地下连续墙槽壁稳定的研究

从三个主要影响地下连续墙槽壁稳定的方面出发,分析和研究影响地下连续墙槽壁稳定的几个因素:地质条件、施工机械和成槽方法、稳定液的类型和质量对槽壁稳定起着至关重要的作用。探讨了槽壁的失稳机理,分析致稳和失稳两方面的因素。通过对槽壁稳定的研究,为解决槽壁坍塌问题提供理论依据和研究方法。     

铀系不平衡与洋中脊下的岩浆形成及其迁移过程

综述了20多年来洋中脊新生玄武岩中铀系不平衡研究成果,分析了铀系不平衡的形成机制和主要影响因素,并探讨了铀系不平衡研究中的一些问题。结果表明:(1)玄武质岩浆中230Th/238U不平衡可能产生于石榴子石稳定的深部源区,也可能来自230Th的"内部增长"(in-growth),过剩230Th更可能形成于含铝单斜辉石;(2)226Ra/230Th不平衡可能来自岩浆的形成过程,也可能来自岩浆迁移过程;(3)铀系不平衡与岩浆滞留时间和上升速率紧密相关,226Ra的大量过剩显示,这个不平衡事件形成于8ka以内,如果不考虑玄武质岩浆迁移过程的事件,则意味着岩浆迁移时间不超过8ka。提出当前亟待解决的问题:①准确模拟地幔部分熔融条件并测定铀系子体在熔体/地幔残留相间的分配系数;②提出更合理的结晶分异模型;③探索流体对226Ra/230Th不平衡的影响。     

Fate of particle-reactive pollutants in the Xiamen Bay

INTRODUCTIONItiswel1knownthattheabilitytopredictthetransportationandfateofPOllutantsinthecoastalenvironmentsisimportanttothemanagementofmarineenvironments,toconservingma-rineorganismsandsafeguardinghumanhealth.ThegeochemicalbehaviourofPOllutantsinama-rineecosystemisgenerallygovernedbybiologicaldegradation,photodegradation,volatilization,waterexchange,incorPorationintosediments,etc.TheincorPOrationofPollutantsinestuarineorcoastalsediments,viaanassociationwithsettlingparticles,hasbeenrec…     

U–Th dating of carbonate nodules from methane seeps off Joetsu, Eastern Margin of Japan Sea

We performed U–Th radioactive disequilibrium analyses of carbonate nodules and sediment samples recovered from methane seep sites off Joetsu, of the eastern margin of Japan Sea, to decipher the active period of the methane seep. The carbonates contain ²³⁰Th, part of which is located in detritus such as silicate and organics, at the time of precipitation. The initial ²³⁰Th renders accurate dating with U–Th radioactive disequilibrium method difficult. We assessed the feasibility of correction using radioactive disequilibrium data of ambient sediment to overcome this difficulty. A (²³⁰Th/²³²Th)–(²³⁴U/²³²Th) isochron drawn by three chips divided from a carbonate nodule (PC05-04-50) passed through data points of local sediments. We conclude that the problem of initial ²³⁰Th can be resolved by measurements of local sediments. Results show that carbonate nodules include local sediment as impurities. Furthermore, the results of trace element analyses such as Rb, Zr, Nb, REE, Pb, and Th also support the idea.In all, 18 carbonate samples were dated with correction of initial ²³⁰Th using the mean value of local sediment in this study. The U–Th correction ages show 12–35ka with an isochron age of 26 ± 3ka. Results indicate that during the time interval of U–Th ages, from 12ka to 35ka, environmental conditions must have been favorable for enhanced methane flux through sediment. The extensive methane flow period at 20ka accords with the lowest-stand sea level during the last glacial age. Results of this study also suggest that U–Th ages of carbonate are useful as a reliable chronometer with regard to methane seep activation. In order to acquire U–Th ages of carbonate at methane seep sites, however, it is important to evaluate the amount of initial ²³⁰Th accurately using the value of sediment.     

Understanding the collapse–eruption link at Stromboli,Italy: A microanalytical study on the products of the recent Secche di Lazzaro phreatomagmatic activity

The Secche di Lazzaro (SDL) phreatomagmatic activity, with the associated Neostromboli sector collapse, represents the most powerful activity of the last 6 ky at Stromboli. As revealed by its present-day activity, Stromboli is one of the most eruptive volcanoes in Italy, and flank instability, along its NW flank, is a common process. Volcano instability is often dramatised by explosive eruptions, thus it is of crucial importance to understand the linking between volcano collapse and the plumbing system itself. The possible role of pre-eruptive magmatic processes as triggers of explosive eruptions can be mainly preserved by minerals and revealed by petrochemical studies. We studied the juvenile components (scoria and pumice) of the pyroclastic deposits from the SDL phreatomagmatic activity with the aim to understand the eruption–collapse link.     

Incomplete high P–T metamorphic transitions within the Kvamsøy pyroxenite complex, west Norway: a case study of disequilibrium

Abstract The Kvamsøy pyroxenite complex consists of olivine websterite, olivine gabbro and leucogabbro-norite which have been subjected to regional high P-T (HPT) metamorphism. The metamorphism has resulted in a range of disequilibrium textures with the development of coronas and pseudomorphism of the igneous phases. Reactions between felsic and mafic mineral domains have been controlled by variable and selective diffusion of elements, resulting in a variety of local plagioclase-breakdown reactions and in significant compositional variations for the product garnet. Restricted diffusion favours transient reaction stages with garnet ± spinel ± corundum ± zoisite after calcic plagioclase in olivine gabbro and olivine websterite and garnet ± spinel ± kyanite ± quartz + sodic plagioclase in leucogabbro-norite. Complete HPT reaction has produced garnet pyroxenite which consists of garnet + diopside + hornblende + zoisite in gabbroic rocks, while amphibolitization continued during the cooling and uplift history. Grt + Ky + Pl + Qtz geobarometry suggests pressures in the range 13-16 kbar for T = 750°C, comparable with the regional eclogite-forming metamorphism.     

Allt Odhar and Dalcharn: Two pre-Late Devensian/Late Weichselian sites in northern Scotland

The lithostratigraphy and biostratigraphy of two sites (Allt Odhar and Dalcharn) in north-central Scotland are described, where pollen spectra of temperate affinity have been obtained from organic deposits that underlie till. The pollen record from Allt Odhar, in association with evidence from plant macrofossils and Coleoptera, shows the expansion of birch woodland and its eventual replacement by open grassland under a climatic regime slightly cooler than that prevailing in the northern highlands of Scotland at the present day. The organic sediments accumulated during an Early Devensian interstadial episode, which has been dated by the uranium series disequilibrium method to ca. 106 ka BP. Evidence for one and possibly two Devensian glaciations may be preserved at the site. The pollen record from Dalcharn, by contrast, reflects the middle and later stages of an interglacial cycle with the transition from pine forest to grassland. The overlying till sequence contains evidence of at least two separate glacial episodes. The age of the warm stage cannot be established precisely on present evidence, but there are indications that it may predate the last (Ipswichian) interglacial. These are the first sites from the mainland of Scotland to provide evidence of wooded conditions during interstadial and interglacial episodes of the Middle/Late Pleistocene.     

大别造山带核部天堂寨和九资河花岗岩的成岩模拟

选用大离子亲石元素 Rb、Sr对大别造山带核部天堂寨和九资河花岗岩进行成岩模拟 ,结果表明 :( 1)天堂寨花岗岩主要与非平衡熔融有关 ,偏基性片麻岩可能是天堂寨花岗岩的主要原岩 ;( 2 )九资河花岗岩主要由片麻岩的平衡非实比批式熔融作用形成 ,但也不排除由偏基性片麻岩发生非平衡熔融形成九资河花岗岩的可能性 ;( 3 )天堂寨与九资河花岗岩熔融方式的差异可能反映了大别造山带燕山晚期不同地壳层次变质岩熔融方式的差别 ,即中下地壳以高温非平衡部分熔融为主 ,而中地壳以低温平衡熔融为主 ,并伴随有局部偏基性片麻岩的非平衡熔融     

钾长石包裹体水和蚀变矿物的H同位素之间关系的探讨

钾长石的6个H同位素组成表明，钾长石包裹体水的δD值与由其蚀变矿物绢云母的δD计算出的δDH2O不可能相等，因为它们是两个不同阶段的产物，二者没有必然的联系，所以由钾长石热液蚀变矿物δDH2O值就不能代表成矿流体（矿物包裹体水）的δD值。