Acta Geochimica最新文献

The study area is situated in the Tianshan region, specifically within the eastern segment of the North Qilian Orogenic Belt (NQLOB). The NQLOB is a critical region for understanding oceanic closure and continental collision processes driven by the Shangdan Ocean subduction-exhumation, which was a segment of the Proto-Tethys Ocean during the Early Paleozoic. Despite significant research, the Early Paleozoic tectonic background and subduction-related orogenic processes, particularly in the eastern NQLOB, remain subjects of debate. This study presents significant petrographic, geochemical, and geochronologic insights into the metavolcanic rocks of the Chenjiahe Group in the eastern NQLOB. Petrographic analysis reveals that these metavolcanic rocks originated in a low-grade metamorphic setting. Zircon laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb dating yielded ages ranging between 449.7–443.4 Ma, indicating Late Ordovician formation. Geochemical signatures of felsic and intermediate rocks exhibit calc-alkaline to high-K calc-alkaline similarities, characterized by high light rare earth elements (LREEs), low heavy rare earth elements (HREEs), and moderate Eu anomalies, consistent with a continental arc setting. In contrast, basaltic rocks display tholeiitic features with elevated large-ion lithophile elements (LILEs), reduced high-field-strength elements (HFSEs), and weak Eu anomalies, suggesting an extensional environment. These findings imply that the metavolcanic rocks evolved in a continental arc-back-arc extension setting connected with the northward subduction and exhumation of the Huluhe back-arc oceanic basin. This process was likely triggered by the northward subduction and closure of the Shangdan Ocean, culminating in the Late Ordovician amalgamation of the Qilian Block and the southwestern North China Block. This study provides critical insight into the tectonic development of the NQLOB and the broader Proto-Tethys Ocean dynamics at the northern periphery of the Eastern Gondwana.

Mafic rocks generated from subduction settings have recorded valuable source information about the mantle source. In this study, we present a comprehensive analysis of zircon U–Pb dating, whole-rock major and trace elements, and Sr–Nd isotopic data for the mafic gabbro located in the Yumen area, on the western part of the Yangtze Block, South China, aiming to constrain the processes of mantle metasomatism within subduction settings. U–Pb dating results for zircon yield crystallization ages of 800 Ma for type 1 mafic gabbro and 753–734 Ma for type 2 mafic gabbro. Type 1 mafic gabbro exhibits higher SiO₂ (44.13%–48.93%) and Al₂O₃ content but lower total Fe₂O₃ and MgO content than type 2 gabbro (SiO₂: 41.02%–43.28%). These gabbros display a high-Mg^# signature (52.50–62.81 for type 1, 50.89–57.04 for type 2), while they are enriched in significant large-ion lithophile elements (LILEs: Rb, Ba, Sr, K) and depleted in high-field-strength elements (HFSEs: Zr, Hf, Nd, Ta, Ti), which indicates an arc-like element signature. The positive whole-rock εNd(t) values (type 1: 3.5–4.4, type 2: 5.6–6.3) combined with a narrow range of (⁸⁷Sr/⁸⁶Sr)_i (type 1: 0.7035–0.7043, type 2: 0.7035–0.7036) of both gabbro types suggest a depleted lithospheric mantle origin. Therefore, these mafic rocks may derive from a metasomatized spinel lherzolite mantle source (with amphibole) due to the interactions of the deep mantle source and subduction fluid materials. We propose that the long-term metasomatism recorded by mafic gabbro in this study supports the fact that the subduction during the Neoproterozoic contributed to the formation of a metasomatized mantle source in the Yumen area, western Yangtze Block, South China.

Numerous Indosinian igneous rocks in the North Qaidam (NQ) provide crucial insights into the tectonic evolution of the Paleo-Tethys Ocean. This paper presents a comprehensive study of the petrography, mineralogy, geochemistry, zircon U–Pb geochronology, and Hf isotope composition of dioritic rocks from the eastern NQ. Zircon U–Pb dating results indicate that the dioritic rocks were formed during the Middle Triassic (244–240 Ma). The rocks exhibit high-K calc-alkaline characteristics with variable SiO₂ (55.25–65.39 wt%) and elevated K₂O + Na₂O (4.81–6.94 wt%) contents. They show enrichment in LILEs (Rb, Ba, K) and depletion in HFSEs (Nb, Ta, Ti), with slight negative Eu anomalies (Eu/Eu* = 0.89–0.97). Zircon ε_Hf(t) values (−20.93 to + 5.60) and T_DM2 ages (0.85–1.72 Ga) suggest mixed sources. Petrographic and mineralogical analysis reveals that the plagioclase phenocrysts exhibit disequilibrium textures (including reverse zoning), primarily composed of andesine and labradorite, with a small amount of oligoclase. The clinopyroxenes are all augites and have high crystallization temperatures (1111–1151 °C). These features, particularly the reverse zoning of plagioclase, support a petrogenetic model involving mantle-derived magma underplating that induced melting of ancient lower crust, followed by mixing of underplated basaltic magma with crust-derived felsic magma. Our results indicate formation in a back-arc extensional setting during subduction of the Zongwulong Paleo-Tethys Ocean.

The present study of metabasalts was carried out to understand the mantle source and geodynamic setting of the Mahakoshal Group in the Central Indian Tectonic Zone. In this study, we present detailed field, petrography, and whole rock geochemistry of the Mahakoshal metabasalts. The Mahakoshal metabasalts are sub-alkaline in nature and belong to the tholeiitic series of rocks. The variation in rare-earth element patterns of metabasalts indicates the different degrees of partial melting at shallow as well as deeper depths. Further, Eu/Eu* varies from 0.8 to 1.1 (except sample KP-144=0.3), Ce/Ce* varies from 0.97 to 1.05, showing no cerium anomaly, and Nb/Nb* ranges from 0.7 to 1.3 (except KP-144=0.1). The magnesium number (Mg#) varies from 0.2 to 0.3, which is quite low, indicating the evolved nature of the metabasalts. The studied metabasalts show E-MORB to OIB-type affinities, which are placed in the trench-distal back-arc setting. The opening of the Mahakoshal Basin is due to retreating orogen in the accretionary orogen setting and is contemporaneous with the assembly of the Columbia Supercontinent (~2.1–1.8 Ga). Hence, field, petrographic, and geochemical signatures indicate that the Mahakoshal basin opened as a back-arc rift basin on the Bundelkhand Craton, and that metabasalts are derived from the mantle that underwent variable degrees of partial melting at different depths.

The western margin of the Yangtze Block hosts diverse Neoproterozoic igneous rocks, with exposed S-type granites serving as key indicators for deciphering regional geological evolution. This study focuses on the Jiudaowan granite pluton, located on the western margin of the Yangtze Block, through systematic petrographic, whole-rock geochemical, zircon and monazite U–Pb geochronology, and whole-rock Nd isotopic analyses aiming to elucidate its petrogenesis and tectonic significance. The Jiudaowan granite pluton is a composite body, consisting of the Luotaijiu, Jiudaowan, and Daheishan units, characterized by biotite monzogranites, muscovite–plagioclase granites, and two-mica monzogranites, respectively. LA-ICP-MS zircon and monazite U–Pb dating reveals crystallization ages between 832 and 798 Ma. The three units are peraluminous, containing minerals such as muscovite, garnet, and tourmaline, and exhibiting high SiO₂ (72.99–77.83 wt%), Al₂O₃ (12.36–15.02 wt%), and A/CNK values (1.06–1.43), confirming their classification as peraluminous S-type granites. Compositional variations within the Jiudaowan granite pluton are primarily controlled by protolith composition and melting mechanisms. The pluton is distinguished by low CaO/Na₂O ratios (0.02–0.18), high Rb/Sr (0.83–113) and Rb/Ba (0.33–15.2) ratios, and negative ε_Nd(t) values (−13.6 to −9.1), indicating derivation from partial melting of heterogeneous metasedimentary sources. MgO, TiO₂, Rb/Sr, and whole-rock Zr saturation temperatures suggest that the Luotaijiu and Daheishan units formed via biotite dehydration melting, whereas the Jiudaowan unit resulted from muscovite dehydration melting. Additionally, the Jiudaowan granite pluton displays a clear negative correlation between Al₂O₃, CaO, Fe₂O₃T, MgO, TiO₂, and SiO₂, along with pronounced Eu negative anomalies and depletions in Sr and Ti, suggesting fractional crystallization of feldspar, mica, and Fe-Ti oxides during magma emplacement. Similarly, variable incompatible element ratios of Nb/U (1.07–18.97) and Nb/La (0.24–26.88) further indicate minor crustal assimilation and contamination during magma evolution. Integrating regional geological data, we propose that the Jiudaowan pluton formed during crustal thickening associated with post-collisional extension, likely related to the breakup of the Rodinia supercontinent.

In this study, copper extraction from low-grade oxide-sulfide ores was investigated using a leaching method combined with response surface methodology (RSM) to optimize operational conditions and assess leaching kinetics. Given copper’s extensive industrial applications, sustainable recovery from low-grade ores is critical. Five key parameters-acid concentration, leaching time, particle size, temperature, and solids percentage-were identified as major influences on copper recovery. The results revealed that leaching time and solids percentage, along with interactions between temperature-time and temperature-solids percentage, had the most significant effects. Optimal conditions for 80% copper recovery while minimizing iron recovery below 3% included an acid concentration of 1.21 mol (text {L}^{-1}), a leaching time of 108 min, a particle size of 438 (upmu)m, a temperature of 45 (^{circ }text {C}), and a solids percentage of 18.2%. Leaching kinetics were analyzed using shrinking core models, with the Dickinson model best describing the process, showing an activation energy of 32.63 kJ (text {mol}^{-1}), indicative of mixed diffusion and chemical reaction control. The final kinetic model effectively predicted the influence of key parameters. These findings highlight the importance of optimizing process variables and selecting suitable kinetic models to enhance extraction efficiency, reduce costs, and improve sustainability in copper recovery.

CB chondrite is a class of meteorite rich in metal composition, and its characteristics are obviously different from other chondrite groups. These meteorites are distinguished by their content of up to 60% to 70% FeNi metals and sulfides, in addition to their extreme lack of volatile and moderately volatile elements, less refractory inclusions, and almost no fine-grained matrix. Sierra Gorda 013 (SG 013) is a metal-rich chondritic meteorite of the CBa type. It has two different lithologies within SG 013: Lithology 1 and Lithology 2. Lithology 1 is an anomalous CBa chondrite containing chromite-pyroxene complex assemblage, whereas Lithology 2 is featured by recrystallization with small chondrules and contains much less iron nickel metal than Lithology 1. Although the two lithologies have essentially the same oxygen isotope composition, their structures are different from each other, suggesting that they probably underwent distinct formation and evolution processes from common precursors. In this study, the mineralogy of SG 013 chondrites is studied by means of petrographic observation, semi-quantitative analysis of chemical composition, fabric identification of minerals and integrated mineral phase analysis, while studying the mineralogy of SG 013, and the fabric characteristics of SG 013 are studied in detail. Different from previous studies, here we find that Lithology 1 of SG 013 contains non-porphyritic chondrules and metallic silicate globules, while Lithology 2 not only contains non-porphyritic chondrules and metallic-silicate globules, but also porphyritic chondrules. In this thesis, Electron backscatter diffraction (EBSD) analysis of magnesium olivine in metal-silicate globules and porphyritic chondrules in L2 of SG 013 shows that some magnesium olivine form under conditions of lower temperature and faster strain rate during uniaxial compression, where deformation of the olivine is dominated by dislocation glide. However, at higher temperatures and slower strain rates, the fabric of B-axis ([100]) is concentrated, indicating that the porphyritic chondrules may be dominated by the compaction of olivine particles, leading to dynamic recrystallization in the peripheral region or outer layer of the magnesium olivine crystal. New grains formed by dynamic recrystallization occur at the edges of residual grains and, their orientation is controlled by stress. It is found that the formation position of magnesium olivine in different chondrules of SG 013 from the inside out, with the gradual reduction of stress and the gradual increase of temperature, these local physicochemical changes reveal the complex thermal history and dynamic processes that chondrules undergo during their formation and evolution.

Supercritical fluids play a crucial role in material transport within Earth's deep interior. Investigating the pressure-dependent atomic structures and transport properties of such fluids is essential for understanding their petrological, chemical, and geophysical behaviors. In this study, we employed first-principles molecular dynamics simulations to explore the structures, self-diffusion coefficients ((D)), and viscosities (η) of supercritical NaAlSi₃O₈–H₂O fluids under conditions of 2000 K and 3–10 GPa, with water contents of 30 wt% and 50 wt%. Our calculations indicate that at a water content of 30 wt%, Q² and Q³ exhibit a certain degree of positive and negative pressure dependence, respectively, while other Qⁿ species (n represents the number of bridging oxygens connected to Si/Al) show minimal changes. At a water content of 50 wt%, Q² and Q⁰ exhibit a certain degree of positive and negative pressure dependence, respectively, while other Qⁿ species show minimal changes. At both water contents, Si–O–H and molecular water in the system exhibit negative pressure dependence, suggesting that the migration of supercritical fluids from deep to shallow regions is accompanied by the release of water. The self-diffusion coefficients in the supercritical NaAlSi₃O₈–H₂O fluid follow the order (D)_Na ≈ (D)_H > (D)_O > (D)_Al ≈ (D)_Si, with an overall weak negative pressure dependence. By comparing the viscosities of anhydrous and hydrous silicate melts from previous studies, we found that the addition of water caused a transition from negative to positive pressure dependence of viscosity, corresponding to a structural change from polymerization to depolymerization. Additionally, we calculated the fluid mobility Δρ/η of supercritical NaAlSi₃O₈–H₂O fluids and found that their mobility is several orders of magnitude higher than that of basalt melt and is also significantly greater than that of carbonate melt. As supercritical fluids ascend from deeper to shallower regions, their mobility is further enhanced, significantly contributing to the transport of elements from subducting slabs to the overlying mantle wedge.

The Rukwa Rift section of the East Africa Rift System presents a type setting for radiogenic helium accumulation in a petroleum free basin. As a prerequisite for accumulation, a considerable high heat flow anomaly is required from tectonothermal events to drive the release and circulation of radiogenic helium in the continental crust. Here we apply statistical analysis on geochemical data observed in thermal springs and recorded heat flow to account for crustal helium mass balance for each tectonothermal event in the region. Our results demonstrate anomalously high heat flow ~ 64–99 mW/m² with a consistent trend of helium isotopic ratio and fluid chemistry in the Rukwa Rift. Mass balance calculation show that the whole crustal volume underlying the East Africa Helium Pool (EAHP) has a capability of producing radiogenic helium of about 9.9 × 10⁶ mol/yr (22 × 10^–6 mol ⁴He/m² yr) while the total radiogenic helium flux ranges between ~2.39 × 10⁶ mol/yr and ~2.68 × 10⁹ mol/yr. The Tanzania Craton contributes largely to radiogenic helium releasing up to 50% of the total capacity in the region. The total ⁴He emission in the Rukwa Rift Basin is about 4.45 × 10⁵–5.01 × 10⁸ mol/yr which is thus equivalent to 19%–21% of the total production capacity in the region. These results imply that the helium accumulation in the EAHP would have started as early as Paleoproterozoic (2.349 Ga). These results provide a qualitative and quantitative insight to assess both helium and geothermal potentiality in the region.

The formation of copper deposits is closely related to hydrothermal processes. Understanding the migration of copper in hydrothermal fluids aids in reconstructing mineralization processes and deciphering deposit genesis. Copper primarily exists as Cu⁺ and Cu²⁺ in hydrothermal solutions, with redox conditions governing their interconversion. In chloride-rich geological fluids, Cu–Cl complexes are considered critical for copper transport. However, the specific types and valence transitions of Cu–Cl complexes under varying hydrothermal conditions remain poorly understood. This study employed in situ Raman spectroscopy to systematically analyze Cu + HCl and CuCl₂ + K₂S₂O₃/H₂ systems under saturated vapor pressure at 25–300 °C, elucidating the effects of temperature, Cl⁻ concentration, and redox conditions on copper speciation. In the Cu + HCl system, copper dissolved as monovalent Cu–Cl complexes. At high temperatures (> 200 °C), [CuCl₂]⁻ is the dominated species, whereas [CuCl₃]²⁻ becomes prevalent at lower temperatures and higher HCl concentrations. For the Cu²⁺–Cl system, the dominant species transitioned from [Cu(H₂O)_n]²⁺ (< 50 °C) to [CuCl₄]²⁻ (100 °C) and further to [CuCl]⁺ and [CuCl₂]⁰ at 300 °C. The introduction of reducing agents (K₂S₂O₃/H₂) facilitated Cu²⁺ → Cu⁺ reduction, thereby stabilizing Cu⁺–Cl complexes and inducing partial copper precipitation. The behavior of copper in chloride-rich hydrothermal fluids observed in this study indicates that high-temperature oxidizing fluids facilitate Cu mobilization, while cooling and redox changes promote deposition and ore minerals formation.