomalies (Eu_N/Eu_N* = 0.14–0.22), slightly positive Ce anomalies (Ce_N/Ce_N* = 1.03–1.13), and low Y/Ho ratios (28–30). By contrast, apatite in barren pegmatite shows middle rare earth element (MREE)-depleted downward-convex patterns [(La/Yb)_N = 1.99–20.4)], strongly negative Eu anomalies (Eu_N/Eu_N* = 0.01–0.14), slightly positive Ce anomalies (Ce_N/Ce_N* = 1.10–1.24), and high Y/Ho ratios (30–55, with an average of 50). Overall, the high concentrations of ΣREE (and Y) and low Th/U and Y/Ho ratios can serve as diagnostic indicators to distinguish apatite in spodumene pegmatite from that in barren pegmatite. Furthermore, the flat REE pattern may represent a common feature of apatite from lithium deposits. Differences in the Ce and Eu anomalies between apatite from these two kinds of pegmatites likely reflect formation under different redox conditions. Consequently, based on calculations derived from apatite volatile compositions, the melt associated with spodumene pegmatite may contain higher water content compared to that of the barren one. Therefore, the mineralized pegmatite system may incorporate substantial amounts of H₂O-rich fluids, which play a crucial role in lithium mineralization.

Over 90% of Earth’s carbon is stored in the mantle and core. The deep carbon cycle plays a critical role in regulating surface carbon fluxes, global climate, and the habitability of Earth. Carbon mainly residing within the sediments, altered oceanic crust, and mantle peridotite as carbonate minerals and organic carbon is transported to the deep Earth via plate subduction. A series of reactions (e.g., metamorphism, dissolution, and melting) occurring in the subducting slab drive the carbon removal. Some of the carbon is recycled to the surface via arc volcanism, while the rest is carried into the deeper Earth. More than two-thirds of the global subduction carbon input comes from sedimentary carbon, whose fate during subduction directly affects the flux in the global carbon cycle. Over the past two decades, the sedimentary carbon cycle in subduction zones has been extensively studied by experiments and computational approaches. Here, we provide a comprehensive review of the sources, species, decarbonation reactions, carbon cycle tracing, and fluxes of sedimentary carbon in subduction zones, and the role of sedimentary carbon subduction in climate evolution and mantle chemistry. Further research is required for our understanding of deep carbon cycle processes and their role in Earth's climate.

The Triassic granitoids and associated diorites in the Qinling orogenic belt reveal critical evidence of crust–mantle interaction during the terminal collision between the North China and Yangtze Blocks. This study presents new constraints from zircon U–Pb age, Lu–Hf isotopes, and amphibole-plagioclase-apatite geochemistry for the Maoerliang diorite in the Foping area. Zircon U–Pb dating yields a crystallization age of 212 ± 2.8 Ma, with εHf(t) values ranging from −8.6 to +3.0 and corresponding two-stage Hf model ages (T_DM2) of 886–1479 Ma, indicative of derivation from an evolved lithospheric mantle source. Petrogenetic indicators reveal a mantle affinity: amphiboles exhibit high MgO (9.8–11.2 wt%) and elevated Nb/Ta ratios (14.3–18.1), while apatites display F-rich (2.1–2.8 wt%) and Cl-poor (0.08–0.15 wt%) characteristics. Thermobarometric calculations based on amphibole chemistry constrain crystallization conditions of 805–866 °C and 211–383 MPa, corresponding to mid-crustal emplacement depths (8–14 km). Both amphibole and zircon indicate elevated oxygen fugacity (ΔNNO = −4.08 to −3.71; ∆FMQ = −1.14 to +3.96) and hydrous magma conditions (H₂O = 4.22–4.94 wt%). Late-stage plagioclase crystallization (An21–26.5) reflects prolonged fractional crystallization in a hydrous dioritic magma. These diagnostic features—mantle-derived signatures, high fO₂, and hydrous nature—exhibit remarkable convergence with gold-mineralized granites in the East Qinling. Our findings suggest that Triassic dioritic magmatism may have played an underappreciated role in facilitating gold enrichment processes within the South Qinling metallogenic belt.