GEOCHEMICAL JOURNAL Vol. 49(2015) No. 1

The occurrence of carbon dioxide (CO₂) in Central Anatolia has been well-known for 50 years. Four gas producing fields (Bozkar, Guneygaz, Karbogaz, and Terra) are located in the region. The aim of this study was to define the composition of these gas occurrences and to determine the gas origin. For this purpose, the molecular and isotopic composition of gas samples from production wells were investigated and interpreted. Gases from the region are rich in CO₂ (>80%). Carbon dioxide concentrations were found to vary from 80.7 to 94.3%. The total amount of methane components (CH₄₊) was less than 0.1%. The isotopic composition of CO₂, with values between -1.76 and 1.02‰, indicated abiogenic origin from limestone. The generation of CO₂ could largely result from the decarbonation of limestone. Helium isotopic values indicated that a minor amount of CO₂ originated from the mantle. δ¹³C values for methane from the Karbogaz Field suggested that the origin of the Aksaray Field methane is thermogenic.

The Laojunshan mining district is an important part of the SE Yunnan W-Sn polymetallic mineral belt. Previous geochronologic data have shown that the main metallogenic stages in this area are Indosinian and Yanshanian in age. In this paper, we present a new dating result that differs from those published previously by using the in situ LA-MC-ICP-MS geochronologic method on a cassiterite sample from the giant Xinzhai tin deposit. Analyses of this sample yielded a U-Pb Tera-Wasserburg age of 419.1 ± 6.7 Ma. This new date identifies a Caledonian metallogenic event at the Xinzhai tin deposit and this age is also consistent with Caledonian magmatic and tectonic activity previously recognized in the Laojunshan mining district. Therefore, not only Yanshanian and Indosinian metallogenic stages but also a Caledonian mineralization event must have occurred in the study area. This new result may play an important role in ore prospecting and metallogenic study in the Laojunshan mining district and, more importantly, in all of SE Yunnan.

Studies have shown that Diuron, Irgarol 1051 and Fenitrothion are toxic to reef building (hermatypic) corals, non-target marine algae and a wide variety of aquatic organisms, respectively. In this study, marine samples were collected from the Seto Inland Sea, Japan, to assess the distribution of Diuron, Irgarol 1051 and Fenitrothion among water, sediments and aquatic organisms (plankton, fish and selected marine animals). Samples were cleaned and extracted by Solid Phase Extraction (SPE) and analysed with reverse phase HPLC system (Shimadzu Corporation, Japan) equipped with a UV-Vis detector. The maximum concentrations for Diuron, Irgarol 1051 and Fenitrothion were 2.18 μgl^-1, 1.07 μgl^-1 and 0.05 μgl^-1 in surface waters, respectively; 0.06 μgl^-1, 0.09 μgl^-1 and 0.04 μgl^-1 in bottom waters, respectively; 0.075 μgg^-1 dry weight (dw), 0.069 μgg^-1 dw and 0.051 μgg^-1 dw in sediments, respectively; 2.83 μgg^-1 dw, 2.04 μgg^-1 dw and 0.46 μgg^-1 dw in plankton, respectively; 4.12 μgg^-1 dw, 3.14 μgg^-1 dw and 0.48 μgg^-1 dw in fish and selected marine animals, respectively. The highest concentrations of Diuron and Irgarol 1051 were found close to a port and ship building industries, whilst maximum concentrations of Fenitrothion were detected near river estuaries. The general trend was that of decreasing pesticide concentrations away from the mouth of rivers flowing into the Seto Inland Sea. Our calculated bioconcentration factors (BCFs) indicate that plankton, whole fish and selected marine animals samples bio-accumulate antifoulants and pesticides. The accumulation gradient in fish samples was viscera > liver > gills > fillet. Measured concentrations of both the antifoulant booster biocide Irgarol 1051 and the insecticide Fenitrothion in both whole fish and marine animals sampled exceeded the Japanese Maximum Residual Limits (MRLs) as did 21% of foods sampled for Diuron.

It is known that Haloxylon has successive cambia and its radial growth rate is not clear as indicated by the fact that the annual boundary cannot be determined by dendrochronological approach. Radial increment through successive cambia (RISC) layers possess similar morphological feature as compared to annual rings by megascopic cross sectional observations. Previous studies have demonstrated that the dendrochronological methods cannot be applied to some species that possess successive cambia. The objective of the present study is to clarify the growth rate of RISC layer in Haloxylon ammodendron by a series of radiocarbon dating. Two H. ammodendron specimens (S1 and S2) were collected from the southern edge of Gurbantünggüt Desert in Northwestern China. Radiocarbon measurements revealed the numbers of annual RISC layer to be 2.98 ± 0.51 (S1) and 3.65 ± 0.53 (S2). Linear regression shows a strong relationship between growth period (x) and radial increment accumulation (y): y = 1.52x + 0.76 (R² = 0.96, P < 0.001) for S1 and y = 1.70x + 4.49 (R² = 0.94, P < 0.001) for S2, respectively. Anatomical observations on the RISC layer using scanning electron microscope (SEM) image showed that: (1) the early wood and late wood were not present or differentiated; (2) axial vessel groups (about 2-10 vessels) are often distributed in the bark-side; and (3) sclerenchyma cells as junctions tightly adhered vessel groups at outside in each RISC layer. These observed features are completely different from those in annual ring morphologies. We tentatively hypothesize that these features are due to the formation of multiple RISC layers within one growing season in order to aid in water storage in the stem to survive in harsh habitat conditions. This research will help further the knowledge in the physiological and ecophysiological researches on H. ammodendron and other successive cambia species.

In this study, we performed U-Pb dating on 1295 zircon grains from 24 samples originating from the North China Craton (NCC); an additional 440 Lu-Hf isotopic analyses were conducted on select zircon grains. The U-Pb ages revealed that the strongest magmatic event in the NCC occurred ca. 2.5 Ga, and a subordinate magmatic event occurred ca. 1.8 Ga. The crustal model ages from Hf isotopic analyses showed that the best estimate for the age of the NCC mantle extraction is ca. 2.8-2.7 Ga, which is consistent with the age of global continental crusts. In recent years, numerous 2.7 Ga rocks have been identified within the NCC. A strong and widespread superimposed tectono-thermal event at ca. 2.5 Ga differentiates the NCC from many other worldwide cratons. However, the timing of the majority of NCC continental crust growth remains highly controversial. In this paper, a quantitative method was used to calculate a continental crust reworking rate. The results revealed that the lowest reworking rate in the NCC occurred at ca. 2.7 Ga and was below 13%. At 2.9 Ga, the reworking rate was 73%, suggesting that a strong intra-crustal magmatic event took place at that time. Combining the reworking rates and Hf isotopic model ages for each period, we concluded that approximately 25% and 23% of the continental crust volume in the NCC was formed at ca. 2.8 Ga and 2.7 Ga, respectively. Approximately 12% of the continental crust volume formed at 2.6 Ga, and only 6% of the continental crust formed at ca. 2.5 Ga. Even with a high reworking rate, 6% of the continental crust formed at 2.9 Ga. Therefore, the main continental crustal growth in the North China Craton occurred at ca. 2.8-2.7 Ga (48% continental crust).

Land use changes can affect soil carbon storage in terrestrial ecosystems by altering either the biotic or the abiotic processes involved in carbon cycling, such as the adsorption of carbon on soil minerals. In this study, the organic carbon contents and their stable carbon isotopic compositions (δ¹³C) of five soil profiles under different land uses in the Maolan karst region in Southwest China were analyzed. Four non-forest samples from the karst were selected and examined to determine whether farmlands or grasslands that were converted from forestland were more effective in sequestering carbon in soils. The soil organic carbon (SOC) contents decreased in the following order: virgin forest, burnt grassland, shrubland, grassland, and farmland. However, no differences were observed in the δ¹³C values at the bottom of the five profiles, which indicated that most of the soil organic carbon was derived from the original virgin forest. The percentages of SOC that resulted from C₄ plants in the virgin forest were significantly lower than the percentages in the other plots, while the percentages of SOC that resulted from C₃ plants in the virgin forest were significantly higher than the percentages in the other plots. The δ¹³C values in the topsoils of the various profiles decreased in the following order: burnt grassland, farmland, grassland, shrubland, and virgin forest. From the surface to the base of the farmland profiles, little variation occurred in the δ¹³C values of the SOC (from -25.1 to -29.1‰). This variation in the δ¹³C values of the SOC in the surface soils was associated with changes in the vegetation cover. In addition, our results suggest that the plant functional type is important for controlling the depth-related changes in the SOC contents and the δ¹³C values of the SOC.

The Bake quartz vein-type gold deposit is one of the most well-known gold deposits in SE Guizhou. The mineralization age of auriferous arsenopyrite determined using Re-Os chronology is 412 ± 21 Ma (MSWD = 2.6), which is in good agreement with the regional-scale geologic evidence and confirms that the Caledonian was an important gold metallogenetic period in the Xuefeng region. Contrastingly, the high initial ¹⁸⁷Os/¹⁸⁸Os ratio (2.7 ± 1.2) suggests a crustal source for the ore-forming material of the deposit. Furthermore, the REE patterns, Eu/Eu*, Ce/Ce* and Y/Ho ratios of the arsenopyrites are all similar to those of the wall rocks, indicating that the ore was perhaps derived from the wall rocks belonging to the Xiajiang Group.

Oxygen isotope ratios were determined using laser fluorination methods on 15 olivines and seven matrix samples separated from the Pali Aike alkali basalt of southern Patagonia. The δ¹⁸O values were measured in ranges of 4.23 to 5.23‰ and 4.64 to 5.26‰ for olivine and matrix, respectively. The δ¹⁸O values of Pali Aike olivines are lower and have a wider range than those of normal upper mantle (5.0-5.4‰). We considered that the heterogeneity of the oxygen isotope compositions of Pali Aike olivine provides evidence of assimilation at a shallow level and the presence of recycled material. The differences between olivine and matrix δ¹⁸O values indicate that Δ¹⁸O_(melt-ol) (0.14 to 0.50) was within equilibrium fractionation for some and in disequilibrium for most samples at magmatic temperature. Oxygen isotope compositions in disequilibrium indicate that the lower δ¹⁸O for the melt is explained by interaction with low δ¹⁸O hydrothermally altered rocks. The low δ¹⁸O_olivine values for low forsterite (Fo) contents of Pali Aike lavas can be explained by the effect of shallow-level assimilation. The oxygen isotope values for the olivine of high-MgO (or high-Fo) compositions are thought to represent oxygen isotope variation in the mantle source region. The low and variable δ¹⁸O signature of Pali Aike olivine can be explained by crustal recycling, such as a contribution from the hydrothermally altered oceanic crustal melt. These heterogeneous oxygen isotope compositions indicate that Pali Aike olivines require both assimilation at a shallow level and a component of the high-μ end-members (HIMU) mantle derived from recycled mantle lithologies in the form of pyroxenite or eclogite.

The distribution of epithermal base metal deposits in the Lanping basin, Yunnan province, SW China is controlled by Cenozoic thrust-nappe systems. The Baiyangping and Wudichang Ag-bearing polymetallic deposits are representative of the epithermal base metal deposits in the Lanping basin. Hydrothermal calcites associated with base metal sulfides in these two deposits yield similar Sm-Nd isochron ages of 30.1 ± 1.9 to 27.4 ± 1.8 Ma, respectively. These results indicate that the ages of mineralization of the Baiyangping Cu-Ag-Co and Wudichang Pb-Zn-Ag ore deposits are contemporaneous with the Cenozoic Indo-Asian continental collision. Such temporal correlation, combined with the apparent regional structural control of the distribution of these type of deposits suggests that Cenozoic thrust-nappe tectonics and associated hydrothermal activity played an important role in the formation of the epithermal Ag-bearing polymetallic base metal ore deposits in the Lanping basin.

We present a simplified method for simultaneous determinations of fluorine (F), chlorine (Cl), and sulfur (S) contents and isotopic abundances in rock samples. After using pyrohydrolysis to extract F, Cl, and S from a sample and transfer it into a sodium hydroxide (NaOH) solution, concentrations of F, Cl, and S as sulfate are measured by ion chromatography. The method is applicable to a variety of rock materials, including peridotite, basalt, gabbro, andesite, rhyolite, sulfide minerals, and possibly to sea salt, with F, Cl, and S contents of several μg g^-1 to several tens of weight percent in 40 to 250 mg of rock powder. F, Cl, and S contents obtained by 5-7 repeated analyses of each of nine geological reference materials were in good agreement with previously reported values. In certain reference materials, sulfite peaks were observed, indicating incomplete oxidation to sulfate during S extraction by pyrohydrolysis. However, total S contents in those samples analysed by ICP-AES were also in good agreement with previous reported values. The RSDs of F, Cl, and S contents in reference materials were <6%, except for samples with F content <10 μg g^-1 (∼20%) or S content <∼20 μg g^-1 (<20%). In addition, Cl isotope compositions of seawater (IAPSO Standard Seawater and Pacific Ocean water) from sample solutions in this study were identical within error to reported values, indicating that Cl isotopes do not fractionate during pyrohydrolysis. After small isotopic fractionation corrections, multiple isotope compositions of S (³²S, ³³S, ³⁴S and ³⁶S) in solutions of sulfide (IAEA-S-1, IAEA-S-2, and IAEA-S-3), IAPSO Standard Seawater, and gabbro (JGb-1), also agree well with their respective reported values. Thus, this method is applicable to obtain accurate Cl and S contents as well as their isotopic compositions from a single aliquot of sample.