LITHOSPHERE-ASTHENOSPHERE INTERACTION: A COMPARATIVE STUDY ON CENOZOIC AND MESOZOIC BASALTS AROUND BOHAI AREA

Mesozoic and Cenozoic basalitc rnagmatism within the basins around Bohai area displays temporal variations in petrochemistry,trace element and isotope geochmistry. Two stages of evolution are recognized. The preextension magmatism (134 - 91 Ma,Jiyang basin) is characterised by small volumes of alkaline basalts and potassic lamprophyres. These rocks are interpreted as results of very small degrees of partial melting of the lithosphere and volatile-rich metasome within the lithosphere induced by initial thermal perturbation. The second stage (74- 27 Ma) coincides with the lithospheric extension. It, is noted that the alkalinity and Dea of basalts increased systematically from 74 to 27 Ma. Major element chemistry,trace element modelling antl experimental data indicate that there is an increase in depth of melting and a decrease in degree of partial melting from 74 to 27 Ma. Such a temporal change in source character and in the depth of origin is best understood when magmatism is considered within the framework of a lithosphere-asthenos phere interaction model where melting is initiated by discrete thermal events related lithospheric extension.

International Conference on Continental Volcanism—IAVCEI 2006

The International Conference on Continental Volcanism, sponsored by the International Association of Volcanology and Chemistry of the Earth＇s Interior （IAVCEI）, was held at White Swan Hotel, Guangzhou, China, May 14th to 18th, 2006. This meeting was supported by the Chinese Academy of Sciences, the Guangzhou Association for Science and Technology, National Natural Science Foun- dation of China, the Association for Science and Technology of Guangdong Province and the Chinese Society for Mineralogy, Petrology and Geochemistry. It was organized by the Guangzhou Institute of Geochemistry and the Chinese Committee for IAVCEI. The conference comprised four-days of indoor oral and poster presentations and two post-conference field excursions to the Emeishan large igneous province and the North China Craton.

乳酸乳球菌表达重组牛乳铁蛋白肽的抑菌活性分析

牛乳铁蛋白肽是由牛乳铁蛋白经消化酶水解产生的一类具有广谱抑菌活性的短肽;乳酸乳球菌作为食品级微生物,既有天然的益生作用,又是理想的表达牛乳铁蛋白肽的载体。【目的】探究重组乳酸乳球菌pAMJ399-LFcinBA/MG1363表达牛乳铁蛋白肽的抑菌活性。【方法】利用牛乳铁蛋白肽标准品绘制定量标准曲线来确定重组牛乳铁蛋白肽的含量,利用牛津杯法及微量肉汤稀释法测定重组牛乳铁蛋白肽对大肠杆菌、金黄色葡萄球菌等35株细菌的抑菌活性及最小抑菌浓度,利用扫描电镜、透射电镜、荧光显微镜、凝胶阻滞试验、黏附试验来探究重组牛乳铁蛋白肽对菌体结构、细菌DNA及黏附力的影响,利用CCK-8检测其对RAW 264.7细胞的毒性作用,并对小鼠红细胞溶血率进行测定。【结果】重组乳酸乳球菌上清中牛乳铁蛋白肽的浓度为24.39μg/mL,重组牛乳铁蛋白肽对测试的25株致病菌均有不同程度的抑制作用,抑菌浓度范围在16–128μg/mL,但对9株乳酸菌以及粪肠球菌没有明显的抑制作用,对大肠杆菌、金黄色葡萄球菌、多杀性巴氏杆菌、鸡白痢沙门菌的菌体完整性具有不同程度的破坏作用,其主要作用靶点为细菌的细胞膜,可以与细菌DNA结合并抑制细菌对Caco-2、IPEC细胞的黏附作用,重组牛乳铁蛋白肽对小鼠红细胞及RAW 264.7细胞没有明显的细胞毒性。【结论】乳酸乳球菌表达重组牛乳铁蛋白肽的抑菌活性与牛乳铁蛋白肽标准品相一致,通过直接作用于细菌细胞膜、胞内核酸或抑制细菌对正常细胞的黏附作用等多方面实现抑制或杀死细菌,发挥广谱的抗菌活性,且对真核细胞没有明显的细胞毒性作用。

The subduction of the west Pacific plate and the destruction of the North China Craton

While a general concensus has recently been reached as to the causal relationship between the subduction of the west Pacific plate and the destruction of the North China Craton, a number of important questions remain to answer, including the initial subduction of west Pacific plate beneath the eastern Asian continent, the position of west Pacific subduction zone during the peak period of decratonization(i.e., Early Cretaceous), the formation age of the big mantle wedge under eastern Asia, and the fate of the subducted Pacific slab. Integration of available data suggests that the subduction of the western Pacific plate was initiated as early as Early Jurrasic and the subduction zone was situated to 2,200 km west of the present-day trench in the Early Creataceous, as a result of eastward migration of the Asian continent over a distance of ca. 900 km since the Early Cretaceous.The retreat of the subducting west Pacific plate started ~145 Ma ago, corresponding to the initial formation of the big mantle wedge system in the Early Cretaceous. The subduction of the Pacific slab excerted severe influence on the North China Craton most likely through material and energy echange between the big mantle wedge and overlying cratonic lithosphere. The evolution history of the west Pacific plate was reconstructed based on tectonic events. This allows to propose that the causes of phases A and B for the Yanshanian orogeny were respectively related to rapid low-angle subduction and to lowering subduction angle of the west Pacific plate. At ca. 130–120 Ma, the subduction of the west Pacific plate was characterized by increasing subducting angle, slab rollback and rapid trench retreat, leading to the final stagnation of the subducting slab within the mantle transition zone. This process may have significantly affected the physical property and viscosity of the mantle wedge above the stagnant slab, resulting in non-steady mantle flows. The ingression of slab-released melts/fluids would significantly lower the viscosity of the mantle wedge and overlying lithosphere, inducing decratonization. This study yields important bearings on the relationship between the subduction of the west Pacific plate and the evolution of the lithospheric mantle beneath the North China Craton.

Generation of Cenozoic intraplate basalts in the big mantle wedge under eastern Asia

The roles of subduction of the Pacific plate and the big mantle wedge(BMW) in the evolution of east Asian continental margin have attracted lots of attention in past years. This paper reviews recent progresses regarding the composition and chemical heterogeneity of the BMW beneath eastern Asia and geochemistry of Cenozoic basalts in the region, with attempts to put forward a general model accounting for the generation of intraplate magma in a BMW system. Some key points of this review are summarized in the following.(1) Cenozoic basalts from eastern China are interpreted as a mixture of high-Si melts and low-Si melts. Wherever they are from, northeast, north or south China, Cenozoic basalts share a common low-Si basalt endmember, which is characterized by high alkali, Fe_2O_3~T and TiO_2 contents, HIMU-like trace element composition and relatively low ^(206)Pb/^(204)Pb compared to classic HIMU basalts. Their Nd-Hf isotopic compositions resemble that of Pacific Mantle domain and their source is composed of carbonated eclogites and peridotites. The high-Si basalt endmember is characterized by low alkali, Fe_2O_3~T and TiO_2 contents, Indian Mantle-type Pb-Nd-Hf isotopic compositions, and a predominant garnet pyroxenitic source. High-Si basalts show isotopic provinciality, with those from North China and South China displaying EM1-type and EM2-type components, respectively, while basalts from Northeast China containing both EM1-and EM2-type components.(2) The source of Cenozoic basalts from eastern China contains abundant recycled materials, including oceanic crust and lithospheric mantle components as well as carbonate sediments and water. According to their spatial distribution and deep seismic tomography, it is inferred that the recycled components are mostly from stagnant slabs in the mantle transition zone,whereas EM1 and EM2 components are from the shallow mantle.(3) Comparison of solidi of garnet pyroxenite, carbonated eclogite and peridotite with regional geotherm constrains the initial melting depth of high-Si and low-Si basalts at <100 km and^300 km, respectively. It is suggested that the BMW under eastern Asia is vertically heterogeneous, with the upper part containing EM1 and EM2 components and isotopically resembling the Indian mantle domain, whereas the lower part containing components derived from the Pacific mantle domain. Contents of H_2O and CO_2 decrease gradually from bottom to top of the BMW.(4) Melting of the BMW to generate Cenozoic intraplate basalts is triggered by decarbonization and dehydration of the slabs stagnated in the mantle transition zone.

The origin of arc basalts:New advances and remaining questions

Whether arc magmatism occurs above oceanic subduction zones is the forefront of studies on convergent plate margins.The most important petrologic issue related to the evolution of arc systems is the origin of arc magmatism,among which arc basalts are the most important one because they provide insights into mantle enrichment mechanism and crust-mantle interaction at oceanic subduction zones.Fluids or melts released either by dehydration or by melting of subducting oceanic slab infiltrate and metasomatize the overlying mantle wedge at varying depth,leading to the formation of source regions of arc basalts.Such processes make most of arc basalts commonly enriched in large ion lithosphile elements and light rare earth elements,but depleted in high-field strength elements and heavy rare earth elements.Small amounts of arc basalts are characterized by relatively high Nb contents or by Nb enrichment.Rare basalts with compositions similar to ocean island basalts or mid-ocean ridge basalt also occur in arc systems.For these peculiar rocks,it remains debated whether their source is affected by subduction-related components.During their ascent and before their eruption,arc basaltic magmas are subjected to crystal fractionation,mixing and crustal contamination.In addition to the contribution of subducting slab components to the mantle source of arc basalts,the materials above the subducting slab at forearc depths would have been transported either by drag or by subduction erosion into the subarc mantle and into the source of arc magmas.Heats and materials brought by corner flows also play important roles in the generation of arc basalts.Despite the important progresses made in recent studies of arc basalts,further efforts are needed to investigate subarc mantle metasomatism,material recycling,the formation of arc magma sources,geodynamic mechanism in generating arc basalts,and their implicationd s for the initiation of plate tectonics on Earth.

Surface microstructures of lunar soil returned by Chang’e-5 mission reveal an intermediate stage in space weathering process

The lunar soils evolution over time is mainly caused by space weathering that includes the impacts of varying-sized meteoroids and charged particles implantation of solar/cosmic winds as well.It has long been established that space weathering leads to the formation of outmost amorphous layers(50–200 nm in thickness)embedded nanophase iron(npFe^(0))around the mineral fragments,albeit the origin of the npFe^(0) remains controversial.The Chang’e-5(CE-5)mission returned samples feature the youngest mare basalt and the highest latitude sampling site,providing an opportunity to seek the critical clues for understanding the evolution of soils under space weathering.Here,we report the surface microstructures of the major minerals including olivine,pyroxene,anorthite,and glassy beads in the lunar soil of CE-5.Unlike the previous observations,only olivine in all crystals is surrounded by a thinner outmost amorphous SiO_(2) layer(∼10 nm thick)and embedded wüstite nanoparticles FeO(np-FeO,3–12 nm in size)instead of npFe^(0).No foreign volatile elements deposition layer and solar flare tracks can be found on the surface or inside the olivine and other minerals.This unique rim structure has not been reported for any other lunar,terrestrial,Martian,or meteorite samples so far.The observation of wüstite FeO and the microstructures support the existence of an intermediate stage in space weathering for lunar minerals by thermal decomposition.