Volcanic sands of Iceland ‐ Diverse origins of aeolian sand deposits revealed at Dyngjusandur and Lambahraun     

D. Baratoux  N. Mangold  O. Arnalds  J.‐M. Bardintzeff  B. Platevoët  M. Grégoire  P. Pinet 《地球表面变化过程与地形》2011,36(13):1789-1808

The origin, formation and evolution of volcanic sands are less well known than the formation of the much more common quartz‐rich sand sheets. Combining active volcanism and a cold climate, Iceland is covered for about 21% of its surface by sandy areas. The sands were analyzed in detail at two sites and results reveal their diverse origins. The first site is Dyngjusandur, located north of Vatnajökull, and the second site is the Lambahraun area, located south of Langjökull. At both sites, the sand origin is determined from field observations (wind directions from ventifacts), chemical and mineralogical analyses of rocks and sands. At Dyngjusandur, the sand is dominated by glass grains, a situation typical of sand plains in Iceland. Hyaloclastite ridges presently buried beneath Vatnajökull are the dominant source of the sand, and only large size plagioclase crystals (0.5 cm) in sands seem to be derived from the lava flows. Hyaloclastite ridges were crushed by glaciers and mechanically eroded sediments were washed out by melt‐water onto flood plains. The sand chemical composition is spatially homogeneous and similar to the average composition of neighboring sub‐aerial lava flows, reflecting efficient mixing of distinct sources below the glacier. The presence of sand north of Dyngjujökull can be taken as a way to explore the average chemical composition of non‐exposed volcanic material beneath the glacier. In the case of Lambahraun, prevailing winds indicate several potential sources of sand at the north of the sand sheet. Comparison of chemical and mineralogical analyses of sands and rock samples helped to refine the exact origin. In contrast with the first site, the sand is dominated by crystals and is chemically consistent with a mixture of material derived from the lava flows of Eldborgir and Skersli shield volcanoes. Analysis of the contact between the lava flows and the glacier reveals that basaltic sand grains formed as the result of recent advances of the glacier abrading the rocks. The direct interaction of glacial and fluvio‐glacial activity with basaltic plains appears to be necessary to produce a large amount of sands in a relatively short period of time (<4000 years). This site appears to be an excellent natural laboratory for further studies concerning the sand evolution and physical sorting processes in basaltic material, which have important implications for understanding aeolian processes on Mars. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

A study of the palaeomagnetism of subglacial basalts, SW Iceland: a comparison with oceanic crust     

J. Helgason  N. A. Van Wagoner  P. J. C. Ryall 《Geophysical Journal International》1990,103(1):13-24

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New Holocene tephras and a proxy climate record from a blanket mire in northern Skye,Scotland     

P. G. Langdon  K. E. Barber 《第四纪科学杂志》2001,16(8):753-759

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Mundane diplomacies for the practice of European geopolitics     

《Geoforum》2015

This paper offers a practice-based account of diplomacy given that diplomats are central to the production and circulation of geopolitics. We contend that there is a changing geography of diplomacy underway from state-centred to “integrative diplomacy”, prompting the need for reorganisation of the modalities that shape and regulate state presence. Such reorganisation brings with it the challenge of fashioning new pathways of diplomatic engagement to counter the disordering of routinized mundane diplomatic practices, alongside new possibilities for diplomatic space to be used by various actors and interests. In sum, the move to integrative diplomacy commands closer academic attention to the contemporary geographies of diplomatic practice, and how these practices are transacted in diverse spatial settings, sites and domains, under conditions of multiple contestation of state authority and legitimacy. Using extensive European empirical materials, we argue that the ways in which diplomats devise, trial, make claims and counter-claims about geopolitical representations are ripe for practice-based analysis. We do this through an exploration of diplomacy’s geographical dimensions, that is, its everyday spaces and places, orderings and transactions and show how practices can go awry in the move to integrative diplomacy.  相似文献   

Holocene displacement field at an emerged oceanic transform-ridge junction: The Husavik-Flatey Fault – Gudfinnugja Fault system,North Iceland     

《Journal of Structural Geology》2015

Our research focuses on Holocene tectonics in a broad area surrounding the junction between the active NW–SE trending Husavik-Flatey transform fault (HFF) and the N–S Gudfinnugja normal fault (GF), an exceptional example of onshore transform-ridge intersection. We mapped 637 minor and major faults, and measured the dip-slip and strike-slip offset components on the major faults. We also mapped 1016 individual tension fractures, as well as opening directions on the most reliable ones. The results indicate that this portion of the HFF comprises major right-stepping segments, with both normal and right-lateral strike-slip components, linked by local normal faults. The entire GF always shows pure dip-slip normal displacements, with a strong decrease in offset at the junction with the HFF. Fissure opening directions are in the range N45°-65°E along the HFF, N90°E along the GF, and N110°E within the area south of the HFF and west of the GF. Fault kinematics and fissure openings suggest a displacement field in good agreement with most of present-day GPS measurements, although our data indicate the possible long-term Holocene effects of the superimposition of magma-related stresses on the regional tectonic stresses. The HFF and the GF work together as a structural system able to accommodate differential crustal block motion, and possibly past dyke intrusions.  相似文献   

基于FY-3A遥感数据的冰岛火山灰云识别   总被引：1，自引：0，他引：1  

赵谊  梁跃  马宝君  李永生  武晓军 《岩石学报》2014,30(12):3693-3700

2010年4月至5月期间冰岛艾雅法拉火山喷发造成了欧洲航空业史无前例的瘫痪以及巨大的经济损失,其严重影响再次显示,对火山灰云进行有效监测的重要性。火山灰云是由火山碎屑物及气体组成的混合物,火山碎屑物主要由直径小于2mm的岩石、矿物、火山玻璃碎片组成,火山灰云中的气体主要包括水汽、CO2、SO2、H2S、CH4、CO、HCL、HF、HBr、和NOx等。使用具有我国自主知识产权的FY-3A/VIRR数据,对此次艾雅法拉火山喷发的不同阶段选取具有典型风向变化的日期,采用分裂窗亮温差算法(SWTD)、RGB真彩色方法、中红外波段数据等进行火山灰云的识别,并将结果与冰岛地区的火山灰监测报告以及前人的研究结果进行对比研究,结果表明:火山喷发初期火山灰云中较高含量的水汽会补偿反面吸收的影响,妨碍分裂窗亮温差算法(SWTD)对火山灰云的识别,而中红外波段数据因对高温物体的敏感性,不受水汽的影响,对喷发初期较高温度的火山灰云识别效果较好;在喷发中期,火山灰云浓度较大时三种方法均表现良好,卫星图像中火山灰云的位置信息及漂移方向均非常清晰,且同气象条件相吻合,验证了识别方法的正确性。该项结果表明,具有我国自主知识产权的FY-3A数据能够达到监测火山灰云的目的,而如何更加清晰地界定火山灰云的边界位置以及更加准确的计算出火山灰云的浓度需要进一步的深入研究。  相似文献   

Application of 50 multi-dimensional discrimination diagrams and significance tests: deciphering compositional similarities and differences between Hawaiian and Icelandic volcanism     

《International Geology Review》2012,54(12):1553-1572

As an innovative approach, I use multi-dimensional diagrams presented by our group during 2004–2013 and respective probability estimates for the newer diagrams to evaluate similarities and differences between the same magma types (subalkaline basalt, basic magma other than subalkaline basalt, and intermediate magma) from the Hawaiian Islands and Iceland. The known ocean island setting of the Hawaiian Islands was reproduced from these 50 multi-dimensional diagrams for basic, intermediate, and acid magmas. The possible influence of the mid-ocean ridge system on Icelandic magmas was also confirmed from the diagrams for basic rocks. Evaluating magma compositional similarities and differences between the Hawaiian Islands and Iceland was complemented by the application of significance tests. Statistical inferences for the chemical elements and, more importantly, their log-ratios, successfully explained the similarities and differences in the tectonic settings for these two regions.  相似文献   

Cryptotephrochronology of the Eemian and the last interglacial–glacial transition in the North East Atlantic     

PETER M. ABBOTT  WILLIAM E. N. AUSTIN  SIWAN M. DAVIES  NICHOLAS J. G. PEARCE  FIONA D. HIBBERT 《第四纪科学杂志》2013,28(5):501-514

The Eemian interglacial and the onset of the subsequent glacial period serve as the most recent analogue for the natural operation of the climate system during the current interglacial. Pronounced climatic oscillations occurred during this period, but their nature and pattern are poorly understood due to dating limitations and unknown phase relationships between different regions and archives. Tephrochronology offers considerable potential for precise correlation of disparate palaeoclimatic archives preserving evidence of these rapid climatic transitions through the tracing of common isochronous tephra horizons. We outline the identification of three previously unknown cryptotephra horizons within a marine core from the Rockall Trough, North East Atlantic. This sequence preserves a high‐resolution record of this interval and shard size, geochemical heterogeneity and the co‐variance of shard concentrations with ice‐rafted debris data are utilized to demonstrate that primary airfall was the most likely transport and depositional pathway. The main geochemical populations of these horizons have similar transitional alkali major and trace element compositions, suggesting that they were derived from a common Icelandic source, potentially the Öræfajökull volcanic system. These tephra horizons represent additions to the North Atlantic event stratigraphy for this period and tentative correlations to Icelandic terrestrial deposits are proposed for two horizons.  相似文献   

Fault systems and paleostresses in the Vestfirdir Peninsula. Relationships with the Tertiary paleo-rifts of Skagi and Snaefells (Northwest Iceland)     

Françoise Bergerat  Jacques Angelier 《Geodinamica Acta》2013,26(2-3):105-118

Abstract

The Vestfirdir Peninsula of northwestern Iceland mainly consists of tholeiitic lava flows, 8–14 Ma old, gently dipping to the southeast. A detailed study of strike-slip and normal faulting allowed identification of two main paleostress regimes. Two sets of normal faults were recognized. The largest set trends ENE-WSW to NNE-SSW; the minor set trends NW-SE to WNW-ESE. Concerning the major extension, the reconstruction of paleostress trajectories shows a gradual change in trend from ESE-WNW, in the northern half of the peninsula, to NNW-SSE to the south. The minor extension also shows a gradual change from NNE-SSW to ENE-WSW trends, from north to south. The nearly constant perpendicularity between the major and minor trends of extension is accounted for by permutation of stress axes within the general pattern of extension related to oceanic rifting. The progressive azimuthal change of the major extension trend, from northeast to southwest across the peninsula, is interpreted as the expression of a change in trend of the extinct Skagi-Snaefells rift, a structure that cannot be reconstructed directly through geological mapping. The average trends of extension in the southern Vestfirdir Peninsula, N150°E, suggest a N60°E trend for the ancient Snaefells rift segment. Likewise, the N100–110°E trends of extension in northern Vestfirdir suggest a N10–20°E trend for the Skagi paleo-rift., © Elsevier, Paris  相似文献   

Subfossil chironomid variability in surface sediment samples from Icelandic lakes: implications for the development and use of training sets     

Naomi Holmes  Peter G. Langdon  Chris J. Caseldine 《Journal of Paleolimnology》2009,42(2):281-295

A suite of surface sediment samples from three Icelandic lakes was analysed for subfossil chironomid head capsules, and a quantitative July air temperature inference model was applied to the data to investigate whether there was significant variability among samples taken from a lake. Ordination and simple regression methods were used to analyse the relationships between environmental and sedimentological variables and the chironomid assemblages and inferred temperature data. Substrate was the most important influence on the chironomid assemblages and inferred temperatures, while water depth at the sampling location had no relationship with the chironomid-inferred temperatures. Within-lake variability of the chironomid assemblages and their inferred temperatures, however, were not significant statistically, suggesting that in lakes of western and northwest Iceland within-lake sampling location has no effect on the data obtained, and therefore on training set samples.  相似文献