Deep crustal source of gneiss dome revealed by eclogite in migmatite (Montagne Noire,French Massif Central)     

Donna L. Whitney  Clémentine Hamelin  Christian Teyssier  Natalie H. Raia  Megan S. Korchinski  Nicholas C. A. Seaton  Brian C. Bagley  Anette von der Handt  Françoise Roger  Patrice F. Rey 《Journal of Metamorphic Geology》2020,38(3):297-327

In orogens worldwide and throughout geologic time, large volumes of deep continental crust have been exhumed in domal structures. Extension-driven ascent of bodies of deep, hot crust is a very efficient mechanism for rapid heat and mass transfer from deep to shallow crustal levels and is therefore an important mechanism in the evolution of continents. The dominant rock type in exhumed domes is quartzofeldspathic gneiss (typically migmatitic) that does not record its former high-pressure (HP) conditions in its equilibrium mineral assemblage; rather, it records the conditions of emplacement and cooling in the mid/shallow crust. Mafic rocks included in gneiss may, however, contain a fragmentary record of a HP history, and are evidence that their host rocks were also deeply sourced. An excellent example of exhumed deep crust that retains a partial HP record is in the Montagne Noire dome, French Massif Central, which contains well-preserved eclogite (garnet+omphacite+rutile+quartz) in migmatite in two locations: one in the dome core and the other at the dome margin. Both eclogites record P ~ 1.5 ± 0.2 GPa at T  ~  700 ± 20°C, but differ from each other in whole-rock and mineral composition, deformation features (shape and crystallographic preferred orientation, CPO), extent of record of prograde metamorphism in garnet and zircon, and degree of preservation of inherited zircon. Rim ages of zircon in both eclogites overlap with the oldest crystallization ages of host gneiss at c. 310 Ma, interpreted based on zircon rare earth element abundance in eclogite zircon as the age of HP metamorphism. Dome-margin eclogite zircon retains a widespread record of protolith age (c. 470–450 Ma, the same as host gneiss protolith age), whereas dome-core eclogite zircon has more scarce preservation of inherited zircon. Possible explanations for differences in the two eclogites relate to differences in the protolith mafic magma composition and history and/or the duration of metamorphic heating and extent of interaction with aqueous fluid, affecting zircon crystallization. Differences in HP deformation fabrics may relate to the position of the eclogite facies rocks relative to zones of transpression and transtension at an early stage of dome development. Regardless of differences, both eclogites experienced HP metamorphism and deformation in the deep crust at c. 310 Ma and were exhumed by lithospheric extension—with their host migmatite—near the end of the Variscan orogeny. The deep crust in this region was rapidly exhumed from ~50 to <10 km, where it equilibrated under low-P/high-T conditions, leaving a sparse but compelling record of the deep origin of most of the crust now exposed in the dome.  相似文献   

Complex networks for climate model evaluation with application to statistical versus dynamical modeling of South American climate     

Jan H. Feldhoff  Stefan Lange  Jan Volkholz  Jonathan F. Donges  Jürgen Kurths  Friedrich-Wilhelm Gerstengarbe 《Climate Dynamics》2015,44(5-6):1567-1581

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Regional climate model sensitivities to parametrizations of convection and non-precipitating subgrid-scale clouds over South America     

Stefan Lange  Burkhardt Rockel  Jan Volkholz  Bodo Bookhagen 《Climate Dynamics》2015,44(9-10):2839-2857

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Fatty acid transfer in the food web of a coastal Mediterranean lagoon: Evidence for high arachidonic acid retention in fish     

Apostolos-Manuel Koussoroplis  Alexandre Bec  Marie-Elodie Perga  Emmanuil Koutrakis  Gilles Bourdier  Christian Desvilettes 《Estuarine, Coastal and Shelf Science》2011,91(3):450-461

The transfer of fatty acids (FAs) in the food web of a Mediterranean lagoon was studied using FA compositional patterns across several trophic levels. The structure of the food web was inferred from C and N stable isotopes values and an isotope mixing model was used in order to estimate the relative contribution of the different potential food sources to the biomass of consumers. Bidimensional plots of FA composition of food web components against their δ¹⁵N values indicated a general trend of increasing proportions of highly unsaturated fatty acids (HUFAs) with increasing trophic levels while the proportions of saturated fatty acids (SAFAs) and 18-carbon polyunsaturated fatty acids (PUFAs) decreased. Using the relative contributions of food sources to consumers and their FA compositions, a model was built in order to estimate the PUFA composition of consumer mixed diets which was compared to consumer PUFA profiles. The latter allowed the identification of the PUFAs which were mostly enriched/retained in consumer lipids. There was a surprisingly high retention of arachidonic acid (ARA), a trend which challenges the idea of low ARA needs in marine fish and suggests the important physiological role of this essential FA for fish in estuarine environments.  相似文献   

Continuous versus event‐based sampling: how many samples are required for deriving general hydrological understanding on Ecuador's páramo region?          下载免费PDF全文

Alicia Correa  David Windhorst  Patricio Crespo  Rolando Célleri  Jan Feyen  Lutz Breuer 《水文研究》2016,30(22):4059-4073

As a consequence of the remote location of the Andean páramo, knowledge on their hydrologic functioning is limited; notwithstanding, these alpine tundra ecosystems act as water towers for a large fraction of the society. Given the harsh environmental conditions in this region, year‐round monitoring is cumbersome, and it would be beneficial if the monitoring needed for the understanding of the rainfall–runoff response could be limited in time. To identify the hydrological response and the effect of temporal monitoring, a nested (n = 7) hydrological monitoring network was set up in the Zhurucay catchment (7.53 km²), south Ecuador. The research questions were as follows: (1) Can event sampling provide similar information in comparison with continuous monitoring, and (2) if so, how many events are needed to achieve a similar degree of information? A subset of 34 rainfall–runoff events was compared with monthly values derived from a continuous monitoring scheme from December 2010 to November 2013. Land cover and physiographic characteristics were correlated with 11 hydrological indices. Results show that despite some distinct differences between event and continuous sampling, both data sets reveal similar information; more in particular, the monitoring of a single event in the rainy season provides the same information as continuous monitoring, while during the dry season, ten events ought to be monitored. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Timing of the younger dryas glacial maximum in western Norway     

Øystein S. Lohne  Jan Mangerud  John Inge Svendsen 《第四纪科学杂志》2012,27(1):81-88

This study precisely constrains the timing of the Younger Dryas (YD) glacial maximum in south‐western Norway by utilizing sediment records from lake basins. Two of the basins, located on the distal side of the mapped Herdla–Halsnøy Moraine, received meltwater directly from the ice sheet only when the ice margin reached its maximum extent during the YD. In the cores, the ice maximum is represented by well‐defined units with meltwater deposits, dominantly laminated silt. Plant macrofossils in the sediment sequences are common and we obtained 18 radiocarbon ages from one of the cores. By applying Bayesian age–depth modelling we obtained a precise date for this meltwater event and thereby also for the timing of the YD glacial maximum. We conclude that the ice‐sheet advance culminated at the Halsnøy Moraine at 11 760 ± 120 cal a BP, and that the ice margin stayed in this position for 170 ± 120 years. The subsequent retreat started at 11 590 ± 100 cal a BP, i.e. close to the YD/Holocene boundary. Withdrawal was probably triggered by abrupt climatic warming at this time. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Flux comparison of Eulerian and Lagrangian estimates of Agulhas leakage: A case study using a numerical model     

Erik van Sebille  Peter Jan van Leeuwen  Arne Biastoch  Wilhelmus P.M. de Ruijter 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(3):319-327

Estimating the magnitude of Agulhas leakage, the volume flux of water from the Indian to the Atlantic Ocean, is difficult because of the presence of other circulation systems in the Agulhas region. Indian Ocean water in the Atlantic Ocean is vigorously mixed and diluted in the Cape Basin. Eulerian integration methods, where the velocity field perpendicular to a section is integrated to yield a flux, have to be calibrated so that only the flux by Agulhas leakage is sampled. Two Eulerian methods for estimating the magnitude of Agulhas leakage are tested within a high-resolution two-way nested model with the goal to devise a mooring-based measurement strategy. At the GoodHope line, a section halfway through the Cape Basin, the integrated velocity perpendicular to that line is compared to the magnitude of Agulhas leakage as determined from the transport carried by numerical Lagrangian floats. In the first method, integration is limited to the flux of water warmer and more saline than specific threshold values. These threshold values are determined by maximizing the correlation with the float-determined time series. By using the threshold values, approximately half of the leakage can directly be measured. The total amount of Agulhas leakage can be estimated using a linear regression, within a 90% confidence band of 12 Sv. In the second method, a subregion of the GoodHope line is sought so that integration over that subregion yields an Eulerian flux as close to the float-determined leakage as possible. It appears that when integration is limited within the model to the upper 300 m of the water column within 900 km of the African coast the time series have the smallest root-mean-square difference. This method yields a root-mean-square error of only 5.2 Sv but the 90% confidence band of the estimate is 20 Sv. It is concluded that the optimum thermohaline threshold method leads to more accurate estimates even though the directly measured transport is a factor of two lower than the actual magnitude of Agulhas leakage in this model.  相似文献   

Preliminary evaluation of the runoff processes in a remote montane cloud forest basin using Mixing Model Analysis and Mean Transit Time     

Patricio Crespo  Amelie Bücker  Jan Feyen  Kellie B. Vaché  Hans‐Georg Frede  Lutz Breuer 《水文研究》2012,26(25):3896-3910

In this study, the Mean Transit Time and Mixing Model Analysis methods are combined to unravel the runoff generation process of the San Francisco River basin (73.5 km²) situated on the Amazonian side of the Cordillera Real in the southernmost Andes of Ecuador. The montane basin is covered with cloud forest, sub‐páramo, pasture and ferns. Nested sampling was applied for the collection of streamwater samples and discharge measurements in the main tributaries and outlet of the basin, and for the collection of soil and rock water samples. Weekly to biweekly water grab samples were taken at all stations in the period April 2007–November 2008. Hydrometric data, Mean Transit Time and Mixing Model Analysis allowed preliminary evaluation of the processes controlling the runoff in the San Francisco River basin. Results suggest that flow during dry conditions mainly consists of lateral flow through the C‐horizon and cracks in the top weathered bedrock layer, and that all subcatchments have an important contribution of this deep water to runoff, no matter whether pristine or deforested. During normal to low precipitation intensities, when antecedent soil moisture conditions favour water infiltration, vertical flow paths to deeper soil horizons with subsequent lateral subsurface flow contribute most to streamflow. Under wet conditions in forested catchments, streamflow is controlled by near surface lateral flow through the organic horizon. Exceptionally, saturation excess overland flow occurs. By absence of the litter layer in pasture, streamflow under wet conditions originates from the A horizon, and overland flow. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The potential of point clouds for the analysis of rock kinematics in large slope instabilities: examples from the Swiss Alps: Brinzauls,Pizzo Cengalo and Spitze Stei     

Kenner  Robert  Gischig  Valentin  Gojcic  Zan  Qu&#;au  Yvain  Kienholz  Christian  Figi  Daniel  Th&#;ny  Reto  Bonanomi  Yves 《Landslides》2022,19(6):1357-1377

Landslides - Lidar measurements and UAV photogrammetry provide high-resolution point clouds well suited for the investigation of slope deformations. Today, however, the information contained in...  相似文献   

Impact of the unpredictable changes in agricultural groundwater use on long-term sustainable exploitation: the case study of Bouhefna-Haffouz aquifer system,central Tunisia     

Jerbi  Hamza  Sebai  Amal  Massuel  Sylvain  Riaux  Jeanne  Leduc  Christian  Tarhouni  Jamila 《Hydrogeology Journal》2023,31(5):1181-1196

Long-term exploitation schemes in many regions are often based solely on hydrodynamic factors, while the agricultural use of groundwater undergoes significant changes over time. The Bouhefna-Haffouz aquifer system in central Tunisia is one of those cases where an aquifer exploitation scheme was well designed hydrodynamically to address the political needs at the time. Fifty years later, a numerical groundwater model has been conducted to assess the sustainability of the scheme. Results show that the scheme aimed to lower the groundwater level to reduce overflow to Merguellil Wadi and maintain it at a level that benefits agricultural profitability. This caused loss of the Merguellil baseflow, forcing farmers to switch from traditional irrigation canals to deep wells and motor pumps, thereby disrupting the hydrological budget even further. The numerical model indicates that the flow to the wadi reached zero in 1978, the average flow by vertical leakage decreased from 8 hm³ in 1970 to 2 hm³ in 2020, and the horizontal percolation between the regional aquifer units increased from 1 hm³ in 1970 to 6 hm³ in 2020. Although the groundwater exploitation scheme was not previously considered a factor in local hydrological changes, the results of this study demonstrate the significant impact of societal behavior following the scheme’s implementation on the hydrological budget of Merguellil Wadi.

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