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The Caledonian and Ellesmerian orogenies were followed by extension and development of intracontinental rift basins since the late Paleozoic, as represented by the Sverdrup Basin along the Canadian Arctic Islands. The initial rifting was accompanied by pulses of volcanic activity during the Carboniferous and Permian. A new occurrence of mafic volcanic rocks, the 'Taconite volcanics' (informal name), was discovered on northern Ellesmere Island between the head of Ayles Fiord and M'Clintock Inlet. The mainly alkali-picritic lavas are exposed within the central part of the Pearya Terrane as an outcrop in faulted contact with upper Carboniferous red beds of the Canyon Fiord Formation. The contact to the Ordovician island-arc volcanic rocks of the Pearya Terrane is unclear. The outcrop is characterized by a small circular magnetic anomaly. Ar-Ar whole-rock geochronology on the volcanic rocks yielded an age of 290 [+ or -] 19 Ma suggesting emplacement of the lavas during the early Permian. Whole rock geochemical analyses for eight samples revealed a geochemical affinity to ocean island basalt (OIB) and indicate variable mixing of low-degree melts in the fields of garnet and spinel peridotite (~80-90 km depth). The involvement of a metasomatized subcontinental lithospheric mantle is indicated by high Pb, Nb, and Ta concentrations. Geochemical differences (as enrichments in Ti, Nb, Zr, and the light rare earth elements (REE)) to the known Carboniferous and Permian spilitic altered basalt occurrences of northwestern Ellesmere and northern Axel Heiberg islands are probably based on differences in the mantle source. The Sr isotope ratios of the Taconite volcanics are primitive ([([.sup.87]Sr/[.sup.86]Sr).sub.t]: 0.7037-0.7042) and its Nd isotope ratios are moderately depleted ([epsilon][Nd.sub.(t)]: +2.20 to +2.85) in contrast to the enriched s[Nd.sub.(t)] values of the Permian Esayoo formation. Key words: Taconite volcanics, rifting, volcanism, Ellesmere Island, Canadian High Arctic, Sverdrup Basin, 1. Introduction The target area of the expedition CASE 11 (Circum-Arctic Structural Events), organized and led by the German Federal Institute for Geosciences and Natural Resources (BGR), in the summer [...]

Stratigraphically well-defined volcanic rocks in Palaeozoic volcano-sedimentary units of the Frankenwald area (Saxothuringian Zone, Variscan Orogen) were sampled for geochemical characterisation and U-Pb zircon dating. The oldest rock suite comprises quartz keratophyre, brecciated keratophyre, quartz keratophyre tuff and basalt, formed in Upper Cambrian to Tremadocian time (c. 497-478 Ma). Basaltic volcanism continued until the Silurian. Quartz keratophyre shows post-collisional calc-alkaline signature, the Ordovician-Silurian basalt has alkaline signature typical of continental rift environments. The combined datasets provide evidence of Cambro-Ordovician bimodal volcanism and successive rifting until the Silurian. This evolution very likely resulted from break-up of the northern Gondwana margin, as recorded in many terranes throughout Europe. The position at the northern Gondwana margin is supported by detrital zircon grains in some tuffs, with typical Gondwana-derived age spectra mostly recording ages of 550-750 Ma and minor age populations of 950-1100 and 1700-2700 Ma. The absence of N-MORB basalt in the Frankenwald area points to a retarded break-off of the Saxothuringian terrane along a continental rift system from Uppermost Cambrian to Middle Silurian time. Geochemical data for a second suite of Upper Devonian basalt provide evidence of emplacement in a hot spot-related ocean-island setting south of the Rheic Ocean. Our results also require partial revision of the lithostratigraphy of the Frankenwald area. The basal volcanic unit of the Randschiefer Formation yielded a Tremadocian age and, therefore, should be attributed to the Vogtendorf Formation. Keratophyre of the Vogtendorf Formation, previously assigned to the Tremadoc, is most likely of Upper Devonian age. [ABSTRACT FROM AUTHOR]

Cenozoic sediments deposited in graben-like basins in the Quadrilátero Ferrífero, southern São Francisco craton, Brazil, have anomalous contents of Hg and Sb. Two localities have been studied: the topaz deposit of Antônio Pereira, and the remains of the old opencast workings at Cata Preta, one of the earliest Au mines of Minas Gerais that dates back to about 1690. At Cata Preta, a brecciated wad-like rock exhibits geochemical fingerprints that point to fractionation of Pt and Pd from Ag. This metal fractionation, reflected in the Au ingots produced in the region, genetically links Cata Preta to the near-surface bonanza ore of Serra Pelada, which formed as a result of a Late-Cretaceous hydrothermal overprint in the Amazon craton. Here, we propose that anorogenic hydrothermal activity in cratonic terrains prepared the ground for the enrichment in precious metals that gave rise to two of the most important Au rushes in Brazilian history. [ABSTRACT FROM AUTHOR]

Ferroselite from Trogtal, the type locality of the cobalt selenide trogtalite, in the Harz Mountains, Germany, forms a trogtalite-ferroselite assemblage in pockets of massive clausthalite in which specular hematite is dispersed. The pockets occur in hematite-impregnated carbonate veins, emplaced in a reddened greywacke of Lower Carboniferous age. Ferroselite contains ~0.2-5.0 ppm Au; trogtalite has even higher Au contents. Ferroselite has Co/Ni ratios mostly above unity. These characteristics likely reflect oxidizing brines with Co/Ni > 1, such as those involved in the formation of sediment-hosted copper deposits. [ABSTRACT FROM AUTHOR]

Coring sediments in subglacial aquatic environments offers unique opportunities for research on paleo-environments and paleo-climates because it can provide data from periods even earlier than ice cores, as well as the overlying ice histories, interactions between ice and the water system, life forms in extreme habitats, sedimentology, and stratigraphy. However, retrieving sediment cores from a subglacial environment faces more difficulties than sediment coring in oceans and lakes, resulting in low yields from the most current subglacial sediment coring methods. The coring tools should pass through a hot water-drilled access borehole, then the water column, to reach the sediment layers. The access boreholes are size-limited by the hot water drilling tools and techniques. These holes are drilled through ice up to 3000–4000 m thick, with diameters ranging from 10–60 cm, and with a refreezing closure rate of up to 6 mm/h after being drilled. Several purpose-built streamline corers have been developed to pass through access boreholes and collect the sediment core. The main coring objectives are as follows: (i) To obtain undisturbed water–sediment cores, either singly or as multi-cores and (ii) to obtain long cores with minimal stratigraphic deformation. Subglacial sediment coring methods use similar tools to those used in lake and ocean coring. These methods include the following: Gravity coring, push coring, piston coring, hammer or percussion coring, vibrocoring, and composite methods. Several core length records have been attained by different coring methods, including a 290 cm percussion core from the sub-ice-shelf seafloor, a 400 cm piston core from the sub-ice-stream, and a 170 cm gravity core from a subglacial lake. There are also several undisturbed water–sediment cores that have been obtained by gravity corers or hammer corers. Most current coring tools are deployed by winch and cable facilities on the ice surface. There are three main limitations for obtaining long sediment cores which determines coring tool development, as follows: Hot-water borehole radial size restriction, the sedimentary structure, and the coring techniques. In this paper, we provide a general view on current developments in coring tools, including the working principles, corer characteristics, operational methods, coring site locations, field conditions, coring results, and possible technical improvements. Future prospects in corer design and development are also discussed. [ABSTRACT FROM AUTHOR]

During the last seasons and ongoing, pre-site seismic surveys have taken place in the Ekströmisen region of Dronning Maud Land, with the primary goal of building a stratigraphic age framework of the under-ice-shelf sediments. These sediments overlie the Explora Wedge, a syn- or post-rift volcanic deposit. Expected ages range from Late Mesozoic to Quaternary. From new vibroseismic profiles, we selected sites for short core seafloor sampling through Hot Water Drill (HWD) holes of the oldest and of the youngest sediment sequences to confine their age time span. There is further potential for drilling deeper sediment cores with the support of international partner. Deep drilling should recover the sediments overlying the Explora Escarpment, in order to discover the nature of the Explora Wedge. We expect the overlying sediment sequences to reveal the history of polar amplification and climate changes in this part of Antarctica, the build-up of the East Antarctic Ice Sheet during past warmer climates, and its Cenozoic and future variability. Having HWD holes through the shelf ice and sampling the sea floor will provide the unique opportunity for further piggy back experiments consisting of multi-disciplinary nature. Experiments and measuring setup for oceanography, sea and ice shelf physics, geophysics, geology, hydrography, biogeochemistry could be planned to characterise the ocean-icesediment interactions, processes and ecosystem observations. The deployment of Autonomous Underwater Vehicles (AUV) either through a HWD hole or launched from a ship or from the fast ice with the power to operate and measure in the sub-ice shelf cavern may become reality during future campaigns. [ABSTRACT FROM AUTHOR]

Scientific Drilling through the ice shelfs of Antarctica is essential to understand ice sheet dynamics, the transition from greenhouse to ice-house in the Eocene to Oligocene, and the breakup of the Gondwana continent. The Alfred-Wegener-Institute, Helmholtz Centre for Polar and Marine Research (AWI) and the Federal Institute for Geosciences and Natural Resources (BGR) jointly conduct a pre-site survey in order to identify potential drilling locations in the vicinity of the German Neumayer III station. There, a sequence of >1000m thick sediments of potentially Late Mesozoic to Quaternary age has been identified on top of the presumed synor post-rift volcanic Explora Wedge between the ice shelf calving line and some 40 km inland under the Eckström Ice Shelf. During a first survey in the Antarctic season 2016/17 eleven high resolution vibro-seismic profiles with a total length of 285 km were obtained (Kuhn et al. 2018, this volume). Based on this data set and additional profiles recorded during the season 2017/18 several locations for sampling of surface sediment were identified. Sampling of the seafloor by retrieving short cores of the oldest and youngest sediments through Hot Water Drill holes was carried out in late December 2017 to late January 2018. As next steps, AWI and BGR agreed to finance a further campaign for additional sampling and oceanographic pre-site studies to be carried out in the following Antarctic season 2018/19. Under the LASCAR and PAIS umbrella we will re-establish a D-ANDRILL group to coordinate these related national projects. An international workshop is then planned to bring together researchers with interest in scientific drilling and to discuss and develop a drilling proposal. We particularly like to encourage scientists from the German polar research community based at universities and other research institutions to contribute to this project. [ABSTRACT FROM AUTHOR]