Application of Distributed Temperature Sensing for coupled mapping of sedimentation processes and spatio‐temporal variability of groundwater discharge in soft‐bedded streams          下载免费PDF全文

Eva Sebok  Carlos Duque  Peter Engesgaard  Eva Boegh 《水文研究》2015,29(15):3408-3422

The delineation of groundwater discharge areas based on Distributed Temperature Sensing (DTS) data of the streambed can be difficult in soft‐bedded streams where sedimentation and scouring processes constantly change the position of the fibre optic cable relative to the streambed. Deposition‐induced temperature anomalies resemble the signal of groundwater discharge while scouring will cause the cable to float in the water column and measure stream water temperatures. DTS applied in a looped layout with nine fibre optic cable rows in a 70 × 5 m section of a soft‐bedded stream made it possible to detect variability in streambed temperatures between October 2011 and January 2012. Detailed monthly streambed elevation surveys were carried out to monitor the position of the fibre optic cable relative to the streambed and to quantify the effect of sedimentation processes on streambed temperatures. Based on the simultaneous interpretation of streambed temperature and elevation data, a method is proposed to delineate potential high‐groundwater discharge areas and identify deposition‐induced temperature anomalies in soft‐bedded streams. Potential high‐discharge sites were detected using as metrics the daily minimum, maximum and mean streambed temperatures as well as the daily amplitude and standard deviation of temperatures. The identified potential high‐discharge areas were mostly located near the channel banks, also showing temporal variability because of the scouring and redistribution of streambed sediments, leading to the relocation of pool‐riffle sequences. This study also shows that sediment deposits of 0.1 m thickness already resulted in an increase in daily minimum streambed temperatures and decrease in daily amplitude and standard deviation. Scouring sites showed lower daily minimum streambed temperatures and higher daily amplitude and standard deviation compared with areas without sedimentation and scouring. As a limitation of the approach, groundwater discharge occurring at depositional and scouring areas cannot be identified by the metrics applied. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Editorial changes – Advances in Water Resources     

《Advances in water resources》2015

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From land grabs to inclusive development?     

《Geoforum》2017

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Lead and Mg isotopic age constraints on the evolution of the HED parent body          下载免费PDF全文

Martin Schiller  James N. Connelly  Martin Bizzarro 《Meteoritics & planetary science》2017,52(6):1233-1243

The large collection of howardite‐eucrite‐diogenite (HED) meteorites allows us to study the initial magmatic differentiation of a planetesimal. We report Pb‐Pb ages of the unequilibrated North West Africa (NWA) 4215 and Dhofar 700 diogenite meteorites and their mass‐independent ²⁶Mg isotope compositions (²⁶Mg*) to better understand the timing of differentiation and crystallization of their source reservoir(s). NWA 4215 defines a Pb‐Pb age of 4484.5 ± 7.9 Myr and has a ²⁶Mg* excess of +2.3 ± 1.6 ppm whereas Dhofar 700 has a Pb‐Pb age of 4546.4 ± 4.7 Myr and a ²⁶Mg* excess of +25.5 ± 1.9 ppm. We interpret the young age of NWA 4215 as a thermal overprint, but the age of Dhofar 700 is interpreted to represent a primary crystallization age. Combining our new data with published Mg isotope and trace element data suggests that approximately half of the diogenites for which such data are available crystallized within the first 1–2 Myr of our solar system, consistent with a short‐lived, early‐formed magma ocean undergoing convective cooling. The other half of the diogenites, including both NWA 4215 and Dhofar 700, are best explained by their crystallization in slowly cooled isolated magma chambers lasting over at least ~20 Myr.  相似文献   

Search for variables in six Galactic open clusters     

《New Astronomy》2017

Variables in open cluster (known distance, age, and metallicity) fields play an important role in stellar astrophysics because they allow to investigate the interior of stars. Therefore, six Galactic open clusters were selected to search for new variables and to complement data for already known variables. As five of these clusters are younger than 40 Myr, we aim at finding variable high-mass stars such as β Cephei and Slowly Pulsating B-type stars as well as classical pulsating stars within the instability strip. About 26 000 images (312 h) photometric images were taken at the 0.8 m (Vienna, Austria) and 1.0 m (Hvar, Croatia) telescope using V and I filters. The differential light curves were analyzed with standard time series analysis methods. In total, 11 variables were found in all investigated clusters. For nine of them, we were able to determine their nature and period. In addition, the membership probabilities from the literature were analyzed.  相似文献   

Preface – The CRONUS-EARTH Volume     

《Quaternary Geochronology》2015

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Barringer,Back to the Future: Airborne Geochemistry and Many Related Topics,Peter Bradshaw,Association of Applied Geochemists,Nepean, ON,Canada (2015), 159 pp. Hard Cover book,including shipping US$ 68.00. Soft Cover book,including shipping US$ 58.00. ISBN: 978-0-09691014-5-1. Available from: www.appliedgeochemists.org     

《Ore Geology Reviews》2016

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Photograph of the month     

《Journal of Structural Geology》2016

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Timing and metal sources for carbonate-hosted Zn-Pb mineralization in the Franklinian Basin (North Greenland): Constraints from Rb-Sr and Pb isotopes     

《Ore Geology Reviews》2016

Carbonate-hosted Zn-Pb (± barite, fluorite) occurrences in the Franklinian Basin of North Greenland were studied using the Rb-Sr method, applied to sphalerite, and combined Sr and Pb isotope analysis of ore and gangue minerals, to place constraints on their age and genesis. The occurrences are located in the easternmost part of the basin in Peary Land and Kronprins Christian Land, and are hosted by Upper Ordovician to lowermost Silurian dolostones of the Turesø Formation.Sphalerite samples from the Zn-Pb occurrence at Børglum, in Peary Land, reflect undisturbed Rb-Sr systems and return an isochron age of 388 ± 4 Ma (MSWD = 1.6, ⁸⁷Sr/⁸⁶Sr_i = 0.70930 ± 1). Sphalerites and their fluid inclusion fractions from an adjacent Zn-Pb occurrence, at Tvilum, exhibit various degrees of isotopic disturbance caused by secondary fluid overprint. They yield no age, however, reconstructive modelling of their Rb-Sr and Pb-Pb signatures indicates original isotope systematics consistent with the Børglum data. Likewise, due to a lack of suitable samples, no Rb-Sr age could be determined for a third occurrence in southeastern Peary Land at Løgum, however, the time-integrated Pb isotopic evolution of fluorite and calcite from this mineralization over c. 390 Ma is compatible with modelled initial signatures for Tvilum and Børglum ores. Consequently, a contemporaneous formation at c. 390 Ma can be assumed for all studied locations in Peary Land. For the Zn-Pb occurrence in Kronprins Christian Land farther east, a Rb-Sr sphalerite age of c. 360–365 Ma has been obtained through a combined isochron and paleomixing line approach.The absolute ages obtained at the studied occurrences, corresponding to Middle to Upper Devonian ages, are in no conflict with the age of the host dolostones of the Turesø Formation, which placed a maximum age limit for the mineralization. Actually, the fact that mineralization was emplaced at least 50 Ma after deposition of the host rocks, which would have been completely lithified by then, warrants the classification of the studied occurrences as epigenetic Mississippi Valley-Type, rather than diagenetic Irish-type. Furthermore, the obtained ages are contemporaneous to the Middle or Upper Devonian to the Lower Carboniferous Ellesmerian Orogeny, indicating that the mineralization likely formed from basinal brines expelled by tectonism and/or hydraulic head caused by Ellesmerian orogenic uplift, as previously suggested for the Polaris carbonate-hosted Zn-Pb deposit (Cornwallis Island, Canada).Pb isotope systematics of base metal mineralization in the Franklinian Basin point to principal metal sources located in the crystalline basement and in basement-derived clastic sediments. These two reservoirs define radiogenic and unradiogenic end components from which lead was mobilized and mixed in different proportions during discrete periods of hydrothermal activity. Distinct thorogenic Pb isotope signatures indicate that specific local sources (lower crustal basement, carbonate rocks and possibly organic-rich shales) were also involved in mineralization.  相似文献   

Metallogeny of Greenland     

《Ore Geology Reviews》2016

Greenland is the largest island on Earth, with 80% of its area covered by a thick ice sheet. The coastal areas are underlain by variable rocks ranging from Eoarchean to the most recent ages. Greenland has a mineral exploration tradition since its colonization in the 18th century, and mining of cryolite started in 1854. Since the 1960s, the country is explored systematically for various commodities, which however resulted only in limited mining activity in only a few successful mines. Most exploration has been based on prospecting followed by exploration around the exposed mineralization.The geology from North-West Greenland along the coast to the south and along the eastern coast north to Kangerlussuaq Fjord is dominated by deeply eroded Archean and Paleoproterozoic rocks. The metallogeny is largely controlled by mid crustal processes and the preservation potential of mineralization in the deeper crust. Significant mineralization is found in orthomagmatic Ni-PGE-Au sulfide and Cr- or Fe-Ti-V oxide systems and hypozonal orogenic gold systems in major shear zones. Interestingly, the ultramafic units of the orthomagmatic systems locally host gemstone-quality corundum mineralization. Graphite mineralization occurs in amphibolite-granulite facies metasedimentary units and in shear zones in Paleoproterozoic orogens. Mesozonal orogenic gold and iron ore in banded iron formation are restricted to localized lower metamorphic grade areas along the west coast. Larger units of preserved Paleoproterozoic metasedimentary and metavolcanic rocks are restricted to South, central East and central West Greenland, where base metal mineralization formed the significant Zn-Pb Black Angel deposit.Widespread sedimentation and localized mafic magmatism started in the late Paleoproterozoic in various continental to shallow marine basins and lasted with interruptions until the start of the Caledonian Orogeny. These late Paleoproterozoic to early Paleozoic sedimentary rocks are variably deformed and metamorphosed by subsequent orogeny and mainly preserved in northern and eastern Greenland. They host stratiform sedimentary base metal mineralization of only limited known extent, except the sedimentary exhalative Zn-Pb Citronen deposit in central North Greenland. The Caledonian and subsequently the Ellesmerian orogens affected the eastern and northern Laurentian margin, respectively. Mineral systems of only limited known extent related to this orogeny are Mississippi Valley Type Zn-Pb in the Ellesmerian foreland, mesozonal orogenic gold in Caledonian shear zones and magmatic-hydrothermal W-Sb ± Au ± Cu systems in and adjacent to Caledonian granites. Renewed and almost continuous sedimentation occurred from the Devonian until Paleogene in eastern Greenlandic basins. The sedimentary units host stratiform sedimentary base metal mineralization of only small known magnitude. The Paleogene in eastern and central West Greenland is characterized by widespread mafic-ultramafic magmatism, forming flood basalt and a series of intrusions in East Greenland. Nickel-sulfide mineralization is locally hosted by the mafic-ultramafic rocks in central West Greenland, whereas eastern Greenlandic mafic and felsic intrusions host significant orthomagmatic PGE-Au mineralization in Skaergaard, and magmatic hydrothermal Mo-Au-Ag mineralization in Malmbjerg and Flammefjeld.Western and southern Greenland was a relative stable shield from Paleoproterozoic times and is intruded by localized Meso- and Neoproterozoic alkaline and carbonatite suites, which form part of a larger Mesoproterozoic rift only in South Greenland. These intrusions host locally significant REE-Nb-Ta-U-Zn-Be in Kvanefjeld, Kringlerne and Motzfeldt deposits of South Greenland and the southern West Greenlandic Sarfartoq deposit. Diamond mineralization is spatially associated with the alkaline and carbonatite intrusions in southern West Greenland.The long and complex geological evolution recorded in Greenland appears to be in contrast with only few examples of successful mineral exploration and mining. Numerous mineral deposits are developed in neighboring Arctic countries, making the remote Arctic setting an unlikely single argument for the situation. Geological knowledge is still relatively basic for many parts of Greenland and modern geophysical and geochemical data is often only available at a regional scale, which makes knowledge- and mineral system-driven exploration difficult and costly. The review of the Greenlandic metallogeny in this paper, however, clearly shows the enormous potential for finding ores in a wide variety of settings.  相似文献