Preliminary report on the Yamato-86032 lunar meteorite: III. Ages, noble gas isotopes, oxygen isotopes and chemical abundances

The isotope abundances of He, Ne, Ar, Kr, and Xe, including ^Kr, the oxygen isotopic composition, and the concentrations of Na, K, Sc, Ti, Cr, Fe, Co, Y, Zr, La, Sm, Eu, Hf, Ta, and W were determined for the lunar meteorite Yamato-86032. Based on the radionuclide ^Kr we obtain a terrestrial age of 72000±30000 years, whereas the cosmic-ray exposure age is 10.6±0.6 Ma assuming exposure of the meteorite as a small object in space. Exposure to cosmic rays occurred at shallow shielding of about 40g/cm^2. The K-Ar gas retention ages of two separate splits are 3680±300 Ma and 3810±400 Ma, respectively. All ages agree with those for the lunar meteorites Y-82192 and Y-82193 recovered in the same area on the antarctic ice. The small amounts of trapped solar wind noble gases indicate that the Y-86032 material was exposed only briefly, some grains perhaps not at all, to the solar wind. The concentrations are similar to those of the Yamato-82 lunar meteorites. The oxygen isotopic composition is within the range of that for lunar rocks. The chemical composition of the samples from Y-86032,Y-82192,and Y-82193 is uniform for most major elements but not for all minor and trace elements, probably due to inhomogeneity of the source material. From the fact that the history of Y-86032 is the same as that of Y-82192/3 we conclude that these three rocks are pieces of the same meteorite fall

Erosion rate study at the Allchar deposit (Macedonia) based on radioactive and stable cosmogenic nuclides (26Al, 36Cl, 3He, and 21Ne)

This paper focuses on constraining the erosion rate in the area of the Allchar Sb-As-Tl-Au deposit (Macedonia). It contains the largest known reserves of lorandite (TlAsS2), which is essential for the LORanditeEXperiment (LOREX), aimed at determining the long-term solar neutrino flux. Because the erosion history of the Allchar area is crucial for the success of LOREX, we applied terrestrial in situ cosmogenic nuclides including both radioactive (26Al and 36Cl) and stable (3He and 21Ne) nuclides in quartz, dolomite/calcite, sanidine, and diopside. The obtained results suggest that there is accordance in the values obtained by applying 26Al, 36Cl, and 21Ne for around 85% of the entire sample collection, with resulting erosion rates varying from several tens of m/Ma to ∼165 m/Ma. The samples from four locations (L-8 CD, L1b/R, L1c/R, and L-4/ADR) give erosion rates between 300 and 400 m/Ma. Although these localities reveal remarkably higher values, which may be explained by burial events that occurred in part of Allchar, the erosion rate estimates mostly in the range between 50 and 100 m/Ma. This range further enables us to estimate the vertical erosion rate values for the two main ore bodies Crven Dol and Centralni Deo. We also estimate that the lower and upper limits of average paleo-depths for the ore body Centralni Deo from 4.3 Ma to the present are 250–290 and 750–790 m, respectively, whereas the upper limit of paleo-depth for the ore body Crven Dol over the same geological age is 860 m. The estimated paleo-depth values allow estimating the relative contributions of 205Pb derived from pp-neutrino and fast cosmic-ray muons, respectively, which is an important prerequisite for the LOREX experiment

Dating the incision of the Yangtze River gorge at the First Bend using three-nuclide burial ages

Incision of the Yangtze River gorge is widely interpreted as evidence for lower crustal flow beneath the southeast margin of the Tibetan Plateau. Previous work focused on the onset of incision, but the duration of incision remains unknown. Here we present cosmogenic nuclide burial ages of sediments collected from caves on the walls of the gorge that show the gorge was incised ~1 km sometime between 18 and 9 Ma. Thereafter, incision slowed substantially. We resolve middle Miocene burial ages by using three nuclides and accounting for in situ muogenic production. This approach explains the absolute concentrations of 10Be, 26Al, and 21Ne, as well as 26Al/10Be and 21Ne/10Be ratios. A declining incision rate challenges existing geodynamic interpretations by suggesting that either (1) surface uplift has ceased immediately south of the plateau margin or (2) gorge incision is not a useful proxy for the timing of surface uplift

Erosion during extreme flood events dominates Holocene canyon evolution in northeast Iceland

Extreme flood events have the potential to cause catastrophic landscape change in short periods of time (10(0) to 10(3) h). However, their impacts are rarely considered in studies of long-term landscape evolution (>10(3) y), because the mechanisms of erosion during such floods are poorly constrained. Here we use topographic analysis and cosmogenic (3)He surface exposure dating of fluvially sculpted surfaces to determine the impact of extreme flood events within the Jökulsárgljúfur canyon (northeast Iceland) and to constrain the mechanisms of bedrock erosion during these events. Surface exposure ages allow identification of three periods of intense canyon cutting about 9 ka ago, 5 ka ago, and 2 ka ago during which multiple large knickpoints retreated large distances (>2 km). During these events, a threshold flow depth was exceeded, leading to the toppling and transportation of basalt lava columns. Despite continuing and comparatively large-scale (500 m(3)/s) discharge of sediment-rich glacial meltwater, there is no evidence for a transition to an abrasion-dominated erosion regime since the last erosive event because the vertical knickpoints have not diffused over time. We provide a model for the evolution of the Jökulsárgljúfur canyon through the reconstruction of the river profile and canyon morphology at different stages over the last 9 ka and highlight the dominant role played by extreme flood events in the shaping of this landscape during the Holocene

Determination of erosion rate at Allchar region with cosmogenic Nuclides

Allchar is a Sb-As-Tl-Au deposit located at the north - western margin of the Kozuf Mountains in Macedonia, close to the Greek border. The mine contains the world’s largest known concentration of thallium-bearing minerals, especially lorandite (TlAsS2). LOREX, the acronym for LORandite EXperiment, is the only geochemical solar neutrino experiment still actively pursued. It addresses the determination of the long-term average of the solar neutrino flux, based on the neutrino-capture reaction 205 Tl + νe → 205 Pb + e - occurring in the lorandite of the Allchar mine. The final step of LOREX will be the extraction of the lorandite and the quantitative determination of the 205Pb / 205Tl ratio, thus providing the product of solar neutrino flux and neutrino-capture cross section, integrated over the lorandite age of 4.31 · 106 yr. Based on the present-day solar luminosity, it is expected that about 23 atoms of 205Pb of solar neutrino origin will be found per gram of lorandite. In contrast with the production of 205 Pb by solar neutrinos, which is independent of depth, cosmogenic 205Pb produced from fast muons of cosmic ray origin is strongly depth-dependent and very sensitive to the longterm erosion history of the field area. For erosion rate determination, we have so far applied three independent series of measurements of cosmogenic 26Al, 10Be and 53Mn. Firstly, the 26Al concentration in quartz was determined using the AMS system at VERA (Vienna Environmental Research Accelerator). Secondly, a series of measurements of the 10Be and 26Al contents was performed at the AMS of PRIME Lab, Purdue University, and finally AMS measurements at the Tandem facility of the TU Munich provided the concentration of 53 Mn in pyrite (FeS2). For the two ore bodies containing lorandite, we derived lower limits of the erosion rate of ~33 m/Myr at Crven Dol (NW part of Allchar deposit) and 67 m/Myr in the central part (SE part of Allchar deposit), in fair agreement with quantitative geomorphologic studies

Surface exposure dating of Holocene basalt flows and cinder cones in the Kula volcanic field (Western Turkey) using cosmogenic He-3 and Be-10

The Kula volcanic field in Western Turkey comprises about 80 cinder cones and associated basaltic lava flows of Quaternary age. Based on geomorphological criteria and K-Ar dating, three eruption phases, beta 2-beta 4, were distinguished in previous studies. Human footprints in ash deposits document that the early inhabitants of Anatolia were affected by the volcanic eruptions, but the age of the footprints has been poorly constrained. Here we use He-3 and Be-10 exposure dating of olivine phenocrysts and quartz-bearing xenoliths to determine the age of the youngest lava flows and cinder cones. In the western part of the volcanic field, two basalt samples from a 15-km-long block lava flow yielded He-3 ages of 1.5 +/- 0.3 ka and 2.5 +/- 0.4 ka, respectively, with the latter being in good agreement with a Be-10 age of 2.4 +/- 0.3 ka for an augen gneiss xenolith from the same flow. A few kilometers farther north, a metasedimentary xenolith from the top of the cinder cone Cakallar Tepe gave a Be-10 age of 11.2 +/- 1.1 ka, which dates the last eruption of this cone and also the human footprints in the related ash deposits. In the center of the volcanic field, a basalt sample and a metasedimentary xenolith from another cinder cone gave consistent He-3 and Be-10 ages of 2.6 +/- 0.4 ka and 2.6 +/- 0.3 ka, respectively. Two beta 4 lava flows in the central and eastern part of the volcanic province yielded He-3 ages of 33 +/- 0.4 ka and 0.9 +/- 0.2 ka, respectively. Finally, a relatively well-preserved beta 3 flow gave a He-3 age of similar to 13 ka. Taken together, our results demonstrate that the penultimate eruption phase beta 3 in the Kula volcanic field continued until similar to 11 ka, whereas the youngest phase beta 4 started less than four thousand years ago and may continue in the future. (C) 2016 Elsevier B.V. All rights reserved