Origin and age of ultramafic rocks and gabbros in the southern Puna of Argentina: an alleged Ordovician suture revisited

Ultramafic rocks and gabbros are exposed in the southern Puna (NW Argentina) in tectonic association with continental arc-related Ordovician (volcano) sedimentary successions and granitoids. The origin of this mafic rock suite has been debated for three decades as either representing an Ordovician terrane suture, primitive Ordovician arc-related rocks or relics of the pre-Ordovician basement in tectonic contact with the Ordovician retro-arc basin successions. We present the first U–Pb ages of primary and inherited zircon from gabbros of this mafic–ultramafic assemblage. LA-ICP-MS analyses on cores and rims of these zircon grains yielded a concordia age of 543.4 ± 7.2 Ma for the gabbroic rocks. Other analysed zircons have Mesoproterozoic, and Early Ediacaran core and rim ages indicating that the magmas also assimilated Meso- and Neoproterozoic crustal material prior to final crystallization. The mafic rocks witnessed higher metamorphic grade than associated Ordovician rocks, which are unmetamorphosed or only affected by anchimetamorphism. The gabbros are mostly tholeiitic and enriched in Zr, Th, as well as other incompatible elements and have εNd _t=540Ma ranging from 1.3 to 7.4 with most of the values between 5 and 7. ¹⁴⁷Sm/¹⁴⁴Nd ratios show evidence of weak crustal contamination. The mafic rocks do not reveal any affinity to mid-ocean ridge basalts in their geochemistry but point instead to an emplacement in an active plate margin arc environment. Chromites from ultramafic rocks show typical Ti, Al, Cr#, Fe³⁺ abundances found in magmatic arc rocks. The formation of the gabbros and the associated ultramafic rocks in the southern Argentine Puna is related to the evolution of the margin of the Pampia terrane, including the Puncoviscana basin, during the Late Neoproterozoic and earliest Cambrian. In contrast to previous interpretations, the rocks predate the Ordovician evolution of the Central proto-Andean active margin. Consequently, interpretations assuming these rocks to represent an oceanic terrane suture of Ordovician age have to be dismissed as much as all palaeotectonic models that define Ordovician terranes in the Central Andes based on assumption that the ultramafic rocks and gabbros exposed in the southern Puna mark plate boundaries.     

Micro-feature-motivated numerical analysis of the coupled bio-chemo-hydro-mechanical behaviour in MICP

Acta Geotechnica - A coupled bio-chemo-hydro-mechanical model (BCHM) is developed to investigate the permeability reduction and stiffness improvement in soil by microbially induced calcite...     

The eastern continuation of the Cadomian orogen: U–Pb zircon evidence from Saxo-Thuringian granitoids in south-western Poland and the northern Czech Republic

We report U–Pb single zircon ages from three pre-Variscan granitoids in the NE part of the Bohemian Massif. The Platerówka granodiorite from the Lausitz-Izera Unit, the Polish Sudetes, has been dated at 533±9 Ma. The Bitouchov granite form the SW part of the South Krkonoe Unit, the Czech Sudetes, gave an age of 540+11/–10 Ma, and the Wdroe granodiorite in the Fore-Sudetic Block yielded 548±9 Ma. All these latest Vendian/Early Cambrian granitoids represent the post-tectonic expression of a late Proterozoic Cadomian orogenic cycle and demonstrate the eastward extent of the Cadomian basement into the Variscan orogen. Granodiorites of similar age have so far been reported from Brittany and especially from the Saxo-Thuringian Terrane to the NE and SW of the Elbe Fault Zone. We conclude that the Saxo-Thuringian Terrane extends across the Elbe and Sudetic Marginal Fault Zones into the Fore-Sudetic Block.     

A 3D gravity and magnetic model for the Entenschnabel area (German North Sea)

International Journal of Earth Sciences - In this study, we focus on structural configuration of the Entenschnabel area, a part of the German exclusive economic zone within the North Sea, by means...     

GPCC's new land surface precipitation climatology based on quality-controlled in situ data and its role in quantifying the global water cycle

In 1989, the need for reliable gridded land surface precipitation data sets, in view of the large uncertainties in the assessment of the global energy and water cycle, has led to the establishment of the Global Precipitation Climatology Centre (GPCC) at Deutscher Wetterdienst on invitation of the WMO. The GPCC has calculated a precipitation climatology for the global land areas for the target period 1951–2000 by objective analysis of climatological normals of about 67,200 rain gauge stations from its data base. GPCC's new precipitation climatology is compared to several other station-based precipitation climatologies as well as to precipitation climatologies derived from the GPCP V2.2 data set and from ECMWF's model reanalyses ERA-40 and ERA-Interim. Finally, how GPCC's best estimate for terrestrial mean precipitation derived from the precipitation climatology of 786 mm per year (equivalent to a water transport of 117,000 km³) is fitting into the global water cycle context is discussed.     

Identification of the uranium speciation in an underground acid mine drainage environment

The subsurface acid mine drainage (AMD) environment of an abandoned underground uranium mine in Königstein/Saxony/Germany, currently in the process of remediation, is characterized by low pH, high sulfate concentrations and elevated concentrations of heavy metals, in particular uranium. Acid streamers thrive in the mine drainage channels and are heavily coated with iron precipitates. These precipitates are biologically mediated iron precipitates and related to the presence of Fe-oxidizing microorganisms forming copious biofilms in and on the Fe-precipitates. Similar biomineralisations were also observed in stalactite-like dripstones, called snottites, growing on the gallery ceilings.The uranium speciation in these solutions of underground AMD waters flowing in mine galleries as well as dripping from the ceiling and forming stalactite-like dripstones were studied by time resolved laser-induced fluorescence spectroscopy (TRLFS). The fluorescence lifetime of uranium species in both AMD water environments were best described with a mono-exponential decay, indicating the presence of one major species. The detected positions of the emission bands and by comparing it in a fingerprinting procedure with spectra obtained for acid sulfate reference solutions, in particular Fe(III) - SO₄²⁻ - UO₂²⁺ reference solutions, indicated that the uranium speciation in the AMD environment of Königstein is dominated in the pH range of 2.5-3.0 by the highly mobile aquatic uranium sulfate species UO₂SO_4(aq) and formation of uranium precipitates is rather unlikely as is retardation by sorption processes. The presence of iron in the AMD reduces the fluorescence lifetime of the UO₂SO_4(aq) species from 4.3 μs, found in iron-free uranium sulfate reference solutions, to 0.7 μs observed in both AMD waters of Königstein and also in the iron containing uranium sulfate reference solutions.Colloids were not observed in both drainage water and dripping snottite water as photon correlation spectroscopy analyses and centrifugation experiments at different centrifugal accelerations between 500g and 46000g revealed. Thus transport and uranium speciation at the investigated AMD sites is neither influenced by U(IV) or U(VI) eigencolloids nor by uranium adsorbed on colloidal particles.This study shows that TRLFS is a suitable spectroscopic technique to identify the uranium speciation in bulk solutions of AMD environments.     

A proposed new type of arsenian pyrite: Composition, nanostructure and geological significance

This report describes a new form of arsenian pyrite, called As³⁺-pyrite, in which As substitutes for Fe [(Fe,As)S₂], in contrast to the more common form of arsenian pyrite, As¹⁻-pyrite, in which As¹⁻ substitutes for S [Fe(As,S)₂]. As³⁺-pyrite has been observed as colloformic overgrowths on As-free pyrite in a hydrothermal gold deposit at Yanacocha, Peru. XPS analyses of the As³⁺-pyrite confirm that As is present largely as As³⁺. EMPA analyses show that As³⁺-pyrite incorporates up to 3.05 at % of As and 0.53 at. %, 0.1 at. %, 0.27 at. %, 0.22 at. %, 0.08 at. % and 0.04 at. % of Pb, Au, Cu, Zn, Ni, and Co, respectively. Incorporation of As³⁺ in the pyrite could be written like: As³⁺+yAu⁺+1-y(□)⇔2Fe²⁺; where Au⁺ and vacancy (□) help to maintain the excess charge. HRTEM observations reveal a sharp boundary between As-free pyrite and the first overgrowth of As³⁺-pyrite (20-40 nm thick) and co-linear lattice fringes indicating epitaxial growth of As³⁺-pyrite on As-free pyrite. Overgrowths of As³⁺-pyrite onto As-free pyrite can be divided into three groups on the basis of crystal size, 8-20 nm, 100-300 nm and 400-900 nm, and the smaller the crystal size the higher the concentration of toxic arsenic and trace metals. The Yanacocha deposit, in which As³⁺-pyrite was found, formed under relatively oxidizing conditions in which the dominant form of dissolved As in the stability field of pyrite is As³⁺; in contrast, reducing conditions are typical of most environments that host As¹⁻-pyrite. As³⁺-pyrite will likely be found in other oxidizing hydrothermal and diagenetic environments, including high-sulfidation epithermal deposits and shallow groundwater systems, where probably kinetically controlled formation of nanoscale crystals such as observed here would be a major control on incorporation and release of As³⁺ and toxic heavy metals in oxidizing natural systems.     

Spatial and seasonal dynamics of soil loss ratio in mountain rangelands of south-western Kyrgyzstan

Vegetation cover is the main factor of soil loss prevention. The C-factor of the RUSLE (Revised Universal Soil Loss Equation) was predicted with NDVI, ground data and exponential regression equation for mountain rangelands of Kyrgyzstan. Time series of C-factor, precipitation and temperature were decomposed into seasonal and trend components with STL (seasonal decomposition by loess) to assess their interrelations. C-factor, precipitation and temperature trend components indicated significant lagged correlation, whereas seasonal components indicated more complex relations with climate factors which can be promoting as well as limiting factors for vegetation development, depending on the season. Rainy springs and hot summers may increase soil loss dramatically, whereas warm and dry springs with rainy summers can decrease it. Steep slopes indicated higher soil loss ratio, whereas flat areas were better protected by vegetation.     

Regional distribution and temporal trends of some contaminants in the water of the Baltic Sea

During a cruise on board RV Gauss in May/June 1988, joint investigations into organochlorine compounds, dissolved trace metals, petroleum hydrocarbons and basic hydrography were carried out at representative stations of the Baltic Monitoring Programme (BMP). The aim of the cruise was to study distribution patterns and — using previous data — to establish temporal trends if at all discernible.Each group of contaminants investigated showed specific characteristics, with differences even between compounds within the same group. The differences are due to: