Chemical characteristics of the lherzolitic shergottite Yamato 000097: magmatism on Mars inferred from the chemical compositions of shergottites

As a part of a consortium study, we analyzed the Martian meteorite Yamato (Y) 000097 by prompt gamma-ray analysis, instrumental neutron activation analysis, and instrumental photon activation analysis. For comparison, we also analyzed Allan Hills (ALH) 77005 using the same methods. The data confirm that Y000097 belongs to lherzolitic shergottites in terms of chemical composition. Although there exist slight differences in elemental abundances among lherzolitic shergottites due to differences in the modal abundances of constituent minerals, they have essentially the same chemical compositions, suggesting they are genetically related and experienced similar formation histories.Zr/Hf ratios obtained for Y000097 and ALH 77005 are subchondritic, consistent with values reported for other lherzolitic shergottites and olivine-phyric shergottites. Such fractionation can be explained by invoking clinopyroxene, ilmenite, or majorite in the petrogenesis of the shergottites' source material. CI-normalized Hf/Sm ratios obtained for Y000097 and ALH 77005 are 1.52 and 1.37, respectively, consistent with superchondritic Hf/Sm ratios reported for shergottites. Based on experimentally derived partition coefficients, majorite is the best candidate mineral for the fractionation of Hf and Sm in shergottites.     

Petrology and geochemistry of Yamato 984028: a cumulate lherzolitic shergottite with affinities to Y 000027, Y 000047, and Y 000097

We report the petrography, mineral and whole-rock chemistry (major-, trace-, and highly-siderophile element abundances, and osmium and oxygen isotope compositions) of a newly recognized lherzolitic shergottite, Yamato (Y) 984028. Oxygen isotopes (Δ¹⁷O = 0.218‰) confirm a martian origin for this meteorite. Three texturally distinctive internal zones and a partially devitrified fusion crust occur in the polished section of Y 984028 studied here. The zones include: 1) a poikilitic region with pyroxene enclosing olivine and chromite (Zone A); 2) a non-poikilitic zone with cumulate olivine, interstitial pyroxene, maskelynite and Ti-rich chromite (Zone B) and; 3) a monomict breccia (Zone C). The pyroxene oikocryst in Zone A is chemically zoned from Wo_3–7En_76–71 in the core region to Wo_33–36En_52–49 at the rim, and encloses more Mg-rich olivine (Fo_74–70) in the core, as compared with olivines (Fo_69–68) located at the oikocryst rim. Constraints from Fe–Mg partitioning between crystals and melt indicate that constituent minerals are not in equilibrium with the corresponding bulk-rock composition, implying that Y 984028 represents a cumulate. The whole-rock major- and trace-element compositions, and initial ¹⁸⁷Os/¹⁸⁸Os value (0.1281 ± 0.0002) of Y 984028 are similar to other lherzolitic shergottites and this sample is probably launch-paired with Y 793602, Y 000027, Y 000047, and Y 000097. The Os isotopic composition and highly-siderophile element (HSE) abundances of Y 984028 and other lherzolitic shergottites are consistent with derivation from a martian mantle source that evolved with chondritic Re/Os.     

西北干旱地区大气降水δ18O的特征及水汽来源

In order to reveal the characteristics and climatic controls on the stable isotopic composition of precipitation over Arid Northwestern China, eight stations have been selected from Chinese Network of Isotopes in Precipitation (CHNIP). During the year 2005 and 2006, monthly precipitation samples have been collected and analyzed for the composition of δD and δ18O. The established local meteoric water line δD=7.42 δ18O+1.38, based on the 95 ob-tained monthly composite samples, could be treated as isotopic input function across the region. The deviations of slope and intercept from the Global Meteoric Water Line indicated the specific regional meteorological conditions. The monthly δ18O values were characterized by a positive correlation with surface air temperature (δ18O (‰) =0.33 T (℃)-13.12). The amount effect visualized during summer period (δ18O (‰) = -0.04P (mm)-3.44) though not appeared at a whole yearly-scale. Spatial distributions of δ18O have properly portrayed the atmospheric circulation background in each month over Arid Northwestern China. The quan-titative simulation of δ18O, which involved a Rayleigh fractionation and a kinetic fractionation, demonstrated that the latter one was the dominating function of condensation of raindrops. Furthermore, the raindrop suffered a re-evaporation during falling processes, and the pre-cipitation vapor might have been mixed with a quantity of local recycled water vapor. Multiple linear regression equations and a δ18O-T relation have been gained by using meteorological parameters and δ18O data to evaluate physical controls on the long-term data. The estab-lished δ18O-T relation, which has been based on the present-day precipitation, could be considered as a first step of quantitatively reconstructing the historical environmental climate.     

西方经济地理学对国家边界及其效应的研究进展

边界作为特殊的区位,受到地理学者的广泛重视。本文通过回顾西方学者对国家边界及其边界效用的研究进展,阐述其当前主要议题,并提出对未来边界及边界效应研究的启示。西方经济地理学对国家边界的研究集中体现在边界效应上。主要经历了以下3个发展阶段:传统区位论对边界的研究主要关注边界作为两国分割线所起到的屏蔽作用;随着全球贸易的激增,20世纪80年代到90年代中期,学者们用大量的数学模型对边界效应及其屏蔽程度进行了深入探讨;近年来,随着全球化进程的深入和区域经济一体化的进展,引起了学者们对一体化和边界效应转化的深入争论。全球化进程中边界和边界效应研究的3大主要议题也随着研究发展阶段贯穿,集中在对边界效应强度的分析,边界地区的一体化效应以及边界效应的转化等方面。根据国外研究进展及我国沿边开放的背景,未来可在边界地区集聚效应、边界地区管治和边界地区合作模式几个方面进行深入研究。     

A model for the active origin and development of source-bordering dunefields on a semiarid fluvial plain: A case study from the Xiliaohe Plain, Northeast China

Source-bordering dunefields have been reported in some drylands of the planet, but scarcely in China where there are extensive drylands. This article reports them in China for the first time, and presents a model for their active origin and development on a semiarid fluvial plain by means of satellite image analyses and field investigations. Local- and regional-scale examples are chosen to analyze the spatial patterns of dunefields, as well as the relationships with the fluvial systems in the central part of Naiman Banner where the Jiaolai River runs, and the lower Laoha River, and the middle and lower Ulijimulun River (principal tributaries of the Xiliaohe River). The active origin and development of source-bordering dunefields can be divided into four stages in terms of the spatial patterns of dunefields and channel dynamics: Stage I — individual dunes on the downwind margins of river valleys where running water constantly erodes the steep slopes of valley and where the downwind slopes orient to local dominant winds; Stage II — individual local-scale dunefields formed by deflation of the steep valley slopes and extending antecedent dunes downwind, together with the downstream displacement of meanders; Stage III — individual large-scale dunefield belts along the downwind margins of river valleys formed through frequent lateral migrations of channel; Stage IV — regional-scale dunefields formed mainly by river diversions due to climatic changes or tectonic movements. On the one hand, it is the running water's lateral migration, especially meandering, that prepares suitable places for aeolian systems in terms of both wind flow fields and sand sources, and subsequently it can further cause separate local-scale source-bordering dunefields to link together as a regional-scale dunefield belt given sufficient time. On the other hand, diversions of the river are bound to occur following changing hydrologic regimes resulting from tectonic movements or significant climate change (at regional and millennium scales). As a result, when some dunefield belts as well as the adjacent channels are abandoned, new channels work elsewhere in the same way to actively form new source-bordering dunefields and even dunefield belts at a regional scale.     

Provenance analysis of detrital monazite,zircon and Cr‐spinel in the northern Tibetan Plateau: Implications for the Paleozoic tectonothermal history of the Altyn Tagh and Qimen Tagh Ranges

Sediment provenance studies have proven to be an effective method to extract the sediment provenance and tectonic process information recorded by detrital minerals. In this contribution, we conducted detrital monazite and zircon U‐Pb geochronology and detrital Cr‐spinel major element chemistry analyses on samples from the Qaidam Basin to reconstruct the spatial and temporal evolution of the Altyn Tagh Range and the Qimen Tagh Range in the northern Tibetan Plateau. Based on the significant variation in [Th/U]_N, [Gd/Lu]_N and [Eu/Eu*]_N and the U‐Pb ages of the monazite and zircon, the South Altyn Tagh subduction‐collision belt and the North Qimen Tagh Range were, respectively, the main provenances of the Ganchaigou section and the Dongchaishan‐Weitai section in the Qaidam Basin in the Cenozoic. Paleozoic peak metamorphism, retrograde granulite‐facies metamorphism and amphibolite‐facies metamorphism in the South Altyn Tagh subduction‐collision belt were well recorded by the detrital monazite. In comparison, the detrital zircon is a better indicator of igneous events than detrital monazite. Synthesizing the detrital monazite, zircon and Cr‐spinel data, we concluded that the South Altyn Tagh Ocean and Qimen Tagh Ocean existed in the early Paleozoic and that the Altyn Tagh terrane and Qimen Tagh terrane experienced different Paleozoic tectonothermal histories. The collision between the Qaidam terrane and the Azhong terrane occurred at ca. 500 Ma. The Middle Ordovician was the key period of transformation from the collision‐induced compressional environment to an extensional environment in the area of the South Altyn Tagh Range. In the early Paleozoic, the Qimen Tagh area was characterized by the subduction of oceanic crust.     

Hydrologic control on the oxygen-isotope relation between sediment cellulose and lake water, western Taimyr Peninsula, Russia: Implications for the use of surface-sediment calibrations in paleolimnology

Systematic variability occurs between the oxygen isotopic composition of lake water sampled in mid-summer 1993 and cellulose extracted from surficial sediments of a suite of lakes spanning the forest-tundra transition near Noril'sk, Russia. Some tundra and all forest-tundra lakes show greater deviation from expected cellulose-water isotopic separation than forest lakes, apparently because of greater sensitivity to ¹⁸O-depleted snowmelt contributions. Cellulose derived from aquatic plants naturally integrates fluctuations in lake water ¹⁸O, providing a signal that is inherently more representative of average thaw season lake water ¹⁸O than the measure of instantaneous ¹⁸O obtained from an individual sample of lake water. Thus, indiscriminate use of empirical cellulose-water relations derived from calibration samples could lead to erroneous assessment of paleohydrology from the oxygen-isotope stratigraphy of sediment cores from arctic lakes. However, deviation from the expected cellulose-water fractionation is a source of lake-specific hydrologic information useful for qualifying paleoenvironmental interpretations and possibly constraining non-isotopic methods that rely on surface-sediment calibrations.     

Palaeovariations in the East-Asian Monsoon Regime Geochemically Recorded in Varved Sediments of Lake Sihailongwan (Northeast China, Jilin Province). Part 2: a 200-Year Record of Atmospheric Lead-210 Flux Variations and its Palaeoclimatic Implications

Palaeovariations of the atmospheric ²¹⁰Pb flux in Northeast China (Long Gang area, Jilin province), quantified by high resolution ²¹⁰Pb measurements on seasonally laminated sediments of Lake Sihailongwan are presented on decadal scale. The mean flux of unsupported ²¹⁰Pb between 1790 and 1970 for the centre of the lake basin is 517 Bq m⁻² yr⁻¹ with maximum deviations between −23% and +27% of this value. Flux rates above this average were found between 1783 and 1813, around 1836, and between 1860 and 1901. The mean ²¹⁰Pb^exc flux rates derived were clearly lower around 1821, 1908, 1930, and 1953. The ²¹⁰Pb^exc flux reached its minimum of 344 Bq m⁻² yr⁻¹ during the period 1977–1982. The atmospheric flux of unsupported ²¹⁰Pb is correlated with the precipitation frequency during the summer monsoon and shows coinciding variability with geochemical proxies that document the groundwater inflow into the lake. Al₂O₃-rich dust of remote provenance scavenged by wet-deposition in the rainy season is the major carrier of the atmospheric ²¹⁰Pb^exc flux.     

国家湿地公园旅游环境容量问题与调控——以杭州西溪湿地为例

国家湿地公园的旅游环境容量问题多来源于园区内部属性和游客行为之间的差异,国家湿地公园面积大、生态系统独特,园区空间布局、管理制度、主题商品与设施建设、服务方面的不合理、不完善导致了局部时段性的超载现象,宜采取以游客行为为导向的容量调控模式(TBCC),从加强园区自身建设和管理入手调控游客空间流动,从内部提升视角解决容量超载问题,实现游客体验、环境保护、科普教育等多功能为一体的湿地公园建设目标。     

Socio‐economic and ecological challenges of small‐scale fishing and strategies for its sustainable management: A case study of the Old Brahmaputra River,Bangladesh

Socio‐economic and ecological challenges faced by the small‐scale fishers dependent on the Old Brahmaputra River, Bangladesh are assessed using a combination of questionnaire survey, co‐monitoring of fish catch, focus group discussions and key informant interviews. Results reveal that the fishers are involved in professional, seasonal or subsistence fishing. Fish catches from the river have declined significantly because of overfishing, destructive use of fishing gear, water pollution, siltation, rapid urbanization and human encroachment, thereby threatening the health of the river ecosystem as well as the future of small‐scale fishing. We evaluate various social, economic and ecological challenges faced by the fisher communities. We propose a conceptual framework that recognizes linkages among social, economic and ecological aspects in devising a sustainable river fisheries management system. We recommend effective legal enforcement of policies and regulations, strong institutional collaboration and active fisher community participation in management to ensure sustainable use of the resource base.