Spatially controlled Fe and Si isotope variations: an alternative view on the formation of the Torres del Paine pluton     

Norbert?A.?GajosEmail author  Craig?C.?Lundstrom  Alexander?H.?Taylor 《Contributions to Mineralogy and Petrology》2016,171(11):93

We present new Fe and Si isotope ratio data for the Torres del Paine igneous complex in southern Chile. The multi-composition pluton consists of an approximately 1 km vertical exposure of homogenous granite overlying a contemporaneous 250-m-thick mafic gabbro suite. This first-of-its-kind spatially dependent Fe and Si isotope investigation of a convergent margin-related pluton aims to understand the nature of granite and silicic igneous rock formation. Results collected by MC-ICP-MS show a trend of increasing δ⁵⁶Fe and δ³⁰Si with increasing silica content as well as a systematic increase in δ⁵⁶Fe away from the mafic base of the pluton. The marginal Torres del Paine granites have heavier Fe isotope signatures (δ⁵⁶Fe = +0.25 ± 0.02 2se) compared to granites found in the interior pluton (δ⁵⁶Fe = +0.17 ± 0.02 2se). Cerro Toro country rock values are isotopically light in both Fe and Si isotopic systems (δ⁵⁶Fe = +0.05 ± 0.02 ‰; δ³⁰Si = ?0.38 ± 0.07 ‰). The variations in the Fe and Si isotopic data cannot be accounted for by local assimilation of the wall rocks, in situ fractional crystallization, late-stage fluid exsolution or some combination of these processes. Instead, we conclude that thermal diffusion or source magma variation is the most likely process producing Fe isotope ratio variations in the Torres del Paine pluton.  相似文献   

Moving boulders in flash floods and estimating flow conditions using boulders in ancient deposits          下载免费PDF全文

Jan Alexander  Mark J. Cooker 《Sedimentology》2016,63(6):1582-1595

Boulders moving in flash floods cause considerable damage and casualties. More and bigger boulders move in flash floods than predicted from published theory. The interpretation of flow conditions from the size of large particles within flash flood deposits has, until now, generally assumed that the velocity (or discharge) is unchanging in time (i.e. flow is steady), or changes instantaneously between periods of constant conditions. Standard practice is to apply theories developed for steady flow conditions to flash floods, which are however inherently very unsteady flows. This is likely to lead to overestimates of peak flow velocity (or discharge). Flash floods are characterised by extremely rapid variations in flow that generate significant transient forces in addition to the mean‐flow drag. These transient forces, generated by rapid velocity changes, are generally ignored in published theories, but they are briefly so large that they could initiate the motion of boulders. This paper develops a theory for the initiation of boulder movement due to the additional impulsive force generated by unsteady flow, and discusses the implications.  相似文献   

Attribution of extreme temperature changes during 1951–2010     

Yeon-Hee Kim  Seung-Ki Min  Xuebin Zhang  Francis Zwiers  Lisa V. Alexander  Markus G. Donat  Yu-Shiang Tung 《Climate Dynamics》2016,46(5-6):1769-1782

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On the impact of airborne gravity data to fused gravity field models     

Dimitrios Bolkas  Georgia Fotopoulos  Alexander Braun 《Journal of Geodesy》2016,90(6):561-571

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Chemical composition and varieties of fahlore-group minerals from Oligocene mineralization in the Rhodope area,Southern Bulgaria and Northern Greece     

Alexander Repstock  Panagiotis Voudouris  Manuela Zeug  Vasilios Melfos  Mingguo Zhai  Hongzhong Li  Tamara Kartal  Julia Matuszczak 《Mineralogy and Petrology》2016,110(1):103-123

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Spatial exposure aspects contributing to vulnerability and resilience assessments of urban critical infrastructure in a flood and blackout context     

Fekete  Alexander  Tzavella  Katerina  Baumhauer  Roland 《Natural Hazards》2016,86(1):151-176

Blackouts aggravate the situation during an extreme river-flood event by affecting residents and visitors of an urban area. But also rescue services, fire brigades and basic urban infrastructure such as hospitals have to operate under suboptimal conditions. This paper aims to demonstrate how affected people, critical infrastructure, such as electricity, roads and civil protection infrastructure are intertwined during a flood event, and how this can be analysed in a spatially explicit way. The city of Cologne (Germany) is used as a case study since it is river-flood prone and thousands of people had been affected in the floods in 1993 and 1995. Components of vulnerability and resilience assessments are selected with a focus of analysing exposure to floods, and five steps of analysis are demonstrated using a geographic information system. Data derived by airborne and spaceborne earth observation to capture flood extent and demographic data are combined with place-based information about location and distance of objects. The results illustrate that even fire brigade stations, hospitals and refugee shelters are within the flood scenario area. Methodologically, the paper shows how criticality of infrastructure can be analysed and how static vulnerability assessments can be improved by adding routing calculations. Fire brigades can use this information to improve planning on how to access hospitals and shelters under flooded road conditions.

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Heat and mass transfer effects during displacement of deepwater methane hydrate to the surface of Lake Baikal     

Alexander V. Egorov  Robert I. Nigmatulin  Aleksey N. Rozhkov 《Geo-Marine Letters》2016,36(3):215-222

The present paper focuses on heat and mass exchange processes in methane hydrate fragments during in situ displacement from the gas hydrate stability zone (GHSZ) to the water surface of Lake Baikal. After being extracted from the methane hydrate deposit at the lakebed, hydrate fragments were placed into a container with transparent walls and a bottom grid. There were no changes in the hydrate fragments during ascent within the GHSZ. The water temperature in the container remained the same as that of the ambient water (~3.5 °С). However, as soon as the container crossed the upper border of the GHSZ, first signs of hydrate decomposition and transformation into free methane gas were observed. The gas filled the container and displaced water from it. At 300 m depth, the upper and lower thermometers in the container simultaneously recorded noticeable decreases of temperature. The temperature in the upper part of the container decreased to –0.25 °С at about 200 m depth, after which the temperature remained constant until the water surface was reached. The temperature at the bottom of the container reached –0.25 °С at about 100 m depth, after which it did not vary during further ascent. These observed effects could be explained by the formation of a gas phase in the container and an ice layer on the hydrate surface caused by heat consumption during hydrate decomposition (self-preservation effect). However, steady-state simulations suggest that the forming ice layer is too thin to sustain the hydrate internal pressure required to protect the hydrate from decomposition. Thus, the mechanism of self-preservation remains unclear.  相似文献   

The hydrogeology of the military inundation at the 1914–1918 Yser front (Belgium)     

Alexander Vandenbohede 《Hydrogeology Journal》2016,24(2):521-534

Protection against flooding by the sea, drainage of rainwater and integrated management of groundwater and surface-water resources are key issues in low-lying coastal areas. However, under exceptional circumstances, knowledge to keep coastal areas dry and habitable can be used otherwise. Inundation for military purposes is such an example. The hydrogeology of the inundation at the Yser River, Belgium, during the Great War is studied. The inundation started in October 1914 to stop the German advance and lasted until 1918. A water balance and groundwater model are combined to derive the water balance before and during the inundation and to study the impact on the groundwater system. It is concluded that a number of hydrogeological factors contributed to the effectiveness of the inundation. Most importantly, the low-permeability subsoil facilitated loss of inundation water mainly by evaporation. Further, the normal water management strategy of the area (aimed at evacuating excess water towards the sea) was reversed to keep water between the opposing armies. However, the duration of the inundation meant a reorganization of the drainage of areas not inundated; truly an exercise in integrated water management.  相似文献   

Tectonic Subsidence of California Estuaries Increases Forecasts of Relative Sea-Level Rise     

Alexander Simms  Laura C. Reynolds  Michael Bentz  Angela Roman  Thomas Rockwell  Robert Peters 《Estuaries and Coasts》2016,39(6):1571-1581

Even along the generally uplifting coast of the Pacific US, local geologic structures can cause subsidence. In this study, we quantify Holocene-averaged subsidence rates in four estuaries (Carpinteria Slough, Goleta Slough, Campus Lagoon, and Morro Bay) along the southern and central California coast by comparing radiocarbon-dated estuarine material to a regional sea-level curve. Holocene-averaged rates of vertical motion range from subsidence of 1.4?±?2.4, 1.2±0.4, and 0.4?±?0.3 mm/year in Morro Bay, Carpinteria Slough, and Goleta Slough, respectively, to possible uplift in Campus Lagoon (?0.1?±?0.9 mm/year). The calculated rates of subsidence are of the same magnitude as rates of relative sea-level rise experienced over the late Holocene and effectively double the ongoing rates of relative sea-level rise experienced over the last five decades on other parts of the coast. The difference in rates of vertical motion among these four estuaries is attributed to their geological settings. Estuaries developed in subsiding geological structures such as synclines and fault-bounded basins are subsiding at much higher rates than those developed within flooded river valleys incised into marine terraces. Restoration projects accounting for future sea-level rise must consider the geologic setting of the estuaries and, if applicable, include subsidence in future sea-level rise scenarios, even along the tectonically uplifting US Pacific Coast.  相似文献   

Sediment storage and release from Himalayan piggyback basins and implications for downstream river morphology and evolution          下载免费PDF全文

Alexander L. Densmore  Rajiv Sinha  Swati Sinha  S. K. Tandon  Vikrant Jain 《Basin Research》2016,28(4):446-461

Piggyback basins developed at the mountain fronts of collisional orogens can act as important, and transient, sediment stores along major river systems. It is not clear, however, how the storage and release of sediment in piggyback basins affects the sediment flux and evolution of downstream river reaches. Here, we investigate the timing and volumes of sediment storage and release in the Dehra Dun, a piggyback basin developed along the Himalayan mountain front in northwestern India. Based on OSL dating, we show evidence for three major phases of aggradation in the dun, bracketed at ca. 41–33 ka, 34–21 ka and 23–10 ka, each accompanied by progradation of sediment fans into the dun. Each of these phases was followed by backfilling and (apparently) rapid fan‐head incision, leading to abandonment of the depositional unit and a basinward shift of the active depocentre. Excavation of dun sediment after the second and third phases of aggradation produced time‐averaged sediment discharges that were ca. 1–2% of the modern suspended‐sediment discharges of the Ganga and Yamuna rivers that traverse the margins of the dun; this sediment was derived from catchment areas that together comprise 1.5% of the drainage area of these rivers. Comparison of the timing of dun storage and release with upstream and downstream records of incision and aggradation in the Ganga show that sediment storage in the dun generally coincides with periods of widespread hinterland aggradation but that late stages of dun aggradation, and especially times of dun sediment excavation, coincide with major periods of sediment export to the Ganga Basin. The dun thus acts to amplify temporal variations in hinterland sediment supply or transport capacity. This conceptual model appears to explain morphological features of other major river systems along the Himalayan front, including the Gandak and Kosi Rivers, and may be important for understanding sediment flux variations in other collisional mountain belts.  相似文献