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151.
Nondestructive spectroscopic and petrochemical investigations of Paleoarchean spherule layers from the ICDP drill core BARB5, Barberton Mountain Land,South Africa
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Jörg Fritz Roald Tagle Luisa Ashworth Ralf Thomas Schmitt Axel Hofmann Béatrice Luais Phillip D. Harris Desirée Hoehnel Seda Özdemir Tanja Mohr‐Westheide Christian Koeberl 《Meteoritics & planetary science》2016,51(12):2441-2458
A Paleoarchean impact spherule‐bearing interval of the 763 m long International Continental Scientific Drilling Program (ICDP) drill core BARB5 from the lower Mapepe Formation of the Fig Tree Group, Barberton Mountain Land (South Africa) was investigated using nondestructive analytical techniques. The results of visual observation, infrared (IR) spectroscopic imaging, and micro‐X‐ray fluorescence (μXRF) of drill cores are presented. Petrographic and sedimentary features, as well as major and trace element compositions of lithologies from the micrometer to kilometer‐scale, assisted in the localization and characterization of eight spherule‐bearing intervals between 512.6 and 510.5 m depth. The spherule layers occur in a strongly deformed section between 517 and 503 m, and the rocks in the core above and below are clearly less disturbed. The μXRF element maps show that spherule layers have similar petrographic and geochemical characteristics but differences in (1) sorting of two types of spherules and (2) occurrence of primary minerals (Ni‐Cr spinel and zircon). We favor a single impact scenario followed by postimpact reworking, and subsequent alteration. The spherule layers are Al2O3‐rich and can be distinguished from the Al2O3‐poor marine sediments by distinct Al‐OH absorption features in the short wave infrared (SWIR) region of the electromagnetic spectrum. Infrared images can cover tens to hundreds of square meters of lithologies and, thus, may be used to search for Al‐OH‐rich spherule layers in Al2O3‐poor sediments, such as Eoarchean metasediments, where the textural characteristics of the spherule layers are obscured by metamorphism. 相似文献
152.
Luthardt Ludwig Hofmann Mandy Linnemann Ulf Gerdes Axel Marko Linda Rößler Ronny 《International Journal of Earth Sciences》2018,107(7):2465-2489
International Journal of Earth Sciences - The Chemnitz Fossil Forest depicts one of the most completely preserved forest ecosystems in late Paleozoic Northern Hemisphere of tropical Pangaea. Fossil... 相似文献
153.
Vojtěch Janoušek Jaroslav Aichler Pavel Hanžl Axel Gerdes Vojtěch Erban Vladimír Žáček Vratislav Pecina Marta Pudilová Kristýna Hrdličková Petr Mixa Eliška Žáčková 《International Journal of Earth Sciences》2014,103(2):455-483
The low-grade metavolcanic/volcanosedimentary complex of the Devonian Vrbno Group (Silesicum, NE Bohemian Massif, Czech Republic) occurs in two ~NE–SW trending belts, separated by tectonic slices of Cadomian metagranitic paraautochton. (1) The basic–intermediate lavas of the calc-alkaline Western Volcanic Belt came from a moderately depleted mantle $ \left( {\varepsilon_{\text{Nd}}^{370} \sim + 3} \right) $ . Rare rhyolites (374.0 ± 1.7 Ma: 2σ, LA–ICP–MS U–Pb Zrn) were derived most likely from immature crust or by extensive fractionation of primary basaltic melts. The rock association is interpreted as a vestige of a deeply dissected continental arc. (2) The Eastern Volcanic Belt consists mainly of (nearly) contemporaneous (371.0 ± 1.4 Ma) felsic alkaline lavas with high HFSE contents, as well as high Ga/Al and Fe/Mg ratios, typical of within-plate igneous setting. The petrology and Nd–Sr isotopic data point to a high-T anatexis of a young metagranitic crust, resembling the Cadomian (Brunovistulian) basement, in a back-arc setting. The attenuated Brunovistulian lithosphere could have partially melted by the heat provided by the upwelling asthenosphere and/or underplating basic magma. (3) Finally, the region was penetrated by numerous subalkaline, MORB/EMORB-like dolerite sheets—a hallmark of the considerable crustal thinning. 相似文献
154.
Samantha?K.?Gebauer Axel?K.?SchmittEmail author Lucia?Pappalardo Daniel?F.?Stockli Oscar?M.?Lovera 《Contributions to Mineralogy and Petrology》2014,167(1):953
The Campi Flegrei volcanic district (Naples region, Italy) is a 12-km-wide, restless caldera system that has erupted at least six voluminous ignimbrites during the late Pleistocene, including the >300 km3 Campanian ignimbrite (CI) which originated from the largest known volcanic event of the Mediterranean region. The Breccia Museo (BM), a petrologically heterogeneous and stratigraphically complex volcanic deposit extending over 200 km2 in close proximity to Campi Flegrei, has long remained contentious regarding its age and stratigraphic relation to the CI. Here, we present crystallization and eruption ages for BM plutonic ejecta clasts that were determined via uranium decay series and (U–Th)/He dating of zircon, respectively. Despite mineralogical and textural heterogeneity of these syenitic clasts, their U–Th zircon rim crystallization ages are indistinguishable with an average age of 49.7 ± 2.5 ka (2σ errors; mean square of weighted deviates MSWD = 1.2; n = 34). A subset of these crystals was used to obtain disequilibrium-corrected (U–Th)/He zircon ages which average 41.7 ± 1.8 ka (probability of fit P = 0.54; n = 15). This age closely overlaps with published CI 40Ar/39Ar eruption ages (40.6 ± 0.1 ka) after recalibration to recently revised flux monitor ages. Concordant eruption ages for BM and CI agree with previous chemostratigraphic and paleomagnetic correlations, suggesting their origin from the same eruption. However, they are at variance with recalibrated 40Ar/39Ar ages which have BM postdate CI by 3 ± 1 ka. BM syenites show similar geochemical and Sr–Nd isotopical features of pre-caldera rocks erupted between 58 and 46 ka, but are distinctive from subsequent caldera-forming magmas. Energy-constrained assimilation and fractional crystallization modeling of Nd–Sr isotopic data suggests that pre-caldera magmas formed a carapace of BM-type intrusions in a mid-crust magma chamber (≥8 km depth) shielding the younger CI magma from contamination by Hercynian basement wall rocks. An ~41–50 ka hiatus in crystallization ages implies rapid solidification of these pre-CI intrusions. This argues against protracted pre-eruptive storage of a large volume of CI magma at shallow crustal levels. 相似文献
155.
Abstract One and a half decades of climate negotiations have directly caused greenhouse gas emissions of about 150,000 t CO2. At prevailing market prices, making the full negotiation process greenhouse-gas-neutral ex post would cost about US$0.5 million, which is a fraction of the cost of the conferences. 相似文献
156.
Axel Michaelowa 《Climate Policy》2013,13(3):353-371
Certified emission reductions (CERs) from Clean Development Mechanism (CDM) projects have traditionally served as an indirect link between cap and trade systems around the world. However, since 2010, import restrictions have increased. Reasons for import limitations include the supplementarity principle, genuine concerns about the environmental integrity of CERs and social benefits of CDM projects, pressure from domestic emissions mitigation industries, concerns about competition in the industries in which reductions take place, as well as the attempt to pressure advanced developing countries to accept national emissions commitments under a future international climate policy regime. It is shown that import limitations lead to a decrease in CER prices and a race to generate CERs as quickly as possible. Such effects are visible in the CDM market after the EU announced its import limitations. The exclusion of CERs from specific project types will distort the CDM supply curve and increase the CER price unless the marginal abatement costs of the excluded project type are above the CER world market price. Similarly, exclusion of CERs from specific host countries will increase the price. Substantial differences are found in CER access to national carbon markets around the world.Policy relevanceCDM regulators could try to improve access of CERs to cap and trade schemes through improvements to additionality testing, standardizing baseline and monitoring methodologies and stakeholder consultation. However, regulators should be aware that standardization is no panacea, and controversies may resurface if standardized additionality determination (e.g. through benchmarks or positive lists) are applied for a certain period and found to be problematic. However, domestic policy concerns such as an unwillingness to send money abroad to buy credits, an inability to control market prices, and competitiveness impacts cannot be resolved by CDM reforms. If, despite such reforms of the CDM, blatant protectionism continues, a challenge before the World Trade Organisation (WTO) could be launched to stop discrimination of service exports from specific countries. 相似文献
157.
158.
159.
Climate Dynamics - Recent work has identified potential multi-year predictability in soil moisture (Chikamoto et al. in Clim Dyn 45(7–8):2213–2235, 2015). Whether this long-term... 相似文献
160.
We combine a convectively driven dynamo in a spherical shell with a nearly isothermal density-stratified cooling layer that mimics some aspects of a stellar corona to study the emergence and ejections of magnetic field structures. This approach is an extension of earlier models, where forced turbulence simulations were employed to generate magnetic fields. A spherical wedge is used which consists of a convection zone and an extended coronal region to ???1.5 times the radius of the sphere. The wedge contains a quarter of the azimuthal extent of the sphere and 150° in latitude. The magnetic field is self-consistently generated by the turbulent motions due to convection beneath the surface. Magnetic fields are found to emerge at the surface and are ejected to the coronal part of the domain. These ejections occur at irregular intervals and are weaker than in earlier work. We tentatively associate these events with coronal mass ejections on the Sun, even though our model of the solar atmosphere is rather simplistic. 相似文献