The relative isotopic abundance of K^(40) in terrestrial and meteoritic samples

Fowler, Greenstein, and Hoyle have proposed that the inner solar system was heavily irradiated during its formation. A consequence of this proposal is that sizable differences in meteoritic and terrestrial K^(41)/K^(40) ratios are possible if the fraction of material which was irradiated was different in the two cases. The isotopic composition of potassium was measured by mass spectrometry for nine stone meteorites, silicate from the Vaca Muerta mesosiderite and the Weekeroo Station iron meteorite, and four terrestrial samples. The measured K^(41)/K^(40) ratios were corrected by normalizing the measured K^(39)/K^(41) ratio to the Nier value of 13.47. This normalization procedure approximately cancels out any variations in the isotopic abundance except those due to nuclear processes. Measurements on enriched standards showed that any variations greater than 1% would certainly have been detected, and variations greater than ½% would probably have been detected with replicate analyses. Within these limits, no variations in the K^(40) abundance between the terrestrial and meteoritic samples could be found which could be ascribed to particle irradiation in the early history of the solar system. Small K^(40) enrichments were observed in Norton County, Weekeroo Station, and Vaca Muerta; however, these appear to have been produced during cosmic-ray irradiation by the Ca^(40)(n, p) reaction. The present results set relatively strong limitations on possible mechanisms for the formation of the earth and the meteorites if the idea of a large-scale irradiation in the early history of the solar system is to be retained. Independent of the model of Fowler et al., limits have been placed on any differential uniform irradiation. The implications of the present work on the K-Ar ages of stone and iron meteorites are discussed. The possibility that iron meteorites are considerably older than the solar system as a whole appears unlikely

K-Ar age determinations on tertiary volcanic rocks: 5. Siebengebirge, Siebengebirge-Graben

Sanidines from 16 tuffs of the first volcanic phase in the Siebengebirge and the Siebengebirge-Graben were dated by the K/Ar-method. Ages range from 24.1 (Nachtigallental) to 22.9 M.y. (core Rott). Three mineral ages from surface outcrops in the Central Siebengebirge (23.9 ± 0.5 M.y.) are statistically indistinguishable from those of the sub-surface samples Stieldorf-1, Stieldorf-2, and Rott (23.0 ± 0.5 M.y.). These ages confirm the Uppermost Oligocene biostratigraphic age of the 'Blatterkohle Rott' which is interlayered with the trachyte tuff. Sanidine and biotite mineral ages from five trachyte samples give similar apparent ages from 26.4 to 24.6 M.y. These results show the trachytes to be older than the tuffs, in disagreement with the geologically established sequence. The sequence of eruptions in the Siebengebirge area however (trachyte-tuff, trachyte, latite and alkaline-basalt) was confirmed wherever outcrops allow observations. This discrepancy is discussed. The apparent ages of three dated latites are in the same range (26.2 to 25.1 M.y.), in agreement with the geological sequence. The latite ages show that the time span between the eruptions of the trachytes and the latites must have been very small. Isolated basalts belonging to a fourth phase yield K/Ar ages from 25 to 19 M.y. Pliocene volcanism could not be verified in the Siebengebirge. In addition, stratigraphically well-dated glauconites from the Tertiary of the Niederrhein area were used to correlate our isotopic age date with the Cenozoic time scale.           ARK: https://n2t.net/ark:/88439/y070559 Permalink: https://geophysicsjournal.com/article/259 &nbsp

Kalium-Argon-Daten zum Alter des Laacher Vulkanismus, der Rheinterrassen und der Eiszeiten

Die Vulkanite des Laacher-See-Gebietes in der Eifel können mit den Terrassenbildungen des Rheines zeitlich korreliert und ihre Föderfolge auf diese Weise stratigraphisch festgelegt werden. Dadurch bietet sich eine Möglichkeit, die K-Ar-Datierungsmethode an Proben von pleistozänem Alter zu testen und zu prüfen, ob die physikalisch bestimmte Sequenz mit der geologischen übereinstimmt. Datierungen wurden vorgenommen an 13 Sanidinen, 7 Biotiten, 2 Augiten und 14 Gesteinen der Eifel, ferner als Ergänzung an 6 Gesteinen der Umgebung von Agde, Dept. Hérault, Südfrankreich. Die meisten Datierungen ergaben geologisch wahrscheinliche Alter. Sie reichen in der Eifel von 570.10³a bis 100.10³a, bei Agde von 1400.10³a bis 640.10³a. Diffusionsexperimente an Sanidinen und Biotiten zeigten, daß das atmosphärische Argon durch Ausheizen nicht zufriedenstellend entfernt werden kann, ohne daß radiogenes Argon verloren geht. Eine Kontrollprobe des abgeheizten radiogenen Gases mit radioaktivem Ar(39) wurde getestet und erwies sich als nützliche Korrekturgröße.researc

Amphibole: A major carrier of helium isotopes in crustal rocks

The first evidence for a specific role of amphiboles in He isotope balance of crustal rocks was presented in early contributions by Gerling et al. (1971, 1976). Since then it was shown that 4He and 3He concentrations in amphiboles generally exceed those in the host rock samples. Recently amphibole was considered as an important carrier of noble gases and other volatiles components in the course of their subduction into the mantle. This paper presents new data on the balance and mobility of noble gas isotopes and major gas constituents in amphibole separates in order to understand sources and evolution of volatile components of 2666 Ma old alkaline granites from Ponoy massif (Kola Peninsula), which underwent metamorphism 1802 Ma ago.In the amphiboles 3He, 4He and 40Ar* were dominantly produced in situ due to radioactive decay of the parent isotopes and associated nuclear reactions. A small fraction of He (≈ 3% of the total) is liberated by crushing and shows 3He/4He ratio indistinguishable from that found by total extraction. The fraction of trapped 40Ar* amounts to ≈ 40%; both these fractions presumably occupy fluid inclusions and show rather low 4He/40Ar* ≈ 0.1, a factor of ≈ 150 below the production ratio (calculated assuming no loss / gain of the species has happened since the time of metamorphism).3He has been better preserved in amphiboles compared with 4He: the retention parameter (measured amount of He / totally produced amount) for 3He (≈ 0.4) exceeds that for 4He (≈ 0.15).He extraction by fast and slow linear heating of amphiboles resulted in different release patterns. The fast heating (within 12 to 40 °C min− 1) revealed a superposition of two peaks. When heating with slower heating rate (below 8 °C min− 1) was applied, the high-temperature peak disappeared (the “disappearing site”). Extractions of He atoms from grain and powder samples at different heating rates have shown that: (1) the “disappearing site” is revealed by the fast heating analyses of different amphibole samples but not only those from the Ponoy massif; (2) amount of He liberated from the “disappearing site” is variable and generally much less than the total amount of He in the sample; (3) analysis of the powder produced in the crushing experiments never reveals the “disappearing site”; the temperature of He release from the powder is lower than that from the mm grain size sample by ≈ 50 °C. Possible explanations of the nature of the “disappearing site” are discussed. However, independently on nature of this effect, repeated gas extractions by heating at different rates would give additional information about structure and its transformation during heating of amphiboles.The simplest explanation of the observed abundances of noble gas isotopes in the amphibole separates from Ponoy granites suggests local production, redistribution and partial loss of noble gases during evolution of the massif

Landscape factors modulating patterns of salmonid distribution during summer in North Patagonian rivers

Understanding how ecosystem processes influencing fish distribution operate across spatial scales is important to understand biological invasions. Salmonids, originally from the Northern Hemisphere, have been repeatedly introduced throughout the world, making them an ideal group to test hypotheses about factors driving invasions. We assessed the influence of environmental variables at the watershed scale on the abundance and structure of salmonid assemblages in the breeding streams of the Upper Limay river basin, Rio Negro, Argentina. We combined field captures with digital map data and geographic information systems to examine landscape-level patterns of salmonid abundance in 35 representative sub-basins of the environmental gradient. We employed a hierarchical cluster analysis and classification and regression tree models to relate the abundance of salmonids and types of species assemblages with environmental characteristics at watershed level. We found stream localization, precipitation regime, altitude and air temperature to be important predictors of the abundance and assemblage structure of salmonids. Total catches showed an increasing gradient of catch-per-unit-effort from west to east and from north to south, with Oncorhynchus mykiss being the most abundant species. O. mykiss relative abundance was westward skewed, where smaller catchments with steeper and shaded valleys are drained by less productive streams with more irregular hydrological regimes, like those found in this species' North American native range. In contrast, the abundance of Salmo trutta abundance was eastward skewed, where larger, sunnier and more gently sloped catchments result in more productive streams with stable hydrological regimes, like those found in that species' European native range. Thus, differential salmonid abundance could result from the interplay between the evolutionary fingerprint left by each species' native environment (especially flow and temperature regimes) and the availability of those conditions in new environments to which they have been translocated. By furthering our understanding of how landscape conditioned invasion success, these findings can help guide the management of economically important introduced fish.Fil: Lallement, Mailén Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Rechencq, Magali. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Fernández, María Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Zattara, Eduardo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Sosnovsky, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Vigliano, Pablo Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Garibotti, Gilda Malena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Alonso, Marcelo Fabián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Lippolt, Gustavo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Macchi, Patricio Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentin

Seasonal and reproductive migrations in the Creole perch Percichthys trucha (Actinopterygii: Percichthydae) promote both intra-lake and inter-lake habitat connectivity

In this research work, biology of Creole perch, Percichthys trucha, the largest top predator in the North Patagonia’s freshwater communities, in a deep oligotrophic lake in the region, focusing on (i) the differential use of littoral depth strata by age, (ii) age at maturity and spawning season and (iii) occurrence of reproductive migrations to vegetated shorelines has been described. Individuals from 12 locations within the lake were sampled and found that P. trucha makes differential use of the littoral zone through the year and through its life stages. From hatching and through their first year, juveniles prefer shallow vegetated littoral strata; 50% of the individuals have reached maturity at 1-year-old, and all are reproductive by 3-year-old. Overall, our results show that the reproductive behavior of P. trucha improves habitat connectivity between different zones of the lake and between the lake and other lakes connected to it by tributary streams.Fil: Fernández, María Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Rechencq, Magali. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Lallement, Mailén Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Zattara, Eduardo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Juárez, Santiago Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Sosnovsky, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Lippolt, Gustavo Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Alonso, Marcelo Fabián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Vigliano, Pablo Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Milano, Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Macchi, Patricio Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentin

Composition, distribution and trophic relationships of the fish fauna of the Negro river, Patagonia Argentina

La provincia ictiogeográfica Patagónica se caracteriza por una llamativa pobreza de especies. El río Negro es el curso de agua más importante de esta región y a pesar de sus dimensiones e importancia socioeconómica su fauna íctica ha sido poco estudiada. Este trabajo describe algunos aspectos biogeográficos y características ecológicas de su ictiofauna. Se muestrearon estacionalmente cinco sitios a lo largo del río, por medio de redes de enmalle, pesca eléctrica, redes de arrastre costero y atarraya. Se analizó la composición y distribución de peces y se estudió la dieta para determinar los roles tróficos y los niveles de competencia y de piscivoría. Se capturaron ejemplares de 13 especies: siete de origen nativo y seis exóticas, de las cuales se destaca la novedosa presencia de la coridora (Corydoras paleatus) y la carpa común (Cyprinus carpio), ampliando su distribución austral. Las especies más importantes fueron las nativas pejerrey patagónico (Odontesthes hatcheri), perca bocona (Percychthis colhuapiensis), perca de boca chica (P. trucha) y madrecita (Jenynsia multidentata). Los índices ecológicos indican que el curso inferior es diferente al resto del río presentando una dominancia de pejerrey patagónico y madrecita. En este sector se observó una mayor importancia de especies exóticas. Se encontraron ocho grupos tróficos, existencia de solapamientos en las dietas entre componentes nativos y exóticos, y evidencia de piscivoría importante entre las especies. La presencia y distribución de los peces en el río Negro está fuertemente influenciada por fenómenos de antropocoria accidental o intencional. Es necesario desarrollar estudios que analicen el impacto generado por las introducciones y la evolución de las relaciones entre los componentes nativos y exóticos, teniendo en cuenta que la trucha arco iris y la carpa común han influido negativamente en otros lugares del mundo.The Patagonic ictiogeographic region is characterized by a low species diversity. Despite that the Negro river is the most important water body in the region, both in terms of the size of its drainage basin and of its socioeconomic importance, its fish fauna has scarcely been studied. The present paper addresses biogeographic and ecological characteristics related to its fish. Gill net gangs, electro fishing and beach seine nets were used to sample seasonally five stations along the river. Fish fauna composition and distribution were analyzed throughout different ecological indexes. Diet composition was also analyzed to establish trophic roles, competition and piscivory. We caught seven native and six exotic species; two of them (Corydoras paleatus and Cyprinus carpio) represent a widening of their austral distribution. The natives Odontesthes hatcheri, Percychthis colhuapiensis, P. trucha and Jenynsia multidentata were more important in terms of numbers in catches. Ecological indexes show that the lower part of the Negro river differs from the rest of the river with higher numbers of O. hatchery and J. multidentata. Eight trophic groups were found as well as evidence of diet overlapping and considerable piscivory. Presence and distribution of fish in the Negro river is strongly influenced by introduction by men, either accidentally or intentionally. Impacts by introduced species need to be addressed, specially in terms of emerging processes between native and exotic fish, taking into special consideration the negative impacts that the rainbow trout and the carp have already had in different parts of the world

Thermal history of the central Gotthard and Aar massifs, European Alps: Evidence for steady state, long-term exhumation

International audienceQuantifying long-term exhumation rates is a prerequisite for understanding the geodynamic evolution of orogens and their exogenic and endogenic driving forces. Here we reconstruct the exhumation history of the central Aar and Gotthard external crystalline massifs in the European Alps using apatite and zircon fission track and apatite (U-Th)/He data. Age-elevation relationships and time-temperature paths derived from thermal history modeling are interpreted to reflect nearly constant exhumation of ∼0.5 km/Ma since ∼14 Ma. A slightly accelerated rate (∼0.7 km/Ma) occurred from 16 to 14 Ma and again from 10 to 7 Ma. Faster exhumation between 16 and 14 Ma is most likely linked to indentation of the Adriatic wedge and related thrusting along the Alpine sole thrust, which, in turn, caused uplift and exhumation in the external crystalline massifs. The data suggest nearly steady, moderate exhumation rates since ∼14 Ma, regardless of major exogenic and endogenic forces such as a change to wetter climate conditions around 5 Ma or orogen-perpendicular extension initiated in Pliocene times. Recent uplift and denudation rates, interpreted to be the result of climate fluctuations and associated increase in erosional efficiency, are nearly twice this ∼0.5 km/Ma paleoexhumation rate

Crustal noble gases in deep brines as natural tracers of vertical transport processes in the Michigan Basin

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94594/1/ggge1543.pd