Cooling rates in the shock veins of chondrites: constraints on the (Mg, Fe)2SiO4 polymorph transformations

The occurrence of γ-phase, a high-pressure polymorph of olivine (α-phase), in the shock veins of Sixiangkou chondrite was due to a greater cooling rate (> 10 000°C·s^-1) in the veins. Because γ-phase partially reverted to β-phase and no back-transformation from β-phase to α-phase took place, the shock veins of Peace River chondrite with a cooling rate of 1 000–2 000δC·s^-1 contain a great amount of β-phase. In the shock veins of Mbale chondrite with a cooling rate of <500°C·s^-1, the majority of γ-phase reverted to α-phase. The heat dissipation in shock veins took place after a stage of shock compression of chondrite parent body, and the parent body was broken into fragmental pieces. Cooling rate in the shock veins constrained the back-transformations of (Mg, Fe)₂SiO₄ high-pressure polymorphs. Project of Chen and Xie supported by the National Natural Science Foundation of China (Grant No. 496720981, Natural Science Foundation of Guangdong Province (Grant No. 960500), and the Science Foundation of Academia Sinica for the returned scholars.     

Effects of pyrene and fluoranthene on the degradation characteristics of phenanthrene in the cometabolism process by Sphingomonas sp. strain PheB4 isolated from mangrove sediments

Cometabolism has been suggested as an attractive approach to enhance the degradation rates of high-molecular-weight polycyclic aromatic hydrocarbons (PAHs). However, the effects of these recalcitrant PAHs on the degradation characteristics of low-molecular-weight PAHs are largely unknown. This study was conducted to investigate the effects of pyrene (PYR) and fluoranthene (FLA) on the degradation characteristics of phenanthrene (PHE) in the cometabolism process by Sphingomonas sp. strain PheB4 isolated from mangrove sediments. Based on the kinetics and characteristics of PHE metabolites, it was proposed that the transformation of hydroxylated PHE into 1-hydroxy-2-naphthoic acid was a rate-limiting step in the degradation of PHE by strain PheB4. Compared to a single addition of PYR or FLA, the presence of a mixture of PYR and FLA decreased the degradation rate of PHE to a larger extent, which was likely because it could inhibit the production of 1-hydroxy-2-naphthoic acid more effectively.     

三峡水库澎溪河消落区土-气界面CO2和CH4通量初探

水库近岸湿地(消落区)温室气体(CO₂、CH₄)产汇是水库温室气体效应问题的重要组成部分.本文以三峡水库支流澎溪河的白家溪、养鹿两处大面积消落区为研究对象,于2010年6 9月水库低水位运行期间,对近岸消落区土-气界面CO₂、CH₄通量进行监测.白家溪消落区土-气界面CO₂通量均值为12.38±2.42 mmol/(m²·h);CH₄通量均值为0.0112±0.0064 mmol/(m²·h).养鹿消落区CO₂、CH₄通量均值分别为10.54±5.17、0.14±0.16 mmol/(m²·h).总体上,6 9月土-气界面CO₂通量呈增加趋势,而CH₄通量水平呈现显著的递减趋势.消落区土地出露后植被恢复,在一定程度上促进了土壤有机质含量的增加,使得6 9月CO₂释放通量的总体趋势有所增加.消落区退耕后,其甲烷氧化菌的活性得到恢复,加之在土地出露曝晒过程中土壤透气性增强,使得消落区土壤对大气中CH₄吸收氧化潜势增强.尽管如此,仍需进一步的研究以明晰消落区土-气界面CO₂、CH₄产汇的主要影响因素.     

夏季金沙江下游水-气界面CO2、CH4通量特征初探

河流是连接大陆和海洋两大碳库的桥梁,在全球碳循环中的作用举足轻重.金沙江作为长江的上游段,对区域碳循环及区域化学风化的影响非常重要.于2015年8月8-18日对金沙江下游水-气界面CO_2与CH_4通量特征进行监测与分析.采用顶空平衡法结合薄边界层模型估算法计算表层水体CO_2与CH_4的分压以及水-气界面的交换通量,并分析环境变量与其之间的相关性.研究发现,金沙江下游表层水体p(CO_2)平均值为2724.84±477.18μatm,表层水体p(CH_4)平均值为59.96±6.74μatm;水-气界面CO_2通量平均值为2.24±0.50 mmol/(m2·h),CH_4通量平均值为0.000163±0.00009 mmol/(m2·h),通量与分压趋势基本保持一致.表层水体p(CO_2)与溶解性无机碳浓度、碱度均呈显著正相关,而p(CH_4)与水温、叶绿素a浓度均呈显著正相关,CO_2通量与p(CO_2)、溶解性无机碳浓度、碱度均呈正相关,CH_4通量与p(CH_4)、风速均呈正相关,其他环境因素对通量的影响不明显,仍需进一步研究.金沙江下游水-气界面CH_4扩散通量较低,而CO_2扩散通量在世界主要河流中属于中等水平.     

Experimental study on N<Subscript>2</Subscript>O and CH<Subscript>4</Subscript> fluxes from the dark coniferous forest zone soil of the Gongga Mountain,China

The static closed chamber technique is used in the study on the CH₄ and N₂O fluxes from the soils of primeval Abies fabri forest, the succession Abies fabri forest and the clear-cut areas of mid-aged Abies fabri forest in the Gongga Mountain from May 1998 to September 1999. The results indicate the following: (i) The forest soil serves as the source of atmospheric N₂O at the three measurement sites, while the fluxes of CH₄ are all negative, and soil is the sink of atmospheric CH₄. The comparative relations of N₂O emissions between the three sites are expressed as primeval Abies fabri forest < clear-cut areas < succession Abies fabri forest, and those of CH₄ consumption fluxes are primeval Abies fabri forest < succession Abies fabri forest < clear-cut areas, (ii) Significant seasonal variations of N₂O emission at various sites were observed, and two emission peaks of N₂O occurr during summer (July—August) and spring (February—March), whereas N₂O emission is relatively low in winter and spring (mid March—April). Seasonal variations of CH₄ consumption at each measurement site fluctuate drastically with unclear regularities. Generally, CH₄ consumption fluxes of succession Abies fabri forest and clear-cut areas are higher from mid May to late July but lower in the rest of sampling time, while the CH₄ flux keeps a relatively high value even up to September in primeval Abies fabri forest. In contrast to primeval Abies fabri forest, the CH₄ absorbabilities of succession Abies fabri forest and clear-cut areas of mid-aged Abies fabri forest are weaker. Particularly, the absorbability of the clear-cut areas is even weaker as compared with the other two sites, for the deforestation reduces the soil absorbability of atmospheric CH₄. (iii) Evident diurnal variation regularity exists in the N₂O emissions of primeval Abies fabri forest, and there is a statistic positive correlation between the fluxes of N₂O and air temperature (R=0.95, n=11, α· 0.01), and also the soil temperature of 5-cm layer (R=0.81, n=11, α> 0.01), whereas the CH₄ diurnal variation regularities are unclear and have no significant correlation with the soil temperature of 5-cm layer and air temperature.     

Geochemical and Sr–Nd isotopic constraints on the petrogenesis of the Goesan monzodiorite pluton in the central Okcheon belt,Korea

The Permian–Triassic high pressure metamorphism and potassic magmatism in central Korea attest to the extension of the Dabie‐Sulu collision belt in central‐eastern China towards the Korean Peninsula and possibly the Japanese Islands. We present major and trace element and Sr–Nd isotope data for a ca. 230 Ma monzodiorite pluton emplaced in the Goesan area, central Okcheon belt, Korea. This pluton shows geochemical features comparable with those of the coeval monzonite–syenite–gabbro–mangerite suite documented recently in the Gyeonggi massif. The metaluminous and alkali–calcic signatures of the Goesan intrusives correspond to the Caledonian‐type post‐orogenic granitoids. The K₂O/Na₂O ratios of all analyzed samples are greater than 1, and are not correlative with their SiO₂ contents. The enrichment of both large‐ion‐lithophile elements and highly compatible elements in the Goesan pluton is probably indicative of metasomatized mantle origin. The elemental fractionation in the source region must have occurred in the distant past, possibly the Paleoproterozoic, to generate significantly negative ε_Nd(t) values (< –16). Chondrite‐normalized rare earth element patterns as well as Rb/Sr and Ba/Rb ranges suggest that the source consists of amphibole‐bearing rocks. Progressive decreases in negative Eu anomaly and Ba, Sr, Ni, Cr and V contents with increasing SiO₂ contents reflect an important role of plagioclase, biotite and hornblende for the fractionation process. Zr is undersaturated in the potassic, metaluminous melt. The initial Sr–Nd isotopic compositions of the samples are correlated with their SiO₂ contents, substantiating a role of crustal assimilation during the magmatic differentiation. The Sr–Nd elemental and isotopic modeling suggests that the Goesan pluton was initially slightly heterogeneous in its isotopic composition, and underwent concurrent assimilation and fractional crystallization. The occurrence of the Goesan pluton provides further evidence corroborating the amalgamation of allochthonous terranes within the Okcheon belt during the Permian–Triassic collisional orogeny.