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- Ricchi, Emmanuelle, et al.
(författare)
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Ion microprobe dating of fissure monazite in the Western Alps : insights from the Argentera Massif and the Piemontais and Briançonnais Zones
- 2020
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Ingår i: Swiss Journal of Geosciences. - : Springer Science and Business Media LLC. - 1661-8726 .- 1661-8734. ; 113:1
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Tidskriftsartikel (refereegranskat)abstract
- Ion probe 208Pb/232Th fissure monazite ages from the Argentera External Massif and from the high-pressure units of the Western Alps provide new insights on its Cenozoic tectonic evolution. Hydrothermal monazite crystallizes during cooling/exhumation in Alpine fissures, an environment where monazite is highly susceptible to fluid-mediated dissolution-(re)crystallization. Monazite growth domains visualized by BSE imaging all show a negative Eu anomaly, positive correlation of Sr and Ca and increasing cheralite component (Ca + Th replacing 2REE) with decreasing xenotime (Y) component. The huttonite component (Th + Si replacing REE and P) is very low. Growth domains record crystallization following chemical disequilibrium in a fissure environment, and growing evidence indicates that they register tectonic activity. Fissure monazite ages obtained in this study corroborate previous ages, recording crystallization at ~ 36 Ma, ~ 32–30 Ma, and ~ 25–23 Ma in the high-pressure regions of the Western Alps, interpreted to be respectively related to top-NNW, top-WNW and top-SW thrusting in association with strike-slip faulting. During this latter transpressive phase, younger fissure monazite crystallization is recorded between ~ 20.6 and 14 Ma in the Argentera Massif, interpreted to have occurred in association with dextral strike-slip faulting related to anticlockwise rotation of the Corsica-Sardinia Block. This strike-slip activity is predating orogen-parallel dextral strike-slip movements along and through the internal part of all other External Crystalline Massifs (ECM), starting only at ~ 12 Ma. Our combined compositional and age data for hydrothermal monazite track crystallization related to tectonic activity during unroofing of the Western Alps for over more than 20 million years, offering chronologic insights into how different tectonic blocks were exhumed. The data show that fissures in the high-pressure units formed during greenschist to amphibolite facies retrograde deformation, and later in association with strike-slip faulting.
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- Schmidt, Christoph, et al.
(författare)
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Quantification and spatial distribution of dose rate relevant elements in silex used for luminescence dating
- 2012
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Ingår i: Quaternary Geochronology. - : Elsevier BV. - 1871-1014 .- 1878-0350. ; 12, s. 65-73
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Tidskriftsartikel (refereegranskat)abstract
- Thermoluminescence (TL) is routinely used to date heated lithic artefacts which mostly consist of silex (a mixture of amorphous opal and microcrystalline chalcedony). Analytical investigations of bulk samples confirmed that these materials contain considerable concentrations of radioactive elements, generating an internal dose rate contribution. Common dosimetric models assume the latter to be homogeneous throughout the sample. If this assumption would prove invalid, this will result in systematic errors in the calculated age, especially in the course of so called 'hot spots' of alpha-emitters (and associated local changes in a-sensitivity) and the dose response characteristics of alpha-radiation. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of 22 silex samples are presented here, quantifying element concentrations at several tens analytical spots per sample. Along with radioactive elements (K, Rb, U, Th), another 21 major, minor and trace elements were measured in order to allow characterization of the impurities present in most of the samples. The dataset provides a detailed picture of the spatial distribution of radionuclides and hence of the uniformity of the internal alpha- and beta-dose rate. It is shown that the silex itself mostly contains low amounts of K (<0.1 wt.%), U (<1.0 mu g g(-1)) and Th (<0.4 mu g g(-1)), and dosimetrically negligible Rb concentrations. Systematically higher concentrations are obtained by ICP-MS measurements of the bulk samples. This matches with the finding that impurities (veins, inclusions) often yield significantly elevated radionuclide concentrations, up to two orders of magnitude higher than the silex values. These veins and inclusions, for example Ca or Mg carbonates and Fe-Mn-oxy-hydroxides, lead to steep gradients mainly in the internal alpha-radiation field. Alternative approaches are required to account for the non-uniform internal dose rate and improve the reliability of TL dates of problematic samples.
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- Visnes, Torkild, et al.
(författare)
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Targeting OGG1 arrests cancer cell proliferation by inducing replication stress
- 2020
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Ingår i: Nucleic Acids Research. - : Oxford University Press (OUP). - 0305-1048 .- 1362-4962. ; 48:21, s. 12234-12251
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Tidskriftsartikel (refereegranskat)abstract
- Altered oncogene expression in cancer cells causes loss of redox homeostasis resulting in oxidative DNA damage, e.g. 8-oxoguanine (8-oxoG), repaired by base excision repair (BER). PARP1 coordinates BER and relies on the upstream 8-oxoguanine-DNA glycosylase (OGG1) to recognise and excise 8-oxoG. Here we hypothesize that OGG1 may represent an attractive target to exploit reactive oxygen species (ROS) elevation in cancer. Although OGG1 depletion is well tolerated in non-transformed cells, we report here that OGG1 depletion obstructs A3 T-cell lymphoblastic acute leukemia growth in vitro and in vivo, validating OGG1 as a potential anti-cancer target. In line with this hypothesis, we show that OGG1 inhibitors (OGG1i) target a wide range of cancer cells, with a favourable therapeutic index compared to non-transformed cells. Mechanistically, OGG1i and shRNA depletion cause S-phase DNA damage, replication stress and proliferation arrest or cell death, representing a novel mechanistic approach to target cancer. This study adds OGG1 to the list of BER factors, e.g. PARP1, as potential targets for cancer treatment.
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