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The Ediacaran period witnessed events that were of significance to the evolution of Earth's environment and early life, especially the Neoproterozoic Oxygenation Event during the Shuram Event (ca. 570–562 Ma) that was followed by the rise of animal life. However, the nature of the climate change that followed the Shuram Event in South China remains unclear. Black shale-hosted Mn‑carbonate deposits have the potential to reveal valuable information about paleo-seawater conditions and paleoclimate. This paper presents results of an investigation of the unique Ediacaran mudstone succession of South China, especially black shale-hosted Mn‑carbonate deposits, and offers a new perspective of the interconnected nature of paleoclimate and Ediacaran deposits. Relying on detailed petrological, sedimentological, and geochemical data, we posit that Ediacaran Mn‑carbonates accumulated in a semi-enclosed basin that experienced oscillating water column redox conditions and enhanced primary productivity. Chemical index of alteration (CIA) values, Rb/Sr ratios, and δ13C − δ15N stratigraphy of the analyzed deposits provide evidence of episodic warming during an otherwise protracted cooling trend following the Shuram Event (ca. 562–551 Ma). This study highlights the significant utility of black shale-hosted Mn‑carbonate strata in reconstructing Earth's paleoclimate during transitions. • New chemostratigraphic data of the Late Ediacaran in northern Yangtze margin. • Genesis of the late Ediacaran black shale-hosted Mn-carbonates in South China. • Climate fluctuation events during the Late Ediacaran in South China. • Climate-controlled "episodic ventilation" model of the black shale-hosted Mn-deposit. [ABSTRACT FROM AUTHOR]

The wolframite series may contain relatively high U and low common Pb contents, and thus has been used for direct U-Pb dating of hydrothermal W mineralization. In this paper, we present in-situ laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) analysis of U–Pb isotopes and trace elements of wolframite crystals from the giant Yaogangxian and Piaotang W deposits in the extensive Nanling metallogenic belt, South China. The objective of this work is to directly constrain the timing of hydrothermal W mineralization in these two deposits. Wolframite crystals from both deposits show textural evidence for two generations. Early wolframite (Wol-1) has higher Fe and lower Mn contents relative to those in the late wolframite (Wol-2). Uranium is correlated positively with Nb5+, tetravalent (Ti, Sn, Zr, Hf), and trivalent (Sc, V, Y, REEs) cations in all wolframite samples, suggesting that the incorporation of U into wolframite is controlled by the coupled substitution mechanisms. The early and late wolframite domains from the Yaogangxian deposit yielded U–Pb ages of 159.1 ± 2.0 Ma (2σ; MSWD = 0.7) and 153.7 ± 0.7 Ma (2σ; MSWD = 0.5), respectively. Similarly, two wolframite generations from the Piaotang deposits yielded U–Pb ages of 159.5 ± 1.3 Ma (2σ; MSWD = 0.3) and 152.1 ± 0.9 Ma (2σ; MSWD = 0.5). The obtained U–Pb ages confirm two successive episodes of hydrothermal W mineralization at ~159 Ma and ~153 Ma in the Yaogangxian and Piaotang deposits. This study demonstrates the potential of U–Pb dating of wolframite by LA-ICPMS and highlights its importance for directly dating hydrothermal ore-forming processes. • In situ LA-ICPMS analysis of wolframite yielded accurate U-Pb dates. • Uranium in wolframite is dominantly structure-bound. • In situ LA-ICPMS U-Pb dating of wolframite provides a useful method for direct dating hydrothermal mineralization. [ABSTRACT FROM AUTHOR]

Abstract Apatite as an excellent tracer of the magmatic and metallogenic processes, can incorporate large amounts of trace elements sensitive to melting and/or ore-fluid evolution. This paper reports a combined study of in situ apatite geochemistry and whole-rock geochemistry for Early Cretaceous ore-bearing (Group I) and ore-barren porphyries (Group II) in the Liguo Fe-Cu-Au deposit for the deciphering of its petrogenesis and the control factors of mineralization. The apatite from both Group I and Group II is magmatic fluorapatite, characterized by Eu negative anomalies, an enrichment of LREEs, and a depletion of HREEs. Meanwhile, both groups have high Sr/Y and δEu, indicating porphyry adakitic characteristics in origin. Compared to isotopes of whole rocks, the variable 87Sr/86Sr (0.70250–0.71262) and δ18O (6.22–9.00) values of both groups of apatite imply contributions of mantle-, crust- and/or sediment-derived materials. Although Group I apatite and II apatite show some similar geochemical characteristics, Group I apatite precedes the crystallization of plagioclase with no Sr-(La/Yb) N /(La/Sm) N /(Sm/Yb) N correlations, whereas Group II apatite coincides with plagioclase crystallization, displaying positive correlations. The geochemistry of the elements (δEu, δCe, MnO and V) of these apatite groups, which are sensitive to a redox state, shows high oxygen fugacity (between HM and NNO), and Group I apatite has systematically higher oxygen fugacity than Group II apatite. More importantly, these different trace elements and oxygen fugacity characteristics between Group I apatite and Group II apatite can be used as an indicator of mineralization, and allow the skarn Fe-Cu-Au mineralization range to be drawn for the first time. Furthermore, the estimated F and Cl contents of the host parent magma (F = 1300–2446 ppm, Cl = 140–4780 ppm) are higher than those in a primitive mantle and average continental crust, suggesting an enrichment process of F and Cl. According to the above adakitic characteristics, high oxygen fugacity, and high F and Cl contents, the Pacific Plate subduction may be the main dynamic mechanism of the diagenesis and mineralization found in Liguo. [ABSTRACT FROM AUTHOR]

This paper presents the results of the geochemical and mineralogical investigation of siderite in the Late Permian coal-bearing strata from western Guizhou, SW China. Siderite occurs as fine-grained ooids, as recrystallized stellate-like forms, as ellipsoidal, rhombohedral, and oolitic aggregates, indicating their authigenic origin. In contrast, pore filling and veinlet siderite are of epigenetic origin. The low sulfur contents, absence of pyrite, and Sr/Ba ratios indicate that the siderite was deposited in a freshwater (non-marine) environment. The V/(V + Ni) values of studied samples, ranging from 0.68 to 0.86, indicate that the siderite developed under anoxic conditions. The presence of authigenic kaolinite and epigenetic siderite in the same samplesuggests that the chemical conditions changed from acidic to alkaline conditions during early diagenesis. Iron in the siderite was not only derived from silicate weathering of high-Ti basalts in the sediment source regions followed by transport as ions by ground and surface waters, but was also generated from in situ alteration of the Fe-bearing minerals within the peat itself. In addition, ascending hydrothermal solutions would also contribute some Fe, with the Fe probably sourced from the leaching of the basaltic basement. The presence of siderite-rich layers indicates enhanced chemical weathering rates in the sediment source regions. The δ 13C PDB , δ 18O PDB , and δ 18O SMOW values of siderite in claystones and mudstones vary within the ranges of −7.7 to 5.8‰, −12.1 to −6.6‰, and 18.4 to 24.1‰, respectively, indicating that carbon and oxygen primarily originated from marine carbonate, dehydroxylation of organic matter, carbonate dissolution, and hydrothermal fluids. The released CO 2 invoked the alteration of reactive silicate minerals in the sediments, and ultimately the formation of siderite. Circulating pore fluids dissolving iron, which is derived from the silicate weathering of high-Ti basalts in the sediment source regions and from in situ alteration of the Fe-bearing minerals within the peat, would transport some iron from the overlying peat into the underlying sediments, and the flow of fluids would be diminished or stopped at the base of the peat due to the mechanical barrier of the impervious claystone or mudstone layers. The ferrous iron was precipitated due to the alkaline environment conditions of the peat, by reaction with HCO 3 − dissolved in the waters to form siderite. [ABSTRACT FROM AUTHOR]

It has been known that the lithospheric mantle underneath eastern China is geochemically heterogeneous, with different isotopic compositions across the South China and North China blocks. The distribution of Cenozoic basalts (<23 Ma) with abundant mantle xenoliths in eastern China is mainly controlled by lithospheric-scale faults. In this paper, we report new Li and O isotopic data for these mantle xenoliths and demonstrate that the mantle was variably modified via the Pacific subduction. Most olivine and orthopyroxene grains from the peridotite xenoliths in the South China block display lower δ18O values (4.43 to 5.77‰ and 4.77 to 5.55‰; respectively) than those of normal mantle, possibly reflecting impregnation of the slab melt of altered gabbroic precursors in the mantle transition zone (MTZ). The positive correlation between Li (1.40–6.54 ppm) and δ7Li (−28.41 to 20.83‰) of olivine grains suggests that the SCLM was metasomatized by hydrated slab-derived, isotopically heavier Li melts penetrating the frontal mantle wedge. The decoupling of Li and O isotopic systems implies that both hydrated mantle wedge and MTZ control the mass transportation and melt/fluid flow circulation beneath South China via the Pacific subduction. Comparatively, the higher δ18O values (4.90–6.41‰) and negative correlations between Li (1.39–6.02 ppm) and δ7Li (−23.55 to 22.54‰) in olivine grains from the North China block suggest a major contribution from the eclogitic slab that was metasomatized by the carbonatitic agent. Our findings corroborate the wide storage of carbonated eclogites in the MTZ beneath North China. We highlight that the stagnant slab in the MTZ might have controlled the refertilization of the lithospheric mantle beneath North China. [ABSTRACT FROM AUTHOR]

Clumped isotope thermometry is an effective tool which allows to understand the post-depositional alteration, including recrystallization and solid-state reordering, of carbonate rocks. However, as both processes are controlled by elevated temperatures, it is frequently a challenge to distinguish between the relative importance of these two processes in deeply buried carbonate successions (depth > 5000 m or formation temperature > 150°C). In this paper, we have established a clumped isotopic framework of paired dolomite and calcite in order to decipher the relative influence of solid-state reordering versus recrystallization and consequently offer an improved understanding of the mechanisms involved. The material studied was derived from two deeply buried successions (Jurassic-Ediacaran) drilled in the central Sichuan Basin of South China. The calcite and dolomite minerals from these cores were separated using buffered acetic acid, and based on a two-component mixing model, the carbon, oxygen and clumped isotopic (Δ 47) compositions of the two endmembers were determined. Based on an evaluation of solid-state reordering models, we conclude that micritic carbonates (dolomite and calcite) from the Jurassic to the Cambrian have been altered during burial by the geothermal gradient as determined by vitrinite reflectance. The Ediacaran micritic dolomite records a hydrothermal event in the transition between the Ediacaran and Cambrian. In contrast, the clumped isotopic temperature of Ediacaran saddle dolomites reflects subsequent hydrothermal activity during the Silurian and Devonian and shows compositional variations controlled by cooling rates. This study highlights the utility of the theoretical framework based on paired dolomite and calcite records to untangle overprinted signals of clumped isotopes in ancient carbonate rocks and gives insight to better understand the complexity of alteration processes in deeply burial carbonate successions. [ABSTRACT FROM AUTHOR]

Shale reservoirs have attracted increasing attention in recent years as a new and promising geological repository for carbon dioxide (CO 2 ) storage. However, their long-term storage mechanism is unclear and the interactions between CO 2 adsorption to shale and the CO 2 -water-rock reactions have not been investigated. A 2-D simplified reactive transport model is developed in this paper based on the properties of a shale reservoir in the Ordos basin in China which has been identified as a promising location for shale gas production and CO 2 storage. The model is used to study the CO 2 -water-rock reactions coupled with gas adsorption and to identify the long-term trapping mechanisms of CO 2 in shale gas. Results show that in short (several decades) to middle term (hundreds of years) CO 2 storage in a shale reservoir, > 60% CO 2 is trapped in the supercritical and adsorbed phases, but in the long term (thousands of years), mineral trapping gradually plays a dominant role among other storage mechanisms. The displacement of CH 4 with CO 2 during injection is also analyzed. Results show that this process can be divided into two stages: the pre-displacement stage during which the adsorbed concentrations of both CH 4 and CO 2 increase due to pressure build-up, but due to low concentration of CO 2 displacement does not occur at this stage; and the displacement stage during which the CO 2 concentration is high enough to displace the CH 4 from the host rock. Also, higher pressure facilitates the displacement of CH 4 by CO 2 in this stage. Study of the interaction between gas adsorption and CO 2 -water-rock reactions shows that by buffering the reservoir pressure during CO 2 injection into the subsurface, gas adsorption can impact the solubility trapping process so as to interfere with the CO 2 -water-rock reactions. Furthermore, this interference is intensified with reduction in CO 2 concentration in the reservoir over time. Sensitivity analysis indicates that variations in the CO 2 adsorption isotherm, abundance of smectite and chlorite, reaction rate and reactive surface area of smectite can significantly affect the CO 2 storage by different trapping mechanisms. The high CO 2 adsorption capacity of shale is very beneficial for CO 2 injection into a shale reservoir; the amount of adsorbed CO 2 is proportional to the CO 2 adsorption isotherm, while CO 2 in other phases (gas/supercritical phase, dissolved phase and mineral phase) is inversely related to the CO 2 adsorption isotherm. Smectite and chlorite are the key minerals that influence the CO 2 -water-rock reactions in Yanchang shale. [ABSTRACT FROM AUTHOR]

Marble-hosted eclogite is volumetrically minor in collisional orogens, but its geochemistry has great bearing on the origin of deeply subducted crustal rocks and the fluid mobility of subduction zones. This paper presents a combined study of whole-rock major-trace elements and Sr Nd isotopes, mineral O isotopes, carbonate C and O isotopes, and zircon U Pb ages and Lu Hf isotopes for marble-hosted ultrahigh-pressure metamorphic eclogites from Rongcheng and Sanqingge in the Sulu orogen. The results provide insights into the protolith nature of eclogites and the fluid mobility of subduction zones. Zircon U Pb dating yields consistent middle Triassic ages for the two occurrences of eclogites, indicating new growth of metamorphic zircon during continental collision. The Sanqingge eclogite shows LREE-enriched patterns and negative ε Nd (t) of − 16.6 to − 14.3 for whole-rock and negative ε Hf (t) of − 27.1 to − 15.2 for metamorphic zircon. A few relict zircon domains show middle Neoproterozoic U Pb ages and negative ε Hf (t) of − 35.2 to − 15.5. Thus, the Sangqingge eclogite was metamorphosed from a mafic rock that was derived from partial melting of an anciently enriched mantle source. In contrast, the Rongcheng eclogite exhibits flat or even LREE-depleted patterns with negative ε Nd (t) values of − 12.2 to − 1.0 for whole-rock but positive ε Hf (t) values of 5.4 to 10.4 for zircon. The occurrence of interstitial and highly cuspate plagioclase along grain boundaries indicates the presence of partial melting in the eclogite. Thus, its positive zircon ε Hf (t) values are ascribed to the eclogite protolith of juvenile origin, whereas the LREE depletion is due to extraction of LREE-rich anatectic melt from the eclogite during the Triassic continental collision. As such, the Rongcheng eclogite was metamorphosed from a mafic rock that was derived from partial melting of a less enriched mantle source. All the eclogites from both areas show variably high δ 18 O values of 9.4‰ to 19.5‰. Oxygen isotope fractionations between mineral pairs mostly yield eclogite-facies temperature of 600 to 800 °C, suggesting that the high δ 18 O signature was inherited from their protoliths before the Triassic subduction. In combination with the field relation between the eclogite and marble, it is inferred that the eclogite protolith is probably basaltic tuff and its high δ 18 O value would be acquired together with the marble protolith during their deposition from the surface water. Therefore, there would be the limited isotopic exchange between marble and eclogite during continental collision. [ABSTRACT FROM AUTHOR]

Fibrous carbonate cement is a common phase in marine phreatic environments — but its origin and diagenetic history are underexplored. This paper compares two fibrous fabrics that are different in terms of their peculiarities but share important similarities regarding their essentials: upper Ediacaran fibrous dolomite cement and Upper Ordovician fibrous calcite cement, both from the Tarim Basin, China. The focus is on the significance of these fabrics as archives of their marine paleoenvironment. Upper Ediacaran fibrous dolomite cement is present as (i) a fascicular-optic and (ii) a radial-fibrous phase. Judging from the optical length-slow character and luminescent zones, radial-fibrous dolomite cement precipitated directly from early diagenetic marine porewater. Fascicular-optic dolomite cement has a length fast optical character and hence likely formed as a high-Mg calcite precursor penecontemporaneously in a reefal, shallow-marine diagenetic environment. Similarly, two types of Upper Ordovician fibrous cement are present: (i) radiaxial-fibrous and (ii) fascicular-optic calcite cement. Fascicular-optic calcite precipitated in a marine phreatic platform environment, whereas radiaxial-fibrous calcite cement formed in an early marine diagenetic porewater environment. Both fabrics arguably replace a magnesium calcite precursor. For the case of the Tarim Basin, cathodoluminescence and redox-sensitive elements indicate predominantly anoxic, upper Ediacaran marine waters (Ce anomaly = 0.8 ± 0.2), and suboxic, Upper Ordovician shallow-marine seawater (0.7 ± 0.2). Based on PHREEQC modeling, the shallow burial, upper Ediacaran porewater (5.1) yields a higher dolomite saturation index than upper Ediacaran (4.8) and Upper Ordovician seawater (3.7). The direct precipitation of radial-fibrous dolomite from Ediacaran porewaters was likely induced due to organic matter decomposition and related seawater oxygen depletion, elevated Mg2+/Ca2+ ratios, and high alkalinity values. Modeling and proxy data show significant hydrogeochemical differences between seawater and porewater in the upper meters of the sediment column. The upper Ediacaran seawater apparently favored fibrous cement formation with magnesium calcite precursors. In contrast, fibrous dolomite cement was directly precipitated in an early-diagenetic marine porewater regime. The comparability of proxy data reflecting seawater and such recording early diagenetic marine porewater is critically discussed. The Ediacaran early diagenetic marine porewater yields higher dolomite saturation index than the Ediacaran seawater and Ordovician seawater. [Display omitted] • Radial-fibrous dolomite with length-slow character and well-preserved zone is primary. • Fascicular-optic calcite and radiaxial-fibrous calcite have precursor of Mg-calcite. • Aqueous chemistry shows variation from shallow seawater to early diagenetic porewater. • Anoxic, elevated Mg2+/Ca2+ ratios and alkalinity favored the precipitation of dolomite. [ABSTRACT FROM AUTHOR]

This paper describes numerous siderite occurrences from Nb-Zr-REY-Ga-enriched beds of tuffaceous mudstone from the Yujingshan borehole, eastern Yunnan, southwestern China. The mineral phases in the samples were identified and characterized through macroscopic observation, XRD (X-ray diffraction) analysis, optical microscopy, and FE-SEM (field emission-scanning electron microscopy). The results show that the siderite occurs in the drill core from depths of 664.07 to 729.21 m, where its content varies from 15.1 to 65.7%, 31.3% on average. Modes of occurrence of authigenic siderite include irregular banded or massive aggregates, discrete fine particles, oolitic aggregates, and double or multi-ring ellipsoid-shaped or rhombohedral aggregates. The mineralogical association with quartz, anatase, ilmenite, chromite, and zircon with sharp-edged outlines, high-temperature cracks and/or corroded embayments, and REE-bearing minerals and geochemical characteristics such as Al 2 O 3 /TiO 2 between 3 and 8, less commonly 8–23.77, indicate that abundant siderite was produced by hydrothermal alteration of airborne volcaniclastic materials. The δ 13C PDB , δ 18O PDB , and δ 18O SMOW values of siderite in the argillized tuff range from −12.56 to −1.32‰, −8.98 to −5.88‰, and 21.60 to 24.80‰, respectively. In the δ 13C PDB - δ 18O SMOW diagram, plots of the studied siderite are distributed between the fields of marine carbonate rocks, sedimentary organic matter, and carbonates of hydrothermal ores. Some siderite from the upper part of the studied borehole is isotopically close to REY carbonates from the Abramovka lignite deposit, Far Eastern Russia, which precipitated from evolved basinal waters mixed with CO 2 from a mantle source. In summary, this indicates a hybrid origin for the studied siderite including carbonate dissolution, dehydroxylation of sedimentary organic matter, and hydrothermal activity. Furthermore, the paleosalinity (Z) and paleotemperature (T) of the ore-forming fluids were calculated based on the age-corrected stable carbon and oxygen isotopic data in the samples. The Z values range from 96.65 to 121.5‰, suggesting the formation of siderite under brackish-water conditions. The T values vary from 19.47 to 47.12 °C, with some sharp fluctuations that may be due to ash falls and/or hydrothermal injections. Overall, our data support the model for critical-metal Nb(Ta)-Zr(Hf)-REY-Ga enrichment in tuffaceous deposits of southwest China including a combination of volcanic activity and terrestrial organic-rich sedimentation under warm and humid conditions, followed by low-temperature alteration evolved from acidic leaching, which is responsible for the Nb-Zr-REY-Ga enrichment, and, subsequently, formation of authigenic siderite with associated quartz, sulfide minerals, and phosphate minerals under reducing neutral/weakly alkaline conditions. • Abundant siderite is documented in the clay-altered tuffaceous horizons. • Fe was primarily derived from airborne pyroclastics. • C and O were sourced from carbonate, organic matter, and hydrotherm. • C-O isotopes show that siderite was affected by seawater and hot fluids. • A genetic model of siderite in Nb-Zr-REY-Ga deposits has been proposed. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports new zircon LA-ICP-MS U–Pb age and Hf-isotope, whole-rock major and trace element, and Sr–Nd isotope data from Cambrian metavolcanic rocks in the central Lhasa subterrane of southern Tibet. These rocks form a bimodal volcanic suite consisting mainly of silicic metavolcanic rocks with subordinate metabasalts. Five silicic metavolcanic samples dated at ca. 492Ma and one metabasalt sample yielding a near-concordant 206Pb/238U age of 492±4Ma indicate that mafic and silicic eruptions were contemporaneous. The metabasalts are mostly high-K calc-alkaline, enriched in Th, U, and light rare earth elements (LREEs), and depleted in Nb, Ta, Ti, Zr, and Hf, geochemically resembling the Andean arc basalts. The silicic metavolcanic rocks are high-K calc-alkaline and low in Nb and Zr. The metabasaltic rocks have negative whole-rock εNd(t) values (−4.7 to −3.5) and varying zircon εHf(t) values (−0.7 to +7.5), differing significantly from those of the silicic metavolcanic rocks, which yield negative whole-rock εNd(t) values of −8.4 to −7.2 and varying zircon εHf(t) values (−13.9 to −4.6). The metabasaltic rocks are interpreted as resulting from partial melting of an enriched lithospheric mantle source that was metasomatized by subduction-related components, whereas the silicic metavolcanic rocks were derived from basaltic melt-induced anatexis of the ancient Lhasa basement with inherited mantle melt signatures. The Western Qiangtang–Amdo–Tethyan Himalaya situated in the Indian proto-Tethyan margin and the Lhasa and other possible microcontinents or terranes (e.g., Gongshan, Baoshan, Tengchong, Burma, and Sibumasu) paleographically located in the Australian proto-Tethyan margin represent an early Paleozoic Andean-type magmatic arc facing the proto-Tethyan Ocean. The emplacement of the bimodal volcanic rocks and the development of the Cambro–Ordovician angular unconformity in the central Lhasa subterrane can be attributed to slab break-off of the proto-Tethyan Ocean lithosphere following the collisional accretion of microcontinents or terranes located outboard of the magmatic arc (possibly Eastern Qiangtang and South China). [Copyright &y& Elsevier]

Abstract: This paper reports on a rare magmatic suite of adakitic rocks and associated magnesian and potassium-rich magmatic enclaves and dikes, which occur in the Tunchang–Fengmu area, Hainan Island (Southeast China). LA-ICP‐MS zircon U–Pb age data show that they were generated in the late Early Cretaceous (~107Ma). The adakitic rocks, consisting mainly of granodiorites and biotite granites, are high-K calc-alkaline and have low Mg# values (0.27–0.50). They are geochemically similar to slab-derived adakites, e.g., with high SiO2, Al2O3, Sr, Sr/Y and La/Yb values, low Y and Yb contents, and negligible Eu and positive Sr anomalies. They also have relatively uniform (87Sr/86Sr)i (0.7086–0.7096), (206Pb/204Pb)i (18.50–18.61), (207Pb/204Pb)i (15.56–15.64) and (208Pb/204Pb)i (38.17–38.44) isotope ratios, with slightly variable εNd(t) (−3.85 to −6.55) and zircon in situ εHf(t) (−4.7 to +1.7) values. The mafic enclaves and dikes display disequilibrium textures (e.g., multiple-zoned clinopyroxene with low-MgO rims in contact with perthite and quartz microcrystals). They are high-K calc-alkaline and shoshonitic, and all but one sample have high Mg# (0.63–0.72) values. These mafic rocks are characterized by light rare earth element enrichment and heavy rare earth element (REE) depletion, negligible Eu and Sr and positive Pb anomalies, and Nb and Ta depletion. They have slightly more variable initial 87Sr/86Sr isotope ratios (0.7064–0.7086), εNd(t) (−5.1 to +0.1) values, and (206Pb/204Pb)i (18.35–18.50), (207Pb/204Pb)i (15.45–15.59) and (208Pb/204Pb)i (38.18–38.70) ratios. One mafic dike sample has zircon in situ ε Hf(t) values (−4.94 to −2.42) similar to those of adakitic rocks (−4.7 to +1.7) in the area. We suggest that the adakitic rocks were most likely generated by partial melting of newly underplated basaltic lower crust with arc-like geochemical characteristics, and the primitive compositions of the mafic enclaves and dikes likely originated from lithospheric+asthenospheric mantle sources metasomatized by subducted oceanic sediments or a relatively juvenile lithospheric mantle source. Mantle-derived primitive magmas likely underwent mixing at depth with minor crustally-derived felsic magmas before being injected into the adakitic magma chamber. Such injections may have broken up the magma into discrete globules and convective motion distributed the enclaves through the adakitic host. Asthenosphere upwelling due to the roll-back of the subducted Paleo-Pacific plate likely triggered the coeval late Early Cretaceous crust- and mantle-derived magmatism, resulting in the magma hybridization observed on Hainan Island. [Copyright &y& Elsevier]

Abstract: In this paper, we present the first annual oxygen isotope (δ18O) record (1902 to 2004) from the latewood cellulose of trees growing in a temperate-moist forest in southwestern China. Tree-ring δ18O ranges from 12.8 to 18.6‰ and averages 15.2‰. δ18O in the latewood negatively correlates with total cloud cover, relative humidity, and precipitation during the moist months (August to October) from 1951 to 2004 and, to a lesser extent, positively correlates with the temperature in June. Spatial correlation analysis revealed that tree-ring latewood δ18O is more strongly related to variability in regional cloud cover and precipitation in autumn. Tree-ring δ18O negatively correlates with the indices of the Indian summer monsoon (1948 to 2004), the western North Pacific monsoon (1948 to 2004), and with the East Asian summer monsoon (1902 to 2000), suggesting that these monsoons strongly influence the regional climate. Under global warming of last century, we found a strong inverse correlation between tree-ring δ18O and the Southern Oscillation index in different periods, indicating a complex association between the El Niño-Southern Oscillation and the regional climate, which in turn affects tree-ring δ18O. Correlation with the global sea surface temperature (SST) indicates that climatic conditions in the Indian Ocean might play a dominant role in modulating cloud cover and precipitation over the study region during the monsoon seasons. We also found a significant correlation between tree-ring δ18O and SST over the western-north Pacific Ocean. Our results suggest strong links between tropical oceans and an ENSO-like climate with the oxygen-isotope sources and discrimination for trees in the study region. [Copyright &y& Elsevier]

Abstract: Organic matter plays an important role in the transport and precipitation of germanium (Ge) in coal-hosted Ge deposits. In this paper, Ge isotopes of coal samples and their combustion products were analyzed in order to investigate the potential use of Ge isotopes as tracers of Ge sources and enrichment mechanisms in coal. Germanium isotopic composition of various samples (mainly Ge-rich lignite) from the Lincang Ge deposit, Yunnan, Southwest China was analyzed using a continuous flow hydride generation system coupled to a Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS) and the standard-sample bracketing approach. Variations of 74 Ge/ 70 Ge ratios are expressed as δ 74 Ge values relative to NIST SRM 3120a Ge standard solution. Ge-rich lignite samples show large Ge isotopic fractionation (δ 74 Ge values range from −2.59‰ to 4.72‰), and their δ 74 Ge values negatively correlate with Ge concentrations. Lignite samples with low Ge concentrations (<500ppm) tend to show positive δ 74 Ge values, while δ 74 Ge values of lignite samples with high Ge concentrations (>1000ppm) are close to zero or negative. Along stratigraphic sections, Ge is mainly concentrated in the top or the bottom of the coal seam, such that high values of δ 74 Ge are usually found in the middle part of the coal seam. Interlayered hydrothermal chert and limestone samples in Ge-rich coal seams also show moderate fractionation (δ 74 Ge values range from −0.14‰ to 2.89‰ and from 0.55‰ to 1.87‰, respectively). The overall variations of δ 74 Ge values of Ge-rich lignite and organic-rich chert samples can be well described by a Rayleigh fractionation model, indicating that preferential enrichment of light Ge isotopes in coal in an open system might be the main factor controlling Ge fractionation in Ge-rich lignite. The germanium isotopic composition of hydrothermal chert (and possibly limestone) might also record the competitive fractionation produced by precipitation of quartz and sorption of coal. Elevated Ge concentrations and/or δ 74 Ge values of some chert, limestone, sandstone, and claystone samples may be attributed to the mixing with Ge-rich organic matter. Furthermore, similar to the fractionation of Zn, Cd and Hg isotopes observed between refinery dust or gas and slag, high temperature coal combustion also fractionates Ge isotopes, with the Ge isotopic compositions of soot being distinctly lighter (up to 2.25 per mil) than those of cinder. The distinct enrichment of potential hazardous elements (i.e., Pb, Cd, and As) and Ge in soot after coal combustion, as well as the common enrichment of Ge in sulfide minerals (e.g. sphalerite), highlights the possibility of using Ge isotopes as useful tracers of sources of heavy metal pollution caused by high temperature industrial processes (coal combustion and Pb-Zn refining) in the environment. [Copyright &y& Elsevier]

Abstract: Silicic and alkali intra-seam tonsteins were discovered earlier in southwestern China. This paper reports new data on the geochemical and mineralogical compositions of tonsteins from the Songzao Coalfield, Chongqing, southwestern China, and provides new insights into the origin and distribution of the minerals and elements present. Three types of tonsteins (silicic, mafic, and alkali) were identified based on their lateral correlation over a large coalfield area and the overall similarity of corresponding mineralogical and chemical compositions. The clay minerals in most tonsteins of different sources and the mafic tuffs in the lower portion of the late Permian are dominated by kaolinite or are mainly composed of mixed layers of illite and smectite. The silicic tonsteins contain high quartz while the mafic tonsteins and mafic tuffs have high contents of anatase. All the tonsteins and tuffs contain pyrite, attributed to the seawater influences. The mafic tonsteins and tuffs have higher pyrite contents, probably due to the higher Fe derived from mafic volcanic ashes. The mafic tonsteins and tuffs are enriched in Sc, V, Cr, Co, and Ni, similar to the normal clay sediments in the southwestern China, indicating similar sources. The alkali tonsteins are characterized by high contents of Nb, Ta, Zr, Hf, REEs (rare earth elements), and Ga. The TiO2/Al2O3 values are 0.02-0.08 for alkali, <0.02 for silicic, and >0.10 for mafic tonsteins and mafic tuffs, indicating different magma sources. Mafic tuffs and alkali tonsteins are enriched in rare earth elements, and silicic tonsteins contain a lowest REE but have the highest fractionation between light REE and heavy REE. Tonsteins and tuffs may be at the periphery of the Emeishan Large Igneous Province and probably resulted from a waning activity of the plume. They were probably derived from different mantle sources that were underwent not only low-degree partial melting but also fluid fractionation and contamination by lithospheric mantle. Their source magmas had an alkali-basalt composition and were similar to that of ocean island basalt. [Copyright &y& Elsevier]

Abstract: It is generally believed that Cenozoic potassic and ultrapotassic volcanic rocks of the Tibetan Plateau were generated by partial melting of enriched mantle. This paper reports new data regarding the elemental and isotopic compositions of the KonglongXiang volcanic rocks (KVR; K2O/Na2O>2 and low MgO contents) in the middle–western Lhasa terrane, Tibetan Plateau. Ar–Ar isotope dating of a sample from the KVR yields an age of 21.3Ma, indicating that the KVR lavas erupted during the Early Miocene. The KVR consists mainly of trachyte and rhyolite. A comparison of the KVR with Cenozoic potassic volcanic rocks of the Tibetan Plateau and the results of melting experiments involving K-rich volcanic rocks, as well as other K-rich volcanic rocks from throughout the world, reveals that the KVR trachytes originated from a mafic lower crust containing K-rich minerals rather than from a mantle source. The KVR rhyolites were probably derived from the middle–upper crust. Based on age data, compositional data, and the regional tectonic setting, we propose that the formation of the KVR and associated N–S grabens was triggered by Early Miocene E–W regional extension in the area of the southern Tibetan Plateau. [Copyright &y& Elsevier]

Abstract: This paper presents the results of an integrated U-Pb detrital zircon geochronology and Si-in-white mica analysis for synorogenic sediments in the Jianghan Basin to the south of the Dabie Orogen. The results provide an improved understanding of the provenance of these sediments and the unroofing pattern of the early Mesozoic Dabie Mountain. Si contents of detrital white micas range from 3.09 to 3.34atoms pfu for the upper Triassic sandstones whereas 3.06 to 3.59atoms pfu for the lower and middle Jurassic sandstones. The majority of detrital white micas in the lower Jurassic sandstones is phengitic and originated exclusively from the Dabie high- to ultrahigh- pressure rocks. The U-Pb dating results of the detrital zircons for seven samples suggest that these synorogenic sediments have a significant change of provenance from late Triassic to early and middle Jurassic. For the upper Triassic sandstone, the U-Pb age clusters of these zircons are characterized by ~420-450Ma, ~750-820Ma, ~1050-1200Ma and ~2500Ma with minor Luliangian (~1700–2000Ma) components. In contrast, the zircon ages of the Jurassic sandstones are dominated by the Luliangian (~1700–2000Ma) ages with only minor Caledonian (~420-450Ma) and Greenville (~1050-1200Ma) ages. In combination with other available geological data, it can be concluded that the Dabie HP-UHP rocks might initially be exposed to the surface at the beginning of early Jurassic (~190Ma). The Jiangnan terrain (also named “Jiangnan old continental in Chinese) to the south of the Jianghan basin provided the predominant supply of upper Triassic sediments, whereas the Paleoproterozoic Yangtze crustal materials (overlying the present Dabie Complex at the time) were the important provenance of the Jurassic sediments in the Jianghan basin. [Copyright &y& Elsevier]

Abstract: The Xiangshan U deposit, the largest hydrothermal U deposit in China, is hosted in late Jurassic felsic volcanic rocks although the U mineralization post dates the volcanics by at least 20 Ma. The mineralization coincides with intrusion of local mantle-derived mafic dykes formed during Cretaceous crustal extension in South China. Ore-forming fluids are rich in CO2, and U in the fluid is thought to have been dissolved in the form of UO2 (CO3)2 2− and UO2 (CO3) 3 4− complexes. This paper provides He and Ar isotope data of fluid inclusions in pyrites and C isotope data of calcites associated with U mineralization (pitchblende) in the Xiangshan U deposit. He isotopic compositions range between 0.1 and 2.0Ra (where Ra is the 3He/4He ratio of air=1.39×10−6) and correlates with 40Ar/36Ar; although there is potential for significant 3He production via 6Li(n,α)3H(β)3He reactions in a U deposit (due to abundant neutrons), nucleogenic production cannot account for either the 3He concentration in these fluids, nor the correlations between He and Ar isotopic compositions. It is more likely that the high 3He/4He ratios represent trapped mantle-derived gases. A mantle origin for the volatiles of Xiangshan is consistent with the δ 13C values of calcites, which vary from −3.5‰ to −7.7‰, overlapping the range of mantle CO2. The He, Ar and CO2 characteristics of the ore-forming fluids responsible for the deposit are consistent with mixing between 3He- and CO2-rich mantle-derived fluids and CO2-poor meteoric fluids. These fluids were likely produced during Cretaceous extension and dyke intrusion which permitted mantle-derived CO2 to migrate upward and remobilize U from the acid volcanic source rocks, resulting in the formation of the U deposit. Subsequent decay of U within the fluid inclusions has reduced the 3He/4He ratio, and variations in U/3He result in the range in 3He/4He observed with U/3He ratios in the range 5–17×103 likely corresponding to U concentrations in the fluids <0.2 ppm. [Copyright &y& Elsevier]

Abstract: Carbon isotopic compositions of total organic carbon (TOC) or leaf waxes in soils have been used to reconstruct past changes in the relative abundance of C3 and C4 plants. However, TOC contains organic matter of different source organisms (plants, animals, fungi, bacteria etc.) and its isotopic ratios could be modified during diagenesis since different organic fractions (e.g., carbohydrates, proteins, lipids etc.) have different isotopic ratios and degradation rates. Leaf waxes, on the other hand, are transported by wind and hence represent vegetation input from a large geographic area. We report in this paper a new approach to extract in-situ paleovegetation information from late Quaternary paleosols by determining carbon isotopic compositions of biomarkers derived from aliphatic bio- and geopolymers of plant origin. We show that C9 to C17 n-alkenes derived from aliphatic bio- and geopolymers are the dominant compounds released by flash pyrolysis of insoluble organic matter isolated from the late Quaternary paleosols in the Chinese Loess Plateau. Because the aliphatic polymeric substances are mainly derived from plant leaves, bark and roots, the isotopic signatures of these alkenes, determined using pyrolysis–gas chromatography–isotopic ratio mass spectrometry, reflect in-situ vegetation changes. Our down-core δ 13C data from the Xifeng loess–paleosol profile show significant coherence among biopolymer-derived n-alkenes, leaf wax n-alkanes, and TOC for the past 40 kyr. However, the different amplitudes of the temporal isotopic changes among these data sets are indicative of variability in in-situ and regional vegetation dynamics, organic sources and effect of diagenesis. Our data also imply that below-ground biomass is a major source of soil organic matter in the central China loess sediment. [Copyright &y& Elsevier]

The late Paleozoic ice age (LPIA) during the Carboniferous and Permian (ca. 360–260 Ma) was vegetated Earth's only recorded icehouse-to-greenhouse transition and provides a deep-time perspective for climate-glaciation-environment coevolution and future climate change. During the LPIA, changes in glacial-interglacial cycles have been closely linked to atmospheric p CO 2. In this paper, we investigate the relationship between volcanism and glacial to interglacial climate cycles during the Pennsylvanian to earliest Cisuralian in the Liujiang Coalfield from the North China Plate (NCP). We use integrated data from Zircon U-Pb dating, Hg/TOC ratios and δ13C org to recover temporal trends in volcanic intensity and relate these to fluctuations in the global carbon cycle and atmospheric p CO 2. Four new radiometric dates from tuffaceous claystones provide a precision stratigraphic framework and constrain the succession to ~322 to 301 Ma. Results date the Benxi Formation to the Bashkirian–Moscovian stages of the Carboniferous, and the Taiyuan Formation ranging from the Kasimovian stage of the Carboniferous to the Asselian stage of the Permian. Results from Hg/TOC ratios record four peaks of volcanic intensity from the Bashkirian to the Carboniferous-Permian (C-P) transition period, and two low ebbs during the early-middle Bashkirian and the early-middle Moscovian. Peaks in volcanic intensity coincide with the four negative excursions of δ13C org and correlate with volcanism in the North China Plate and NW Europe, inferring volcanic drivers for the carbon isotope excursions and perturbations in the global carbon cycle. Periods of higher atmospheric p CO 2 correlate to interglacial intervals, the two lower ebbs in p CO 2 correlate with two positive isotope plateaus, while periods of lower atmospheric p CO 2 and cooling correlate with glacial intervals C3 and C4 recognized from other sections globally. Results suggest volcanism to be a significant driver for late Pennsylvanian to earliest Cisuralian shifts in global climates from glacial to interglacial through greenhouse gas emissions and changes to the global carbon cycle. Our results represent an important contribution to the development of an accurate chronostratigraphy for the continental facies of the NCP during the Pennsylvanian and earliest Permian, enabling correlation of volcanic and climate events including glacial and interglacial cycles. [ABSTRACT FROM AUTHOR]

Karst environments are globally significant, and the soils that develop on these landscapes often have unique geochemical features, including elevated–levels of metals. However, it has not been determined whether the enrichment of metals in soils is mainly controlled by parent rocks or secondary enrichment during weathering. In this paper, we studied the control of the accumulation of heavy metals in soils by parent materials and/or the process of soil formation. We examined the un–weathered carbonate and clastic bedrocks, as well as surface soils in a typical karst area in Guangxi of China. The spatial distribution of heavy metal (Cd, As, Cr, Cu, Hg, Ni, Pb, and Zn) concentrations in soils was mainly controlled by the geological background. Except for Cd, the concentrations of heavy metals in carbonate rocks were much lower than those in clastic rocks, whereas the soils derived from the carbonate rocks were highly enriched with heavy metals than those in clastic area. The enrichment of Cd in surface soils from the carbonate substrates was the result of the dual effect of secondary enrichment and parent rock inheritance, whereas the enrichment of other metals was mainly the result of secondary enrichment. During the weathering process of carbonate bedrock, great majority of the quantities of inherent heavy metals were leached, with only 2% of Cd being retained in situ. The high concentrations of soil Fe, Al, and Mn oxides, organic carbon and clay content (Al 2 O 3 /SiO 2) were closely related to the enrichment of heavy metals in studied surface soils. • Geological background controlled spatial distribution of soil metal concentrations. • Secondary enrichment and bedrock inheritance caused Cd enrichment in karstic soil. • Secondary enrichment caused the other metal (As, Cr, Cu, Hg, Ni, Pb, and Zn) enrichment in karstic soil. • 2% of Cd being retained in situ during the weathering of carbonate bedrock. • Soil Fe/Al/Mn oxides, organic carbon and clay content controlled metal accumulation in soils. [ABSTRACT FROM AUTHOR]

The upper Ediacaran-lower Cambrian (551–526 Ma) sedimentary succession of the Yangtze Block, South China, hosts abundant chert that formed contemporaneously with the Neoproterozoic Oxidation Event and the Cambrian Explosion. The effect of biological evolution, especially the rise of silica-secreting organisms, on marine Si cycling during the Ediacaran-Cambrian (E-C) transition remains controversial. This paper describes results of a petrological and geochemical investigation aimed at elucidating the origin of the chert and silica biogeochemical cycling during the E-C transition. Our results reveal that the studied chert is dominated by quartz and carbonate. The widespread presence of relict carbonate in inferred peritidal chert deposits suggests that carbonate replacement was an especially common silicification pattern of this facies, whereas the lack of carbonate precursors in subtidal strata argues in favor of primary and biogenic silica precipitation in deposits of this facies. Silicon isotope compositions, relative abundances of Al, Fe, and Mn and rare earth element (REE) + Y concentrations suggest that seawater rather than high-temperature hydrothermal fluid was the primary silica source of the studied cherts. Secular variation of chert Si isotopes reveals that marine silica cycling was closely linked with biological activity. Although silicification was abiological during the Precambrian, it may have been facilitated by microbial activities, especially the widespread formation of cyanobacterial mats. The flourishing of siliceous sponges and radiolarians in the early Cambrian ocean may have served as a global silica sink thus enhancing biological control of the silica cycle after Cambrian time. The studied chert deposits not only demonstrate the silica-rich nature of the global ocean during the E-C transition, but also record the transition of silica cycling from abiological to biological processes and the effect of the evolutionary radiation of silica-secreting organisms during the Cambrian Explosion on silica cycling. Unlabelled Image • Carbonate replacement is the principal silicification pattern of peritidal facies. • Primary and biogenic silica precipitation dominates silicification of subtidal facies. • Seawater was the primary silica source of widespread E-C chert deposits. • Post-Cambrian marine silica cycling is closely linked to biological activity. [ABSTRACT FROM AUTHOR]

The Qilian orogeny formed by subduction of the proto-Tethyan ocean along the northern margin of Gondwana. In this paper we report geochemical, zircon U-Pb-Hf, and mapping data of the Duoruonuoer volcanic rocks from the western Qilian Orogen. Based on distinct geochemical compositions, four melt types can be distinguished: boninite-like basalt, OIB-like basalt, MORB, and high-K to shoshonitic volcanic rocks (HKSV). Field relationships show a compositional change from HKSV, MORB, OIB to boninite-like basalt, from north to south. The boninite-like basalt is low to medium-K calc-alkaline, with low TiO 2 (0.13–0.18 < 0.5 wt%) and high CaO/Al 2 O 3 ratio (0.72–0.80), similar to high-Ca back-arc boninite. The geochemical characteristics of Duoruonuoer OIB-like basalt, MORB, and HKSV are similar to those of the Izu-Bonin (IB) back-arc magmatic assemblages. Boninite-like basalt is enriched in LILEs, and has low Ce/Pb, and high Sr/Nd, Ba/Nb ratios, indicating an addition of a shallow subduction-derived fluid phase. Inferred pressures of magma segregation are 0.9–1.4 GPa with temperatures of 1200–1370 °C consistent with melting of a highly depleted, low pressure hydrous mantle source. The MORB-like rock formed by mixing of depleted mantle and a subduction component, and is identical to back-arc basin floor basalt (BABB). The HKSV, dated at 475 Ma, shares the characteristics with lava from the IB back-arc seamount chains (rear-arc). Their low Ce/Pb and high Th/Yb and Th/Nb ratios are compatible with contributions from melts of deep subducting sediment and oceanic crust. High pressure (1.8–2.0 GPa) may reflect sourcing from a mantle melt at the base of thickened arc crust. The OIB-like basalts have high TiO 2 , Zr/Yb, Nb/Yb and Ce/Pb ratios, suggesting an enriched component from partial melting of the asthenosphere. The high-Fe 8 and Ti 8 composition of the Duoruonuoer OIB-like basalt is produced by fractional melting, similar to a spreading ridge segment developed a deeper source. The variety of Duoruonuoer back-arc magmatism highlights the importance of changes to the melt source region linked to replenishment of the mantle wedge by material extracted from the subducting slab and influx of more fertile mantle material. It is also controlled by evolution of the mantle wedge over time in the building of the back-arc basin. These findings provide evidence for c.475 Ma back-arc basin developed on a thickened arc lithosphere at the western Qilian Orogen. [ABSTRACT FROM AUTHOR]

Covering extensive parts of China, karst is a critically important landscape that has experienced rapid and intensive land use change and associated ecosystem degradation within only the last 50 years. In the natural state, key ecosystem services delivered by these landscapes include regulation of the hydrological cycle, nutrient cycling and supply, carbon storage in soils and biomass, biodiversity and food production. Intensification of agriculture since the late-20th century has led to a rapid deterioration in Critical Zone (CZ) state, evidenced by reduced crop production and rapid loss of soil. In many areas, an ecological 'tipping point' appears to have been passed as basement rock is exposed and 'rocky desertification' dominates. This paper reviews contemporary research of soil processes and ecosystems service delivery in Chinese karst ecosystems, with an emphasis on soil degradation and the potential for ecosystem recovery through sustainable management. It is clear that currently there is limited understanding of the geological, hydrological and ecological processes that control soil functions in these landscapes, which is critical for developing management strategies to optimise ecosystem service delivery. This knowledge gap presents a classic CZ scientific challenge because an integrated multi-disciplinary approach is essential to quantify the responses of soils in the Chinese karst CZ to extreme anthropogenic perturbation, to develop a mechanistic understanding of their resilience to environmental stressors, and thereby to inform strategies to recover and maintain sustainable soil function. [ABSTRACT FROM AUTHOR]