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.

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.

表面微结构研究揭示了太空风化作用下嫦娥5号月壤演化的中间阶段

月球土壤的组份和微结构会随时间推移发生明显变化,主要原因是其受到微陨石轰击、太阳风或宇宙射线中的带电粒子辐射等太阳风化作用.前期研究表明,太空风化会造成月壤样品表面形成50~200 nm厚的非晶层,层内包裹着大量2~10 nm的金属铁,但该类表面形貌和组成的起源仍存在争议.嫦娥5号取回的月壤样品属于最年轻的玄武岩,并且取样点的纬度最高,为理解月壤在太空风化作用下的演化规律提供了新的机会和线索.本文系统研究了月壤如铁橄榄石、辉石、长石和玻璃珠的表面形貌及化学组成.与以往报道不同的是,仅在铁橄榄石表面观察到了薄的SiO_(2)非晶层(厚度大约10 nm),发现其中包裹着2~12 nm的方铁矿FeO,并且没有观察到任何纳米金属铁颗粒.同时,在所研究的5种样品表面和内部,没有观察到任何易挥发的外来化学元素(如硫、氯等)和太阳耀斑穿过的痕迹.方铁矿FeO和表面微结构的确立暗示着本研究的月壤可能处于太阳风化所引起的热分解中间阶段.