Search results for "PLUT"
showing 10 items of 153 documents
Zircon ages and Hf isotopic compositions of Ordovician and Carboniferous granitoids from central Inner Mongolia and their significance for early and …
2016
Abstract We present zircon ages and Hf-in-zircon isotopic data for plutonic rocks and review the evolution of central Inner Mongolia, China, in the early and late Paleozoic. Zircons of a granodiorite yielded a 206 Pb/ 238 U age of 472 ± 3 Ma that reflects the time of early Paleozoic magmatism. Zircon ages were also obtained for a tonalite (329 ± 3 Ma), quartz-diorite (320 ± 3 Ma), and granite vein (297 ± 2 Ma). Our results, in combination with published zircon ages and geochemical data, document distinct magmatic episodes in central Inner Mongolia. The dated samples are mostly granodiorite, tonalite and quartz-diorite in composition with intermediate to high-silica, high Na 2 O (3.08–4.26 w…
Pre-3000 Ma thermal history of the Archean Kaap Valley puton, South Africa
1992
The Kaap Valley pluton is one of several early Archean (3200-3500 Ma) tonalitetrondhjemite plutons that surround the Barberton Greenstone belt, southern Africa. Precise dating using single-grain 207 Pb/ 206 Pb evaporation of zircon and 40 Ar/ 39 Ar laser step-heating of hornblende and biotite indicates that, in its interior, the Kaap Valley pluton preserves a memory of its initial intrusion and cooling, which spanned a time from 3225 to 3142 Ma. The pluton also records the effect of a low-temperature thermal event at its margin as seen by a 40 Ar/ 39 Ar biotite age of 3035 Ma, which is perhaps related to hydrothermal activity and gold mineralization in the adjacent Barberton Greenstone belt…
Elements of the Archean thermal history and apparent polar wander of the eastern Kaapvaal Craton, Swaziland, from single grain dating and paleomagnet…
1989
Abstract Single grains of zircon, hornblende, biotite and feldspar have been dated to define the thermal history of the Archean Mbabane Pluton, Swaziland. Coincident207Pb/206Pb zircon and40Ar/39Ar hornblende ages suggest that the pluton underwent rapid cooling to about 450°C at the time of emplacement at ∼ 2690 Ma. Because the Mbabane Pluton is one of a suite of granites which represent the last major Archean intrusive event in the eastern Kaapvaal Craton, this time of emplacement marks the end of cratonization. Much younger biotite and feldspar ages indicate argon loss, perhaps due to several low-temperature events related to dike intrusion at 2000–2300 Ma. From such a thermal history, the…
Melt extraction and accumulation from partially molten rocks
2004
Current models for melt segregation and ascent are not adequate to accurately describe transport and accumulation in combination. We propose that transport is discontinuous and in batches, and that accumulation occurs by stepwise merging of batches. A simple numerical model of jostling spheres that merge when they touch was used to represent stepwise accumulation and transport of batches by propagation of hydrofractures. Results of the numerical model indicate that such a system may quickly develop into a self-organised critical (SOC) state. In this state, the distribution of melt batch volumes can be described by a power law, with an exponent m that lies between 2/3 and 1. Once a self-orga…
Trace Analysis of Plutonium and Technetium by Resonance Ionization Mass Spectrometry Using an Atomic Beam and a Laser Ion Source
1990
A method for low level detection of plutonium and technetium is described with a detection limit of less than 107 atoms. Plutonium is a very toxic element due to its radioactive decay as well as its chemical behaviour. It was released to the environment in large amounts during the fifties and sixties of his century, principally by nuclear-weapon tests and some accidents. As a result about 0.4 − 4 mBq per gram 239Pu(T1/2 = 24390 y), corresponding to 4 × 108 − 4 × 109 atoms, can be found in the Northern Hemisphere in soil samples.
Barking at the Threshold
2019
Over the past few years, students of ancient Mediterranean societies have shown consistent interest in the cultural construction of dogs as reflected in texts, artefacts, and other media. However, whereas the cultural and literary implications of the Greek representation of dogs have been the subject of thorough investigations, Roman dogs have remained at the margins of the scholarly debate. By adopting an interdisciplinary methodology that combines cognitive theory, rhetorical analysis, and socio-anthropological research, the present paper discusses some affordances of dogs (in the terms of James Gibson’s 'ecological approach to visual perception') that are given special significance withi…
Herakleides Pontikos und die ps.-Plutarchische Schrift Peri Mousikes
2020
Si cerca di dimostrare che gli studiosi finora (seguendo Westphal) hanno attribuito troppe parti del trattatello ps.-plutarcheo "De musica" a Eraclide Pontico; a quest´ ultimo l´ ignoto autore ha attinto in realta´ solo quello che dice di aver letto nell´ iscrizione di Sicione. We try to show that up to now scholars (following Westphal) have attributed too many parts of the ps.-plutarcheo tract "De musica" to Eraclide Pontico; the unknown author drew from the latter only what he says he read in Sicyon's inscription.
High-resolution laser spectroscopy of long-lived plutonium isotopes
2017
Long-lived isotopes of plutonium were studied using two complementary techniques, high-resolution resonance ionisation spectroscopy (HR-RIS) and collinear laser spectroscopy (CLS). Isotope shifts have been measured on the $5f^67s^2\ ^7F_0 \rightarrow 5f^56d^27s\ (J=1)$ and $5f^67s^2\ ^7F_1 \rightarrow 5f^67s7p\ (J=2)$ atomic transitions using the HR-RIS method and the hyperfine factors have been extracted for the odd mass nuclei $^{239,241}$Pu. Collinear laser spectroscopy was performed on the $5f^67s\ ^8F_{1/2} \rightarrow J=1/2\; (27523.61\text{cm}^{-1})$ ionic transition with the hyperfine $A$ factors measured for $^{239}$Pu. Changes in mean-squared charge radii have been extracted and s…
Applicability of pulse shape analysis methods in measurements of low energy gamma rays from human lungs
2015
Pulssimuoto-analyysi menetelmiä sovellettiin gammaspektrometrisiin mittauksiin, tavoitteena vähentää matala-energistä Compton taustaa spektrissä. Tarkasteltu käytännön sovellus oli sisäänhengitetyn plutoniumin havaitseminen suorissa keuhkomittauksissa. Vuorovaikutussyvyyden ja pulssin nousuajan välillä ei löydetty mittauksissa yhteyttä. Mittauksissa käytetyssä plutonium-239 keuhkot sisältävässä phantomissa oli ei-toivottu americium-241 kontaminaatio. Työssä keskustellaan myös mittarisuunnittelun keinoista, joilla pulssimuotoanalyysin tehokkuutta voitaisiin parantaa. Pulse shape analysis methods were applied to gamma spectroscopy measurements in an attempt to reduce the contribution from low…