荒漠植被红砂（Reaumurta soongorica）水热响应的年轮学研究     

肖生春  肖洪浪  宋耀选  段争虎  陆明峰 《中国沙漠》2006,26(4):548-552

 红砂是黄土高原荒漠植被带主要建群植物种之一，在植被恢复重建和生态建设中具有重要意义。本文以皋兰县40 a天然植被封育区为例，运用树木年轮学方法，对不同坡向红砂与当地水热条件变化的时空响应及分布格局进行了研究。研究结果表明，红砂具有明显的年轮特征，可以进行树木年轮方面的研究。虽然不同坡向水分条件和植被状况有很大差异，但红砂径向生长对区域水热变化具有非常一致的响应模式：同生长季降水呈正相关关系，尤以7月降水量最为显著；同生长季气温呈负相关关系，以6月最为显著。根据不同坡向红砂年龄分布格局分析结果，并考虑到水土流失的防治效果，黄土高原西部荒漠植被带的封育期限不宜少于10 a。  相似文献   

The impact of cover rock rheology on the style of folding in the Zagros fold-thrust belt     

M. Sepehr  J. Cosgrove  M. Moieni 《Tectonophysics》2006,427(1-4):265

The present day morphology of the Zagros fold-thrust belt is dominated by magnificent exposures of NW–SE trending folds. These folds differ in their size and geometry and these differences are related mainly to the rheological profile of the cover rock. The cover rock succession of the Zagros consists of a sequence of competent and incompetent units which vary both along and across the belt. Field based study combined with the use of satellite images reveals that the thickness and facies distribution of the cover rock succession has a significant impact on the style of deformation. During the shortening linked to the current convergence of the Arabian and Iranian plates, the incompetent units act as detachment horizons which localise thrusting and which act as décollement above which detachment folds form. In addition, where these incompetent units are thick (e.g.> 1 km), they allow the deformation above and below them to become completely decoupled enabling disharmonic folding to occur. As a result the folds above and below the incompetent units in the central part of the Zagros Folded Belt, have significantly different geometries and wavelengths. As the Zagros folds host the majority of the hydrocarbon reserves in Iran and Iraq, an understanding of the processes that influence their geometry and spatial organization at different levels in the cover rock is crucial for the future exploration in the region.  相似文献   

Early diagenesis of nurtrients （C, N, P and Si） stored in sediments of two reservoirs in southwestern China     

Yuchun WANG Jun ZHU Congqiang LIU 《中国地球化学学报》2006,25(B08):161-162

Damming is a common anthropogenic intervention along the course of rivers, which is defined as ＂artificial-lake effect＂, both in China and across the world. Today as many as 48000 dams and/or reservoirs are in operation in the Changjiang River （Yangtze River） drainage area, and more are being constructed. While damming is well known to affect riverbome nutrient loads, and thus the riverine ecosystems owing to removal of carbon fixation, and removal of particles in reservoir sediments, there is limited information on the detailed early diagenesis of sediments in reservoirs including the regeneration processes of nutrients deposited in sediments and exchange flux across the sediment-water interface, which is important for mass balance of riverbome nutrients. In the present study, two large-size reservoirs, Wujiangdu Reservoir （WJDR） and Dongfeng Reservoir （DFR）, located on the main steam of the Wujiang River and with uniformity hydrography and discrepancy biogeochemical activity （e. g. primary production）, were selected for a comparative study on the detailed processes of nutrient regeneration. Water, pore water and sediment were sampled from these two reservoirs and dissolved organic carbon （DOC）, NH4^＋, NO3^-, PO4^3-, dissolved silica （DSi） in the overlying water and pore water, and total organic matter in sediments were determined. The results of correlation analysis suggested that in these two reservoirs, processes of nutrient regeneration near the sediment-water interface were significantly different. As a result of rapid decomposition of algae-derived ＂labile＂ organic matter in upper sediments, nutrient regeneration processes and upward fluxes in WJDR are dramatically stronger than those of DFR. NH4^＋ upward flux from sediment in WJDR was about 17 times higher than that in DFR. PO4^3- flux in WJDR is about 13 times above that in DFR. DOC flux in WJDR is larger that in DFR by 5 times, and DSi by 1 time.  相似文献   

The bimodal rift-related Juscelândia volcanosedimentary sequence in central Brazil: Mesoproterozoic extension and Neoproterozoic metamorphism     

Renato Moraes  Reinhardt A. Fuck  Mrcio Martins Pimentel  Simone M.C.L. Gioia  Maria H.B.M. de Hollanda  Richard Armstrong 《Journal of South American Earth Sciences》2006,20(4):287-301

The Barro Alto Complex and Juscelândia volcanosedimentary sequence are exposed in the central part of the Neoproterozoic Brasília belt of central Brazil. The former is a large (approximately 150 km long), boomerang-shaped, mafic-ultramafic, layered complex formed by two different intrusions metamorphosed under granulite facies. These rocks are tectonically overlain by rocks of the Juscelândia volcanosedimentary sequence, represented mainly by biotite-gneiss and amphibolite, or amphibolite facies metamorphic equivalents of rhyolite and basalt, respectively. New SIMS U–Pb zircon data and Sm–Nd isochron data presented herein help clarify the igneous and metamorphic evolution of the Juscelândia volcanosedimentary sequence, as well as its relationship with the Barro Alto Complex. Zircon grains from two biotite gneisses were analyzed by SIMS (SHRIMP) and indicate Mesoproterozoic dates, approximately 1.28 Ga, interpreted as the time of bimodal volcanism in a tectonic setting transitional between a continental rift and an ocean basin. Metamorphism is constrained by Sm–Nd garnet-whole-rock isochrons for garnet amphibolite and pelitic schists of the Juscelândia sequence, as well as for clinopyroxene-garnet amphibolite and garnet granulite of the Barro Alto Complex, which give ages between 0.74 and 0.76 Ga, in agreement with SIMS dates for metamorphic zircon rims. These new data are significant, because they establish that a single metamorphic event affected both the Barro Alto Complex and the Juscelândia sequence. Based on these new data, we present a modified tectonic model for the Brasília belt.  相似文献   

Geologic correlation between the Neoproterozoic Sergipano belt (NE Brazil) and the Yaoundé belt (Cameroon, Africa)     

E.P. Oliveira  S.F. Toteu  M.N.C. Araújo  M.J. Carvalho  R.S. Nascimento  J.F. Bueno  N. McNaughton  G. Basilici 《Journal of African Earth Sciences》2006,44(4-5):470

The Yaoundé belt (Cameroon) and the Sergipano belt (NE Brazil) belonged to a major and continuous Neoproterozoic orogen at the northern margin of the ancient Congo-São Francisco craton. The Yaoundé belt comprises schists, quartzites, gneisses and migmatitic gneisses grouped into three domains; the low-grade Mbalmayo Group in south and the medium- to high-grade Yaoundé and Bafia Group in north. The Sergipano belt is divided into six domains, the three southernmost of which are mostly made up of clastic and chemical metasedimentary rocks whereas the others are more diverse with a migmatite–gneiss complex, and two metavolcanicplutonic complexes. In general, the two belts show structural vergence and decrease of metamorphic grade towards the craton; three main deformation phases are recognized in the Sergipano belt in contrast with two described in the Yaoundé belt. The minimum age of Pan-African-Brasiliano collision in the Sergipano belt is constrained at 628 ± 12 Ma on syn-collision granites, whereas in the Yaoundé belt collision took place between 620 and 610 Ma, i.e. the age of granulite facies metamorphism. Sm–Nd isotope geochemistry and U–Pb age dating indicate that most clastic metasedimentary rocks in both belts were derived from sources to the north and, to a lesser degree, from the cratons to the south.  相似文献   

A new tectonic scenario for the Sanandaj–Sirjan Zone (Iran)   总被引：3，自引：0，他引：3  

A. Ghasemi  C.J. Talbot 《Journal of Asian Earth Sciences》2006,26(6):683-693

Recent geochemical studies of volcanic rocks forming part of the ophiolites within the Zagros and Naien-Baft orogen indicate that most of them were developed as supra-subduction ophiolites in intra-oceanic island arc environments. Intra-oceanic island arcs and ophiolites now forming the Naien-Baft zone were emplaced southwestward onto the northeastern margin of the South Sanandaj–Sirjan Zone, while those now in the High Zagros were emplaced southwestward onto the northern margin of Arabia. Thereafter, subduction continued on opposite sides of the remnant oceans. The floor of Neo-Tethys Ocean was subducted at a low angle beneath the entire Sanandaj–Sirjan Zone, and the floor of the Naien-Baft Ocean was subducted beneath the Central Iranian Micro-continent. The Naien-Baft Ocean extended into North-West Iran only temporarily. This failed ocean arm (between the Urumieh-Dokhtar Magmatic Assemblage and the main Zagros Thrust) was filled by thick Upper Triassic–Upper Jurassic sediments. The Naien-Baft Ocean finally closed in the Paleocene and Neo-Tethys closed in the Early to Middle Eocene. After Arabia was sutured to Iran, the Urumieh-Dokhtar Magmatic Assemblage recorded slab break-off in the Middle Eocene.  相似文献   

The Ore-forming Fluid of the Gold Deposits of Muru Gold Belt in Eastern Shandong, China - a Case Study of Denggezhuang Gold Deposit   总被引：1，自引：0，他引：1  

Qingdong Zeng    Jianming Liu    Hongtao Liu    Ping Shen  Lianchang Zhang 《Resource Geology》2006,56(4):375-384

Abstract. Denggezhuang gold deposit is an epithermal gold‐quartz vein deposit in northern Muru gold belt, eastern Shandong, China. The deposit occurs in the NNE‐striking faults within the Mesozoic granite. The deposit consists of four major veins with a general NNE‐strike. Based on crosscutting relationships and mineral parageneses, the veins appear to have been formed during the same mineralization epochs, and are further divided into three stages: (1) massive barren quartz veins; (2) quartz‐sulfides veins; (3) late, pure quartz or calcite veinlets. Most gold mineralization is associated with the second stage. The early stage is characterized by quartz, and small amounts of ore minerals (pyrite), the second stage is characterized by large amounts of ore minerals. Fluid inclusions in vein quartz contain C‐H‐O fluids of variable compositions. Three main types of fluid inclusions are recognized at room temperature: type I, two‐phase, aqueous vapor and an aqueous liquid phase (L+V); type II, aqueous‐carbonic inclusions, a CC₂‐liquid with/without vapor and aqueous liquid (LCO₂+VCC₂+Laq.); type III, mono‐phase aqueous liquid (Laq.). Data from fluid inclusion distribution, microthermometry, and gas analysis indicate that fluids associated with Au mineralized quartz veins (stage 2) have moderate salinity ranging from 1.91 to 16.43 wt% NaCl equivalent (modeled salinity around 8–10 wt% NaCl equiv.). These veins formatted at temperatures from 80d? to 280d?C. Fluids associated with barren quartz veins (stage 3) have a low salinity of about 1.91 to 2.57 wt% NaCl equivalent and lower temperature. There is evidence of fluid immiscibility and boiling in ore‐forming stages. Stable isotope analyses of quartz indicate that the veins were deposited by waters with δ^O and δD values ranging from those of magmatic water to typical meteoric water. The gold metallogenesis of Muru gold belt has no relationship with the granite, and formed during the late stage of the crust thinning of North China.  相似文献   

Methylmercury and human biomarkers： Questioning the evidence     

《中国地球化学学报》2006,25(B08):239-239

Methylmercury （MeHg） is a powerful neurotoxicant in humans. In terms of biomarkers of MeHg exposure, hair and blood have long been used in epidemiological studies as the biomarkers of choice. In fact, total hair mercury （Hg） content as well as organic blood Hg concentrations reflects exposure to organic Hg from food consumption. Extensive studies, establishing a constant and linear relation between MeHg intake versus Hg levels in hair and blood, were conducted by governmental officials to establish guidelines on safe levels of MeHg exposure, which were translated into threshold daily fish consumption rates （usually expressed as μg MeHg per kg bodyweight）. Nowadays, in most epidemiologic studies blood or hair mercury （Hg） level is commonly used as a valid proxy to estimate human exposure to methylmercury （MeHg） through fish consumption without relating this signal to actual fish consumption patterns among populations. Human variability in mercury toxicokinetics was identified and measurement error has been pointed out to be a substantial contributor to observed variability, particularly where dietary information is retrospective and self-reported. However, experimental evidence indicates that significant variability among individuals may exist in the biokinetics of mercury. Also recent findings from previous population-based studies through COMERN initiative also revealed that MeHg metabolic processes might greatly vary across populations. In fact, it is unlikely that the magnitude of the difference measured between observed and expected levels of mercury, given the reported intake, can be entirely explained by laboratory measurement errors or reporting bias.  相似文献   

Towards Formulation of a Space-borne System for Early Warning of Floods: Can Cost-Effectiveness Outweigh Prediction Uncertainty?     

Faisal Hossain 《Natural Hazards》2006,37(3):263-276

The three most important components necessary for functioning of an operational flood warning system are: (1) a rainfall measuring system; (2) a soil moisture updating system; and, (3) a surface discharge measuring system. Although surface based networks for these systems can be largely inadequate in many parts of the world, this inadequacy particularly affects the tropics, which are most vulnerable to flooding hazards. Furthermore, the tropical regions comprise developing countries lacking the financial resources for such surface-based monitoring. The heritage of research conducted on evaluating the potential for measuring discharge from space has now morphed into an agenda for a mission dedicated to space-based surface discharge measurements. This mission juxtaposed with two other upcoming space-based missions: (1) for rainfall measurement (Global Precipitation Measurement, GPM), and (2) soil moisture measurement (Hydrosphere State, HYDROS), bears promise for designing a fully space-borne system for early warning of floods. Such a system, if operational, stands to offer tremendous socio-economic benefit to many flood-prone developing nations of the tropical world. However, there are two competing aspects that need careful assessment to justify the viability of such a system: (1) cost-effectiveness due to surface data scarcity; and (2) flood prediction uncertainty due to uncertainty in the remote sensing measurements. This paper presents the flood hazard mitigation opportunities offered by the assimilation of the three proposed space missions within the context of these two competing aspects. The discussion is cast from the perspective of current understanding of the prediction uncertainties associated with space-based flood prediction. A conceptual framework for a fully space-borne system for early-warning of floods is proposed. The need for retrospective validation of such a system on historical data comprising floods and its associated socio-economic impact is stressed. This proposal for a fully space-borne system, if pursued through wide interdisciplinary effort as recommended herein, promises to enhance the utility of the three space missions more than what their individual agenda can be expected to offer.  相似文献   

Secular variations of the upper crust composition: Implication of geochemical data on the Upper Precambrian shales from the Southern Urals western flank and Uchur-Maya region     

A. V. Maslov  V. N. Podkovyrov  Yu. L. Ronkin  M. T. Krupenin  E. Z. Gareev  V. M. Gorozhanin 《Stratigraphy and Geological Correlation》2006,14(2):126-149

In the mid-1980s, it was concluded based on geochemical study that Th, Sc, La concentrations and ratios Th/Sc, La/Sc and Eu/Eu* did not wary significantly in the post-Archean time. It was impossible to judge about compositional variations of upper crust during the Riphean and Vendian, because data of that time characterized a limited number of samples from the post-Archean basins of Australia, New Zealand, and Antarctic. Considered in this work are variations of Eu/Eu*, LREE/HREE, Th/Sc, and La/Sc ratios in Upper Precambrian fine-grained siliciclastic rock of the Southern Urals western flank (Bashkirian meganticlinorium) and Uchur-Maya region (Uchur-Maya plate and Yudoma-Maya belt). As is established, only the Eu anomaly in the studied siliciclastic rocks is practically identical to this parameter of the average post-Archean shale. Three other parameters plot on the Riphean-Vendian variation curves with positive and negative excursions of diverse magnitude, which do not coincide always in time. It is assumed that these excursions likely mark stages of local geodynamic activity, destruction of pre-Riphean cratons, and progressing recycling of sedimentary material during the Riphean.  相似文献