Guangzhou Institute of Geochemistry
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Late Cretaceous cooling and pulsed cenozoic uplift in the Fenghuang Shan: Insights into the tectonic evolution of the Qinling Orogen, central China
No full textReactivation of the Qinling Orogen since the Late Jurassic has been controlled by the combined effects of the convergence between the South and North China blocks, the subduction of the Pacific Plate, and the northeastward expansion of the Tibetan Plateau. In this study, we present new apatite (U-Th)/He ages from a vertical transect in the Fenghuang Shan located in the North Daba Mountains, where rapid cooling at similar to 95-90 Ma is identified. Inverse thermal history modeling results reveal another pulse of accelerated exhumation at similar to 50 Ma. In addition, we analyzed longitudinal profiles of rivers draining the northern flank of the Fenghuang Shan and identified knickpoints that break channels into gentle upstream and steep downstream segments. We deduce that these knickpoints were initiated by an increase in the mountain-bounding fault throw, based on nearly constant chi values (an integral to the upstream drainage area distribution) and a reliance of knickpoints' retreat distances on catchment areas. Assuming a linear slope exponent and erodibility of 10(-6) m(0.1)/a, we estimated knickpoint ages to be similar to 5.7 +/- 1.7 Ma. We interpret the Late Cretaceous cooling as a result of lithospheric extensional collapse following the Late Jurassic intra-continental compression between the North and South China blocks. The early Cenozoic exhumation might relate to the active normal faulting, as a far-field response to the west Pacific back-arc extension. The expansion of the NE Tibetan Plateau may have triggered the late Miocene uplift of the mountain range. The multiple episodes of tectonic events in the Fenghuang Shan might correspond to various geodynamic regimes on the tectonic evolution in the Qinling Orogen
Genesis of the Late Cretaceous mafic-intermediate intrusions in the giant Gejiu Sn-Cu ore field and its metallogenic significance
No full textThe giant Gejiu ore field, located in the southeastern Yunnan Province, China, developed a large-scale Sn-Cu mineralization related to the Cretaceous felsic-mafic magmatism. However, the genesis of Cretaceous mafic-intermediate intrusions remains controversial, which limits our understanding of the Cu source, Sn-Cu symbiotic mechanism, and geodynamic setting of the Gejiu region. To elucidate these issues, we conducted geochronological and geochemical evaluations on the Gejiu mafic-intermediate intrusions, including gabbro, syenite, and monzonite. The mafic-intermediate intrusions formed in 82.1-83.8 Ma, which are contemporaneous with ore-forming granites and ore bodies within the error range. Combined with the cumulus texture in gabbro, linear or parallel elemental plots, and similar and enriched Sr-Nd-Hf isotopes ((87Sr/86Sr)I = 0.708870-0.709811; epsilon Nd(t) = - 5.24-- 7.70; epsilon Hf(t) = - 4.8-2.5), the gradually increased Sr isotopes from gabbro through syenite to monzonite indicated that the Gejiu mafic-intermediate intrusions were formed by fractional crystallization and varying degrees of crustal assimilation of partial melts of an enriched lithospheric mantle. Based on the above research, we compiled geochronological and geochemical data of magmatic-metallogenic events in the region. The Sr-Nd isotopic and elemental ratios (i.e., Zr/Hf, Nb/Ta, Rb/Sr and Ba/Rb) of the Gejiu granites are located between the mafic-intermediate intrusions and spatially temporally connected Laojunshan granites, which indicate that the magma mixing between the enriched mantle-derived Cu-rich magma and metasedimentary rock-derived Sn-rich granitic magma generated Sn-Cu-rich granitic magma. This magma then evolved into the giant Gejiu Sn-Cu deposit via crystal fractionation and fluid exsolution. Combined with the regional geological data and spatiotemporal framework of Sn-polymetallic deposits, the magmatic-metallogenic model of the giant Gejiu Sn-Cu ore field further demonstrates that the southwestern slab rollback of the NeoTethyan oceanic plate during the Late Cretaceous controlled its formation
Reconstructing volatile exsolution in a porphyry ore-forming magma chamber: Perspectives from apatite inclusions
No full textPorphyry-type deposits in the shallow crust (3-5 km) are formed from metal-rich fluids exsolved from underlying magma chambers (5-15 km). However, a direct volatile record of the fluid exsolution in the magma chamber is commonly lacking. Here, we analyze the compositions of apatite inclusions (in biotite and plagioclase phenocrysts and fully/partly included in zircon microphenocrysts) and the apatite in groundmass from the largest Cretaceous Luoboling porphyry Cu-Mo deposit in South China. In combination with thermodynamic models, we reconstructed the volatile behavior in the ore-forming magma. The analyzed apatites are magmatic in origin, without hydrothermal overprint, as indicated by their homogeneous cathodoluminescence (CL) and higher Cl and REE contents than typical hydrothermal apatite. Apatite inclusions fully enclosed in zircon show decreasing XClAp/XOHAp (1.5-0.1) with increasing XFAp/XOHAp (0.4-3.3) and XFAp/XClAp (0.5-21), and display a steep drop in XClAp at approximately constant XOHAp in the ternary F-Cl-OH plot. These trends follow the modeled compositional trajectories of isobaric, H2O-saturated crystallization, indicating volatile exsolution during or before zircon crystallization in the magma chamber. Groundmass apatite crystals, phenocryst-hosted apatite inclusions, and apatite inclusions that are partially enclosed by zircon microphenocrysts have comparable volatile compositions, with much higher XFAp/XOHAp (1.7-78.8) and XFAp/XClAp (2.3-37.5) but lower XOHAp and XClAp than those fully enclosed in zircon. Compositional similarities between these crystals in different textural associations indicate that the phenocryst-hosted apatite inclusions do not preserve their original volatile records at the time of entrapment, and the volatile compositions were overprinted by later re-equilibration with the residual melt and the exsolved magmatic fluids. Given the porphyry magma is highly oxidized, and sulfides phases would be unstable in such circumstance, we suggest that volatile exsolution in the magma chamber is essential for Cl and Cu-Mo extraction from the melts and therefore the porphyry mineralization. In this study, only zircon-hosted apatite inclusions appear to best record the magmatic volatile compositions in a porphyry system. Therefore, using apatite hosted in other minerals or groundmass compositions to unravel magma volatile contents in porphyry Cu systems should be conducted with caution
Insights Into Formation and Aging of Secondary Organic Aerosol From Oxidation Flow Reactors: A Review
No full textPurpose of ReviewThis review aims to provide a comprehensive examination of oxidation flow reactor (OFR) studies and their applications in both laboratory and field investigations. OFRs play a crucial role in understanding secondary organic aerosol (SOA) formation and aging processes in the atmosphere. By evaluating the advancements and limitations of OFR technology, this review seeks to identify key research directions and challenges for future studies in atmospheric chemistry and air quality research.Recent FindingsIn recent years, OFR has emerged as an encouraging alternative to smog chambers for SOA study. The high oxidative capacity and short residence time of OFR enable its wide application in both laboratory and field studies. Research utilizing OFR has uncovered the critical role of semi-volatile and intermediate-volatility organic compounds (S/IVOCs) in the formation of SOA from various sources, including vehicle emissions, biomass burning, cooking activities, and non-traditional emissions such as volatile chemical products. Notably, field studies have observed considerable variability in the SOA formation potential across different environments globally, generally showing higher formation potential in urban areas compared to rural and forest regions.SummaryOFR studies have significantly advanced our understanding of SOA formation and aging processes, identifying key precursors, evaluating influencing factors, and quantifying SOA formation potential. However, challenges remain in unraveling detailed mechanisms due to the complexity of SOA sources and properties. Future OFR research should focus on innovations in OFR design, study non-traditional emissions, conduct long-term field observations, develop standardized calibration procedures, and establish SOA yield parameterization schemes for S/IVOCs
Formation of layered intrusion: A perspective from vanadium isotopes
No full textLayered intrusions, characterized by their multiple layers, serve as remarkable geological archives of magma evolution in the Earth's crust. However, the magmatic evolution processes that lead to the formation of the chemically diverse layers in the intrusions are still difficult to trace. Here we present V isotope data of whole rocks and mineral separates (clinopyroxene and magnetite) from the Panzhihua layered intrusion in southwest China. The intrusion can be divided into four zones from the base upward: the marginal zone, lower zone, middle zone and upper zone. Both the marginal and upper zones mirror the chemical compositions of the parental magma, with the V isotopic composition being about -0.83%o +/- 0.19%o (n = 4, 2 s). The lower zone is characterized by Fe-Ti oxide layers, where the whole rocks have a similar V isotopic composition as those of clinopyroxene and magnetite at each depth. The consistency in V isotopic compositions between whole rock and mineral separates reflects the control of silicate liquid immiscibility in forming the Fe-Ti oxide layers. Along the depth profile, whole rocks from the lower zone show limited variations in delta 51V values ranging from -0.82%o to -0.49%o. Such observation reveals the dynamic process of crystallization-mush-immiscibility-layering in charging the generation of repetitive oxide layers. After the formation of the lower zone, the middle zone has a large variation of delta 51V values from -0.35%o to 1.70%o, which can be attributed to fractional crystallization of FeTi oxides. Consequently, the V isotopic signatures indicate that the Panzhihua intrusion was originated from a common basaltic magma and the layering in lower and middle zones resulted from continuous evolution of a single, massive magma unit
Three-dimensional textures of Ryugu samples and their implications for the evolution of aqueous alteration in the Ryugu parent body
No full textSamples collected from the surface/subsurface of C -type asteroid 162173 Ryugu by the Hayabusa2 mission were nondestructively analyzed in three dimensions (3D). Seventy-three small particles (approximately 10-180 mu m in size) were observed using X-ray nanotomography, with an effective spatial resolution of approximately 200 nm. Detailed descriptions of these samples in terms of mineralogy, petrology, and variations among particles were reported. The 57 most common particles consisted of a phyllosilicate matrix containing mineral grains, mainly magnetite, pyrrhotite, dolomite and apatite. The remaining particles were mostly monomineralic particles (pyrrhotite, dolomite, breunnerite, apatite, and Mg-Na phosphate) with two unique particles (calcite in a Al 2 Si 2 O 5 (OH) 4 matrix, and CaCO 3 , phyllosilicate, and tochilinite-chronstedtite inclusions in a carbonaceous material matrix). The results confirmed that the samples correspond to Ivuna-type carbonaceous chondrites (CI chondrites) or related materials. Many small inclusions of voids and carbonaceous materials were detected in pyrrhotite, dolomite, breunnerite, and apatite. However, no fluid inclusions were observed, except for those in pyrrhotite that have already been reported. Magnetite exhibited a wide variety of morphologies, from irregular shapes (spherulites, framboids, plaquettes, and whiskers) to euhedral shapes (equants, rods, and cubes), along with transitional shapes. In contrast, the other minerals exhibit predominantly euhedral shapes (pyrrhotite: pseudo -hexagonal plates, dolomite: flattened rhombohedrons, breunnerite: largely flattened rhombohedrons, and apatite: hexagonal prisms) or aggregates of faceted crystals, except for Mg-Na phosphate. The matrices were heterogeneous with variable phyllosilicate particle sizes, Mg/Fe ratios, density (1.7 +/- 0.2 g/cm 3 ), nanoporosities (36 +/- 9 %), and abundances of nanograins of Fe(-Ni) sulfides. The macroporosity of the particles was estimated as 12 +/- 4 %. The observed textural relationships among the minerals suggest a precipitation sequence of: magnetite (spherulite -> plaquette/framboid -> rod/equant) -> pyrrhotite (pentlandite -> pyrrhotite) -> apatite -> dolomite -> breunnerite -> coarse phyllosilicates. Fe -bearing olivine (or low -Ca pyroxene) might have precipitated later than dolomite, indicating a high Mg activity in the aqueous solution. This precipitation sequence corresponds to a transition from irregular crystal forms (as seen in some magnetite) to regular forms of euhedral crystals (observed in some magnetite and other minerals). Based on the precipitation sequence and mineral morphologies, together with previously reported observations, a model for aqueous alteration in the Ryugu parent body was proposed as follows: CO 2 -H 2 O ice, amorphous silicates (GEMS -like material), and some minerals (mostly metal, sulfides, and anhydrous silicates) accumulated to form the parent body of Ryugu. Amorphous silicates and Fe-Ni metal quickly dissolved into the melted ice to form a highly supersaturated aqueous solution. Poorlycrystalized phyllosilicate and spherulitic magnetite precipitated first, followed by plaquette/framboidal magnetites with decreasing degree of supersaturation due to precipitation. Pseudo -hexagonal pyrrhotite plates were formed by dissolution and reprecipitation under relatively low supersaturation. Subsequently, apatite, dolomite, and breunnerite precipitated in this order in response to decreasing supersaturation
Early Cretaceous fayalite-, ferrosilite-, and biotite-bearing rhyolitic porphyries in the Baishuizhai area, South China: Formation by fractional crystallization in the shallow crust
No full textFayalite- and ferrosilite-bearing felsic igneous rocks are a distinctive category of A-type granitic magmas, and the origins of these rocks have proved controversial. In addition, the shallow-crust high-silica rhyolitic magmas responsible for such rocks are considered to have higher viscosities than their plutonic equivalents, which casts doubt on whether fractional crystallization could have occurred during the evolution of these high-silica melts. Here, we report a study of earliest Early Cretaceous (145-142 Ma) fayalite- and ferrosilite-bearing rhyolitic porphyries (FFBRPs) and closely associated biotite-bearing rhyolitic porphyries (BBRPs) from the Baishuizhai area, Guangzhou, Guangdong Province, South China. The Baishuizhai suite provides an excellent opportunity to establish the magmatic origins and evolutionary processes responsible for the FFBRPs. Rocks from the Baishuizhai suite have SiO2 contents of 73.2-77.7 wt%, Na2O + K2O contents of 7.83-9.42 wt%, and Fe2O3T contents of 1.52-2.97 wt%. They have A-type granite features including mineral assemblages (euhedral fayalite and ferrosilite in addition to anhedral amphibole and biotite) and geochemical characteristics [e.g., high 10,000 x Ga/Al values (3.7-4.7), high FeOT/MgO ratios (13.0-34.8), and high Zr (245-514 ppm) and Nb (56.4-96.5 ppm) contents]. The rocks have slightly enriched in situ plagioclase Sr [(Sr-87/Sr-86)(i) = 0.7070-0.7076] and whole-rock Nd [epsilon(Nd)(t) = -2.3 to -2.0] compositions and depleted zircon Hf isotopic compositions [epsilon(Hf)(t) = -0.9 to +7.0] relative to chondrite, as well as higher zircon delta O-18 values (6.3 parts per thousand-7.8 parts per thousand) and intermediate in situ plagioclase Pb isotopic compositions [(Pb-206/Pb-204)(i) = 18.368-18.727, (Pb-207/Pb-204)(i) = 15.488-15.673, and (Pb-208/Pb-204)(i) = 38.049-38.801] compared with depleted mantle. We infer that the primary magmas of this rock suite were formed by mixing of mantle-derived magmas with subordinate (20%-50%) metasedimentary-rock-derived magmas. Fayalite and ferrosilite in the FFBRPs were most likely crystallized from dry, hot, and reduced magma in a lower (<16.5 km depth) chamber. The lower magma gradually evolved during ascent to a water-enriched magma in an intermediate chamber at a shallow depth (3-4 km), forming the FFBRPs (elevation: 129-168 m). Finally, the residual melts migrated upward and resided in an upper (<3 km depth) chamber, forming the BBRPs (elevation: 196-824 m). According to the established temporal-spatial distribution of Early Cretaceous A-type granites and adakitic rocks in South China, we suggest that the Paleo-Pacific plate underwent diachronous rollback, starting during the earliest Early Cretaceous. This rollback enhanced the degree of crust-mantle interaction in the Guangzhou area
Persistent organic pollutants in feathers of various terrestrial and aquatic bird species: Interspecies difference and source apportionment
No full textFeathers are regarded as important nondestructive biomonitoring tools for bird pollutants. However, external contamination of feathers by different pollutants in different bird species remains unclear. In the present study, the feathers of 16 bird species, including terrestrial, freshwater, and marine birds, were analyzed for persistent organic pollutants (POPs). Bird feathers from an abandoned e-waste recycling site had higher POP concentrations and were more correlated with the POP muscle concentrations than those from the less polluted areas. The significant and positive POP correlations between the feathers and muscles of different species indicate that feathers are a good indicator of inter-species and spatial pollution. For individual species, the most hydrophobic POPs in feathers, such as hepta- to deca-polybrominated diphenyl ethers, had higher proportions than in muscles and worse correlations with muscle POPs compared with other POPs. Results of the chemical mass balance (CMB) model revealed that the gaseous phase, internal pollution, and atmospheric particle phase were the main contributors to low-, medium-, and high-hydrophobicity POPs in feathers, respectively. Overall, this study provides a preliminary but meaningful framework for distinguishing between internal and external contamination in feathers and gives information concerning the fitness of feathers as POP indicators with specific physicochemical properties
Intermittent terrane arrival induces pulses of inland tectonic cycles
No full textPulsing volcanotectonic cycles characterized by short-lived (10 s Myr) switches in magmatic and tectonic patterns have been broadly identified in active margins. However, the specific mechanism that causes these switches remains ambiguous, i.e., whether the subduction continuity and/or terrane arrival (accretion, underthrusting, or subduction of buoyant continental/oceanic blocks with a thicker crust than their surrounding oceanic plate) plays a crucial role in controlling the observed volcanotectonic cycles remains controversial. Here, by modeling subduction processes involving the sequential arrival of buoyant terranes, we show that 1) in scenarios where the oceanic plate is weakly coupled with terranes, the entraining of the terrane into the subduction induces slab breakup to occur between the partially subducted terrane and its adjacent oceanic slab, with the terrane then rebounding and moving away from the trench. This evolution causes switches in the magmatic and tectonic patterns within the overriding plate. 2) In these models, the exposed terrane materials can preserve characteristic pressure-temperature-time trajectories, i.e., nearly isothermal compression to isothermal decompression and/or isobaric heating after partial exhumation. 3) slab breakup does not guarantee the occurrence of a trench jump; only when the terrane has a medium scale (-300 km) will a new trench tend to develop prominently behind the rebounded terrane. 4) in scenarios where the composite slab (terrane and oceanic portions) resists yielding deformation and the terrane density is close to that of the oceanic plate (<0.6% density contrast), continuous subduction will occur. In this latter scenario, slab deformation (revealed by subduction angle and slab curvature), instead of slab breakup, will control the magmatic and tectonic patterns in the overriding plate. By further comparing model results with observations, we demonstrate that intermittent subduction interrupted by the subduction of terranes can be a tectonic driver for episodes of compression-to-extension transformations and magmatism (or piston-like volcanotectonic cycles) in two representative accretionary belts - with or without trench jumps (exemplars in south-central-Tibet and eastern-Mediterranean). In contrast, continuous subduction with strongly coupled upper and subducting plates could have contributed to similar cycles in the example without accretion (e.g., the Altiplano in the Central Andes). Therefore, over 10 s of Myr, the scale and frequency of terrane arrivals could essentially control the specific motion pattern of the subducting plate, creating the observed short-lived volcanotectonic switches at these three subtypes of active margins
Comparison of three source apportionment methods based on observed and initial HCHO in Taiyuan, China
No full textIdentifying the sources of formaldehyde (HCHO) is key to reducing the pollution of HCHO and ozone (O3) on the ground level. Using the same datasets applied to the positive matrix factorization (PMF) model by (Hua et al., 2023), the initial concentrations of HCHO were estimated using the photochemical age and the sources of observed and initial HCHO were apportioned based on multiple linear regression (MLR) and photochemical agebased parameterization (PCAP) methods. These results suggest that the source of the initial HCHO can better reflect its contribution. The secondary formation contributed to 49.3-69.1 % of initial HCHO at four sites in Taiyuan based on MLR, which was higher (7.4-36.2 %) than the contributions of secondary formation from observed HCHO. The HCHO was mainly affected by anthropogenic secondary (10.8-34.4 %) and background sources (17.4-78.7 %) based on the PCAP method. We compared the results of the HCHO sources from the MLR, PCAP, and PMF models under photochemical loss. There was good agreement among the emission ratios of acetylene-based HCHO obtained by the different methods at the four sites. The correlation analysis of different source apportionment methods illustrated that primary emissions from the PCAP and the MLR model had the greatest correlation (0.22-0.60). Secondary formations from the PMF and MLR models showed good correlations at all four sites, with R values ranging from 0.42 to 0.83. The HCHO peak of diurnal variation simulated by MLR appeared late compared to the other methods, and the difference in daily variation of HCHO from the PMF model was significantly higher than that of PCAP and MLR. The overlapping conclusions of different source apportionment methods should be considered and used to guide efforts to improve air quality