Geochemistry, petrology and ages of the lunar meteorites Kalahari 008 and 009: New constraints on early lunar evolution     

A.K. Sokol  V.A. Fernandes  T. Schulz  A. Bischoff  R.N. Clayton  K. Nishiizumi  L. Schultz  K. Mezger 《Geochimica et cosmochimica acta》2008,72(19):4845-4873

Kalahari 008 and 009 are two lunar meteorites that were found close to each other in Botswana. Kalahari 008 is a typical lunar anorthositic breccia; Kalahari 009 a monomict breccia with basaltic composition and mineralogy. Based on minor and trace elements Kalahari 009 is classified as VLT (very-low-Ti) mare basalt with extremely low contents of incompatible elements, including the REE. The Lu-Hf data define an age of 4286 ± 95 Ma indicating that Kalahari 009 is one of the oldest known basalt samples from the Moon. It provides evidence for lunar basalt volcanism prior to 4.1 Ga (pre-Nectarian) and may represent the first sample from a cryptomare. The very radiogenic initial ¹⁷⁶Hf/¹⁷⁷Hf (εHf = +12.9 ± 4.6), the low REE, Th and Ti concentrations indicate that Kalahari 009 formed from re-melting of mantle material that had undergone strong incompatible trace element depletion early in lunar history. This unusually depleted composition points toward a hitherto unsampled basalt source region for the lunar interior that may represent a new depleted endmember source for low-Ti mare basalt volcanism. Apparently, the Moon became chemically very heterogeneous at an early stage in its history and different cumulate sources are responsible for the diverse mare basalt types.Evidence that Kalahari 008 and 009 may be paired includes the similar fayalite content of their olivine, the identical initial Hf isotope composition, the exceptionally low exposure ages of both rocks and the fact that they were found close to each other. Since cryptomaria are covered by highland ejecta, it is possible that these rocks are from the boundary area, where basalt deposits are covered by highland ejecta. The concentrations of cosmogenic radionuclides and trapped noble gases are unusually low in both rocks, although Kalahari 008 contains slightly higher concentrations. A likely reason for this difference is that Kalahari 008 is a polymict breccia containing a briefly exposed regolith, while Kalahari 009 is a monomict brecciated rock that may never have been at the surface of the Moon.Altogether, the compositions of Kalahari 008 and 009 permit new insight into early lunar evolution, as both meteorites sample lunar reservoirs hitherto unsampled by spacecraft missions. The very low Th and REE content of Kalahari 009 as well as the depletion in Sm and the lack of a KREEP-like signature in Kalahari 008 point to a possible source far from the influence of the Procellarum-KREEP Terrane, possibly the lunar farside.  相似文献   

A novel time-series station in the Wadden Sea (NW Germany): First results on continuous nutrient and methane measurements     

Maik Grunwald  Olaf Dellwig  Gerd Liebezeit  Bernhard Schnetger  Rainer Reuter  Hans-Jürgen Brumsack 《Marine Chemistry》2007

In autumn 2002 a time-series station was installed in the tidal inlet between the Islands of Langeoog and Spiekeroog (Southern North Sea, NW Germany) to continuously measure physical, chemical, and meteorological parameters, even during extreme weather conditions (gale-force storms, drifting ice). Inside the pole of the station sensor tubes are installed in direction of the prevailing tidal currents. The tubes are equipped with hydrographic sensors (pressure, temperature, conductivity) and allow retrieval of water for nutrient analysis by automated instruments located inside the pole. Dissolved methane and the nutrients ammonia, nitrite, nitrate, phosphate, and silicate are measured at the station.  相似文献   

Classification of CM chondrite breccias—Implications for the evaluation of samples from the OSIRIS‐REx and Hayabusa 2 missions     

Sarah Lentfort  Addi Bischoff  Samuel Ebert  Markus Patzek 《Meteoritics & planetary science》2021,56(1):127-147

CM chondrites are complex impact (mostly regolith) breccias, in which lithic clasts show various degrees of aqueous alteration. Here, we investigated the degree of alteration of individual clasts within 19 different CM chondrites and CM‐like clasts in three achondrites by chemical analysis of the tochilinite‐cronstedtite‐intergrowths (TCIs; formerly named “poorly characterized phases”). To identify TCIs in various chondritic lithologies, we used backscattered electron (BSE) overview images of polished thin sections, after which appropriate samples underwent electron microprobe measurements. Thus, 75 lithic clasts were classified. In general, the excellent work and specific criteria of Rubin et al. (2007) were used and considered to classify CM breccias in a similar way as ordinary chondrite breccias (e.g., CM2.2‐2.7). In BSE images, TCIs in strongly altered fragments in CM chondrites (CM2.0‐CM2.2) appear dark grayish and show a low contrast to the surrounding material (typically clastic matrix), and can be distinguished from TCIs in moderately (CM2.4‐CM2.6) or less altered fragments (CM2.7‐CM2.9); the latter are bright and have high contrast to the surroundings. We found that an accurate subclassification can be obtained by considering only the “FeO”/SiO₂ ratio of the TCI chemistry. One could also consider the TCIs’ S/SiO₂ ratio and the metal abundance, but these were not used for classification due to several disadvantages. Most of the CM chondrites are finds that have suffered terrestrial weathering in hot and cold deserts. Thus, the observed abundance of metal is susceptible to weathering and may not be a reliable indicator of subtype classification. This study proposes an extended classification scheme based on Rubin’s scale from subtypes CM2.0‐CM2.9 that takes the brecciation into account and includes the minimum to maximum degree of alteration of individual clasts. The range of aqueous alteration in CM chondrites and small spatial scale of mixing of clasts with different alteration histories will be important for interpreting returned samples from the OSIRIS‐REx and Hayabusa 2 missions in the future.  相似文献   

Shock stage distribution of 2280 ordinary chondrites—Can bulk chondrites with a shock stage of S6 exist as individual rocks?     

Addi Bischoff  Maximilian Schleiting  Markus Patzek 《Meteoritics & planetary science》2019,54(10):2189-2202

The brecciation and shock classification of 2280 ordinary chondrites of the meteorite thin section collection at the Institut für Planetologie (Münster) has been determined. The shock degree of S3 is the most abundant shock stage for the H and LL chondrites (44% and 41%, respectively), while the L chondrites are on average more heavily shocked having more than 40% of rocks of shock stage S4. Among the H and LL chondrites, 40–50% are “unshocked” or “very weakly shocked.” Considering the petrologic types, in general, the shock degree is increasing with petrologic type. This is the case for all meteorite groups. The main criteria to define a rock as an S6 chondrite are the solid‐state recrystallization and staining of olivine and the melting of plagioclase often accompanied by the formation of high‐pressure phases like ringwoodite. These characteristics are typically restricted to local regions of a bulk chondrite in or near melt zones. In the past, the identification of high‐pressure minerals (e.g., ringwoodite) was often taken as an automatic and practical criterion for a S6 classification during chondrite bulk rock studies. The shock stage classification of many significantly shocked chondrites (>S3) revealed that most ringwoodite‐bearing rocks still contain more than 25% plagioclase (74%). Thus, these bulk chondrites do not even fulfill the S5 criterion (e.g., 75% of plagioclase has to be transformed into maskelynite) and have to be classified as S4. Studying chondrites on typically large thin sections (several cm²) and/or using samples from different areas of the meteorites, bulk chondrites of shock stage S6 should be extremely rare. In this respect, the paper will discuss the probability of the existence of bulk rocks of S6.  相似文献   

Northwest Africa 11024—A heated and dehydrated unique carbonaceous (CM) chondrite     

Samuel Ebert  Addi Bischoff  Dennis Harries  Sarah Lentfort  Jean‐Alix Barrat  Andreas Pack  Jrme Gattacceca  Robbin Visser  Peter Schmid‐Beurmann  Stephan Kimpel 《Meteoritics & planetary science》2019,54(2):328-356

Based on the high abundance of fine‐grained material and its dark appearance, NWA 11024 was recognized as a CM chondrite, which is also confirmed by oxygen isotope measurements. But contrary to known CM chondrites, the typical phases indicating aqueous alteration (e.g., phyllosilicates, carbonates) are missing. Using multiple analytical techniques, this study reveals the differences and similarities to known CM chondrites and will discuss the possibility that NWA 11024 is the first type 3 CM chondrite. During the investigation, two texturally apparent tochilinite–cronstedtite intergrowths were identified within two thin sections. However, the former phyllosilicates were recrystallized to Fe‐rich olivine during a heating event without changing the textural appearance. A peak temperature of 400–600 °C is estimated, which is not high enough to destroy or recrystallize calcite grains. Thus, calcites were never constituents of the mineral paragenesis. Another remarkable feature of NWA 11024 is the occurrence of unknown clot‐like inclusions (UCLIs) within fine‐grained rims, which are unique in this clarity. Their density and S concentration are significantly higher than of the surrounding fine‐grained rim and UCLIs can be seen as primary objects that were not formed by secondary alteration processes inside the rims. Similarities to chondritic and cometary interplanetary dust particles suggest an ice‐rich first‐generation planetesimal for their origin. In the earliest evolution, NWA 11024 experienced the lowest degree of aqueous alteration of all known CM chondrites and subsequently, a heating event dehydrated the sample. We suggest to classify the meteorite NWA 11024 as the first type 3 CM chondrite similar to the classification of CV3 chondrites (like Allende) that could also have lost their matrix phyllosilicates by thermal dehydration.  相似文献   

The Allende multicompound chondrule (ACC)—Chondrule formation in a local super‐dense region of the early solar system          下载免费PDF全文

Addi Bischoff  Gerhard Wurm  Marc Chaussidon  Marian Horstmann  Knut Metzler  Mona Weyrauch  Julia Weinauer 《Meteoritics & planetary science》2017,52(5):906-924

In Allende, a very complex compound chondrule (Allende compound chondrule; ACC) was found consisting of at least 16 subchondrules (14 siblings and 2 independents). Its overall texture can roughly be described as a barred olivine object (BO). The BO texture is similar in all siblings, but does not exist in the two independents, which appear as relatively compact olivine‐rich units. Because of secondary alteration of pristine Allende components and the ACC in particular, only limited predictions can be made concerning the original compositions of the colliding melt droplets. Based on textural and mineralogical characteristics, the siblings must have been formed on a very short time scale in a dense, local environment. This is also supported by oxygen isotope systematics showing similar compositions for all 16 subchondrules. Furthermore, the ACC subchondrules are isotopically distinct from typical Allende chondrules, indicating formation in or reaction with a more ¹⁶O‐poor reservoir. We modeled constraints on the particle density required at the ACC formation location, using textural, mineral‐chemical, and isotopic observations on this multicompound chondrule to define melt droplet collision conditions. In this context, we discuss the possible relationship between the formation of complex chondrules and the formation of macrochondrules and cluster chondrites. While macrochondrules may have formed under similar or related conditions as complex chondrules, cluster chondrites certainly require different formation conditions. Cluster chondrites represent a mixture of viscously deformed, seemingly young chondrules of different chemical and textural types and a population of older chondrules. Concerning the formation of ACC calculations suggest the existence of very local, kilometer‐sized, and super‐dense chondrule‐forming regions with extremely high solid‐to‐gas mass ratios of 1000 or more.  相似文献   

Cosmic‐ray exposure ages of six chondritic Almahata Sitta fragments          下载免费PDF全文

M. E. I. Riebe  K. C. Welten  M. M. M. Meier  R. Wieler  M. I. F. Barth  D. Ward  M. Laubenstein  A. Bischoff  M. W. Caffee  K. Nishiizumi  H. Busemann 《Meteoritics & planetary science》2017,52(11):2353-2374

The Almahata Sitta strewn field is dominated by ureilites, but contains a large fraction of chondritic fragments of various types. We analyzed stable isotopes of He, Ne, Ar, Kr, and Xe, and the cosmogenic radionuclides ¹⁰Be, ²⁶Al, and ³⁶Cl in six chondritic Almahata Sitta fragments (EL6 breccia, EL6, EL3‐5, CB, LL4/5, R‐like). The cosmic‐ray exposure (CRE) ages of five of the six samples have an average of 19.2 ± 3.3 Ma, close to the average of 19.5 ± 2.5 Ma for four ureilites. The cosmogenic radionuclide concentrations in the chondrites indicate a preatmospheric size consistent with Almahata Sitta. This corroborates that Almahata Sitta chondrite samples were part of the same asteroid as the ureilites. However, MS‐179 has a lower CRE age of 11.0 ± 1.4 Ma. Further analysis of short‐lived radionuclides in fragment MS‐179 showed that it fell around the same time, and from an object of similar size as Almahata Sitta, making it almost certain that MS‐179 is an Almahata Sitta fragment. Instead, its low CRE age could be due to gas loss, chemical heterogeneity that may have led to an erroneous ²¹Ne production‐rate, or, perhaps most likely, MS‐179 could represent the true 4π exposure age of Almahata Sitta (or an upper limit thereof), while all other samples analyzed so far experienced exposure on the parent body of similar lengths. Finally, MS‐179 had an extraordinarily high activity of neutron‐capture ³⁶Cl, ~600 dpm kg^?1, the highest activity observed in any meteorite to date, related to a high abundance of the Cl‐bearing mineral lawrencite.  相似文献   

Die tektonische Evolution der Erde von Pangäa zur Gegenwart ein plattentektonisches Modell     

Prof. Dr. Gerhard Bischoff 《International Journal of Earth Sciences》1985,74(2):237-249

Zusammenfassung Das hier vorgestellte Modell basiert auf der Annahme, daß sich unter großen Landmassen, wie Pangäa zum Beispiel, in tektonischen Ruheperioden Wärme aus dem Erdinneren anstaut. Infolgedessen entwickelte sich vom Perm bis zur Kreide ein weites Konvektionstumorsystem; Pangäa zersplitterte und die kontinentalen Platten bewegten sich vom afrikanischen Zentrum weg. Die ozeanischen Rücken des Atlantiks und Indiks folgten den abwandernden Platten wie sich »öffnende Ringe«. Panthalassa, der Eo-Pazifik, wurde von allen Seiten überdriftet. Es muß einen Gegenstrom vom Pazifik im Mantel geben, welcher für die Auffüllung der zwischen den Pangäabruchstücken entstehenden ozeanischen Räume mit Mantelmaterial sorgt. Auch die ozeanischen Platten des Pazifiks bewegen sich vom zentralen »Darwin-Rise« weg. Der ostpazifische Rükken folgte der Bewegung und bildet heute einen ausgedehnten ostwärts gekrümmten Bogen. In den ozeanischen »Außenbögen« bildeten sich infolge der Dehnung Querrifts. Die Transformstörungen sind in beiden Systemen radial angeordnet. Die Terrains an Nordamerikas Westküste können nur östlich eines ostpazifischen Rückens aus ihrer ursprünglichen Position im zentralen Pazifik herausgewandert sein, also synchron mit dem sich öffnenden Pazifik. Die Kontinente bewegen sich möglicherweise solange von ihrer ursprünglichen Position weg, bis erneut eine große Landmasse zusammengedriftet ist. Unterhalb einer solchen »Neogäa« könnte sich wieder ein Konvektionstumor infolge von Wärmestau entfalten. Das findet vielleicht in Intervallen von einigen hundert Millionen Jahren statt und könnte die WILSON-Zyklen der Erdgeschichte erklären.

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The tectonic evolution of the earth from Pangea to the present a plate tectonic model

The model proposed here is based on the assumption that beneath giant landmasses (e.g. Pangea) heat from the inner earth is stored up and accumulated during periods of tectonic inactivity. Consequently below Pangea a huge convection bulge system developed from the Permian to the Cretaceous; Pangea split up and the continental plates moved away from the African centre. The oceanic ridges of the Atlantic and the Indic also followed the movement of the withdrawing continents like »opening rings«. The oceanic ridges always maintained their position in the middle of the spreading oceans above unidirectional flows in the upper mantle. Panthalassa which surrounded Pangea, was over-drifted from all sides. Since the »expansion« of Pangea is continuing even today, there must be a counter current of mantle material from the Pacific area, compensating the gaps between the fragments of Pangea. Consequently at the subduction zones a suction should exist, which pulls the Pacific plates under the advancing plates of the former Pangean continent. In the centre of Panthalassa another bulge from the upper mantle developed simultaneously with the bulge under Pangea. The Pacific oceanic plates moved away outwards from this central »Darwin rise«. The Eastpacific ridge also followed this movement eastwards and forms today a wide, ringlike arc. In the outer arcs of the Pangean and Pacific spreading ocean systems transverse ridges developed as a result of the extension of the older oceanic crust. The transform faults are radial structures in both »expanding« systems. The hotspot spurs of the Hawaii and Polynesian islands can be explained as the result of material derived from an independent slowly ESE moving deeper part of the mantle. The terrains on North Americas West cost moved away from their original position in the central Pacific ocean synchronously with the opening ocean on the east side of the advancing East Pacific ridge.The energy which drives the whole system is residual plus radioactive heat. Kinetic movements compensate the heat surplus of the earth. The continental plates of the Pangean system are moving away from their original position until a new giant landmass is formed by collision. Below such a stationary »Neogea« a heat bulge can develop again. This may take place perhaps in intervals of hundred of million years, explaining the WILSON-cycles in earth history.

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Résumé Le modèle présenté ici est basé sur l'hypothèse qu'endessous des grandes masses continentales — comme la Pangée p.ex. - il s'accumule, pendant les périodes de calme tectonique, de la chaleur d'origine interne. En conséquence, depuis le Permien jusqu'au Crétacé, un vaste système de convection s'est développé; la Pangée s'est morcelée et les plaques continentales se sont éloignées du centre africain. Les dorsales océaniques circum-africaines ont suivi le mouvement de ces plaques à la manière d'»anneaux concentriques«. La Panthalassa, précurseur du Pacifique, a été chevauchée de tous les côtés. Il doit s'être établi, dans le manteau, à partir du Pacifique, un contre-courant qui compense l'ouverture des océans en formation entre les fragments de la Pangée. Le Pacifique a donné lieu, lui aussi, à une expansion centrifuge; la dorsale est-pacifique a suivi le mouvement et forme aujourd'hui un arc bombé vers l'est. Dans les arcs océaniques extérieurs, l'expansion a provoqué la formation de dorsales transverses. Les failles transformantes montrent, dans les deux systèmes, des dispositions radiales. Les terrains de la côte W de l'Amérique du N ne peuvent provenir que d'une région située à l'Est de la dorsale est-pacifique dans sa position d'origine. Les continents s'éloigment et forme aujourd'hui un arc bombé vers l'est. Dans les arcs océaniques extérieurs, l'expansion a provoqué la forSous une telle »Néogée«, une nouvelle cellule de convection pourrait ensuite se développer. Ces phénomènes pourraient se dérouler dans un intervalle de quelques centaines de millions d'années, expliquant ainsi les cycles de Wilson dans l'histoire de la Terre.

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The Transiometer: An Alternative Method of Soil Moisture Measurement in Slowly Permeable Soils     

Todd P. Trooien  Alan R. Bender  John H. Bischoff 《Ground Water Monitoring & Remediation》1986,6(2):99-105

The union of a piezoresistive pressure transducer and a porous ceramic cup was termed "transiometer." The transiometer was constructed from economical and readily available materials. It could be used to measure soil water potentials in both saturated and unsaturated conditions, and was well suited to continuous monitoring with data acquisition equipment.
Transiometer testing was conducted at two sites, one of moderate permeability and the other of slow permeability. The slowly permeable site was instrumented with four replications of the following: (1) transiometers installed at four depths, (2) a transi-ometerwithout the ceramic cup, (3) apiezometer, and (4) access tubes for monitoring soil moisture with a neutron probe. The moderately permeable site was instrumented with a transiometer, two piezometers, and an access tube for monitoring with a neutron probe.
In saturated conditions the transiometer had a faster response time after installation than the piezometer. Faster response makes the transiometer more desirable for use in slowly permeable soils, especially when monitoring dynamic soil water.
Calculated random error of the transiometer measuring system, including a digital voltmeter and a scanner, was typically 0.09 feet (2.8cm), with a maximum calculated to be 0.38 feet (11.5cm). The two most significant components were imprecision of the scanner card and calibration shift. The transiometer was sensitive to atmospheric pressure fluctuations, with sensitivity to atmospheric pressure change increasing with installation depth.  相似文献   

The solubility of quartz in aqueous sodium chloride solution at 350°C and 180 to 500 bars     

Robert O. Fournier  Robert J. Rosenbauer  James L. Bischoff 《Geochimica et cosmochimica acta》1982,46(10):1975-1978

The solubility of quartz in 2, 3, and 4 molal NaCl was measured at 350°C and pressures ranging from 180 to 500 bars. The molal solubility in each of the salt solutions is greater than that in pure water throughout the measured pressure range, with the ratio of solubility in NaCl solution to solubility in pure water decreasing as pressure is increased. The measured solubilities are significantly higher than solubilities calculated using a simple model in which the water activity in NaCl solutions decreases either in proportion to decreasing vapor pressure of the solution as salinity is increased or in proportion to decreasing mole fraction of water in the solvent.  相似文献