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Birnessite occurs as a major manganese oxide in sediments. It is characterized by a high adsorption capacity for trace elements, including arsenic. However, the effects of birnessite on arsenic cycling were less intensively investigated than that of goethite, a commonly recognized arsenic host. Therefore, this study utilizes arsenic-bearing solutions containing 0.1–50 ppm arsenic to synthesize birnessite and uses arsenic sequential extraction procedure (SEP) analysis to quantify its arsenic co-precipitation and adsorption capacity. SEPs showed that adsorbed/structural arsenic ratio grew from 0:100 to 60:40, with arsenic concentration increasing from 0.1–50 ppm, implying saturation of structural arsenic. SEPs quantify the adsorbed and structural As of birnessite being 0.831 and 1.308 mg/g, respectively. However, the low arsenic concentrations of < 1% in residual solutions indicate nonattainment of the maximum adsorption capacity. Subsequent adsorption experiments using higher initial arsenic concentrations reaching 250 ppm determined the maximum arsenic adsorption capacity to be 19.81 mg/g at pH 7, comparable to the values of 15.3–22.5 mg/g at pH 6.5 (Manning et al., 2002; Singh et al., 2010) and that of 3.79–15.73 mg/g for goethite. It then appears that birnessite adsorption/desorption is more effective than precipitation/dissolution in controlling arsenic cycling. However, the consideration based on the maximum adsorption capacity might overrate the controls of adsorption/desorption relative to precipitation/dissolution because the natural water generally contains less arsenic than that used for the adsorption experiments. Therefore, we conducted adsorption experiments with low arsenic concentrations of 0.5 ppm and a solid/liquid ratio of 0.01 to 0.001. The results showed that adsorption capacity rose abruptly to 1.416 mg/g in two weeks and then slowly increased to 1.523 mg/g after three months. This feature indicated incomplete filling of the adsorption sites on the surface of birnessite at low As concentration despite its large specific surface area. Another controlling factor was the abundance of birnessite in sediments. If 10% of MnO (0.05–0.15%) in the Chianan sediments in southern Taiwan occurred as birnessite, the adsorbed arsenic was calculated to be 0.0005–0.022 mg, corresponding to < 2 % of adsorbed arsenic in 1 g sediments, based on the SEP data of Yang et al. (2016). In the extreme case that all the Mn occurred as birnessite, birnessite could account for up to 25% of the adsorbed arsenic. Apparently, birnessite is not a major contributor to surface arsenic cycling. However, this inference must be evaluated by considering the adsorption and co-precipitation data from goethite and goethite proportions in sediments.

The Plio-Pleistocene orogeny resulted in the exhumation of a regional metamorphic belt, comprising low- to high-grade metapelites in the Central Range, Taiwan. In this study, we analyze the distributions of B isotopes along a prograde metamorphic profile (argillite to greenschist) in the western Central Range to constrain the effects of metamorphic fluids generated during dehydration on the redistribution of the mobile elements. From west to east, peak metamorphic temperatures increase from ~200 °C to 320 °C. B concentrations and δ11B values generally decrease to the east with ~50% loss of B, and the δ11B values roughly decrease from −5‰ to −15‰. The X-ray diffraction (XRD) analysis results of these mineral compositions, except for calcite, show no correlation with B contents and δ11B. And the mixing monitoring of mineralogical compositions cannot account for the observed B contents and δ11B coherent and W-E distribution trend. As the B isotopes may be fractionated between rock and fluid during dehydration, a Rayleigh distillation equation was applied into a model under similar conditions. The results indicate that the measured δ11B values are consistent with the modeled equilibrium of fluid-rock B isotope fractionation within the constrained temperature ranges, thereby supporting the hypothesis that dehydration processes act as a major control on the distribution of B isotopes in the low-grade metapelites. This model also estimates a δ11B value of 5.8‰ for the integrated expelled fluids when getting totally 50% loss of B. Any B sequestering by tourmalines in meta-sediment is an important factor to retain B to a greater depth in subducting slabs. However, our results suggest this factor is not significant for the low-grade metapelites. This study constrains the effect of dehydration on B flux and B isotope distributions during low-grade metamorphism and how the heterogenetic mineralogical compositions may affect its variations, and may contribute to a better understanding of B mass cycling in subduction environments.

This research is aimed toward an understanding of the effects of the chemical characteristics and mineral compositions of sandstone and formation water based on saline water-rock-supercritical CO2 interaction simulation experiments. These experiments were conducted to assess whether toxic trace elements could be dissolved and released in formation water from sandstone in a CO2 storage layer after CO2 geological sequestration, thus affecting groundwater quality. The experimental results reveal that the concentrations of Cd and Pb in the water under examination exceeded the national primary drinking standard as a result of saline/fresh water-rock-supercritical CO2 interactions after 40 d of sandstone immersion in saline/fresh water and 20 d of interaction. In addition, the Mn concentration in the saline/fresh water exceeded the national secondary drinking standard after 40 d of sandstone immersion and 20–80 d of interaction. However, Cd, Pb, and Mn were released to a greater extent (in terms of concentration, 2-fold for Cd, 7-fold for Pb, and 1.7-fold for Mn) in the presence of salinity, revealing that salinity may enhance the dissolution of Cd, Pb, and Mn after 20 d of saline water-rock-scCO2 interaction. After a long period of supercritical CO2-sandstone interaction, the trace metals previously mobilized can be immobilized again by an increase in alkalinity due to aragonite dissolution.

Tectonic affinities of accreted basalts provide constraints on mass transport in convergent boundaries, improving our understandings on the evolution of regional geology. In this study, nineteen accreted basalts from the southernmost tip of Taiwan Island, which is on the convergent boundary between the Eurasian and Philippine Sea Plates, were analyzed for element concentrations as well as Sr, Nd, Hf, and Pb isotope ratios to investigate their tectonic affinities. All the samples contain > 3% LOI, reflecting post-magmatic alteration. LOI and Nb variation diagrams together with comparisons to oceanic basalt compositions indicated that the concentrations of most major elements and Rb, Sr, and Ba were modified by post-magmatic processes to varying extents, while P2O5, REE and HFSE remained immobile. Although some samples show Pb loss, most samples have Pb concentrations not affected by post-magmatic processes. Isotope ratios of Pb, Nd and Hf, generally reflect the mantle source characteristics. The eNd–eHf relationship and trace element abundance ratios indicated that the LREE-depleted samples were mostly scraped off the subducting South China Sea floor, reflecting the volumetric dominance of N-MORB on ocean floors. The overriding Philippine Sea Plate contributed both N-MORB and E-MORB to the accretionary prism. The tectonic affinities of the LREE-enriched samples, however, could not be unambiguously determined for the large geochemical variability of OIB from both subducting and overlying slabs. Based on our results, it is proposed that the tectonic affinity of the basalts in an accretionary prism can indicate the subduction polarity of the associated convergent boundary, providing a constraint for regional geology evolution.

We report, for the first time, a detailed study at river water and hyporheic zone systems through collection and analyses of shallow sediments and selected source rocks, pore water, and river water from forty-two locations at the Chianan Plain (CP), SW Taiwan. The study was focused to understand the possible changes in the river water and sediment chemistry as a consequence of high arsenic (mean±SD=71.28±16.24μg/L, n=46) groundwater discharge to three major rivers in the plain. The study shows, except few locations, As concentration in river sediments corresponds to average As concentration in soil and upper crustal abundance and of source rock. Sequential extraction indicates that As is mostly bound to FeOOH. No enrichment of arsenic in river sediments or depletion of aqueous As and iron in pore water was observed down to the maximum sampling depth of 1.7m although manganese is enriched in sediments. Dissolved As concentrations in the river sediments are much lower compared to the hotspots in the CP aquifers. This suggests that no As attenuation processes are active or they cannot be detected in this zone. Mn precipitates at higher redox level compared to Fe and As and thus attenuates in the studied zone.

Field relationships, mineralogy, petrology, geochemistry, geochronology, and Nd-Hf-O isotopes of the mafic-ultramafic rocks from the east part of the Qilian block are studied in the present work. The Aganzhen intrusive body only exposed in the Zhigoumen, Shiguanzi, Xianggoumen outcrops and includes Hornblende peridotite, wehrlite, olivine-bearing pyroxenite, hornblende-bearing pyroxenite, websterite, clinopyroxenite, hornblendite, olivine-bearing gabbro. The gabbroic rocks are also layered or massive cumulates with rock types varying continuously from noritic gabbro through hornblende gabbro to dioritic norite. Contact metamorphic zones are well developed between the Aganzhen intrusive body and the country rock. Major element contents of Aganzhen ultramafic-mafic rocks show subalkalic series and are characterized by low SiO2 contents (38.09-54.96 %), low TiO2 contents (0.09-0.72 %), low P2O5 contents (0.00-0.36 %) and alkali contents (Na2O+K2O 0.01-5.35 %), but high MgO contents (9.68-33.06 %), Ni contents (116-1505 ppm), Cr contents (713-2808 ppm). Similar LREE-rich pattern ((Ce/Yb)N =0.95-3.80 except two Samples) and tiny Eu anomaly (Eu/Eu* =0.6-1.2) indicate the Aganzhen ultramafic-mafic rocks have the same magma source. Trace elements are enriched in LILE (Rb, Th, U, K), relatively depleted in HFSE (Nb and Ta), and the La/Yb, Ce/Yb, Th/Yb, Nb/La, La/Sm values suggest the limited crustal contamination during the rise of the magma. The εNd (430 Ma) values are −6.9–+2.5 and TDM values are 3.6–1.4 Ga. The SHRIMP ages are 433±2 Ma for the Zhigoumen websterite(101-2101A), 434±3 Ma for Shiguanzi hornblendite(101-2104A) and 412±3 Ma for the Xianggoumen serpentinite(101-2107A). In situ zircon O-Hf isotope, the δ18O compositions of vary from +9.03 to +9.50 (except three points +11.33, +12.38, +12.44) and εHf(t) value is +0.29 to +4.13 for the Zhigoumen pyroxenite(101-2101A), the δ18O compositions of vary from +6.39 to +7.12 and εHf(t) value is +7.76 to +13.26 for Shiguanzi gabbro(101-2104A), and the δ18O compositions of vary from +4.68 to +5.31 and εHf(t) value of +0.28 to +2.79 for the Xianggoumen serpentinite(101-2107A). According to the above datum, we suggest that middle Paleozoic magmatisms last ~20 m.y. (434-412 Ma) on the northern margin of the Qilian Block was related to the Early Paleozoic continental collision between the Qilian and Alax blocks, and to subsequent subduction and thermal underplating.

High arsenic abundance of 50-700μg/L in the groundwater from the Chianan Plain in southwestern Taiwan is a well-known environmental hazard. The groundwater-associated sediments, however, have not been geochemically characterized, thus hindering a comprehensive understanding of arsenic cycling in this region. In this study, samples collected from a 250m sediment core at the centre of the Chianan Plain were analyzed for arsenic and TOC concentrations (N=158), constituent minerals (N=25), major element abundances (N=105), and sequential arsenic extraction (N=23). The arsenic data show a prevalence of >10mg/kg with higher concentrations of 20-50mg/kg concentrated at 60-80 and 195-210m. Arsenic was extracted mainly as an adsorbate on clay minerals, as a co-precipitate in amorphous iron oxyhydroxide, and as a structural component in clay minerals. Since the sediments consist mainly of quartz, chlorite, and illite, the correlations between arsenic concentration and abundances of K2O and MgO pinpoint illite and chlorite as the major arsenic hosts. The arsenic-total iron correlation reflects the role of chlorite along with the contribution from amorphous iron oxyhydroxide as indicated by arsenic extraction data. Organic matter is not the dominant arsenic host for low TOC content, low arsenic abundance extracted from it, and a relatively low R(2) of the arsenic-TOC correlation. The major constituent minerals in the sediments are the same as those of the upriver metapelites, establishing a sink-source relationship. Composition data from two deep groundwater samples near the sediment core show Eh values and As(V)/As(III) ratios of reducing environments and high arsenic, K, Mg, and Fe contents necessary for deriving arsenic from sediments by desorption from clay and dissolution of iron oxyhydroxide. Therefore, groundwater arsenic was mainly derived from groundwater-associated sediments with limited contributions from other sources, such as mud volcanoes.

The petrology, geochemistry, geochronology, and Sr–Nd–Hf isotopes of the backarc granitoids from the central part of the Qilian block are studied in the present work. Both S- and I-type granitoids are present. In petrographic classification, they are granite, alkali feldspar granite, felsic granite, diorite, quartz diorite, granodiorite, and albite syenite. The SHRIMP ages are 402–447 Ma for the S-type and 419–451 Ma for the I-type granitoids. They are mostly high-K calc-alkaline granitoids. The S-type granitoids are weakly to strongly peraluminous and are characterized by negative Eu anomalies (Eu/Eu* = 0.18–0.79). The I-type granitoids are metaluminous to weakly peraluminous and are characterized mostly by small negative to small positive Eu anomalies (Eu/Eu* = 0.71–1.16). The initial (87Sr/86Sr) values are 0.708848–0.713651 for the S-type and 0.704230–0.718108 for the I-type granitoids. The eNd(450 Ma) values are − 8.9–−4.1 and − 9.7–+ 1.9 for the S-type and I-type granitoids, respectively. The TDM values are 1.5–2.4 Ga for the S-type and 1.0–2.3 Ga for the I-type granitoids. For the Qilian block, the backarc granitoid magmatism took place approximately 60 million years after the onset of the southward subduction of the north Qilian oceanic lithosphere and lasted approximately 50 million years. Partial melting of the source rocks consisting of the Neoproterozoic metasedimentary rocks of the Huangyuan Group and the intruding lower Paleozoic basaltic rocks could produce the S-type granitoid magmas. Partial melting of basaltic rocks mixed with lower continental crustal materials could produce the I-type granitoid magmas. Major crustal growth occurred in the late Archean and Meso-Paleoproterozoic time for the Qilian block. The magma generation was primarily remelting of the crustal rocks with only little addition of the mantle materials after 1.0 Ga for the Qilian block.

Elevated concentration of arsenic (As) prevailed in deep aquifers of Chianan Plain, Taiwan. Arsenic release in relation to microbially induced transformations and shift in bacterial communities in deep aquifer sediments of Budai, southwestern Taiwan were investigated using microcosm experiments and substrate amendments over 90 days of anaerobic incubation. The results revealed that As reduction was independent of Fe reduction and a modest rate of sedimentary As release into aqueous phase occurred at the expense of the native organic carbon. Addition of lactate resulted in a parallel increase in As(III) (3.7-fold), Fe(II) (6.2-fold) and Mn (3.5 fold) in aqueous phase compared to un-amended slurries and the enrichment of sequences related to mostly Bacillus, Flavisolibacter, and Geobacter spp, suggesting the important role of these bacteria in As enrichment through reductive dissolution of As-bearing Fe and Mn minerals. The increase in phosphate-extractable As in solid phase with concomitant rise in As in aqueous phase over the course of incubation further attested to the importance of reductive dissolution in promoting As release. Furthermore, the increase in arrA gene abundance with addition of labile carbon suggests that dissimilatory As reduction also may contribute to As enrichment in the water of the deep aquifer of Budai.

Basic-oxygen furnace (BOF) slag is the second abundant by-product from the steel-making process. It is not readily recycled for high phosphorus content and volume instability. To eliminate its phosphorus-hosting dicalcium silicate (C2S) and volumetrically unstable free-lime, reductive heating experiments on BOF-slag are carried out at 1300–1600 °C using quartz-sand or serpentine as a basicity modifier. In the products, C2S and free-lime are consumed through reacting with CaO and MgO, which are produced by Ca-ferrite and Mg-wustite reduction, respectively, to form merwinite and akermanite. The products are also characterized by silicate–metal segregation and the extent of that increases with increasing temperature and decreasing particle size of starting mixtures. Thermodynamic calculations show that phosphorus in C2S is mostly converted to Fe2P in the metal domain. Compared to the slag–serpentine experiments, the slag–quartz experiments resulted in higher extents of silicate–metal segregation with lower phosphorus contents of ≈0.1% in the silicate domain, which therefore is recyclable. To optimize silicate–metal segregation for recycling BOF-slag, it is suggested (i) bringing the BOF-slag composition within the low-temperature side of the C2S–merwinite–akermanite Alkemade triangle by adding quartz-sand; (ii) reductively heating to 1500–1600 °C; and (iii) cooling slowly then quenching to suppress C2S crystallization from melts.

New major, trace and rare earth element (REE) data, and Sr-Nd isotopic compositions of jadeitite and REE-Hf-O isotopic compositions of zircon in jadeitite of the Syum-Keu ultramafic complex of the Polar Urals are used to constrain its origin and source. The jadeitites have high contents of Na 2 O (12.80–14.56 wt%), Al 2 O 3 (20.30–23.81 wt%), SiO 2 (58.47–59.50 wt%), and are enriched in Sr, Ba, Zr, Hf and depleted in Nb relative to primitive mantle values. Chondrite-normalized REE patterns of the jadeitite display weakly U-shaped distribution patterns, with La N /Yb N ratios of 0.82–2.42, and very weak positive Eu anomalies (δEu = 1.2–1.6). The initial Sr isotopic compositions of the jadeitite range from 0.704000 to 0.703519 ( t = 368 Ma), and the initial Nd-isotope ratios (e Nd = +0.77 to +5.61) differ from those of ancient ocean water, oceanic sediments and eclogite, metagranite, and metasediments in the nearby Marun-Keu complex. Zircons from the jadeitite have variable REE contents (37–587 ppm) and are enriched in HREE, with La CN /Yb CN ratios ranging from 0.001 to 0.01, and Lu CN /Gd CN ratios ranging from 10 to 83. Cerium shows positive anomalies with Ce/Ce* values ranging from 2.8 to 72, and δEu from 0.53 to 1.02. The 176 Hf/ 177 Hf ratios of the zircons range from 0.282708 to 0.283017, with initial Hf isotope compositions ranging from 6.5 to 17.4. These characteristics resemble those of zircons from depleted mantle-derived magmas. The δ 18 O isotope compositions of the zircons range from 5.03‰ to 6.04‰, with an averaged value of 5.45 ± 0.11‰, similar to those of mantle rocks, suggesting that the zircons were acquired from precursor igneous rocks, and then transported and reworked by fluids from the subducting slab. Our new results show that the jadeitite was precipitated from material mainly produced by fluid interaction with mafic-ultramafic rocks in a subduction zone environment.

Basic-oxygen furnace slag (BOF-slag) contains >35% CaO, a potential component for CO2 sequestration. In this study, slag-water-CO2 reaction experiments were conducted with the longest reaction duration extending to 96hr under high CO2 pressures of 100-300kg/cm(2) to optimize BOF-slag carbonation conditions, to address carbonation mechanisms, and to evaluate the extents of V and Cr release from slag carbonation. The slag carbonation degree generally reached the maximum values after 24hr slag-water-CO2 reaction and was controlled by slag particle size and reaction temperature. The maximum carbonation degree of 71% was produced from the experiment using fine slag of ≤0.5mm under 100°C and a CO2 pressure of 250kg/cm(2) with a water/slag ratio of 5. Vanadium release from the slag to water was significantly enhanced (generally >2 orders) by slag carbonation. In contrast, slag carbonation did not promote chromium release until the reaction duration exceeded 24hr. However, the water chromium content was generally at least an order lower than the vanadium concentration, which decreased when the reaction duration exceeded 24hr. Therefore, long reaction durations of 48-96hr are proposed to reduce environmental impacts while keeping high carbonation degrees. Mineral textures and water compositions indicated that Mg-wustite, in addition to CaO-containing minerals, can also be carbonated. Consequently, the conventional expression that only considered carbonation of the CaO-containing minerals undervalued the CO2 sequestration capability of the BOF-slag by ~20%. Therefore, the BOF-slag is a better CO2 storage medium than that previously recognized.

Excess carbon dioxide emission was considered as the most important cause of increased trend of global warming. Significant amounts of research were devoted to the reduction of CO2 emission and CO2 sequestration. Sequestration of CO2 in empty oil reservoirs was considered as one of the most promising options. However, the effects of metal release and mobility as a result of CO2 injection were not studied in detail, particularly under super-critical CO2 (scCO2) conditions. In this study, the release of selected metals immersed in distilled water for varying amounts of time in the absence and presence of scCO2 was assessed in simulated conditions at 90°C and 24 MPa. Significant increases in dissolution of Fe, Sr, and Ba by 3, 8, and 24 times were found when the storage rock sandstone or caprock shale was immersed in DI water for different time period. However, in the presence of scCO2, the dissolution of these metals was reduced by 80% for Fe, suggesting permanent sequestration of scCO2 into carbonate minerals. The trend in changes of pore water chemistry in the sandstone and shale after being immersed in DI water showed dissolution of Sr-bearing mineral and precipitation of Ba-bearing mineral.

The whole-rock Hf, Sr and Nd isotope data of five high-Fe–Ti eclogites, nine high-Al eclogites, and a garnetite from the Sulu ultrahigh pressure (UHP) metamorphic terrane at eastern China were analyzed to resolve the causes for the decoupling of the Lu–Hf, Sm–Nd, and Rb–Sr isotope systems in these UHP rocks and to infer their protolith characteristics. Seven of the nine high-Al eclogites define an 87Rb/86Sr–87Sr/86Sr errorchron age of 192 ± 43 Ma (MSWD = 2.8), which is within the time span of retrograde metamorphism despite the large uncertainty. The high-Fe–Ti eclogites and garnetite, however, have low 87Rb/86Sr ratios of < 0.031 with scattered 87Sr/86Sr ratios of 0.7042–0.7058. Accordingly, it is inferred that the Rb–Sr isotope system in the samples reflects the effects of processes postdating the UHP metamorphism. Despite having different constituent mineral assemblages and whole rock geochemistry, the samples, however, define a 147Sm/144Nd–143Nd/144Nd errorchron age of 232 ± 36 Ma (MSWD = 4.6). Although the uncertainty of ± 36 Ma implies incomplete Nd isotope equilibrium among the samples, the large overlap between this errorchron age span and the mineral isochron ages of 245–210 Ma for the UHP metamorphism indicates the control of peak metamorphism on the Sm–Nd isotope system. The incomplete Nd isotope re-equilibration was accompanied by metamorphic modification on the Sm/Nd ratios as indicated by the U-shaped LREE patterns. The initial eNd(780) values of the protolith rocks calculated from the Sm/Nd ratios of the samples deviate from the igneous initial eNd(t)–eHf(t) trend to significantly lower values, consistent with the metamorphic increase in the Sm/Nd ratios. In contrast, the Lu/Hf ratios are generally within the range for basalts and do not vary systematically with the 176Hf/177Hf ratios. The protolith eHf(780) values calculated from the Lu/Hf ratios of the samples are nearly identical to the initial eHf(t) values of the ~ 780 Ma magmatic zircon cores from the Yangtze craton, suggesting the dominance of protolith characteristics on the Lu–Hf isotope system. Being controlled by different processes, the Rb–Sr, Sm–Nd, and Lu–Hf isotope systems of the investigated samples are therefore decoupled. The eNd(220)–eHf(220) compositions of the samples deviate from the eNd(t)–eHf(t) trend of intraplate lavas to high eHf(220) at a given eNd(220) and are within the arc lava field. The protolith eNd(780)–eHf(780) compositions calculated from metamorphic initials using igneous Sm/Nd and Lu/Hf ratios show a similar distribution pattern, strengthening the arc affinity of the eclogites. These arc signatures together with the felsic–mafic bimodal geochemical features of the UHP rocks from the Sulu terrane are explained as the characteristics of protoliths generated by backarc rifting.

Eclogites from the Baijingsi area in the North Qilian orogen at NW China were analyzed for major and trace element abundances as well as Sr, Nd, and Hf isotope ratios to evaluate the impacts from subduction processes on these compositional parameters and to reveal the complexity in protolith characteristics. The major element compositions of the Baijingsi eclogites are within the ranges for basalts. However, the absence of systematic variations among major oxides indicates varying extents of metamorphic modifications. Seven samples are characterized by profound Nb and Ta depletions. Six of them form coherent trends in the La versus Th, HFSE, and LREE plots. They are classified as the Group 1 samples. Other eight samples, referred to as the Group 2 samples, define distinct La–Zr and La–Sm trends and have flat variation patterns with slight Th–Nb–Ta–LREE depletions in the primitive mantle-normalized multiple-element diagram. Group 1 dominates the 87Sr/86Sr–87Rb/86Sr, 143Nd/144Nd–147Sm/144Nd and 176Hf/177Hf–176Lu/177Hf trends for relatively larger variations in the isotope and abundance ratios. Based on the errorchron ages from the samples, closure temperatures of the isotope systems, and isotope ratio versus 1/X plots (e.g., 87Sr/86Sr–1/Sr), it is inferred that the Rb–Sr isotope system was subjected to metamorphic modification, whereas the Sm–Nd and Lu–Hf isotope systems mainly reflect protolith characteristics. In addition to the Nb and Ta depletions, the Group 1 samples generally have eHf(510) values (protolith initial at 510 Ma) higher than those of MORB at a given eNd(510), reflecting derivation from relatively high Lu/Hf ratio sources. They also plot within the fields for arc lavas in the Ta/Yb–Th/Yb and Th–Ta–Hf/3 diagrams. All these features are consistent with derivation from protoliths of an arc origin. In contrast, the Group 2 samples have eNd(510) values slightly higher than those of the Group 1 samples at a given eHf(510), plotting on the low eNd(510) margin of the MORB field. They also deviate from the Ta/Yb–Th/Yb trend defined by MORB and OIB toward higher Th/Yb values within the fields of back-arc basin basalts. Therefore, it is inferred that the protoliths of the Group 2 samples were generated as back-arc basin basalts possibly associated with the protoliths of the Group 1 samples in a common supra-subduction zone. The eNd(510)–eHf(510) relationship of the Baijingsi eclogites shows an affinity to the Indian ocean type mantle, implying protolith generation at the southern hemisphere on the margin or a fragment of the Gondwana continent, most likely in the Qilian Block. Based on the current tectonic configuration, a southward subduction is required for protolith generation and might eclogitize the arc protoliths by subduction erosion. Alternatively, the northward subduction in a bidirectional subduction system might become dominant during the amalgamation of the Qilian Block and the North China Craton to eclogitize the arc protoliths in the Qilian Block. Resolving these two possibilities requires more petrological, geochemical, and structural evidence from the North Qilian orogen.

The Pliocene Yutengping Sandstone (depth 1642e1882 m) and its overlying caprock shale (depth 1395 -1642 m) in Hsinchu City, central Taiwan, were intended for a storage site of CO2. Formation water was collected from a gas well located at a depth of 1827-1846 m. This study investigated changes in water chemistry and dissolution of trace elements from the sandstone and shale at 25 MPa and 90 degrees C in the presence and absence of supercritical CO2 (scCO2) over 7 days. The results showed substantial dissolution of V, Cr, Co, Cu, and Rb from the sandstone and shale into formation water in the presence of scCO2 fluid, while the release of Zn, Se, Mo, and Cd from the sandstone and shale was minimal. Desorption of V, Cr,Mn, Fe, Sr, and Ba was more pronounced from the sandstone than from shale, whereas Co, Ni, Cu, As, and Mo desorbed more from the shale. The concentration of As in formation water increased from 1.4 mg/L to 130 mg/L after in contact with scCO2. Such a high As concentration may present a significant threat to shallow groundwater quality in this region, particularly if leakage along faults and rock fractures in the region occurred.

Cordilleran-type batholiths are useful in understanding the duration, cyclicity and tectonic evolution of continental margins. The Dalat zone of southern Vietnam preserves evidence of Late Mesozoic convergent zone magmatism superimposed on Precambrian rocks of the Indochina Block. The Dinhquan, Deoca and Ankroet plutons and their enclaves indicate that the Dalat zone transitioned from an active continental margin producing Cordilleran-type batholiths to highly extended crust producing within-plate plutons. The Deoca and Dinhquan plutons are compositionally similar to Cordilleran I-type granitic rocks and yield mean zircon U/Pb ages between 118 ± 1.4 Ma and 115 ± 1.2 Ma. Their Sr–Nd whole rock isotopes (ISr = 0.7044 to 0.7062; eNd(T) = − 2.4 to + 0.2) and zircon Hf isotopes (eHf(T) = + 8.2 ± 1.2 and + 6.4 ± 0.9) indicate that they were derived by mixing between a mantle component and an enriched component (i.e. GLOSS). The Ankroet pluton is chemically similar to post-orogenic/within-plate granitic rocks and has a zircon U/Pb age of 87 ± 1.6 Ma. Geobarometric calculations indicate that amphibole within the Ankroet pluton crystallized at a depth of ~ 6 kbar which is consistent with the somewhat more depleted Sr–Nd isotope (ISr = 0.7017 to 0.7111; eNd(T) = − 2.8 to + 0.6) and variable eHf(T) compositions suggesting a stronger influence of crustal material in the parental magma. The compositional change of the Dalat zone granitic rocks during the middle to late Cretaceous indicates that the tectonic regime evolved from a continental arc environment to one of post-orogenic extension. The appearance of sporadic post-90 Ma magmatism in the Dalat zone and along the eastern margin of Eurasian indicates that there was no subsequent orogenic event and the region was likely one of highly extended crust that facilitated the opening of the South China Sea during the latter half of the Cenozoic.

The field occurrence, petrography, geochemistry, Sm–Nd isotopes, and geochronology of the Neoproterozoic granitoids exposed at Tuole, Huangyuan, Gahai, Haiyan, Riyueshan, Baokuhe, and Maxianshan in the Qilian block were studied. The Neoproterozoic granitoids in the Qilian block form two age groups: ca. 800 Ma and ca. 900 Ma. The ca. 800 Ma group granitoids consist of granodiorite and granite, whereas the ca. 900 Ma group granitoids quartz diorite, granodiorite, and potassic granite. They have intruded the Huangyuan Group in the basement sequence of the Qilian block. The foliations are moderately to well-developed and are concordant with those of the country rocks. The granitoids of both age groups all show enrichment in LREEs, but this enrichment is more pronounced in the ca. 800 Ma group than in the ca. 900 Ma group. All granitoids show negative europium anomalies, but the ca. 800 Ma group granitoids are more varied in Eu/Eu* values (0.23–0.83) than most of the ca. 900 Ma group granitoids (0.54–0.98). Spider diagrams of both groups also exhibit enrichment in large ion lithophile elements, i.e., Rb, Th, U, and K, and negative anomalies in Nb–Ta, Sr, P, Ti, and, with exception of the Maxianshan quartz diorite, Ba. The ɛNd(1 Ga) and TDM are −6.7 to −12.7 and 2.2–3.0 Ga for the ca. 800 Ma granitoids and are −4.3 to −5.2 and 2.0–2.3 Ga for the ca. 900 Ma granitoids. The granitoids of the ca. 900 Ma group are interpreted to have formed in an arc tectonomagmatic environment on an active continental margin, whereas those of the ca. 800 Ma group are thought to form in a continental rift environment. The ca. 900 Ma granitoids are I-type and could be formed from partial melting of K-rich metabasalt or eclogite with significant amount of mantle components at a pressure of 1–4 GPa in the lower crust. The strongly peraluminous or peraluminous Gahai granites and Haiyan granodiorite are S-type and could be derived from melting of clay-poor, mature psammitic sources. Similarities in age and tectonic environment of magma genesis suggest a correlation of Neoproterozoic granitoid magmatism between the Qilian and South China block. This correlation gives a strong support to the consideration that the two blocks might be unified in the Neoproterozoic. In other words, the Qilian block might be a part of the South China block or, more precisely, the Sibao orogen, in the Neoproterozoic time.

The Wuchagou and Halaha volcanic fields are located in the central Great Xing'an Range, Northeast China, cover an area of ~ 1400 km2 in China, and continue westward into Mongolia. These regions provide an important opportunity to study temporal changes in magma source regions accompanying the evolution of geodynamic-processes. Late Miocene (10.5–8.0 Ma) volcanic rocks from the Wuchagou volcanic field are composed of basaltic andesite and andesite. The characteristics of these rocks include a high concentration of Si (SiO2 = 55.7–59.2 wt.%), a pronounced negative Nb―Ta anomaly, and a slightly LREE enriched pattern with (La/Yb)N ratios varying from 2.1 to 6.9. They have Sr and Nd isotopic compositions indicative of long-term incompatible element enrichment (87Sr/86Sr = 0.7053–0.7067, 143Nd/144Nd = 0.5118 to 0.5122), with a trend toward the EM1 component. Their isotopic compositions can also be described as Dupal-like, but with less-radiogenic Pb isotopic ratios (206Pb/204Pb = 16.99–17.83, 207Pb/204Pb = 15.46–15.52, 208Pb/204Pb = 37.42–37.91). Quaternary (2.0 Ma to Holocene) lavas from the Halaha volcanic field consist of alkali olivine basalt and olivine tholeiite, which show alkalic affinities and are characterised by ocean island basalt-like REE and trace element patterns, typical of an intraplate sodic basalt composition. The low 87Sr/86Sr (0.7034–0.7041), high 143Nd/144Nd (0.5128 to 0.5130), and moderately radiogenic 206Pb/204Pb (18.39–18.55), 207Pb/204Pb (15.54–5.55), and 208Pb/204Pb (38.32–38.47) ratios are similar to those of most late Cenozoic basalts of South China and the Abaga region, Inner Mongolia. The different melt compositions between the volcanic rocks of the two volcanic fields are most likely due to changes in geodynamic processes and magma sources. A possible scenario for the genesis of these volcanic rocks is that Wuchagou andesitic magma formed by high degrees of partial melting of the subcontinental lithospheric mantle with some lower-crust contamination as a result of the thermal reactivation of the continental lithosphere by shallow-level rifting following the cessation of the Japan Sea opening. During the Quaternary, extensive volcanism resumed, with eruptions along deep rifting systems in the Halaha volcanic field, which might have been related to the geodynamic forcing of the continuous piling up and upward thickening of the stagnant subducted Pacific slab beneath Northeast China. Basaltic magmas of this stage were primarily produced by melting of convecting asthenosphere. Using the batch melting of a hypothetical LREE-enriched mantle source in the garnet stability field proposed by Xu et al. (2005) , we estimated that the Halaha basalts could be generated from 9 to 14% of partial melting of garnet peridotites.

In this study, the geochemical characteristics of mud volcanoes were investigated to seek their possible linkage with arsenic mobilization in the region. Among the mud volcanoes of southern Taiwan, the largest and well-preserved active mud volcanoes are situated in Wushanting (WST) and Hsiaokunshui (HKS). These two selected active mud volcanoes are exhaling mainly methane (CH4>95%) along with other gases like O2, CO2, CO, SO2, H2S, NO, and N2. The content of CH4 in the HKS active mud volcano is very close to that of the WST mud volcano. High Na+ and Cl- concentrations in mud liquids and mudstone deposits indicate their origin in a marine depositional source. However, a newly erupted active mud volcano in WST reflects the presence of a high level of SO4 2-. Significant variations (p≤0.05) in trace and transition element (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Mo, Cd and Ba) concentrations in the liquids and sediments of mud volcanoes are noticed at different eruption periods, suggesting different elemental compositions and release mechanisms in different locations. The weathering of micas as well as clay minerals seems to be responsible for the enrichment in trace metals in mud volcano sediments and fluids. Several trace elements (V, Cr, Mn, Fe, Co, Ni, and Zn) are strongly bound to the sediments, but concentrations of Cu, Se, and Sr are significantly higher in the fluids. The presence of higher As contents in the sediment of HKS was observed in contrast to its fluid. As a reducing agent, humic substances seem to play an important role in binding with trace elements and particularly As in the sediments. Fourier Transform Infrared (FTIR) spectra of humic substances from muds showed the presence of possible functional groups of primary and secondary amines, ureas, urethanes (amide) and silica.

Cenozoic (Miocene to Pleistocene) basaltic rocks in Jiangsu province of eastern China include olivine tholeiite and alkali basalt. We present major, trace element and Sr-Nd isotopic data as well as Ar-Ar dating of these basalts to discuss the petrogenesis of the basalts and identify the geological processes beneath the study area. On the basis of chemical compisitions and Ar-Ar dating of Cenonoic basaltic rocks from Jiangsu province, we suggest that these basalts may belong to the same magmatic system. The alkali basalts found in Jiangsu province have higher σFeO, MgO, CaO, Na2O, TiO2 and P2O5 and incompatible elements, but lower Al2O3 and compatible elements contents than olivine tholeiite which may be caused by fractional crystallization of olivine, pyroxene and minor plagioclase. In Jiangsu basaltic rocks the incompatible elements increase with decreasing MgO/σFeO ratios. The primitive mantle-normalized incompatible elements and chondrite-normalized REE patterns of basaltic rocks found in Jiangsu province are similar to those of OIB. Partial loss of the mantle Uthosphere accompanied by rising of asthenospheric mantle may accelerate the generation of the basaltic magma. The 143Nd/144Nd vs. 87Sr/86Sr plot indicates a mixing of a depleted asthenospheric mantle source and an EM1 component in the study area. According to Shaw's equation, the basalts from Jiangsu province may be formed by 1%–5% partial melting of a depleted asthenospheric mantle source. On the basis of Ar-Ar ages of this study and the fractional crystallization model proposed by Brooks and Nielsen (1982), we suggest that basalts from Jiangsu province may belong to a magmatic system with JF-2 as the primitive magma which has undergone fractional crystallization and evolved progressively to produce other types of basalts.

Many studies were conducted to investigate arsenic mobilization in different alluvial plains worldwide. However, due to the unique endemic disease associated with arsenic (As) contamination in Taiwan, a recent research was re-initiated to understand the transport behavior of arsenic in a localized alluvial plain. A comprehensive approach towards arsenic mobility, binding, and chemical speciation was applied to correlate groundwater hydrogeochemistry with parameters of the sediments that affected the As fate and transport. The groundwater belongs to a Na-Ca-HCO3 type with moderate reducing to oxidizing conditions (redox potential = −192 to 8 mV). Groundwater As concentration in the region ranged from 8.89 to 1131 μg/L with a mean of 343 ± 297 μg/L, while the As content in the core sediments varied from 0.80 to 22.8 mg/kg with a mean of 9.9 ± 6.2 mg/kg. A significant correlation was found between As and Fe, Mn, or organic matter, as well as other elements such as Ni, Cu, Zn, and Co in the core sediments. Sequential extraction analysis indicated that the organic matter and Fe/Mn oxyhydroxides were the major binding pools of As. Batch adsorption experiments showed that the sediments had slightly higher affinity for As(III) than for As(V) under near neutral pH conditions and the As adsorption capacity increased as the contents of Fe oxyhydroxides as well as the organic matter increased.

Phytoremediation of arsenic (As)-contaminated soil by hyperaccumulator Pteris vittata is promising. A better understanding of the rhizosphere microbial dynamics that regulate As availability and plant growth is important to optimize the phytoremediation process. In this study, Illumina sequencing of 16S rRNA genes was applied to assess the rhizosphere microbial community structure of P. vittata. Microbial functionality was monitored by soil enzyme activities and MPN-PCR targeting genes of interest. Arsenic (100mgkg-1 AsV) addition to soil significantly increased DOC, root exudates, As and P uptake and the frond biomass of P. vittata. Moreover, As-enrichment significantly increased soil enzyme activities involved in N, P and S cycling and the gene abundance of As transforming bacteria, Fe- and S-reducing bacteria and N and C fixing bacteria in the rhizosphere of P. vittata. Together, the results revealed that the combined selective pressure of As and rhizosphere resulted in stimulation of microbial community, which most likely has a role in reductive dissolution of Fe and S, As and P mobilization, C degradation and fixation, and N fixation. These changes appeared to have a role in mitigation of As toxicity and to promote growth and the As uptake ability of P. vittata under As-enriched conditions.

The southeastern Eurasian continental margin has been characterized by formation of rift basins associated with intraplate basaltic volcanism since early Cenozoic time. In contrast to Paleogene volcanic rocks that occur sporadically in the basins, Neogene basalts are more widespread on land as lava flows and pyroclastics in the Taiwan Strait (Penghu Islands) and northwestern Taiwan. To better understand the tectonomagmatic evolution, in particular the initial rifting record, this study reports new age, major- and trace-elemental, and Sr-Nd-Pb isotope data of volcanic rocks drilled from several locations in the Taiwan Strait and western Taiwan. 40Ar/39Ar dating results show two main episodes of volcanic activities: ~ 56-38 Ma (Eocene) and ~ 11-8 Ma (late Miocene). The volcanic rocks are composed dominantly of basalts and basaltic andesites, and subordinately of dacites and rhyolites of Eocene age. The two episodes of basaltic volcanism have distinct geochemical characteristics. Comparatively, the Eocene basalts are more depleted in basaltic components such as Ca, Fe and Ti, but have higher Al content. They are also more enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), and show depletions in high field strength elements (HFSE). Sr-Nd-Pb isotope compositions of the late Miocene basalts are relatively more uniform and unradiogenic (eNd = + 6.0 to + 3.8), similar to those of Miocene basalts from NW Taiwan and Penghu Islands, and broadly coeval OIB-type basalts from the South China Sea. However, the Eocene basalts have a wider range in isotope ratios (e.g., eNd(T) = + 5.6 to -3.2) pointing towards an enriched mantle source. The overall geochemical characteristics suggest two distinct mantle sources: (1) a more refractory mantle source metasomatized by subduction-related processes to generate the Eocene basalts and (2) a fertile but isotopically depleted mantle source for the late Miocene basalts. These two source components are proposed to reside in the lithospheric mantle and asthenosphere, respectively. The change in magma sources with time reflects the evolution of an extensional regime within the Eurasian continental margin from an initial rifting to a well-established stage accomplished by thinning of the lithosphere and associated upwelling of the asthenosphere. The Eocene bimodal volcanism entails a transition from the latest Cretaceous magmatism in the western Taiwan Strait that not only signals incipient rifting in the region, but also records geochemical inputs from the subducted Paleo-Pacific plate to the southeastern Eurasian lithospheric mantle. As the preexisting, subduction-related component had been preferentially overprinted by the Eocene magma generation, there was a magmatic quiescence in the Oligocene before the onset of Miocene basaltic volcanism that resulted essentially from decompression melting of the ascended asthenospheric mantle.

In this contribution, we present new petrological, geochemical, zircon U–Pb and Hf isotopic data for eclogitic metasediments from the north Qilian orogenic belt, in which early Paleozoic ophiolitic sequences and HP/LT metamorphic rocks have been previously recognized. The studied metasediments contain eclogite facies assemblages reflecting P–T conditions of 450–560 °C and 1.9–2.4 GPa, consistent with those of adjacent eclogites. REE compositions of the eclogitic metasediments overlap those of average upper continental crust. The SHRIMP and LA-MC-ICPMS U–Pb data of zircons from metasediments demonstrate input from sources with major age components about 500 Ma and 1600–1900 Ma (peak at ~ 1800 Ma), with a smaller population at 660–800 Ma (peak at 750 Ma), and minor > 1.9 Ga zircon ages. The youngest detrital zircons suggest a maximum depositional age of ca. 475 Ma, and combined with P–T conditions and previously determined metamorphic age suggest a burial rate of > 0.6–0.7 cm/yr. Zircon Hf isotopic analyses show that 500 Ma zircons have positive eHf(t) (mainly between + 8 and + 16). By contrast, Meso- to Paleoproterozoic detrital zircons show a broad spectrum of eHf(t) (mainly between − 5 and + 10) with T DM Hf of 1800–2500 Ma. These data suggest that eclogitic metasediments are derived from a mixture of Proterozoic continent crust and juvenile early Paleozoic oceanic and/or island arc crust, and their protoliths likely were deposited in a terrigenous-dominated continental margin basin rather than a pelagic oceanic crust environment. The new results are consistent with subduction erosion of the active continental margin during south-dipping subduction, as these sediments, formed in a fore-arc environment close to the Qilian block to the south, were transported in the subduction zone to 60–70 km depth prior to their exhumation.

The amphibolite-facies metamorphosed mafic rocks exposed in the Maxianshan area, Qilian block, NW China, intruded granitic gneisses of the Maxianshan Group. In the field, they are seen to inject into and capture fragments of the surrounding granitic gneisses. Their rock types range from amphibole-rich amphibolite to plagioclase-rich amphibolite. Their whole-rock major element compositions suggest that their protoliths were subalkalic gabbroic rocks. The rare earth element patterns show slight light rare earth element enrichment with a very small europium negative anomaly. The amphibolites exhibit enrichment in large ion lithophile elements and negative anomalies of titanium, strontium, niobium and tantalum on the basis of their spider diagrams. The SHRIMP U–Pb ages of the zircon grains are 919 ± 10 Ma for the amphibole-rich amphibolite and 905 ± 6 Ma for the plagioclase-rich amphibolite, indicating the ages of protolith formation. The e Nd (910 Ma) values are in the range of −1.6 and −2.4, consistent with generation in a continental arc. Tectonic discriminations by whole-rock trace element compositions suggest that they originated in a continental arc environment. The gabbroic protoliths were metamorphosed under amphibolite-facies conditions. The Maxianshan amphibolite-facies metamorphosed mafic rocks could be correlated with the mafic–ultramafic rocks from marginal areas of the Yangtze block. This correlation implies that the Qilian block and marginal areas of the Yangtze block were active continental margins in the early Neoproterozoic and provides evidence for a strong tectonic affinity of the Qilian block with the South China block and even for a unified Qilian-South China block at that time. It is inferred that the Qilian block carrying Maxianshan mafic rocks underwent amphibolite-facies metamorphism after it was rifted away from the South China block in the late Neoproterozoic as a result of the breakup of the Rodinia supercontinent and collided with the Alaxa block in the early Paleozoic.

Permian volcanic rocks, including picrites, flood basalts and silicic volcanic rocks, crop out in the Song Da district, northern Vietnam. They occur as a ∼300-km-long belt emanating from the southernmost part of the Emeishan large igneous province, SW China. The belt represents a detached part from the province and was displaced ∼600 km southeastward along the Ailao Shan-Red River shear zone during the mid-Tertiary in response to the India–Eurasia collision. We report here geochemical and Sr–Nd isotopic data on the Song Da volcanic rocks to decipher the petrogenetic processes responsible for their formation. The picrites show evidence of olivine fractionation and formed from high-Mg magmas (MgO = 20–25 wt.%) originated from depleted mantle peridotites from the Emeishan plume head. The plume head is characterized by eNd(t) value of +8. Some picrites and low-Ti basalts have low Nb/La, Nb/U and eNd(t), which are indicative of plume–lithosphere interaction in various degrees. Contamination of continental crustal rocks (

In order to constrain the tectonic consequences of the collision of the Luzon arc with the SE Chinese continental margin during the Neogene Taiwan orogeny, we assess the thermal history of the poly-metamorphic para-autochtthonous rocks of the continental margin in Taiwan. To accomplish this we report a new SIMS U–Pb age of prograde metamorphic zircons and interpret this age in the context of existing geochronology and thermochronology. Zircons extracted from the Fenniaolin amphibolite near Nanao, Taiwan, in the contact aureole of a granodiorite, are interpreted to have crystallized during the first lower amphibolite facies prograde metamorphism based on [1] their equant shape rather than the prismatic shape typical of magmatic zircon, [2] their microcrystalline or “micro-saccharoidal” aggregate structure and patchy and sector zoning rather than oscillatory zoning visible in cathodoluminescent imaging, [3] their low concentrations of U (most 206 Pb/ 238 U age of 86 ± 1 Ma, analytically indistinguishable from the age of the adjacent pluton that caused the contact metamorphism. We thus conclude that the contact metamorphism of this intrusion caused the first lower amphibolite facies metamorphism of these rocks in the mid-Cretaceous. Existing 40 Ar/ 39 Ar and Rb–Sr cooling ages of both amphibole and muscovite at ~ 80 Ma (e.g. Lan, 1990; Lo and Onstott, 1995) show that the granodiorite and its contact aureole cooled rapidly from ~ 700° to The crustal history reconstructed from these data shows that the regional ‘gneissic’ terrane of the northern Tananao complex may have been caused by coalescing contact aureoles of multiple mid-Cretaceous intrusions (the ‘Nanao intrusive event’), and not by the Neogene Taiwan orogeny. On the contrary, the Tananao rocks probably achieved middle greenschist conditions and 15–20 km depth in a forearc setting in the Early Cretaceous. This intrusive event caused ‘regional contact metamorphism’ at about 85 Ma, after which the passive margin setting preserved these rocks at mid-crustal depths until the beginning of the Taiwan orogeny (~ 5 Ma). These depths (10–12 km) and temperatures (~ 200–250 °C) were high enough to account for the late Miocene lower greenschist facies cleavages and the Pliocene–Pleistocene fission track cooling ages without additional loading and heating from the Taiwan orogeny.

Boreholes (50 m depth) and piezometers (50 m depth) were drilled and installed for collecting As-rich sediments and groundwater in the Ganges, Brahmaputra, and Meghna flood plains for geochemical analyses. Forty-one groundwater samples were collected from the three areas for the analyses of cations (Ca(2+), Mg(2+), K(+), Na(+)), anions (Cl(-), NO(3)(-), SO(4)(2-)), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction (XRD) and X-ray fluorescence (XRF) were performed to characterize the major mineral and chemical contents of aquifer sediments. In all three study areas, results of XRF analysis clearly show that fine-grained sediments contain higher amounts of trace element because of their high surface area for adsorption. Relative fluorescent intensity of humic substances in groundwater samples ranges from 30 to 102 (mean 58 ± 20, n = 20), 54-195 (mean 105 ± 48, n = 10), and 27-243 (mean 79 ± 71, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Arsenic concentration in groundwater (20-50 m of depth) ranges from 3 to 315 μg/L (mean 62.4 ± 93.1 μg/L, n = 20), 16.4-73.7 μg/L (mean 28.5 ± 22.4 μg/L, n = 10) and 4.6-215.4 μg/L (mean 30.7 ± 62.1 μg/L, n = 11) in the Ganges, Brahmaputra and Meghna flood plains, respectively. Specific ultra violet adsorption (SUVA) values (less than 3 m(-1) mg(-1) L) indicate that the groundwater in the Ganges flood plain has relatively low percentage of aromatic organic carbon compared to those in the Brahmaputra and Meghna flood plains. Arsenic content in sediments ranges from 1 to 11 mg/kg (mean 3.5 ± 2.7 mg/kg, n = 17) in the three flood plains. Total organic carbon content is 0.5-3.7 g/kg (mean 1.9 ± 1.1 g/kg) in the Ganges flood plain, 0.5-2.1 g/kg (mean: 1.1 ± 0.7 g/kg) in the Brahmaputra flood plain and 0.3-4.4 g/kg (mean 1.9 ± 1.9 g/kg) in the Meghna flood plain. Arsenic is positively correlated with TOC (R(2) = 0.50, 0.87, and 0.85) in sediments from the three areas. Fourier transform infrared (FT-IR) analysis of the sediments revealed that the functional groups of humic substances in three areas include amines, phenol, alkanes, and aromatic carbon. Arsenic and Fe speciation in sediments were determined using XANES and the results imply that As(V) and Fe(III) are the dominant species in most sediments. The results also imply that As (V) and Fe (III) in most of the sediment samples of the three areas are the dominant species. X-ray absorption fine structure (EXAFS) analysis shows that FeOOH is the main carrier of As in the sediments of three areas. In sediments, As is well correlated with Fe and Mn. However, there is no such correlation observed between As and Fe as well as As and Mn in groundwater, implying that mobilizations of Fe, Mn, and As are decoupled or their concentrations in groundwater have been affected by other geochemical processes following reductive dissolution of Fe or Mn-hydroxides. For example, dissolved Fe and Mn levels may be affected by precipitation of Fe- and Mn-carbonate minerals such as siderite, while liberated As remains in groundwater. The groundwaters of the Brahmaputra and Meghna flood plains contain higher humic substances in relative fluorescence intensity (or fluorescence index) and lower redox potential compared to the groundwater of Ganges flood plain. This leads to the release of arsenic and iron to groundwater of these three plains in considerable amounts, but their concentrations are distributed in spatial variations.

Two boreholes and ten piezometers in the Ganges flood plain were drilled and installed for collecting As-rich sediments and groundwater. Groundwater samples from the Ganges flood plain were collected for the analysis of cations (Ca2+, Mg2+, K+, Na+), anions (Cl−, NO3 −, SO4 2−), total organic carbon (TOC), and trace elements (As, Mn, Fe, Sr, Se, Ni, Co, Cu, Mo, Sb, Pb). X-ray powder diffraction was performed to characterize the major mineral contents of aquifer sediments and X-ray fluorescence (XRF) to analyze the major chemical composition of alluvial sediments. Results of XRF analysis clearly show that fine-grained sediments contain higher amounts of trace element because of their high surface area for adsorption. Relative fluorescence index (15–38 QSU) of humic substance in groundwater was measured using spectrofluorometer, the results revealed that groundwater in the Ganges flood plain contains less organic matter (OM). Arsenic concentration in water ranges from 2.8 to 170 μg/L (mean 50 μg/L) in the Ganges flood plain. Arsenic content in sediments ranges from 2.1 to 14 mg/kg (mean 4.58 mg/kg) in the flood plains. TOC ranges from 0.49 to 3.53 g/kg (mean 1.64 g/kg) in the Ganges flood plain. Arsenic is positively correlated with TOC (R 2 = 0.55) in sediments of this plain. Humic substances were extracted from the sediments from the Ganges flood plain. Fourier transform infrared analysis of the sediments revealed that the plain contains less humic substances. The source of organic carbon was assigned from δ13C values obtained using elemental analysis-isotope ratio mass spectrometry (EA-IRMS); the values (−10 to −29.44‰) strongly support the hypothesis that the OM of the Ganges flood plain is of terrestrial origin.

Core sediments from three boreholes (to a depth of 50 m) and groundwater from 20 As-enriched water wells were collected in the Chapai-Nawabganj area of northwestern Bangladesh for geochemical analyses. Multivariate statistical analyses including factor analysis, cluster analysis and multidimensional scaling were applied to the hydrogeochemical data. The results show that a few factors adequately represent the traits that define water chemistry. Sodium, Cl, SO4, total dissolved solids (TDS), and electrical conductivity (EC) are grouped under the first factor representing the salinity sources of waters. The second factor, represented by As and Mn, is related to As mobilization processes. The third factor of Fe and alkalinity is strongly influenced by bacterial Fe(III) reduction which would raise both Fe and HCO 3 - concentrations in water. The fourth factor of Ca and Mg reflects the hardness of the Ca–HCO3 type of groundwater, which is confirmed by the hydrochemical facies analysis. Cluster analysis leads to the formulation of four water types including highly, moderately, and slightly As-enriched groundwater as well as groundwater with elevated SO 4 2 - , from anthropogenic sources. Multivariate analyses of the geochemical parameters suggest that Fe- and Mn-oxyhydroxides and mineral phases of phyllosilicates (e.g., biotite) are the main hosts of As in the sediments. Statistical analysis also shows that As is closely associated with Fe and Mn in sediments while As is positively correlated with Mn in groundwater. These correlations along with results of sequential leaching experiments suggest that reductive dissolution of MnOOH and FeOOH mediated by anaerobic bacteria represents an important mechanism for releasing As into the groundwater.

Groundwater and core sediments of two boreholes (to a depth of 50m) from the Chapai-Nawabganj area in northwestern Bangladesh were collected for arsenic concentration and geochemical analysis. Groundwater arsenic concentrations in the uppermost aquifer (10-40m of depth) range from 2.8microgL(-1) to 462.3microgL(-1). Groundwater geochemical conditions change from oxidized to successively more reduced, higher As concentration with depth. Higher sediment arsenic levels (55mgkg(-1)) were found within the upper 40m of the drilled core samples. X-ray absorption near-edge structure spectroscopy was employed to elucidate the arsenic speciation of sediments collected from two boreholes. Environmental scanning electron microscopy and transmission X-ray microscopy were used to investigate the characteristics of FeOOH in sediments which adsorb arsenic. In addition, a pH-Eh diagram was drawn using the Geochemist's Workbench (GWB) software to elucidate the arsenic speciation in groundwater. The dominant groundwater type is Ca-HCO(3) with high concentrations of As, Fe and Mn but low levels of NO(3)(-) and SO(4)(2-). Sequential extraction analysis reveals that Mn and Fe hydroxides and organic matter are the major leachable solids carrying As. High levels of arsenic concentration in aquifers are associated with fine-grained sediments. Fluorescent intensities of humic substances indicate that both groundwater and sediments in this arsenic hotspot area contain less organic matter compared to other parts of Bengal basin. Statistical analysis clearly shows that As is closely associated with Fe and Mn in sediments while As is better correlated with Mn in groundwater. These correlations along with results of sequential leaching experiments suggest that reductive dissolution of MnOOH and FeOOH mediated by anaerobic bacteria represents an important mechanism for releasing arsenic into the groundwater.

Huayu, the only non-basalt islet in the Penghu Islands, consists mainly of andesite lavas intruded by some intermediate (dacite/granodiorite) and felsic (rhyolite/granite) dikes. The LA-ICPMS U–Pb zircon age determination yields 437 ± 13 Ma (n = 16, MSWD = 6.9) for the andesite lava and 63.3 ± 1.5 Ma (n = 7; MSWD = 2.9) for its potassic altered zone, and 58.7 ± 0.8 Ma (n = 14; MSWD = 2.5) for one rhyolite dike. The old and young groups of zircon show distinctive Hf isotope compositions: eHf(T) = −9 for ∼437 Ma zircons vs. eHf(T) = +9 to +6 and +9 to −1 for ∼63 Ma and ∼59 Ma zircons. On the other hand, Sr and Nd isotopic compositions of the andesite lava (ISr = 0.7034 and eNd(T) = +3.9 if T = 437 Ma) are more depleted than the alteration zone and rhyolite dike (ISr = 0.7051 and eNd(T) = −1.3 to −1.9). Decoupling of zircon eHf(T) and whole-rock eNd(T) values of the andesite lava rules out the possibility of 437 ± 13 Ma to be the eruption time. Alternatively, based on the similarity between the published zircon fission track ages (65 ± 3 Ma for the andesite lava and 61 ± 2 Ma for the rhyolite dike; [Yang, H.C., Chen, W.S., Huang, J.C., Wang Lee, C.M., 2008. Volcanic lithofacies of the Huayu Island. Bulletin of Central Geological Survey 21, 143–164 (in Chinese with English Abstract)]) and our U–Pb zircon ages of the altered andesite zone and rhyolite dike, the span of 65–63 Ma is suggested to be the formation time of Huayu andesites. Since Huayu is situated in a NE–SW trending high-magnetic anomaly belt which has been generally interpreted as a remnant magmatic terrain, these data, along with the geochemical results, provide insights of this belt as a split part of the Southeast Coast Magmatic Belt in which Huayu volcanics represent the younger arc volcanism comparable with those appeared in southern Fujian.

Adakitic intrusive rocks of ∼ 430–450 Ma were discovered in the North Qilian orogenic belt, the western section of the Central Orogenic System (COS) in China. These adakitic rocks were lower crust melts rather than slab melts as indicated by their crustal Ce/Pb, Nb/U, Ti/Eu, and Nd/Sm ratios and radiogenically enriched (87Sr/86Sr)i of 0.7053–0.7066 and eNd(t) of − 0.9 to − 1.7. While they are all characterized by low Yb ( 65) and (La/Yb)N (> 13.7) ratios, these adakitic rocks are classified into the low-MgO–Ni–Cr and high-MgO–Ni–Cr groups. The low-MgO samples were derived from partial melting of thickened lower crust, whereas the high-MgO samples were melts from delaminated lower crust, which subsequently interacted with mantle peridotite upon ascent. Adakitic rocks from the adjacent North Qinling orogenic belt also originated from thickened lower crust at ∼ 430 Ma. In addition, the North Qilian and North Qinling orogenic belts both consist of lithological assemblages varying from subduction-accretionary complexes at south to central arc assemblages, which include adakitic rocks, then to backarc phases at north. Such a sequence reflects northward subduction of the Qilian and Qinling oceans. In these two orogenic belts, the occurrence of adakitic rocks of common origin and ages together with the similarities in tectonic configurations and lithological assemblages are considered to be the evidence for the continuity between eastern Qilian and western Qinling, forming a > 1000 km Early Paleozoic orogenic belt. In such a tectonic configuration, the Qilian and Qinling oceans that subducted from south possibly represent parts of the large “Proto-Tethyan Ocean”. This inference is supported by the coexistence of Early Paleozoic coral and trilobite specimens from Asia, America and Australia in the North Qilian orogenic belt. Post-400 Ma volcanic rocks occur in the North Qinling orogenic belt but are absent in the North Qilian orogenic belt, indicating that these two orogenic belts underwent distinct evolution history after the closure of the Proto-Tethyan Ocean (∼ 420 Ma).

Field relationships, mineralogy and petrology, whole-rock chemistry, and age of the Zhamashi mafic–ultramafic intrusion in the North Qilian Mountains, northwest China, have been studied in the present work. The Zhamashi intrusive body consists of ultramafic, gabbroic, and dioritic rocks in a crudely concentrically zoned structure. The ultramafic rocks are layered cumulates with rock types varying continuously from dunite through wehrlite and olivine clinopyroxenite to clinopyroxenite. The gabbroic and dioritic rocks are also layered or massive cumulates with rock types varying continuously from noritic gabbro through hornblende gabbro to diorite. The ultramafic and adjoining gabbroic rocks are discontinuous in lithology and discordant in structure across the interface. The interface is steep, sharp, and fractured. Contact metamorphic zones are well developed between the Zhamashi intrusive body and the country rock. The concentrically zoned structure of the intrusive body and the intrusion into the continental crust are the two main pieces of evidence for considering that the Zhamashi intrusion is Alaskan-type. The mineral chemistry of the chromian spinels (Cr-spinels) and clinopyroxenes, and the variation trend of the whole-rock compositional plot in the (Na2O + K2O)–FeO–MgO (AFM) diagram are also supportive of this consideration. The age of the Zhamashi intrusive body, determined with sensitive high mass-resolution ion microprobe on the zircon grains, is 513.0 ± 4.5 Ma. Parental magma of the Zhamashi intrusion is compositionally close to the primitive magma produced by partial melting of the mantle peridotite. It was differentiated by fractional crystallization at low total pressure and under H2O-rich conditions in an arc environment to form all the major rock types. The concentrically zoned structure of the Zhamashi intrusive body was constructed in two stages: formation of a stratiform-type layered sequence, followed by diapiric re-emplacement. The occurrence of the Alaskan-type intrusion suggests an active continental margin and Cambrian arc magmatism for the northern margin of the Qilian Block.

The sediments in Lake Huguang Maar in coastal South China were previously thought to originate mainly from wind-blown dust transported from North China, such that the lake sediments recorded the varying strength of the Asian winter monsoon. An alternative explanation was that the local pyroclastic rocks supplied the lake sediments, but the actual contributions from the different sources remained unclear. Geochemical analyses including 87Sr/86Sr and 143Nd/144Nd and trace elements support the local pyroclastic rock as the dominant source

The Xitieshan HP/UHP metamorphic unit is a polyphase paragneiss–orthogneiss–metabasite complex preserving relics of an early eclogite facies metamorphism (as deduced from the presence of clinopyroxene + plagioclase symplectite after omphacite in metabasite) followed by decompression through the granulite and amphibolite facies. Paragneisses contain garnet, kyanite (partially replaced by sillimanite), feldspar, quartz and biotite, with minor rutile and zircon. The metabasite consists of garnet, amphibole and plagioclase with relict clinopyroxene + plagioclase symplectite. Two main high-temperature metamorphic stages are distinguished: (1) a high-pressure granulite stage, characterized by the assemblage garnet–kyanite–K-feldspar–plagioclase–quartz–rutile in the paragneisses and garnet–clinopyroxene–plagioclase–quartz in the metabasite; (2) a medium–low pressure granulite to upper amphibolite facies stage, leading to the formation of sillimanite in the paragneisses and overgrowth of amphibole on Cpx–Pl symplectite in the metabasite. SHRIMP U–Pb analyses of metamorphic zircons, in conjunction with LA-ICPMS REE data and rare mineral inclusions in zircons, show that the high-pressure granulite metamorphism recorded by these rocks occurred between 451 and 461 Ma and the medium–low pressure granulite–upper amphibolite facies metamorphic overprint between 423 and 427 Ma, suggesting about 30 Ma residence time in medium–lower crustal levels after an earlier eclogite facies metamorphism (ca. 480 Ma). Based on comparison with other HP/UHP metamorphic units in the North Qaidam Mountains (NQD), these results suggest diachronous subduction and exhumation in the different units of the NQD.

The widespread Mesozoic granitoids in South China (∼135,300 km2) were emplaced in three main periods: Triassic (16% of the total surface area of Mesozoic granitoids), Jurassic (47%), and Cretaceous (37%). Though much study has been conducted on the most abundant Jurassic Nanling Mountains (NLM) granites, their rock affinities relative to the Triassic Darongshan (DRS) and Cretaceous Fuzhou–Zhangzhou Complex (FZC) granites which are typical S- and I-type, respectively, and the issue of their petrogenetic evolution is still the subject of much debate. In this study, we discuss the petrogenesis of NLM granites using apatite geochemistry combined with whole-rock geochemical and Sr–Nd isotope compositions. Sixteen apatite samples from six granite batholiths, one gabbro, and three syenite bodies in the NLM area were analyzed for their major and trace element abundances and compared with those collected from DRS (n = 7) and FZC (n = 6) granites. The apatite geochemistry reveals that Na, Si, S, Mn, Sr, U, Th concentrations and REE distribution patterns for apatites from DRS and FZC granites basically are similar to the S and I granite types of the Lachlan Fold Belt (Australia), whereas those from NLM granites have intermediate properties and cannot be correlated directly with these granite types. According to some indications set by the apatite geochemistry (e.g., lower U and higher Eu abundances), NLM apatites appear to have formed under oxidizing conditions. In addition, we further found that their REE distribution patterns are closely related to aluminum saturation index (ASI) and Nd isotope composition, rather than SiO2 content or degree of differentiation, of the host rock. The majority of apatites from NLM granites (ASI = 0.97–1.08 and eNd(T) = −8.8 to −11.6) display slightly right-inclined apatite REE patterns distinguishable from the typical S- and I-type. However, those from few granites with ASI > 1.1 and eNd(T) −6.6 and gabbro and syenite are similar to FZC apatites (strongly right-inclined). In light of Sr and Nd isotope compositions, magmas of NLM intrusives, except gabbro and syenite, and few granites with eNd(T) > −8, generally do not involve a mantle component. Instead, they fit with a melt derived largely from in situ melting or anatexis of the pre-Mesozoic (mainly Caledonian) granitic crust with subordinate pre-Yanshanian (mainly Indosinian) granitic crust. We suggest that an application, using combined whole-rock ASI and eNd(T) values, is as useful as the apatite geochemistry for recognizing possible sources for the NLM granites.

The Abaga volcanic field is one of the largest and least known areas of late Cenozoic intraplate igneous activities in eastern China. Twenty-seven Abaga basaltic rocks were analyzed for major and trace element contents, Sr‐Nd‐Pb isotopic compositions, and K‐Ar dating. These basalts predominantly consist of alkali basalt with subordinate transitional olivine tholeiite and rare quartz tholeiite. Combining our data of ten K‐Ar dates with previously published data showed that the time of the principal volcanic eruption was from the Miocene to the Quaternary (14.57~0.19 Ma). A large amount of volcanic activity is believed to have begun in the northwestern portion of the AVF and gradually migrated southeastwards with geological time. The Abaga basalts exhibit chondrite-normalized REE patterns, incompatible elements and isotopic ratios ( 87 Sr/ 86 Sr of 0.703654~0.704286 and 143 Nd/ 144 Nd of 0.512845~0.512891) affiliated with oceanic island basalts (OIBs). In general, they have relatively homogenous Pb isotopic compositions ( 206 Pb/ 204 Pb of 18.409~18.521, 207 Pb/ 204 Pb of 15.514~15.546, and 208 Pb/ 204 Pb of 38.259~38.447), indicating that these lava suites have a similar source. But the alkali basalts are relatively enriched in incompatible elements when compared to the tholeiites. This compositional difference may be attributable to the different degrees of partial melting in the mantle source. The Sr‐Nd‐Pb isotopic data indicated that the mantle sources of the late Cenozoic Abaga basalts display a DMM-EM2 array similar to those of Southeast Asia. The 208 Pb/ 204 Pb vs. 206 Pb/ 204 Pb plot was also significantly displaced above the Northern Hemisphere reference line in a pattern clustering near the less-depleted end of the field for the Indian Ocean mid-oceanic ridge basalt (MORB) that shows Dupal signatures. Therefore, we suggest that the Abaga basaltic magmas were dominantly derived from an Indian Ocean MORB-like depleted asthenospheric source with fewer contributions of an enriched mantle component (EM2) from the subcontinental lithospheric mantle.

Origin and tectonic evolution of the Qilian Precambrian basement on NW China were investigated using zircon U-Pb ages with collaborating stratigraphic and paleontological evidence. Zircon grains were separated from two schists, two granitic gneisses and one mylonized gneiss and dated with SHRIMP. Seventy percent of sixty-one detrital zircon ages from two schists ranges from 0.88 Ga to 3.09 Ga, mostly within 1.0 Ga to 1.8 Ga with a peak at 1.6 Ga to 1.8 Ga, and twenty percent varies from 2.0 Ga to 2.5 Ga. A few falls in the Archean and Neoproterozoic periods. The two granitic gneisses were dated 930±8 Ma and 918±14 Ma, whereas the mylonized granitic gneiss was dated 790±12 Ma. These ages represent two periods of magmatisms, which can be correlated with the early and late stages of magmatisms associated with the Jinningian movement on the Yangtze Blocks.

The Dongcaohe ophiolite, located at the south of the North Qilian subduction complexes, is a tectonic block with an exposed area of about 3 km×6 km. It consists of an intrusive section overlain by an extrusive section. The lower part of the intrusive section consists of cyclic layers of cumulate dunites, troctolites, anorthosites, anorthositic gabbros, and gabbros with small discordant dunite and troctolite bodies. This layered sequence grades upward to isotropic gabbros and gabbronorites, which are overlain by the extrusive sequence of diabasic sheeted dikes and basaltic lavas. The overall mineral crystallization sequence was olivine±Cr-spinel, plagioclase, clinopyroxene, orthopyroxene, and Fe-Ti oxides. The Cr-spinel (Mg#: 42–66, Cr#: 41–57) in these layered cumulates and present-day abyssal peridotites have similar compositions. Also, the compositional variations of the plagioclase and clinopyroxene in the intrusive section reflect crystallization from melts compositionally similar to the present-day ocean basalts. Moreover, the rare earth element (REE) and multi-element distribution patterns of the intrusive and extrusive lithologies in the Dongcaohe ophiolite are consistent with crystallization of mid-ocean ridge basalts. The zircon grains separated from the gabbronorite have an SHRIMP average 206Pb/238U weighted age of 497 ± 7 Ma, which is considered as the tectonic emplacement age of the Dongcaohe ophiolite. The field occurrence, mineral and whole-rock compositions indicate that the Dongcaohe ophiolite represents a well-persevered oceanic crustal fragment composed of a complete oceanic crustal section of layered cumulates at bottom upgrading through isotropic cumulates to sheeted dikes and lava flows.

Eclogite protoliths provide clues for understanding paleomagmatism and tectonic architecture. A subgroup of eclogites from Maobei in the Sulu metamorphic terrane in eastern China are characterized by (1) low SiO2 contents of 38.2–42.8%, (2) high FeOtotal abundances of 16.7–20.9%, (3) high TiO2 concentrations of 3–4%, and (4) decoupling between high field strength elements (HFSE), specifically, Ti enrichment accompanied by relative depletions in Nb–Ta–Zr–Hf. These features are also characteristic of eclogites cored by the Chinese Continental Scientific Drilling (CCSD) project at the depth range of 530–600 m (subunit 8). Except for the relatively low SiO2 concentrations, major element concentrations of these high Fe–Ti eclogites are comparable to those of basalts and gabbros. The low SiO2 reflects the combined effect of fluid infiltration and garnet enrichment by metamorphic segregation. In contrast, there is no evidence for rutile segregation, and the high TiO2 contents are protolith characteristics. The major and trace element abundances as well as the decoupling between Ti and other HFSEs in these high Fe–Ti eclogites are interpreted as characteristics of gabbroic cumulates crystallized from melts with compositions similar to that of the CCSD eclogites cored at depth ranges of 318–380 and 420–470 m (subunits 4 and 6, respectively). The mineral proportions of such cumulates are ∼41% plagioclase, ∼39% clinopyroxene, ∼8% olivine and ∼12% Fe–Ti oxides, consistent with crystallization at 2–8 kbar. The basaltic melts in equilibrium with the gabbroic protoliths of the high Fe–Ti eclogites must be depleted in Nb, Ta, Zr and Hf. These are the characteristics of arc lavas and crustally contaminated continental basalts. An arc origin for these protoliths is consistent with the existence of arc belts on the margins of the Yangtze Block during protolith formation. However, this does not preclude contemporary plume magmatism within the interior of the Yangtze block.

Although rice cultivated under water-saturated conditions as opposed to submerged conditions has received considerable attention with regard to reducing As levels in rice grain, the rhizosphere microbiome potentially influencing As-biotransformation and bioavailability in a rice ecosystem has rarely been studied. In this study, the impacts of flooded, non-flooded and alternate wetting and drying (AWD) practices on rhizosphere bacterial composition and activities that could potentially impact As speciation and accumulation in rhizosphere soil and pore water, As fractions in rhizosphere soil and As speciation and distribution in plant parts were assessed. The results revealed that in addition to pore water As concentration, non-specifically sorbed As fraction, specifically sorbed As fraction and amorphous iron oxide bound As fraction in soil were bio-available to rice plants. In the flooded treatment, As(III) in the pore water was the predominant As species, accounting for 87.3-93.6% of the total As, whereas in the non-flooded and AWD treatments, As(V) was the dominant As species, accounting for 89.6-96.2% and 73.0-83.0%, respectively. The genera Ohtaekwangia, Geobacter, Anaeromyxobacter, Desulfuromonas, Desulfocapsa, Desulfobulbus, and Lacibacter were found in relatively high abundance in the flooded soil, whereas the genera Acinetobacter, Ignavibacterium, Thiobacillus, and Lysobacter were detected in relatively high abundance in the non-flooded soil. Admittedly, the decrease in As level in rice cultivated under the non-flooded and AWD conditions was mostly linked to a relatively high soil redox potential, low As(III) concentration in the soil pore water, a decrease in the relative abundance of As-, Fe- and sulfur-reducing bacteria and an increase in the relative abundance of As-, Fe- and sulfur-oxidizing bacteria in the rhizosphere soil of the rice. This study demonstrated that with substantial reduction in grain As levels and higher water productivity, AWD practice in rice cultivation should be favored over the non-flooded and continuously flooded rice cultivations in As-contaminated sites.