Shock-effects on the K-Ar system of plagioclase feldspar and the age of anorthosite inclusions from North-Eastern Minnesota

Artificial shock pressures up to 52.5 GPa have no influence on the K-Ar system of plagioclase feldspar. The ⁴⁰Ar-³⁹Ar analysis of feldspar (labradorite An₆₇ from anorthosite of North-Eastern Minnesota) shocked up to 45 GPa—in vacuo, to prevent massive entrapment of atmospheric argon-shows that the age spectra and the argon diffusion properties remain unaltered. Similar feldspar samples (labradorite An₅₁ from Nain, Labrador), shocked in air up to 52.5 GPa and dated by the conventional K-Ar method, also yield the same age as unshocked samples but with a higher atmospheric argon contribution. The Minnesota anorthosite has an ⁴⁰Ar-³⁹Ar age of 1075 ± 10 m.y. No information on a possible previous history of the anorthosite became apparent.     

Surface analysis of stratospheric dust particles

Abstract— A controversially discussed and yet central question in interplanetary dust particle (IDP) research is the degree of alteration of these particles during their residence in the stratosphere. Especially, the typical enrichment of Br in chondritic IDPs (on the average ～21 × CI) has been inferred to be a result of contamination processes, probably invoking aerosol droplets. With time-of-flight secondary ion mass spectrometry (TOF-SIMS), we examined the surfaces of 13 stratospheric particles from the dust collector U2071. Six particles had severe, surface-bound, silicone oil residues preventing a proper analysis of their surfaces. Six other particles—-according to our scanning electron microscopy, energy dispersive x-ray spectrometer (SEM-EDS) studies preclassified as one (Fe,Ni)S-rich IDP, one Ca-rich particle, and four aluminum-oxide spheres—-carry the halogens F, Cl, and Br on the surface. At least for the aluminum-oxide spheres, we provide unequivocal evidence for a surface correlation of halogens. This evidence, taken together with that from previous studies, proves a general stratospheric contamination process which has to be considered in IDP research.     

The Jebel Hadid structure (Al Kufrah Basin,SE Libya)—A possible impact structure and potential hydrocarbon trap?

The Jebel Hadid structure that formed in the Nubian Sandstone of the southern Al Kufrah Basin is a ∼4.7 km circular feature with a set of multiple concentric annular ridges. The age of the structure is probably post-Early Cretaceous to pre-Pliocene. As the prevalent geological processes that usually account for the formation of circular structures (magmatism, diapirism, sand volcanism, karst dissolution, glacial erosion) can be widely excluded in this region, we suggest that the Jebel Hadid structure might represent an eroded, complex impact structure. In particular, the Jebel Hadid structure bears a strong morphological resemblance to the impact structure of Tin Bider in Algeria; general host rock properties may be compared to those at the Upheaval Dome impact structure, USA. Numerous terrestrial impact structures are hosts to hydrocarbon reservoirs. This investigation provides a first prospective approach based on remote sensing, discussing the economic potential of a circular structure of suspected impact origin. The still underexplored Al Kufrah Basin is considered as a high potential area for future hydrocarbon exploration. If we consider a possible impact origin of the Jebel Hadid structure, this feature might provide local secondary pathways and traps for hydrocarbon migration/accumulation in the Nubian Series and, thus, ought to be considered as a preferential site for oil and gas exploration.     

Brecciation and chemical heterogeneities of CI chondrites

Fragments in the size range from 40 μm to several hundred μm in the CI chondrites Orgueil, Ivuna, Alais, and Tonk show a wide range of chemical compositions with variations in major elements such as iron (10.4-42.4 wt% FeO), silicon (12.7-42.2 wt% SiO₂), and sulfur (1.01-15.8 wt% SO₃), but also important minor elements such as phosphorous (up to 5.2 wt% P₂O₅) or calcium (up to 6.6 wt% CaO). These variations are the result of the varying mineralogical compositions of these fragments. The distribution of phyllosilicates, magnetites, and possibly ferrihydrite, in particular, control the abundances of these elements. High REE contents—up to 150 times the solar abundances—were observed in phosphates, while matrix and sulfates are REE-depleted. The studied 113 fragments were subdivided into eight lithologies with similar mineralogical and thus chemical properties. The most common is the CGA lithology, consisting of a groundmass of Mg-rich, coarse-grained phyllosilicates and varying abundances of inclusions such as magnetite. The second most abundant lithology is the FGA lithology, consisting of a groundmass of fine-grained Fe-rich phyllosilicates. A rare, but important lithology consists of fragments with high contents of phosphates and other minerals. The proposed model for the evolution of these lithologies is based on a closed system alteration, where mineralogical differences in the lithologies reflect heterogeneities in the starting material. Comparison of our results with literature data indicates a general similarity of the four CI chondrites analyzed. Further comparison of bulk analyses suggests that the mass ‘threshold’ for chemical heterogeneities in CI chondrite samples is smaller than ∼1-2 g.     

The behavior of jet streams in potential fallout situations

Summary It is shown from a case study that the splitting of jet streams into several branches, which is frequently observed over the United States on the leading edges of intense maxima, may be explained by conservation of potential vorticity within an atmospheric layer moving over an obstacle. Such an obstacle may be a large mountain barrier, such as the Rocky Mountains, or a slowmoving dome of cold air in the lower troposphere, as is typical for cold outbreaks associated with strong jet streams.

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Zusammenfassung An Hand eines konkreten Falles wird gezeigt, daß die Aufspaltung des Jet Streams in mehrere Äste, wie dies häufig über den Vereinigten Staaten an der Vorderseite intensiver Jet Maxima beobachtet wird, mit der Erhaltung der potentiellen Vorticity innerhalb einer Luftschicht, die sich über ein Hindernis bewegt, erklärt werden kann. Ein derartiges Hindernis kann einerseits durch ein Gebirge gegeben sein, wie etwa die Rocky Mountains, andererseits aber auch durch eine sich nur langsam fortbewegende Kaltluftmasse in der unteren Troposphäre. Eine solche ist für Kaltluftausbrüche im Zusammenhang mit intensiven Strahlströmen charakteristisch.

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Résumé En se basant sur un cas particulier, on montre que la subdivision d'un courant jet en plusieurs bras distincts — fait souvent observé au dessus des Etats Unis d'Amérique à l'avant de la zone d'intensité maximum — peut s'expliquer par la conservation de l'énergie tourbillonnaire potentielle d'une couche d'air se déplaçant sur un obstacle. Un tel obstacle peut être soit une importante chaîne de montagnes telles que les Rocheuses, soit une masse d'air froid se déplaçant lentement dans la basse troposphère, comme c'est typiquement le cas lorsqu'une invasion d'air froid est liée à un fort courant jet.

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With 3 Figures     

Is atmospheric carbon dioxide removal a game changer for climate change mitigation?

The ability to directly remove carbon dioxide from the atmosphere allows the decoupling of emissions and emissions control in space and time. We ask the question whether this unique feature of carbon dioxide removal technologies fundamentally alters the dynamics of climate mitigation pathways. The analysis is performed in the coupled energy-economy-climate model ReMIND using the bioenergy with CCS route as an application of CDR technology. BECCS is arguably the least cost CDR option if biomass availability is not a strongly limiting factor. We compare mitigation pathways with and without BECCS to explore the impact of CDR technologies on the mitigation portfolio. Effects are most pronounced for stringent climate policies where BECCS is a key technology for the effectiveness of carbon pricing policies. The decoupling of emissions and emissions control allows prolonging the use of fossil fuels in sectors that are difficult to decarbonize, particularly in the transport sector. It also balances the distribution of mitigation costs across future generations. CDR is not a silver bullet technology. The largest part of emissions reductions continues to be provided by direct mitigation measures at the emissions source. The value of CDR lies in its flexibility to alleviate the most costly constraints on mitigating emissions.     

A Carnian 40Ar/39Ar age for the Paasselkä impact structure (SE Finland)—An update

A recrystallized band of pale feldspathic impact melt in a gneissic impact breccia from the approximately 10 km Paasselkä impact structure in southeast Finland was dated via ⁴⁰Ar/³⁹Ar step‐heating. The newly obtained plateau age of 228.7 ± 1.8 (2.2) Ma (2σ) (MSWD = 0.32; p = 0.93) is equal to the previously published pseudoplateau age of 228.7 ± 3.0 (3.4) (2σ) for the impact event. According to the current international chronostratigraphic chart and using the most recent published suggestions for the K decay constants, a Carnian (Late Triassic) age for the Paasselkä impact structure of 231.0 ± 1.8 (2.2) Ma (2σ) is calculated and considered the most precise and accurate age for this impact structure. The new plateau age for Paasselkä confirms the previous dating result but is, based on its internal statistics, much more compelling.