Ulrich A. Glasmacher

Spatially resolved detection of luminescence: a unique tool for archaeochronometry

Abstract. Archaeochronometry uses luminescence dating to reveal ages of sediments and artefacts. Uncertainties in luminescence ages are partly related to the dating procedure, which uses grain separates. This is particularly true for stone surfaces, which require an imaging method for luminescence detection. Here we present the development of a novel luminescence device with high spatial resolution as well as signal-to-noise ratio and data processing software that now allows us to determine palaeodoses and potentially the dose-rate for cut sections of rocks and artefacts. The determination of the luminescence age of single mineral grains within sections and even of selected zones within grains becomes feasible, opening up a wide field of new applications.

The metamorphic complex of Beloretzk, SW Urals, Russia — a terrane with a polyphase Meso- to Neoproterozoic thermo-dynamic evolution

Abstract An integrated geological study of the tectono-metamorphic evolution of the metamorphic complex of Beloretzk (MCB) which is part of the eastern Bashkirian mega-anticlinorium (BMA), SW Urals, Russia shows that the main lithological units are Neoproterozoic (Riphean and Vendian age) siliciclastic to carbonate successions. Granitic, syenitic and mafic intrusions together with subaerial equivalents comprise the Neo- and Mesoproterozoic magmatic rocks. The metamorphic grade ranges from diagenetic and very low grade in the western BMA to high-grade in the MCB. The N–S trending Zuratkul fault marks the change in metamorphic grade and structural evolution between the central and eastern BMA. Structural data, Pb/Pb-single zircon ages, 40 Ar/ 39 Ar cooling ages and the provenance signature of Riphean and Vendian siliciclastic rocks in the western BMA give evidence of Mesoproterozoic (Grenvillian) rifting, deformation and eclogite-facies metamorphism in the MCB and a Neoproterozoic (Cadomian) orogenic event in the SW Urals. Three pre-Ordovician deformation phases can be identified in the MCB. The first SSE-vergent, isoclinal folding phase (D 1 ) is younger than the intrusion of mafic dykes (Pb/Pb-single zircon: ∼1350 Ma) and older than the eclogite-facies metamorphism. High P /low T eclogite-facies metamorphism is bracketed by D 1 and the intrusion of the Achmerovo granite (Pb/Pb-single zircon: ≤970 Ma). An extensional, sinistral, top-down-to-NW directed shearing (D 2 ) is correlated with the first exhumation of the MCB. E-vergent folding and thrusting (D 3 ) occurred at retrograde greenschist-facies metamorphic conditions. The tremolite 40 Ar/ 39 Ar cooling age (718±5 Ma) of amphibolitic eclogite and muscovite 40 Ar/ 39 Ar cooling ages (about 550 Ma) of mica schists indicate that a maximum temperature of 500±50xa0°C was not reached during the Neoproterozoic orogeny. The style and timing of the Neoproterozoic orogeny show similarities to the Cadomian-aged Timan Range NW of the Polar Urals. Geochronological and thermochronological data together with the abrupt change in structural style and metamorphism east of the Zuratkul fault, suggest that the MCB is exotic with respect to the SE-margin of the East European Platform. Thus, the MCB is named the ‘Beloretzk Terrane’. Recognition of the ‘Beloretzk Terrane’ and the Neoproterozoic orogeny at the eastern margin of Baltica has important implications for Neoproterozoic plate reconstruction and suggests that the eastern margin of Baltica might have lain close to the Avalonian–Cadomian belt.

Thermotectonic evolution of the Barrandian, Czech Republic, as revealed by apatite fission-track analysis

Abstract A fission-track (FT) study was carried out on apatite from Upper Proterozoic to Upper Carboniferous sedimentary and volcanic rocks in the Barrandian, Czech Republic. Apatite FT-ages vary between 324±8 Ma (Lower Carboniferous) and 196±14 Ma (Lower Jurassic). Mean confined track lengths range from 11.68±1.76 to 13.30±1.41 μm. The temperature–time path of selected samples was simulated by applying the Laslett-annealing model and independent geological constraints from the Barrandian. The first stage of increased temperature that is recorded in nearly all samples occurred at the Upper Devonian/Lower Carboniferous boundary. The change in temperature is due to the thickening of the crust by increased sediment load and stacking of sedimentary rocks along thrusts. FT-data indicate a limitation of the extension of thrust sheets towards the West. Cooling during the Carboniferous is attributed to exhumation of parts of the Barrandian. Deposition of Upper Carboniferous to Lower Permian sediments caused a second increase in temperature in Lower Permian time. Variation in maximum temperature indicates variable thickness of the sedimentary cover. The second cooling during the Mesozoic is linked to the long-term slow to medium exhumation process of the Central Variscan belt.

Contrasting provenance signals in Riphean and Vendian sandstones in the SW Urals (Russia): constraints for a change from passive to active continental margin conditions in the Neoproterozoic

Abstract Two contrasting provenance areas for Neoproterozoic sandstones can be distinguished in the southwestern Urals by light and heavy mineral analyses as well as by mineral chemistry. These reflect a dramatic change of geotectonic conditions at the eastern border of the Baltica protocontinent at around 610–620 Ma. Detritus from Riphean and Lower Vendian sandstones representing about 1 Ga of continuous sedimentation is characterised by a ‘continental platform provenance’ reflecting its derivation from the Proterozoic basement of the East European platform. Source rocks include mainly minerals and few lithic clasts from granitoids and high-grade metamorphic rocks as well as reworked clastic sediments and silicic volcanic rocks. The provenance signal changes abruptly with Upper Vendian detritus representing a ‘recycled orogenic provenance’. This includes mineral and lithic clasts of low-grade siliciclastic metasediments and mylonites containing phengites with a high-pressure signature as well as clasts of bimodal volcanic rocks and reworked siliciclastic sediments. The composition of phengites contrasts strongly with those of detrital white mica in the Riphean rocks. Also, the composition of tourmalines derived from a metapsammopelitic source indicates a mainly Al-poor metasediment provenance, whereas Riphean tourmalines were derived from mainly Al-rich metapsammopelites. Zircon morphology, tourmaline zoning and a reduced heavy mineral spectrum provide evidence for polycyclic sedimentation during Riphean and Vendian. Upper Vendian sedimentary rocks were deposited in a foreland basin derived from a proximal uplift to the east. Provenance characteristics of the Upper Vendian detritus are consistent with areas affected by a high-pressure/low-temperature metamorphism during a pre-Uralian orogenic event, most likely from the metamorphic complex of Beloretsk, which was emplaced and exhumed during the Upper Vendian. The change of geotectonic conditions in the Upper Vendian reflects a change from a passive continental margin in the South Urals throughout the entire Riphean since at least 1350 Ma to a convergent continental margin within a presumed transpressional setting.

Heavy-ion induced defects in phlogopite imaged by scanning force microscopy

Abstract A new geological dating method uses alpha-recoil tracks (ART) created by the natural α-decay of U, Th, and their daughter products. When visualizing ART by optical microscopy, the age range is restricted to the last 10 6 a. Recording of etched ART by scanning force microscopy (SFM) enables the access to track densities beyond 10 8 cm −2 and thus extends ART dating to ages >10 6 a. In the present work, natural radiation damage induced by ions was simulated by irradiating phlogopite samples, originating from Quaternary and Tertiary volcanic rocks of the Eifel (Germany) and Kerguelen Islands (Indian Ocean), with U, Ni (11.4 MeV/u), Xe, Cr, Ne (1.4 MeV/u), and Bi (200 keV) ions. Before and after irradiation and etching with HF, the phlogopite surfaces were imaged by SFM. On freshly cleaved natural phlogopite, latent ART, located near to the cleavage plane, form small hillocks. In addition, numerous similar hillocks develop in air, not related to ART since they do not transform to etch pits. Due to these hillocks, whose origin is still unknown, it is presently not possible to study latent ART with SFM. A further kind of hillock arises after irradiation with energetic heavy ions. The damage trails created by these ions are etchable, providing hexagonal etch pits in the case of U, Xe and Cr ions, whereas the pits of Ni, Ne and Bi ion tracks are triangular. The transition from triangular to hexagonal shape occurs between the electronic energy loss values 5.4 and 8.1 keV/nm for Ni and Cr ions, respectively, coinciding with a sharp increase of the track etch velocity.

Alpha-recoil tracks in natural dark mica: Dating geological samples by optical and scanning force microscopy

Alpha-recoil tracks (ART) are lattice defects caused by the a-decay of 238 U, 235 U, 232 Th, and daughter products. Visualization of etched ARTs in dark mica by phase-contrast microscopy allows dating of Quaternary geological as well as archaeological materials. Visualization of etched ARTs by Nomarski-differential-interference-contrast microscopy (NDICM) and scanning force microscopy (SFM) enables the access to areal densities (qa) of ART etch pits beyond 10 4 mm � 2 and thus the extension of the new ART-dating technique to an age range >1 Ma. The successful application of SFM as a new tool in geochronology could open the way to a field to be characterized as nanogeochronology. In order to visualize ARTs by NDICM and SFM, dark mica was etched with 4% HF at 21 C for 5–107 min. A linear relationship between qa and etching time (te) was observed for phlogopites from the Kerguelen Islands (French territory, Indian Ocean), and the Kovdor magmatic complex (Russia). The volume density (qv) of ART is a function of etching speed (veff ) and slope of the q a -growth curve. The ART-age equation allows the calculation of an individual q v -growth curve for the phlogopite analysed by us using the uranium and thorium content. The ART-ages were determined by combining the experimentally obtained volume density with the individual qv-growth curve.

Thermotectonic evolution of the western fold-and-thrust belt, southern Uralides, Russia, as revealed by apatite fission track data

Abstract The Uralides, a linear N–S trending Palaeozoic fold belt, reveals an intact, well-preserved orogen with a deep crustal root within a stable continental interior. In the western fold-and-thrust belt of the southern Uralides, Devonian to Carboniferous siliciclastic and carbonate rocks overlay Mesoproterozoic to Neoproterozoic sedimentary rocks. Deformation in the Devonian, Carboniferous and Permian caused thick-skinned tectonic features in the western and central parts of the western fold-and-thrust belt. A stack of several nappes characterizes the deformation in the eastern part. Along the E–W transect AC-TS96 that crosses the western fold-and-thrust belt, apatite fission track data record various stages of the geodynamic evolution of the Uralide orogeny such as basin evolution during the Palaeozoic, synorogenic movements along major thrusts, synorogenic to postorogenic exhumation and a change in the regional stress field during the Upper Jurassic and Lower Cretaceous. The Palaeozoic sedimentary cover and the Neoproterozoic basement of the Ala-Tau anticlinorium never exceed the upper limit of the PAZ since the Devonian. A temperature gradient similar to the recent one (20 °C/km) would account for the FT data. Reactivation of the Neoproterozoic Zilmerdak thrust was time equivalent to the onset of the Devonian and Carboniferous collision-related deformation in the east. West-directed movement along the Tashli thrust occurred in the Lower Permian. The Devonian and Carboniferous exhumation path of the Neoproterozoic siliciclastic units of the Tirlyan synclinorium mirrors the onset of the Uralian orogeny, the emplacement of the Tirlyan nappe and the continuous west-directed compression. The five main tectonic segments Inzer Synclinorium, Beloretzk Terrane, Ala-Tau anticlinorium, Yamantau anticlinorium and Zilair synclinorium were exhumed one after another to a stable position in the crust between 290 and 230 Ma. Each segment has its own t–T path but the exhumation rate was nearly the same. Final denudation of the western fold-and-thrust belt and exhumation to the present surface probably began in Late Tertiary. In Jurassic and Cretaceous, south-directed movements along W–E trending normal faults indicate a change in the tectonic regime in the southern Uralides.

Artificial ion tracks in volcanic dark mica simulating natural radiation damage: A scanning force microscopy study

Abstract A new dating technique uses alpha-recoil tracks (ART), formed by the natural α-decay of U, Th and their daughter products, to determine the formation age of Quaternary volcanic rocks ( 10 8 cm −2 and thus extend the new ART-dating technique to an age range >106 a. In order to simulate natural radiation damage, samples of phlogopite, originating from Quaternary and Tertiary volcanic rocks of the Eifel (Germany) and Kerguelen Islands (Indian Ocean) were irradiated with U, Ni (11.4 MeV/u), Xe, Cr, Ne (1.4 MeV/u) and Bi (200 keV) ions. After irradiation and etching with HF at various etching times, phlogopite surfaces were visualized by SFM. Hexagonal etch pits are typical of U, Xe and Cr ion tracks, but the etch pits of Ni, Ne and Bi ion tracks are triangular. Surfaces irradiated with U, Xe, Cr and Ni ions do not show any significant difference between etch pit density and irradiation fluence, whereas the Ne-irradiated surface show ∼14 times less etch pit density. The etching rate vH (parallel to cleavage) depends on the chemical composition of the phlogopite. The etching rate vT′ (along the track) increases with energy loss.

Etching behaviour of alpha-recoil tracks in natural dark mica studied via artificial ion tracks

Abstract Alpha-recoil tracks (ARTs) created by the α-decay of U, Th, and their daughter nuclei, are used by a new dating method to determine the formation age of dark mica bearing Quaternary and Neogene volcanic rocks and the cooling age of plutonic and metamorphic rocks [Chem. Geol. 166 (2000) 127, Science 155 (1967) 1103]. The age equation combines the volumetric density of ARTs with the U and Th contents. Etching latent ARTs (diameter 30–100 nm) in the mica mineral phlogopite by HF and measuring the areal density of triangular etch pits by optical and scanning force microscopy (SFM) leads to a linear growth of ART areal density versus etching time. The ART volume density is a function of the slope of the areal density and the etching rate (veff). Therefore, the determination of veff is essential for the calculation of an age value. To determine the etching parameters such as etching efficiency and veff, phlogopite samples were irradiated with 80 keV Au ions. Irradiated surfaces were etched with 4% HF at 23±2 °C during successive time intervals and after each interval studied with SFM. The etching rate veff was determined by different techniques. To evaluate the threshold of etchability, the energy losses of the Au ions and α-recoil nuclei in phlogopite were calculated with the SRIM00 code. The etching efficiency of the Au ion tracks was then used to predict the corresponding etching efficiency of the natural radioactive nuclei.

Spectroscopic study on ion irradiated calcites and gypsum

N. Schöppner †1, S. Dedera1, U.A. Glasmacher1, M. Burchard1, M. Zdorovets2,3, and Christina Trautmann4 1Institute of Earth Sciences, University of Heidelberg, Germany; 2Institute of Nuclear Physics, Almaty, Kazakhstan; 3Gumilyov Eurasian National University, Astana, Kazakhstan; 4TU Darmstadt and GSI Helmholtzzentrum Darmstadt, Germany Within geosciences, the use of fission tracks in various minerals as a thermochronological analytical technique is of high importance. The visualization of spontaneous and induced fission tracks uses the well established etching technique. Carbonate minerals have been tested in the past with differentiated results. The latest research clearly indicates that fission tracks develop in carbonate minerals and that they can be revealed by specific etching conditions [1], [2]. As carbonate minerals are excellent minerals for spectroscopic analytical techniques, the application of those techniques to non-destructively deduce information on fission tracks was tested. Various carbonate minerals were irradiated within two different ion energy ranges. Ions of GeV kinetic energy were available at the GSI, while irradiations at lower energy were performed at the RGP Institute Yadernoi Fiziki, Astana, Kazakhstan. Mono crystalline samples of carbonate used in these experiments are trigonal calcite (CaCO3), rhomboedric aragonite (CaCO3), monocline malachite (Cu2[(OH)2/CO3]), trigonal rhodochrosite (MnCO3), trigonal dolomite (MgCO3), and monocline gypsum (CaSO4*2H2O). At GSI, the carbonate minerals were irradiated at the UNILAC accelerator with 11.1 MeV/u Au and Bi ions, applying fluences of 1×106, 5×106, 1×107, 5×107, 1×108, 1×1011, and 1×1012 ions/cm. At the RGP Institute, the samples were irradiated at the Astana accelerator with 1.7 MeV/u Kr ions applying fluences between 1×1010 and 1×1012 ions/cm. The lower mass and energy of these Kr ions is closer to the conditions given by natural fission fragments from U. All crystals were analyzed by Raman spectroscopy using the LabRam HR800 UV spectrometer equipped with an OLYMPUS BXFM-ILHS optical microscope, a grating with 1800 grooves per millimeter and a Peltier-cooled CCD detector. During the spectroscopic measurements an objective of 50x magnification was used. The spectra were excited by laser light of wavelength 473.03 nm. The lateral resolution was ∼2 μm, the wave number accuracy 0.5 cm−1 and the spectral resolution was 1 cm−1. First results are provided for irradiated calcite and gypsum (Figs. 1, 2). The revealed Raman spectra are similar up to a fluences of 5×1011 Kr-ions/cm. Above those fluences a new Raman band appears at about ∼430 cm−1. In addition, at 5×1011 Kr-ions/cm a shoulder appears at the left side of the main Raman band at about 1100 cm−1. Significant changes in the Raman spectra of gypsum ap-