The ln(Zr/Rb) count ratio derived from X‐ray fluorescence (XRF) core scanning holds potential as a high‐resolution tracer for grain‐size variations of glaciomarine sediments, and hence current ...strength. To evaluate this approach, we conducted high‐resolution grain‐size measurements, together with Rb and Zr measurements by XRF core scanning and inductively coupled plasma‐mass spectrometry (ICP‐MS), on a series of sediment cores from different regions of the Southern Ocean. Downcore changes of the ln(Zr/Rb) count ratio from XRF core scanning are consistent with Zr/Rb concentration ratios derived from ICP‐MS analyses, even though Rb and Zr counts deviate significantly from concentrations due to specimen and matrix effects. The ln(Zr/Rb) count ratio displays discrepancies with the bulk mean grain‐size, but correlates well with the mean grain‐size of the sediment fractions that do not include unsorted sand delivered by ice‐rafting. These observations are supported by evidence from a grain‐size separation experiment, which indicates that Zr and Rb are concentrated in different grain‐size fractions. Consistent with its lack of sensitivity to coarse grain‐size fractions derived from ice‐rafting, the ln(Zr/Rb) ratio records similar trends to the sortable silt percent (SS%) and sortable silt mean (SS¯) grain‐size. Universal gradients exist in plots of SS% versus ln(Zr/Rb), and SS¯ versus ln(Zr/Rb), such that the ln(Zr/Rb) ratio provides a convenient way to estimate the magnitude of changes in SS% and SS¯. Overall, our results support the use of the ln(Zr/Rb) ratio as an indicator of bottom current strength in cases where the sediment is current‐sorted.
Key Points
Ln(Zr/Rb) co‐varies with the iceberg rafted debris‐corrected mean grain‐size of glaciomarine sediments from the Southern Ocean
Ln(Zr/Rb) reflects changes in bottom current strength if the sediment is bottom current‐sorted
Constant gradients observed in plots of ln(Zr/Rb) versus SS%, and ln(Zr/Rb) versus SS¯
We present high-resolution analyses of clay mineral assemblages combined with analysis of Sr–Nd–Pb isotopic compositions of the <2 μm silicate fraction of sediments from Integrated Ocean Drilling ...Program (IODP) Site U1430 in the southern Sea of Japan, in order to trace the sources of clay minerals and reconstruct proxy records of past changes in Asian eolian input to the basin since 15 Ma. The clay mineral assemblages at IODP Site U1430 mainly consist of smectite (∼51%) and illite (∼36%), with minor kaolinite (∼7%) and chlorite (∼6%). Provenance analysis suggests that the fine-grained sediment at the study site is a two end-member mixture of eolian dust from Central Asia and fluvial input from the Japanese islands. The Central Asian end member supplied illite-rich and high 87Sr/86Sr and low εNd(0) eolian dust to the study site by wind, while the Japanese end member, characterized by young volcanic rocks, contributed smectite-rich, low 87Sr/86Sr and high εNd(0) weathering products via rivers. The ratio of illite/smectite and εNd(0) values of clay-sized silicate sediments at Site U1430 were used as proxies for tracing the changing strength of central Asian eolian input to the Sea of Japan, and thus reconstruct the aridification history of its source region. Our study presents for the first time a continuous, high-resolution record that highlights the four-step drying of Central Asia that occurred at ∼11.8 Ma, 8 Ma, 3.5 Ma and 1.2 Ma. Considered the nature and timing of major climatic and tectonic events in Asia, we conclude that the strengthened aridification of Central Asia starting at ∼11.8 Ma was possibly driven by the combined effect of Tibetan surface uplift and global cooling, whereas the rapid drying at ∼8 Ma was caused primarily by the uplift of the northern Tibetan Plateau. In contrast, global cooling, overwhelming the influence of Tibetan Plateau uplift, has become the primary control on Central Asia aridification since ∼3.5 Ma.
•We show a long-term record of Asian eolian input to Japan Sea since 15 Ma.•Highlight the four steps drying of Central Asia at 11.8 Ma, 8 Ma, 3.5 Ma and 1.2 Ma.•Asian drying was driven by combined effect of Tibetan uplift and global cooling.
Clay minerals contain a massive amount of nanopores and play a significant role in gas adsorption in shale. Although the pore structure of clay minerals has been widely studied, the characteristic of ...pores with diameter < 1 nm remains unclear. To investigate the pore characteristics of different clay minerals, especially for micropores, and to reveal the effect of pore structure on the methane adsorption capacity, the isotherm types, pore size distribution, pore volume, and surface area, as well as the CH4 adsorption capacity of pure clay mineral samples, including kaolinite, montmorillonite, illite, and illite–smectite mixed layer (I/S), were investigated based on low-pressure N2 and CO2 adsorption and CH4 adsorption isotherm measurements. The results show that the isotherm types of the studied clay minerals based on N2 adsorption are all type IV, characterized by the presence of hysteresis loops. According to the features of hysteresis loops, it can be inferred that kaolinite mainly has cylindrical pores and slit-shaped pores, while pores in montmorillonite, illite, and I/S are dominated by inkbottle-shaped pores, with a small amount of slit-shaped pores. The studied clay minerals all display pore width peaks around 0.56–0.66 nm and 0.82–0.87 nm. Pores with diameters < 1 nm in kaolinite, illite, and I/S are all interparticle pores. Montmorillonite has microporous interlayer pores in addition to the interparticle pores, leading to its relatively large micropore volume and surface area. The CH4 sorption capacity on different clay minerals is mainly influenced by the surface area, and montmorillonite has the highest CH4 adsorption capacity.
The major (Al) and trace metal (Cu, Pb, Zn, Cr, Cd, and As) concentrations in 29 surface sediment samples from the intertidal Jiaozhou Bay (JZB) are evaluated to assess the contamination level. The ...results show that the overall sediment quality in the area has been obviously impacted by trace metal contamination. The geoaccumulation index and the enrichment factor values indicate that no Cr or Cu contamination has occurred on the whole, only a few stations have been polluted by As, and some areas have been polluted by Cd, Pb, and Zn. Principal component analysis suggests that the Cu, Pb, Zn, and Cd are derived from anthropogenic inputs and that Cr, As, Cu, and Zn are influenced by natural weathering processes. Cu and Zn may originate from both natural and anthropogenic sources. The contamination in the northeastern JZB is higher than that in other areas of the bay.
•The trace metal concentrations in the intertidal Jiaozhou Bay are analyzed.•The area's sediments are characterized by high levels of trace metals.•Possible trace metal sources are discussed.•The anthropogenic inputs of Cd and Pb are the most significant.
Comprehensive information about the concentrations, distribution, and modes of occurrence of elements in coal are important from the environmental and economic point of view. Although a great number ...of previous studies have investigated the geology of coalbed methane in the Qinshui Basin, only a few studies focused on the inorganic constituents in coal. More specifically, the mode of occurrences of valuable element Li in the No. 3 Coal is still unclear, although Li was found enriched. In this study, we present mineral characteristics, as well as multi-element data on the Permian No. 3 Coal from the Sucun and Gaohe Mines, Changzhi City, southern Qinshui Basin. The studied coals are characterized by low- to medium-ash yield (Ad = 5.72%- 28.18%, 12.34% on average), low volatile matter yield (Vdaf = 8.49–15.17%, 10.96% on average), suggesting a low volatile bituminous coal to semi-anthracite. NH4-illite and kaolinite are the main minerals in the coals detected by XRD, and trace amount of minerals calcite, dolomite, quartz, pyrite and diaspore can also be found. The major elements of the studied No. 3 coals are dominated by SiO2 and Al2O3, ranging 2.49–16.45 wt% and 2.13–12.9 wt% (on a whole-coal basis), respectively. Li is enriched in the No. 3 coals (5 < CC < 10). Li in the studied coals is positively correlated with Al2O3, SiO2 and ash yield, with the correlation coefficients (r) of 0.86, 0.8, and 0.78, respectively. The sequential leaching results show that 96.6%–99.4% of Li in the coals was removed by HF. The proportion of Li present as the ion-exchange form and water soluble form accounts for <1.1% and < 0.29% of the total Li respectively in the coals. Li in the studied coals are probably bound to clay minerals kaolinite and illite, residing mainly in non-exchangeable positions, either in the octahedral or pseudo-hexagonal sites.
•Major minerals identified by XRD are NH4-illite and kaolinite in the coal.•Li is enriched in the coal, with a concentration coefficient of 6.92.•The sequential leaching results show that over 90% of Li was removed by HF.•Li resides in octahedral or pseudo-hexagonal sites in clay minerals.
The processes and time scales of magma mixing in shallow silicic magma chambers prior to eruptions in the Okinawa Trough (OT) are still poorly understood. Here, we employed in situ major-trace ...elements and Sr isotopic analyses, coupled with textural investigations, on plagioclase phenocrysts in the mafic magmatic enclaves (MMEs) and their host dacites from the southwestern OT to address this issue. The plagioclase phenocrysts in the MMEs have high An% contents (82–88) and Sr/Ba ratios (7.2–17.2) and relatively unradiogenic 87Sr/86Sr ratios (0.70536–0.70595), suggesting that they crystallized in the chilled basaltic andesitic magma. In contrast, plagioclase phenocrysts in the host dacites show a wide composition range, with An% contents of An47 to An93, Sr/Ba ratios of 3.4–18.0, and 87Sr/86Sr ratios of 0.70535–0.70791. The plagioclase phenocrysts are zoned, with high-An% cores characterized by resorption textures and mantled by euhedral low-An% rims. The transition between cores and rims is very abrupt, with a decrease of 30 to 40 mol% An. This shift coincides with large and abrupt changes in Sr/Ba ratios. The plagioclase phenocryst rims have low Sr/Ba values (3.4–5.1) and 87Sr/86Sr ratios (0.70632–0.70675) that are similar to those of the whole-rock dacites, suggesting that the plagioclase rims grew from the host dacitic magma. In contrast, Sr isotopes in the plagioclase cores are either radiogenic (0.70724–0.70791) or unradiogenic (0.70535–0.70595) compared with rims, combined with glomerocryst textures, consistent with their derivation from distinct deep mafic crystal mush zones, and were then entrained by ascending melts and transported rapidly to the shallow silicic magma chamber and underwent decompression during ascent, leading to plagioclase core resorption. Mg diffusion calculations indicate that incorporation of the calcic cores into the shallow silicic magma chamber experienced a long pre-eruptive storage (~600 years). The distinct Sr isotopes of the plagioclase, particularly the different compositions of titanomagnetite in the MMEs and host dacites, reflect the mafic magma injection into the silicic magma chamber and formation of the MMEs must have occurred over very short time scales before eruption to inhibit complete re-equilibration, which likely triggered the dacitic magma to finally erupt. Hence, the silicic magma in the southwestern OT contains a crystal cargo with a complex, open-system crystallization history and that magma mixing/mingling is an important process for controlling the chemical and textural diversity of these silicic magmas as well as a likely eruption trigger.
•Remarkable variations in the chemical compositional of plagioclase in the dacite.•A relatively long-lived magma storage history of the shallow silicic magma chamber.•Forceful injection of the new hot mafic magma triggered the dacitic magma eruption.
Magmatic sulfide saturation and dissolution are increasingly thought to play important roles in controlling the behavior of chalcophile metals in arc-related magma. However, the mechanisms of these ...processes during magma evolution in the Okinawa Trough (OT) are still poorly known. Here, we firstly report magmatic sulfides characterized by variable oxidation and dissolution in basaltic andesites from the southern OT. Pyrrhotite (Po) is the main sulfide mineral identified in the clinopyroxene phenocrysts and groundmass in these rocks. Thermodynamic modeling suggests that the oxygen fugacity (fO2), temperature (T) and pressure (P) in equilibrium with Po are ~∆FMQ + 1.5, ~1050 °C, and ~ 3 kbar, respectively. The positive δ34SV-CDT values (1.57 ± 0.35‰) of magmatic sulfides and the extremely nonradiogenic Sr and radiogenic HfNd isotope compositions of the basaltic andesites (mean of 87Sr/86Sr = 0.703816, εHf = 17.72 and εNd = 6.19) indicate that the incorporation of external crustal sulfur is not the reason for sulfide saturation in the oxidized magma. Instead, sulfide saturation is driven by a decrease in the sulfur content at sulfide saturation (SCSS) due to changes in melt chemistry and dropping temperatures along with a concurrent increase in S contents during magmatic differentiation. The S content in the glasses (~362 ppm) is far lower than the SCSS for the basaltic andesitic magma in the magma chamber (~1 wt%), revealing that extensive S degassing occurred during final magma ascent and decompression. The associated drop in S fugacity (fS2) and increase in fO2 induced resorption and oxidation of those sulfides, which were not shielded in the clinopyroxenes, to Fe-oxides and released their Cu and S back into the melt. These elements were then likely partitioned into the vapor phase, resulting in the formation of a metal-rich magmatic fluid emitted to the ocean during magma ascent and degassing. Therefore, magmatic sulfide saturation and dissolution play vital roles in controlling the behavior of chalcophile elements during magmatic differentiation and degassing.
•First report of magmatic sulfide saturation and dissolution in the OT basaltic lavas•Drop in SCSS along with increase in S content trigger magmatic sulfide saturation.•Syn-eruptive degassing causes oxidation and resorption of magmatic sulfides.•Magmatic sulfide is a significant source of metals and S for magmatic fluids.
The heavy metals in surface sediments of the continental shelf of the South Yellow Sea (SYS) and the East China Sea (ECS) collected in 2016 were analyzed to assess the heavy metal distributions, ...contamination status, and likely sources. The metal concentrations generally met the China Marine Sediment Quality criteria. However, the enrichment factor and geoaccumulation index values clearly showed elevated Cd and Pb concentrations in the region. Cd and Pb contamination occurred mostly to the southwest of the Changjiang River mouth and to the east of the Shandong Peninsula because of rapid economic and industrial development. The results are likely to be useful for authorities responsible for sustainable coastal zone management.
•Heavy metals in the sediment of the continental shelf of the SYS and ECS were analyzed.•The sediments are characterized by low levels of heavy metals.•The anthropogenic inputs of Cd and Pb are the most significant.•Heavy contamination occurred along the eastern coast of Shandong Peninsula and southwest of the Changjiang River mouth.
Arc basalts typically have higher Fe3+/ΣFe ratios but lighter Fe isotopic compositions than mid-ocean ridge basalts (MORB); however, the reasons for these differences are unclear. Here, we report new ...Fe isotope data for fresh lavas from the Mariana subduction zone, along with available Fe-B-Sr-Nd isotope and B/Nb ratio data for global arc basalts, to constrain the role of serpentinite dehydration in sub-arc mantle oxidation. The basaltic lavas from the Mariana Arc, like other arc basalts from cold subduction zones in the west Pacific, have lighter Fe isotope compositions (δ56Fe = 0.02 ± 0.02‰; 1SD; n = 9) than the MORB-like δ56Fe values of the middle Mariana Trough basalts (δ56Fe = 0.09 ± 0.02‰; 1SD; n = 8). Notably, the significant negative correlations between the δ56Fe values and the proxy for the addition of serpentinite-derived fluids (i.e., B isotopes and B/Nb ratios) indicate that the serpentinite-derived fluid contribution is a first-order control on the across-arc Fe isotope variations. Dehydration of subducted slab serpentinites or dragged-down forearc serpentinites at sub-arc depths can release isotopically light Fe fluids in the form of Fe2+–SOx complexes. Sulfate-rich fluids containing adequate Fe to metasomatize the sub-arc mantle can cause light Fe isotope compositions and high Fe3+/ΣFe ratios in arc basalts. Alternatively, the low δ56Fe values and high Fe3+/ΣFe ratios of arc magmas may be generated by direct melting of the mélange, which includes dragged-down sulfate-rich forearc serpentinites. Comparatively, serpentinite-derived components are absent at back-arc depths because of the earlier breakdown of serpentine minerals. Accordingly, the back-arc basin basalts exhibit MORB-like δ56Fe-δ11B values and B/Nb–Fe3+/ΣFe ratios. Therefore, the across-arc Fe isotope variations and the decoupling of Fe3+/ΣFe and δ56Fe in global arc magmas can be explained by the different contributions of subducted serpentinites.
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