The recognition of former melt flux through high‐strain zones          下载免费PDF全文

Catherine A. Stuart  Sandra Piazolo  Nathan R. Daczko 《Journal of Metamorphic Geology》2018,36(8):1049-1069

High‐strain zones are potential pathways of melt migration through the crust. However, the identification of melt‐present high‐strain deformation is commonly limited to cases where the interpreted volume of melt “frozen” within the high‐strain zone is high (>10%). In this contribution, we examine high‐strain zones in the Pembroke Granulite, an otherwise low‐strain outcrop of volcanic arc lower crust exposed in Fiordland, New Zealand. These high‐strain zones display compositional layering, flaser‐shaped mineral grains, and closely spaced foliation planes indicative of high‐strain deformation. Asymmetric leucosome surrounding peritectic garnet grains suggest deformation was synchronous with minor amounts of in situ partial melting. High‐strain zones lack typical mylonite microstructures and instead display typical equilibrium microstructures, such as straight grain boundaries, 120° triple junctions, and subhedral grain shapes. We identify five key microstructures indicative of the former presence of melt within the high‐strain zones: (a) small dihedral angles of interstitial phases; (b) elongate interstitial grains; (c) small aggregates of quartz grains with xenomorphic plagioclase grains connected in three dimensions; (d) fine‐grained, K‐feldspar bearing, multiphase aggregates with or without augite rims; and (e) mm‐ to cm‐scale felsic dykelets. Preservation of key microstructures indicates that deformation ceased as conditions crossed the solidus, breaking the positive feedback loop between deformation and the presence of melt. We propose that microstructures indicative of the former presence of melt, such as the five identified above, may be used as a tool for recognising rocks formed during melt‐present high‐strain deformation where low (<5%) volumes of leucosome are “frozen” within the high‐strain zone.  相似文献   

Titanite dates crystallization: Slow Pb diffusion during super‐solidus re‐equilibration     

Michael I. H. Hartnady  Christopher L. Kirkland  Chris Clark  Catherine V. Spaggiari  R. Hugh Smithies  Noreen J. Evans  Brad J. McDonald 《Journal of Metamorphic Geology》2019,37(6):823-838

Titanite can be found in rocks of wide compositional range, is reactive, growing or regrowing during metamorphic and hydrothermal events, and is generally amenable to U–Pb geochronology. Experimental evidence suggest that titanite has a closure temperature for Pb ranging from 550 to 650°C, and thus titanite dates are commonly interpreted as cooling ages. However, this view has been challenged in recent years by evidence from natural titanite which suggests the closure temperature may be significantly higher (up to 800°C). Here, we investigate titanite in an enclave of migmatitic gneiss included within a granite intrusion. The titanite crystals exhibit textural features characteristic of fluid‐mediated mass transfer processes on length scales of <100 µm. These textural features are associated with variation in both Pb concentrations and distinct U–Pb isotopic compositions. Zr‐in‐titanite thermometry indicates that modification of the titanite occurred at temperatures in excess of 840°C, in the presence of a high‐T silicate melt. The Pb concentration gradients preserved in these titanite crystals are used to determine the diffusivity of Pb in titanite under high‐T conditions. We estimate diffusivities ranging from 2 × 10^?22 to 5 × 10^?25 m²/s. These results are significantly lower than experimental data predict yet are consistent with other empirical data on natural titanites, suggesting that Pb diffusivity is similar to that of Sr. Thus our data challenge the wide‐held assumption that U–Pb titanite dates only reflect cooling ages.  相似文献   

Applying VGI to collaborative research in the humanities: the case of ARTL@S     

Catherine Dossin  Nicole Ningning Kong 《制图学和地理信息科学》2017,44(6):521-538

ABSTRACT

Using Artl@s as an example of a project that relies on volunteered geographic information (VGI), this article examines the specific challenges that exist, beyond those frequently discussed in general VGI systems (e.g., participants’ motivation and data quality control) in regard to sharing research data in humanities: (1) most data from the humanities is qualitative and collected from multiple data sources which are often inconsistent and unmappable; (2) data is usually interconnected with multiple relationships among different tables which creates challenges for both mapping and query functionality; (3) data is both geographical and historical. Consequently addresses that no longer exist have to be geolocated and visualized on historical basemaps and spaces must be represented diachronically; (4) the design of web map application needs to balance both sophisticated research requirements and a user-friendly interface; (5) finally contributors expect their data to be cited or acknowledged when used in other studies and users need metadata and citation information in order to reuse and repurpose datasets.

In this article, we discuss how Artl@s, a project which developed a georeferenced historical database of exhibition catalogues, addresses these challenges. Artl@s provides a case study for VGI adoption by digital humanities scholars for research data sharing, as it offers features, such as flexible batch data contribution, interrelated spatial query, automatic geolocalization of historical addresses, and data citation mechanisms.  相似文献   

The Dominican Republic–Central American Free Trade Agreement’s Symbolic Nod to Environmental Protection: Legal Perspectives on the Citizen Submission Process     

J. Christopher Upton  Catherine M. Tucker  Seleste Sanchez 《社会与自然资源》2017,30(10):1277-1287

The Dominican Republic–Central America Free Trade Agreement (CAFTA) contains a chapter on the environment, ostensibly included to mitigate the North American Free Trade Agreement (NAFTA) environmental oversights. The environment chapter created a citizen submission process designed to foster public participation in supporting each participating nation’s environmental laws. This article examines the outcomes to date of the citizen submission process, based on an analysis of the articles of the agreement and an examination of the rulings made on each case submitted under the citizen submission process. The analysis shows that CAFTA poses significant obstacles to citizen participation and has made minimal, if any, contributions to environmental law enforcement among the Parties to the agreement.  相似文献   

Crossing Boundaries in a Collaborative Modeling Workspace     

Jeffrey T. Morisette  Amanda E. Cravens  Brian W. Miller  Marian Talbert  Colin Talbert  Catherine Jarnevich 《社会与自然资源》2017,30(9):1158-1167

There is substantial literature on the importance of bridging across disciplinary and science–management boundaries. One of the ways commonly suggested to cross boundaries is for participants from both sides of the boundary to jointly produce information (i.e., knowledge co-production). But simply providing tools or bringing people together in the same room is not sufficient. Here we present a case study documenting the mechanisms by which managers and scientists collaborated to incorporate climate change projections into Colorado’s State Wildlife Action Plan. A critical component of the project was the use of a collaborative modeling and visualization workspace: the U.S. Geological Survey’s Resource for Advanced Modeling (RAM). Using video analysis and pre/post surveys from this case study, we examine how the RAM facilitated cognitive and social processes that co-produced a more salient and credible end product. This case provides practical suggestions to scientists and practitioners who want to implement actionable science.  相似文献   

Verification of short-term runoff forecasts for a small Philippine basin (Marikina)     

David Kneis  Catherine Abon  Axel Bronstert  Maik Heistermann 《水文科学杂志》2017,62(2):205-216

Storm runoff from the Marikina River Basin frequently causes flood events in the Philippine capital region Metro Manila. This paper presents and evaluates a system to predict short-term runoff from the upper part of that basin (380 km²). It was designed as a possible component of an operational warning system yet to be installed. For the purpose of forecast verification, hindcasts of streamflow were generated for a period of 15 months with a time-continuous, conceptual hydrological model. The latter was fed with real-time observations of rainfall. Both ground observations and weather radar data were tested as rainfall forcings. The radar-based precipitation estimates clearly outperformed the raingauge-based estimates in the hydrological verification. Nevertheless, the quality of the deterministic short-term runoff forecasts was found to be limited. For the radar-based predictions, the reduction of variance for lead times of 1, 2 and 3 hours was 0.61, 0.62 and 0.54, respectively, with reference to a “no-forecast” scenario, i.e. persistence. The probability of detection for major increases in streamflow was typically less than 0.5. Given the significance of flood events in the Marikina Basin, more effort needs to be put into the reduction of forecast errors and the quantification of remaining uncertainties.  相似文献   

A method for uncertainty constraint of catchment discharge and phosphorus load estimates          下载免费PDF全文

Michael J. Hollaway  Keith J. Beven  Clare Mc W. H. Benskin  Adrian L. Collins  Robert Evans  Peter D. Falloon  Kirsty J. Forber  Kevin M. Hiscock  Ron Kahana  Christopher J. A. Macleod  Mary C. Ockenden  Martha L. Villamizar  Catherine Wearing  Paul J. A. Withers  Jian G. Zhou  Nicholas J. Barber  Philip M. Haygarth 《水文研究》2018,32(17):2779-2787

River discharge and nutrient measurements are subject to aleatory and epistemic uncertainties. In this study, we present a novel method for estimating these uncertainties in colocated discharge and phosphorus (P) measurements. The “voting point”‐based method constrains the derived stage‐discharge rating curve both on the fit to available gaugings and to the catchment water balance. This helps reduce the uncertainty beyond the range of available gaugings and during out of bank situations. In the example presented here, for the top 5% of flows, uncertainties are shown to be 139% using a traditional power law fit, compared with 40% when using our updated “voting point” method. Furthermore, the method is extended to in situ and lab analysed nutrient concentration data pairings, with lower uncertainties (81%) shown for high concentrations (top 5%) than when a traditional regression is applied (102%). Overall, for both discharge and nutrient data, the method presented goes some way to accounting for epistemic uncertainties associated with nonstationary physical characteristics of the monitoring site.  相似文献   

History of scoria-cone eruptions on the eastern shoulder of the Kenya–Tanzania Rift revealed in the 250-ka sediment record of Lake Chala near Mount Kilimanjaro     

Catherine Martin-Jones  Christine Lane  Maarten Van Daele  Thijs Van Der Meeren  Christian Wolff  Heather Moorhouse  Emma Tomlinson  Dirk Verschuren 《第四纪科学杂志》2020,35(1-2):245-255

Reconstructions of the timing and frequency of past eruptions are important to assess the propensity for future volcanic activity, yet in volcanic areas such as the East African Rift only piecemeal eruption histories exist. Understanding the volcanic history of scoria-cone fields, where eruptions are often infrequent and deposits strongly weathered, is particularly challenging. Here we reconstruct a history of volcanism from scoria cones situated along the eastern shoulders of the Kenya–Tanzania Rift, using a sequence of tephra (volcanic ash) layers preserved in the ~250-ka sediment record of Lake Chala near Mount Kilimanjaro. Seven visible and two non-visible (crypto-) tephra layers in the Lake Chala sequence are attributed to activity from the Mt Kilimanjaro (northern Tanzania) and the Chyulu Hills (southern Kenya) volcanic fields, on the basis of their glass chemistry, textural characteristics and known eruption chronology. The Lake Chala record of eruptions from scoria cones in the Chyulu Hills volcanic field confirms geological and historical evidence of its recent activity, and provides first-order age estimates for seven previously unknown eruptions. Long and well-resolved sedimentary records such as that of Lake Chala have significant potential for resolving regional eruption chronologies spanning hundreds of thousands of years.  相似文献   

Effect of Decadal Changes in Freshwater Flows and Temperature on the Larvae of two Forage Fish Species in Coastal Nurseries of the St. Lawrence Estuary     

Catherine M. Couillard  P. Ouellet  G. Verreault  S. Senneville  S. St-Onge-Drouin  D. Lefaivre 《Estuaries and Coasts》2017,40(1):268-285

Since 2002, the abundance of larvae of rainbow smelt (Osmerus mordax) and Atlantic herring (Clupea harengus) has been monitored in July in coastal nurseries (Anse Ste.-Anne (ASA) and Banc de Rivière-du-Loup (BRL)) in the Middle St. Lawrence Estuary (MSLE), Canada. The two species are spatiotemporally segregated, with smelt larvae being more abundant at the upstream, less saline site (ASA) and having an earlier hatching date. Despite these differences, the abundances of both species from 2002 to 2013 were strongly and positively related to the early spring flow of tributaries at the time of larval smelt emergence and weakly and negatively related to sea-surface temperatures in the nurseries. Larval herring abundance was weakly associated with the upstream bottom residual transport flow of the MSLE’s estuarine circulation in June, at the time of their emergence. Larval herring lengths in BRL were positively related to the sum of degree days (SDD) from hatching to sampling, with the greatest length but lowest condition in 2012. The relationship between body lengths of ASA smelt larvae and SDD was dome-shaped, suggesting lower growth than expected in the warmest years, 2006 and 2012. The highest larval abundances were observed in 2008 and 2011, both years with late tributary freshets, high tributary flows in the early spring and moderately warm summer temperatures. In contrast, low abundances occurred in 2006 and 2012, which were years with low spring tributary flows and high summer temperatures. These results suggest that the dynamics of local tributary freshets is a key driver of larval recruitment success for two key forage species in coastal nurseries until summer and support the use of fish larvae as indicators of environmental changes in the MSLE.  相似文献   

Connections Between Cold Air Pools and Mountain Valley Fog Events in Salt Lake City     

Catherine N. Chachere  Zhaoxia Pu 《Pure and Applied Geophysics》2016,173(9):3187-3196

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