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…     

豫皖湘赣承接产业转移与创新产出的非均衡格局及影响因素研究

采用地理集中度、不均衡指数、不一致指数及地理加权回归对豫皖湘赣57个地级市2010—2016年承接产业转移与创新产出的非均衡格局及影响因素进行研究。结果表明：1）产业转移集中度指数变化较小但各地区之间产业转移集聚格局变化较为显著,总体上集中度高和较高的地区分布在豫北、豫中、皖中、皖南以及赣北地区;2）创新产出空间差异显著,呈现出以芜湖和郑州为中心向四周扩散的格局;3）豫皖湘赣地区大部分地区的承接产业转移与创新产出能力呈现出较强的不一致性;不均衡指数波动较大,呈现出上升、缓慢下降、快速上升的趋势;4）从影响因素回归系数来看,平均工资和教育占财政支出百分比与不一致指数成负相关,网络通讯发展水平与不一致指数呈正相关,而集聚效应与不一致状况关系较为复杂,具体表现为豫皖湘赣东部合肥等地和西部怀化等地为正高集聚区和北部郑州等地和南部赣州等地为负高值集聚区。     

高铁新时代下中国铁路交通可达性分布格局及其均衡程度的研究

基于交通可达性指数对2009—2016年期间中国主要城市的交通可达性及其区域差异进行了比较分析,整体上所有主要城市的交通可达性均得到了大幅提升。从范围上来看,无论时间可达性还是经济可达性,东部城市都高于中部和西部城市。高铁建设导致经济活动向区域中心城市的集聚,经济可达性的分布呈现出显著的以各区域中心城市为核心的“中心-外围”结构。但集聚外溢效应同样存在,这种外溢效应主要集中在中心城市的近邻地区,向周边中等规模以上城市扩展。这些现象说明我国区域间交通成本仅仅出现了中等程度的下降,由此导致区域经济集聚程度的提高,尚处在交通成本与区域经济差距之间“倒U字曲线”的中前期阶段。     

Metamorphic evolution of the late Archaean Cadillac tectonic zone, McWatters, Abitibi belt, Quebec

Abstract Archaean greenstone belts are often cut by major shear zones, for example the Cadillac tectonic zone (CTZ) of the southern Abitibi region in north-western Quebec. At McWatters, the CTZ contains slices of metavolcanic units bounded by corridors of highly strained and altered rocks. Mineral assemblages of the metabasites record the metamorphic evolution of the CTZ.
The McWatters metabasalts and metagabbros have similar chemistry but different mineral assemblages consisting of variable amounts of actinolite, hornblende, chlorite, albite, epidote, quartz, carbonates, titanite, biotite, rutile, magnetite, ilmenite and sulphides. The different mineral assemblages, which coexist in a single tectonic slice, can be divided into three types, characterized by (A) presence of hornblende and actinolite, (B) presence of actinolite and epidote, and (C) absence of amphibole and epidote. Partial replacements indicate that these mineral assemblages are not in equilibrium. The hornblende of the least altered and deformed samples of the type A assemblage is a relict of a prograde metamorphic event, contemporaneous with the development of the main schistosity. The prograde conditions are estimated at P = 5 kbar, T = 475° C with low P_f . The more altered and deformed samples of the type C assemblage record a later retrograde metamorphic event. Conditions of the later event are estimated at P = 4 kbar, T = 400° C with higher P_f . Widespread calcite precipitation occurred during a later episode. The diversity of the mineral assemblages results from permeability variations along the high-strain zones of the CTZ.     

A history of violence: magma incubation,timing and tephra distribution of the Los Chocoyos supereruption (Atitlán Caldera,Guatemala)

The climactic Los Chocoyos (LCY) eruption from Atitlán caldera (Guatemala) is a key chronostratigraphic marker for the Quaternary period given the extensive distribution of its deposits that reached both the Pacific and Atlantic Oceans. Despite LCY tephra being an important marker horizon, a radioisotopic age for this eruption has remained elusive. Using zircon (U–Th)/He geochronology, we present the first radioisotopically determined eruption age for the LCY of 75 ± 2 ka. Additionally, the youngest zircon crystallization ²³⁸U–²³⁰Th rim ages in their respective samples constrain eruption age maxima for two other tephra units that erupted from Atitlán caldera, W-Fall (130 ⁺¹⁶/₋₁₄ ka) and I-Fall eruptions (56 ^+8.2/_−7.7 ka), which under- and overlie LCY tephra, respectively. Moreover, rim and interior zircon dating and glass chemistry suggest that before eruption silicic magma was stored for >80 kyr, with magma accumulation peaking within ca. 35 kyr before the LCY eruption during which the system may have developed into a vertically zoned magma chamber. Based on an updated distribution of LCY pyroclastic deposits, a new conservatively estimated volume of ~1220 ± 150 km³ is obtained (volcanic explosivity index VEI > 8), which confirms the LCY eruption as the first-ever recognized supereruption in Central America.     

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.     

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。     

不平衡铀系定年的新技术突破——高精度、高灵敏度238U-234U-230Th同位素质谱测定和应用

80年代中期发展起来的高精度、高灵敏度不平衡铀系热电离质谱定年新技术是同位素定年技术的一次革命性突破，并已在古气候、古环境、古海洋、考古学以及近代火山—岩浆作用研究中取得了一系列重要成果，本文介绍了这方面的研究进展。这一新技术已引起越来越广泛的重视，显示出巨大的应用前景。尽快开展不平衡铀系热电离质谱定年技术的应用，对提高我国的高分辩率第四纪年代学分析技术和应用研究水平有重要意义。     

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.