High-P (P = 1.5–1.8 GPa) blueschist from Elba: Implications for underthrusting and exhumation of continental units in the Northern Apennines     

Samuele Papeschi  Giovanni Musumeci  Hans-Joachim Massonne  Francesco Mazzarini  Eric James Ryan  Giulio Viola 《Journal of Metamorphic Geology》2020,38(5):495-525

The Acquadolce Subunit on the Island of Elba, Italy, records blueschist facies metamorphism related to the Oligocene–early Miocene stages of continental collision in the Northern Apennines. The blueschist facies metamorphism is represented by glaucophane- and lawsonite-bearing metabasite associated with marble and calcschist. These rock types occur as lenses in a schistose complex representing foredeep deposits of early Oligocene age. Detailed petrological analyses on metabasic and metapelitic protoliths, involving mineral and bulk-rock chemistry coupled with P–T and P–T–X(Fe₂O₃) pseudosection modelling using PERPLE_X, show that the Acquadolce Subunit recorded nearly isothermal exhumation from peak pressure–temperature conditions of 1.5–1.8 GPa and 320–370°C. During exhumation, peak lawsonite- and possibly carpholite- or stilpnomelane-bearing assemblages were overprinted and partially obliterated by epidote-blueschist and, subsequently, albite-greenschist facies metamorphic assemblages. This study sheds new light on the tectonic evolution of Adria-derived metamorphic units in the Northern Apennines, by showing (a) the deep underthrusting of continental crust during continental collision and (b) rapid exhumation along ‘cold’ and nearly isothermal paths, compatible with syn-orogenic extrusion.  相似文献   

An analytical approach to ascertain saturation‐excess versus infiltration‐excess overland flow in urban and reference landscapes     

Ryan D. Stewart  Aditi S. Bhaskar  Anthony J. Parolari  Dustin L. Herrmann  Jinshi Jian  Laura A. Schifman  William D. Shuster 《水文研究》2019,33(26):3349-3363

Uncontrolled overland flow drives flooding, erosion, and contaminant transport, with the severity of these outcomes often amplified in urban areas. In pervious media such as urban soils, overland flow is initiated via either infiltration‐excess (where precipitation rate exceeds infiltration capacity) or saturation‐excess (when precipitation volume exceeds soil profile storage) mechanisms. These processes call for different management strategies, making it important for municipalities to discern between them. In this study, we derived a generalized one‐dimensional model that distinguishes between infiltration‐excess overland flow (IEOF) and saturation‐excess overland flow (SEOF) using Green–Ampt infiltration concepts. Next, we applied this model to estimate overland flow generation from pervious areas in 11 U.S. cities. We used rainfall forcing that represented low‐ and high‐intensity events and compared responses among measured urban versus predevelopment reference soil hydraulic properties. The derivation showed that the propensity for IEOF versus SEOF is related to the equivalence between two nondimensional ratios: (a) precipitation rate to depth‐weighted hydraulic conductivity and (b) depth of soil profile restrictive layer to soil capillary potential. Across all cities, reference soil profiles were associated with greater IEOF for the high‐intensity set of storms, and urbanized soil profiles tended towards production of SEOF during the lower intensity set of storms. Urban soils produced more cumulative overland flow as a fraction of cumulative precipitation than did reference soils, particularly under conditions associated with SEOF. These results will assist cities in identifying the type and extent of interventions needed to manage storm water produced from pervious areas.  相似文献   

New isotopic evidence bearing on bonanza (Au-Ag) epithermal ore-forming processes   总被引：1，自引：0，他引：1  

James A. Saunders  Ryan Mathur  George D. Kamenov  Toru Shimizu  Matthew E. Brueseke 《Mineralium Deposita》2016,51(1):1-11

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Response of low‐angle dunes to variable flow          下载免费PDF全文

Megan L. Hendershot  Jeremy G. Venditti  Ryan W. Bradley  Ray A. Kostaschuk  Michael Church  Mead A. Allison 《Sedimentology》2016,63(3):743-760

Current understanding of bedform dynamics is largely based on field and laboratory observations of bedforms in steady flow environments. There are relatively few investigations of bedforms in flows dominated by unsteadiness associated with rapidly changing flows or tides. As a consequence, the ability to predict bedform response to variable flow is rudimentary. Using high‐resolution multibeam bathymetric data, this study explores the dynamics of a dune field developed by tidally modulated, fluvially dominated flow in the Fraser River Estuary, British Columbia, Canada. The dunes were dominantly low lee angle features characteristic of large, deep river channels. Data were collected over a field ca 1·0 km long and 0·5 km wide through a complete diurnal tidal cycle during the rising limb of the hydrograph immediately prior to peak freshet, yielding the most comprehensive characterization of low‐angle dunes ever reported. The data show that bedform height and lee angle slope respond to variable flow by declining as the tide ebbs, then increasing as the tide rises and the flow velocities decrease. Bedform lengths do not appear to respond to the changes in velocity caused by the tides. Changes in the bedform height and lee angle have a counterclockwise hysteresis with mean flow velocity, indicating that changes in the bedform geometry lag changes in the flow. The data reveal that lee angle slope responds directly to suspended sediment concentration, supporting previous speculation that low‐angle dune morphology is maintained by erosion of the dune stoss and crest at high flow, and deposition of that material in the dune trough.  相似文献   

C-IMAGE: city cognitive mapping through geo-tagged photos   总被引：3，自引：0，他引：3  

Liu Liu  Bolei Zhou  Jinhua Zhao  Brent D. Ryan 《GeoJournal》2016,81(6):817-861

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Qualitative GIS: An Open Framework Using SpatiaLite and Open Source GIS          下载免费PDF全文

Ryan Garnett  Pavlos Kanaroglou 《Transactions in GIS》2016,20(1):144-159

Qualitative GIS is a relatively new methodological approach for analyzing and visualizing qualitative data within a geographic context. Qualitative data can take many forms, including interviews, documents, photographs, and audio and video clips. Content analysis for example, is an effective qualitative method for analyzing text‐based data. We argue that basic concepts, (i.e. how to store data, data requirements, visualization techniques, and modes of analysis) within qualitative GIS have not been adequately defined, rendering difficult the replication of work performed and hindering the development of incremental knowledge in the field. Database management systems provide a means for storing, managing, and analyzing qualitative GIS data. A standardized and well‐designed open source database system provides a mechanism for qualitative GIS projects, ensuring consistency and project replication. Qualitative GIS data stored in a database allows for additional visualization options, such as geographic word clouds. To demonstrate the concepts we performed content analysis on Master Transportation Plans from Calgary and Montreal using SpatiaLite, an open source database system. We developed Structured Query Language (SQL) queries to generate and populate groups and theme tables within the SpatiaLite database. We present our database design and queries in the hopes that they will help others conducting qualitative GIS research.  相似文献   

Spatial and temporal constraints on regional-scale groundwater flow in the Pampa del Tamarugal Basin,Atacama Desert,Chile   总被引：1，自引：0，他引：1  

Richard S. Jayne  Ryan M. Pollyea  Justin P. Dodd  Elizabeth J. Olson  Susan K. Swanson 《Hydrogeology Journal》2016,24(8):1921-1937

Aquifers within the Pampa del Tamarugal Basin (Atacama Desert, northern Chile) are the sole source of water for the coastal city of Iquique and the economically important mining industry. Despite this, the regional groundwater system remains poorly understood. Although it is widely accepted that aquifer recharge originates as precipitation in the Altiplano and Andean Cordillera to the east, there remains debate on whether recharge is driven primarily by near-surface groundwater flow in response to periodic flood events or by basal groundwater flux through deep-seated basin fractures. In addressing this debate, the present study quantifies spatial and temporal variability in regional-scale groundwater flow paths at 20.5°S latitude by combining a two-dimensional model of groundwater and heat flow with field observations and δ¹⁸O isotope values in surface water and groundwater. Results suggest that both previously proposed aquifer recharge mechanisms are likely influencing aquifers within the Pampa del Tamarugal Basin; however, each mechanism is operating on different spatial and temporal scales. Storm-driven flood events in the Altiplano readily transmit groundwater to the eastern Pampa del Tamarugal Basin through near-surface groundwater flow on short time scales, e.g., 10⁰–10¹ years, but these effects are likely isolated to aquifers in the eastern third of the basin. In addition, this study illustrates a physical mechanism for groundwater originating in the eastern highlands to recharge aquifers and salars in the western Pampa del Tamarugal Basin over timescales of 10⁴–10⁵ years.  相似文献   

Fish,Macroinvertebrate and Epifaunal Communities in Shallow Coastal Lagoons with Varying Seagrass Cover of the Northern Gulf of Mexico     

Rachel B. McDonald  Ryan M. Moody  Ken L. Heck  Just Cebrian 《Estuaries and Coasts》2016,39(3):718-730

Coastal lagoons are ubiquitous along coastlines worldwide. Here, we compare the abundance of epifauna, seagrass-associated macroinvertebrates, and small fish across a gradient of seagrass cover in shallow coastal lagoons of the northern Gulf of Mexico. Two of the lagoons had little or no seagrass cover (0–18.8 %), and four had high cover (83.8–97.5 %). All of the lagoons were partially covered with fringing marsh. We hypothesized that, due to habitat redundancy between seagrass beds and fringing marshes, seagrass-associated fish and macroinvertebrates would not be largely reduced despite the large differences in seagrass cover among the lagoons. Our results support this hypothesis. For most sampling dates, we did not find significant differences in fish and macroinvertebrate abundance among the lagoons and, when we did, several highly vegetated lagoons did not have larger abundances than sparsely vegetated lagoons. The extreme shallowness of the lagoons studied (<1 m) may also provide further protection from large predatory fishes in the absence of seagrasses. Our results also suggest that marsh detritus, by providing habitat for epifauna and helping maintain prey availability, may further temper reductions in seagrass-associated fishes and macroinvertebrates following seagrass decline. The results highlight the importance of marsh-bordered, shallow lagoons as habitat for small fish and macroinvertebrates regardless of seagrass cover. This study contributes to the characterization of habitat redundancy in coastal ecosystems and pinpoints the importance of considering all habitats in concert for the proper understanding and management of coastal ecosystems.  相似文献   

江西德兴铜矿区水系的Cu同位素地球化学特征及其地质意义     

陈丹丹  宋世明  Mathur Ryan  郭坤一  康文凯  李双喜  赵晓丹  张飞 《地质通报》2016,35(1):188-195

江西德兴铜矿水系样的δ65Cu值具有极大的变化范围(-5.8‰~+24.4‰),是迄今为止已报道发现的最大的Cu同位素分馏值。水体中铜的来源可分为黄铜矿源和黄铁矿源,二者具有明显不同的Cu同位素特征。根据水体的Cu同位素值分布特征,圈出了流经矿体(矿体上方)水、矿体外围水和尾矿库水3个源区。水体中的Cu主要以离子态和微粒态存在,二者具有明显不同的65Cu特征,尾矿库中黄铁矿65Cu对水体的Cu同位素组成具有较大的影响作用。Cu同位素在示踪找矿及地质环境监测方面具有良好的应用潜力。  相似文献   

A New Generation Earth Mantle Model from Global Adjoint Tomography     

Youyi Ruan  Wenjie Lei  Matthieu Lefebvre  Ryan Modrak  James Smith  Ridvan Orsvuran  Ebru Bozdag  Judith Hill  Norbert Podhorszki  Dave Pugmire  Jeroen Tromp 《《地质学报》英文版》2018,92(Z1):140-140

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