Terrestrial Ages Of Meteorites Research Articles

Characteristics of the Sahara as a meteorite recovery surface

AbstractWe describe the geological, geomorphological, and paleoclimatic setting of the Sahara of North Africa in particular, focused on the main meteorite dense collection areas (DCA; Morocco, Algeria, Tunisia, and Libya). We report on the outcome of several meteorite recovery field expeditions in Morocco and Tunisia since 2008, by car and by foot, that applied systematic search methods. The number of meteorites collected is 41 ordinary chondrites and one brachinite. The statistics of unpaired ordinary chondrites indicates that H chondrites are more abundant (21) than L chondrites (12), while LL chondrites are rare (2). Our meteorite density estimates for Tunisia and Morocco are in the order of magnitude of 1 met km−2. An estimate of the total maximum number of meteorites that could be recovered from the Sahara is 780,000 meteorites. We selected 23 meteorites from Aridal, Bou Kra, Bir Zar, and Tieret DCAs for 14C dating. The results show a wide range of terrestrial ages from 0.4 to more than 40 kyr with a majority of meteorites showing ages between 0.4 and 20 kyr. The weathering degree of these meteorites is ranges from minor (W1) to strong (W4). The highest weathering grades result from repeated oscillations between high and low humidity in the Sahara. However, there appears to be no correlation between weathering grade and terrestrial age of meteorites.

Modification of REE distribution of ordinary chondrites from Atacama (Chile) and Lut (Iran) hot deserts: Insights into the chemical weathering of meteorites

AbstractThe behavior of rare earth elements (REEs) during hot desert weathering of meteorites is investigated. Ordinary chondrites (OCs) from Atacama (Chile) and Lut (Iran) deserts show different variations in REE composition during this process. Inductively coupled plasma–mass spectrometry (ICP‐MS) data reveal that hot desert OCs tend to show elevated light REE concentrations, relative to OC falls. Chondrites from Atacama are by far the most enriched in REEs and this enrichment is not necessarily related to their degree of weathering. Positive Ce anomaly of fresh chondrites from Atacama and the successive formation of a negative Ce anomaly with the addition of trivalent REEs are similar to the process reported from Antarctic eucrites. In addition to REEs, Sr and Ba also show different concentrations when comparing OCs from different hot deserts. The stability of Atacama surfaces and the associated old terrestrial ages of meteorites from this region give the samples the necessary time to interact with the terrestrial environment and to be chemically modified. Higher REE contents and LREE‐enriched composition are evidence of contamination by terrestrial soil. Despite their low degrees of weathering, special care must be taken into account while working on the REE composition of Atacama meteorites for cosmochemistry applications. In contrast, chondrites from the Lut desert show lower degrees of REE modification, despite significant weathering signed by Sr content. This is explained by the relatively rapid weathering rate of the meteorites occurring in the Lut desert, which hampers the penetration of terrestrial material by forming voluminous Fe oxide/oxyhydroxides shortly after the meteorite fall.

Uranium-series chronology and cosmogenic 10Be– 36Cl record of Antarctic ice

We present new uranium-series and cosmogenic nuclide age data obtained by sensitive thermal ionization and accelerator mass spectrometric techniques for samples of dusty polar ice from Allan Hills, Antarctica. These data are used to further evaluate the applicability of these nuclides for direct radiometric dating of polar ice. In order to minimize artifacts during sample processing we developed an improved method utilizing ethylenediaminetetraacetic acid (EDTA) to stabilize uranium-series nuclides dissolved in polar ice during ice melting and filtration. Our measurements revealed low uranium-series daughter abundances and large uranium-series ( 234U/ 238U, 230Th/ 234U, 226Ra/ 230Th, 231Pa/ 235U) disequilibria in the filtered <0.05-μm fraction of these ice samples. Both the long-lived uranium-series disequilibria and 10Be/ 36Cl ratios are most likely recently inherited from precipitation. The short-lived daughter 226Ra is the exception and is enhanced in the <0.05-μm fraction, presumably due to recoil effects from dust bands present in the ice. Based on a simplified recoil model, ice ages of approximately 30 ka are obtained from our data. Absence of measurable 238U– 234U– 230Th– 226Ra disequilibria in the volcanic dust bands also suggests that ice ages are greater than 10 ka, consistent with recoil-based ages. Our relatively young ice ages can be compared with previously published relatively old terrestrial ages of meteorites from this area and suggests that meteorites at Allan Hills have experienced a multi-stage history of ice accumulation and/or ice flow. Our results also suggest that large uranium-series disequilibria can be inherited from precipitation, which may provide a method for dating clear ice samples.

Natural Thermoluminescence and Terrestrial Ages of Meteorites from a Variety of Temperature Regimes

Natural Thermoluminescence and Terrestrial Ages of Meteorites from a Variety of Temperature Regimes

Natural Thermoluminescence and Terrestrial Ages of Meteorites from a Variety of Temperature Regimes

Natural Thermoluminescence and Terrestrial Ages of Meteorites from a Variety of Temperature Regimes

Update on terrestrial ages of Antarctic meteorites

Cosmic-ray-produced 36Cl (half-life = 3.01 × 10 5 years) has been measured in 90 Antarctic meteorites by accelerator mass spectrometry. The terrestrial ages of the meteorites were calculated from the results. After excluding possible paired objects, 138 terrestrial ages from 18 different locations are available from 14C, 81Kr, and 36Cl measurements for application to Antarctic meteorite and glaciological studies. The terrestrial ages of Allan Hills meteorites vary from 2000 years to 1 million years and are clearly longer than those of Yamato meteorites and other Antarctic meteorites. The oldest Allan Hills meteorites were found close to the eastern edge and in the southeast of the main icefield. Among all Antarctic meteorites measured to date, only L and LL chondrites have terrestrial ages older than 370,000 years.

Terrestrial ages of meteorites

Terrestrial ages of meteorites

Thermoluminescence and the terrestrial age of meteorites: Some recent results

This paper reports the results of an examination of the thermoluminescence (TL) of 23 meteorites which were observed to fall, and 17 meteorite finds which have had their terrestrial age determined by the 14C method. The terrestrial ages of the observed falls range from 1 to 205 years, whilst the 14C terrestrial ages range from 1200 ± 2000 to >20,000 years. A statistically significant correlation has been observed between the natural TL — as expressed as the ratio of the intensity of the low-temperature TL peak to that of the high-temperature peak — and the terrestrial age of the 40 meteorites. Furthermore, peak height ratios in excess of 3.0 are only observed in falls which fell within the last 250 years, suggesting that finds with peak height ratios as large as this, such as Allan Hills A77003 and Plainview (1917), fell within the last few hundred years. The present results are consistent with evidence that meteorite TL decay is a non-first-order process. The implications of the results for estimates of the terrestrial ages of 8 meteorite finds, for which there are no 14C data, are also discussed.

Thermoluminescence and terrestrial age of the Estacado meteorite

THE terrestrial age of a meteorite is the number of years which has elapsed since the meteorite fell to Earth. The terrestrial ages of most meteorites are not known directly, as most are ‘finds’ rather than observed ‘falls’. Here we discuss the various methods which have been suggested to determine the terrestrial age of the ‘finds’, and these may be conveniently divided into two categories: (1) those which use the decay of spallation-produced radioactive isotopes1–4; (2) those which use the thermal drainage of thermoluminescence (TL) from the material5,6.