Combined garnet and zircon geochronology of the ultra-high temperature metamorphism: Constraints on the rise of the Orlica-Śnieżnik Dome, NE Bohemian Massif, SW Poland

Garnet and zircon geochronology combined with trace element partitioning and petrological studies provide tight constraints on evolution of the UHT-(U)HP terrain of the Orlica-Śnieżnik Dome (OSD) in the NE Bohemian massif. Lu-Hf dating of peritectic garnet from two mesocratic granulites constrained the time of its initial growth at 346.9 ± 1.2 and 348.3 ± 2.0 Ma recording peak 2.5 GPa pressure and 950 °C temperature. In situ, U-Pb SHRIMP dating of zircon from the same granulite gave a younger age of 341.9 ± 3.4 Ma. Ti-in-zircon thermometry indicates crystallization at 810–860 °C pointing to zircon formation on the retrograde path. Lu partitioning between garnet rim and zircon suggest equilibrium growth and thus U-Pb zircon age constrain the terminal phase of garnet crystallization which lasted about 6 Ma. All Sm-Nd garnet ages obtained for mesocratic and mafic granulites are identical and consistently younger than the corresponding Lu-Hf dates. They are interpreted as reflecting cooling of granulites through the Sm-Nd closure temperature at about 337 Ma. The estimated PTt path documents the ca. 10 Ma evolution cycle of the OSD characterized by two distinct periods: (1) 347 - > 342 Ma period corresponds to nearly isothermal decompression resulting from crustal scale folding and vertical extrusion of granulites, and (2) at > 342–337 Ma which corresponds to a fast, nearly isobaric cooling.This study was financed by Polish Ministry of Science and Higher Education grant No. N N307 057734 and financially supported by Polish Academy of Sciences, Institute of Geological Sciences grant No. HPT. R. Anczkiewicz acknowledges funding from internal IGS PAS grant. The research of J. Szczepanski was funded by the University of Wroclaw grant 1017/S/ING

Garnet growth and mineral geochronology constrains the diachronous Neoproterozoic convergent evolution of the southern Dom Feliciano Belt, Uruguay

The Dom Feliciano Belt of southern Brazil and Uruguay represents part of a larger Neoproterozoic orogenic system formed during the amalgamation of Western Gondwana. The hinterland and foreland domains in parts of the belt preserve deformation structures and metamorphic assemblages that developed during early crustal thickening from c. 650 Ma. However, the metamorphic history of the southern foreland, in Uruguay, and its relationship with the hinterland, is not so well understood. We show that metamorphism in the southern hinterland is characterized by near-isothermal decompression from ~10 kbar (~770°C) down to ~6 kbar, reflecting exhumation from depths of ~40 km during convergent thrusting and crustal thickening. This metamorphic event and associated magmatism is constrained by garnet Lu–Hf and zircon U–Pb dating to c. 655–640 Ma, supporting age and P–T constraints from previous studies. In contrast, prograde metamorphism in the foreland supracrustal rocks reached maximum lower-amphibolite facies conditions (~6–7 kbar and ~550–570°C) and is constrained by garnet Lu–Hf dating to 582 ± 23 Ma. An exposed sheet of imbricated foreland basement rocks reached partial melting at upper-amphibolite facies conditions, and metamorphism is similarly constrained to c. 585–570 Ma by monazite U–Pb dating. The data indicate that metamorphism in the foreland occurred during a sinistral transpressional event c. 55–85 Ma after the start of crustal thickening recorded in the hinterland, whereby strain partitioning during sinistral transpression led to imbrication in the foreland and oblique thrusting of the basement over more distal supracrustal rocks. This event is coeval with transpressional deformation in the Kaoko and Gariep belts, indicating a distinct two-stage tectonic history driven by the three-way convergence between the Congo, Kalahari, and South American cratons

Tracing human mobility in central Europe during the Upper Paleolithic using sub-seasonally resolved Sr isotope records in ornaments

Mobility of people and goods during the Upper Paleolithic has proven difcult to reconstruct given the relative rareness of remains. Nevertheless, archaeological contexts like the Late Pleistocene horizon of Borsuka Cave (Southern Poland) represent a unique opportunity to explore patterns of objects’ transportation across Central Europe. We investigated the origin of four ornaments made of European elk (Alces alces L.) incisors recovered at Borsuka Cave – the oldest known burial site in Poland, possibly a child grave. Laser-ablation plasma source mass spectrometric analyses of trace elements and Sr isotopic compositions revealed that one elk was roaming within a geologically uniform area while the others changed their pastures during their lifetimes. The non-local origin of the elk teeth is inferred from their exotic Sr isotopic compositions and the lack of evidence for the presence of elk in this territory during the Pleistocene. Instead, the elks’ Sr isotopic composition show good agreement with sites near the Austria-Slovakia border region and northern Hungary, ~250km away from the study site. We argue that the artefacts were most likely brought to Borsuka Cave by humans or by a network of exchange, so far never reported in the time range 32.5–28.8 ka cal BP for Southern Poland

Plutonium, 90Sr and 241Am in human bones from southern and northeastern parts of Poland

The paper presents the results of our study on 238Pu, 239Pu, 240Pu, 241Am and 90Sr concentration in human bones carried out on a set of 88 individual samples of central Europe origin. Bone tissue samples were retrieved under surgery while introducing hip joint implants. The conducted surgeries tend to cover either southern or northeastern parts of Poland. While for the southern samples only global fallout was expected to be seen, a mixed global and Chernobyl fallout were to be reflected in the others. Alpha spectrometry was applied to obtain activity concentration for 238Pu, 239?240Pu, 241Am, while liquid scintillation spectrometry for 90Sr and mass spectrometry to receive 240Pu/239Pu mass ratio. Surprisingly enough, and to the contrary to our expectations we could not see any significant differences in either Pu activity or Pu mass ratio between the studied populations. In both populations Chernobyl fraction proved marginal. The results on 90Sr and 241Am confirm similarities between the two examined groups

The timing of strike-slip shear along the Ranong and Khlong Marui faults, Thailand

The timing of shear along many important strike-slip faults in Southeast Asia, such as the Ailao Shan-Red River, Mae Ping and Three Pagodas faults, is poorly understood. We present 40Ar/39Ar, U-Pb SHRIMP and microstructural data from the Ranong and Khlong Marui faults of Thailand to show that they experienced a major period of ductile dextral shear during the middle Eocene (48–40 Ma, centered on 44 Ma) which followed two phases of dextral shear along the Ranong Fault, before the Late Cretaceous (>81 Ma) and between the late Paleocene and early Eocene (59–49 Ma). Many of the sheared rocks were part of a pre-kinematic crystalline basement complex, which partially melted and was intruded by Late Cretaceous (81–71 Ma) and early Eocene (48 Ma) tin-bearing granites. Middle Eocene dextral shear at temperatures of ~300–500°C formed extensive mylonite belts through these rocks and was synchronous with granitoid vein emplacement. Dextral shear along the Ranong and Khlong Marui faults occurred at the same time as sinistral shear along the Mae Ping and Three Pagodas faults of northern Thailand, a result of India-Burma coupling in advance of India-Asia collision. In the late Eocene (<37 Ma) the Ranong and Khlong Marui faults were reactivated as curved sinistral branches of the Mae Ping and Three Pagodas faults, which were accommodating lateral extrusion during India-Asia collision and Himalayan orogenesis

40Ar39Ar^{40}Ar^{39}Ar dating of alkaline lamprophyres from the Polish Western Carpathians

Amphiboles from two types of alkaline lamprophyres from the Silesian Nappe in the Polish Western Carpathians were dated by $^{40}Ar^{39}Ar$ stepwise heating technique. Three teschenite samples representing mesocratic type of lamprophyres yielded similar ages of 122.3±1.6 Ma, while leucocratic lamprophyre represented by a syenite dyke gave 120.4±1.4 Ma date. These ages are interpreted as the time of magmatic emplacement during Early Cretaceous extensional episode within the Silesian Basin. Ages for both types of lamprophyres are identical within error limits, which points to fast (probably ca. 5 Ma) magma evolution from meso to leucocratic stage