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We describe a new high-purity germanium (HPGe) detector setup for low-background γ-ray spectrometry. The GeMSE facility (Germanium Material and meteorite Screening Experiment) is dedicated to material screening for rare event searches in astroparticle physics as well as to the characterization of meteorites. It is installed in a medium depth (∼620 m.w.e.) underground laboratory in Switzerland in a multi-layer shielding and is equipped with an active muon veto. We have reached a very competitive integral background rate of (246 ± 2) counts/day (100-2700 keV) and measured a sensitivity of ∼0.5-0.6 mBq/kg for long-lived isotopes from the 238 U/ 232 Th chains in a ∼1 kg sample screened for ∼27 days. An extrapolation to higher sample masses and measurement times suggests a maximum sensitivity in the O(50) µBq/kg range. We describe the data analysis based on Bayesian statistics, background simulations, the efficiency calibration and first sample measurements.

The metamorphic evolution of the Tjeliken eclogite, occurring within the Seve Nappe Complex of northern Jämtland (Swedish Caledonides), is presented here. The prograde part of the pressure and temperature (P-T) path is inferred from the mineral inclusions (pargasitic amphibole) in garnet and intracrystalline garnet exsolutions in omphacite. Peak metamorphic conditions of 25-26 kbar at 650-700 8C are constrained from geothermobarometry for the peak-pressure assemblage garnet + omphacite + phengite + quartz + rutile, using the garnet-clinopyroxene Fe-Mg exchange thermometer in combination with the net-transfer reaction (6 diopside + 3 muscovite ¼ 3 celadonite +2 grossular + pyrope) geobarometer, the average P-T method of Thermocalc and pseudosection modelling. Quartz inclusions with well-developed radial cracks were identified within omphacite, which suggest that the studied rock could have been buried down to the coesite stability field. Post-peak P-T evolution is inferred from diopside-plagioclase symplectites and amphibole coronas around garnet. Previous studies in northern Jämtland suggest a substantial gap between the P-T conditions of the Lower and Middle Seve nappes: 14-16 kbar and 550-680 8C and 20-30 kbar and 700-800 8C, respectively.

Radionuclide activities were measured in the low-background gamma-ray spectrometry facility GeMSE in eight meteorite falls (Lost City, Tamdakht, Huaxi, Boumdeid, Xining, Kamargaon, Degtevo, and Ouidiyat Sbaa) and two finds (SaU 606 and M€ urtschenstock) to evaluate the use of radionuclides for terrestrial age estimates. Results indicate that these meteorites were all derived from small-(r < 25 cm) to medium-sized (r < 65 cm) meteoroids. Short-lived 48 V (t 1/2 = 16.0 d) and 51 Cr (t 1/2 = 27.7 d) were only detected in Oudiyat Sbaa (EH), while 7 Be (t 1/2 = 53.1 d) was also detected in Degtevo (H) and Kamargaon (L), in agreement with reported fall dates. The 22 Na/ 26 Al activity ratio in Huaxi agrees with the previously reported short cosmic-ray exposure age of this meteorite while 22 Na/ 26 Al in Kamargaon likely records a complex exposure history. Bayesian statistical analysis verifies the detection of very low activities of 44 Ti (t 1/2 = 60 a) in the relatively large H chondrites (>100 g) Degtevo, Huaxi, Tamdakht, Lost City, and SaU 606. Additionally, large samples from Oudiyat Sbaa (EH) and Kamargaon (L) gave positive detections. For H chondrite target compositions, detected 44 Ti(Fe+Ni)/ 26 Al averaged 0.055 AE 0.013. Activities of 22 Na and 54 Mn in SaU 606 show that this meteorite fell between July and September 2012, making SaU 606 the second recent fall from Oman identified using gamma-ray spectrometry. The upper activity limit of 22 Na in the M€ urtschenstock meteorite shows that it fell prior to 1999 and is not related to a bolide observation in 2015. M€ urtschenstock shows 137 Cs~109 higher than previously determined in Oman meteorites, likely due to Chernobyl fallout.

We combine the search for young meteorites in the Omani‐Swiss collection (˜1140 fall events collected 2001–2018) using 22Na and 44Ti with luminescence and 14C sediment ages from the Ramlat Fasad (RaF) dense collection area (DCA) of Oman to obtain combined terrestrial ages and maximum accumulation times, and test whether the proportion of young meteorites is consistent with the models of meteorite flux and weathering. Gamma‐ray spectrometry data for 22Na show that two (0.17%) of the meteorites in the collection fell during the 20 yr preceding this study, consistent with the rates of meteorite accumulation. In the RaF DCA, meteorites are found on Quaternary to Neogene sediments, providing constraints for their maximum terrestrial ages. 44Ti activities of the RaF 032 L6 strewn field found on deflated parts of active dunes indicate an age of 0.2–0.3 ka while dune sand optically stimulated luminescence ages constrain an upper age of 1.6 ka. Extensive sediment dating using luminescence methods in the RaF DCA area showed that all other meteorite finds were made on significantly older sediments (>10 ka). Dense accumulations of meteorites in RaF are found on blowouts of the Pliocene Marsawdad formation. Our combined results show that the proportion of meteorites with low terrestrial ages is low compared to other find areas, consistent with the previously determined high average terrestrial age Oman meteorites and significantly older than suggested by models of exponential decay. Oman meteorites may commonly have been buried within dunes and soils over extended periods, acting as a temporary protection against erosion.