Extracting meaningful U-Pb ages from core–rim mixtures

We used an ion microprobe (SHRIMP‐RG) for U‐Pb dating of individual zircons in high‐grade metamorphic basements of the felsic Sredinny and mafic Ganal Massifs in Kamchatka. Thirty percent of zircons from paragneisses of the Sredinny Massif contain Archean (2800–2500 Ma), early Proterozoic (1700–2100 Ma), and late Proterozoic (∼1000 Ma) detrital cores. In addition, a broad and almost uninterrupted range of Phanerozoic detrital cores (460–175 Ma) is present, with Jurassic to Lower Cretaceous (150–96 Ma) zircons forming the youngest detrital age group. Ubiquitous $$77\pm 2$$‐Ma rims signify the age of regional metamorphism, though yet another metamorphism is defined by four 47–53‐Ma zircons. The abundance of Archean, Proterozoic, and Paleozoic zircon cores, as well as the short ∼20‐m.yr. time lag between the youngest detrital zircon cores and the age of metamorphic rims, argues strongly against a long trans‐Pacific transport and the origin of the Sredinny Massif as a piece of a continent other than Siberia. We suggest that the Sredinny Massif is an eastern part of the exposed basement (leading edge) of the Sea of Okhotsk (Okhotomorsk) microcontinent and that it represents a polymetamorphic accretionary wedge whose clastic sediments were derived from Siberia. Zircon ages from amphibolites and gabbro in the Ganal Massif exhibit two age groups, one at 60–80 Ma and the other at 18–40 Ma, and lack Precambrian cores. We interpret the Ganal Massif as the lower crust of an intraoceanic island arc. The Sredinny and Ganal Massifs, despite their present proximity, belong to different tectonic units and do not represent upper and lower crustal fragments of the same unit. We present a tectonic model that explains the origin of both Massifs as a part of Mesozoic and Cenozoic geodynamic history in the NW Pacific.

Tectonic models for the North Atlantic Caledonides typically show Baltica being subducted below Laurentia prior to late orogenic collapse and exhumation of deep crustal rocks, conveniently explaining the high‐ and ultrahigh‐pressure provinces in the Scandinavian Caledonides. However, these models offer no tectonic explanation for the deformation and overthickening of the overriding Laurentian plate. Here we document major anatectic midcrustal ultraductile top to the (N)W shear zones in the east Greenland Caledonides that may account for this orogenic thickening. U‐Pb dating of monazite and 40Ar/39Ar dating suggests that high‐grade fabrics (∼ 435–424 Ma) and granites (∼427 and 422 Ma) involved in these zones show that these were contemporaneous with syntectonic granites involved in the Fjord Region Detachment Zone (FRDZ), a major top to the east extensional fault. More than 100 km of top to the NW overthrusting has been documented in the foreland of the orogen, yet we show that rocks in the hanging wall of the thrust were thinned by orogen‐parallel extension rather than thickened during emplacement, thereby exhuming the underlying active midcrustal thrust zones. This is documented by Late Silurian (∼419 Ma) to Early Devonian (∼401 Ma) 40Ar/39Ar‐muscovite cooling dates from rocks uplifted along major normal faults and intrusion of mafic dikes (∼ 419 Ma) into extensional faults. Folding and thrusting in the foreland probably continued well beyond this time, and underthrust high‐grade nappes probably were exhumed in the triangular zone between the thrust faults (west) and the structurally higher FRDZ (east) before final NW vergent thrust emplacement over low‐grade sedimentary rocks. Final cooling of the metamorphic core below closure temperatures for Ar diffusion in K‐teldspar occurred in the early Carboniferous. Major folds previously regarded as having formed during the main Caledonian event at ∼425 Ma may in part be up to 100 m.y. younger. Some of these folds also deform sedimentary rocks associated with collapse basins of Middle Devonian to Carboniferous age.

U-Pb zircon data from selected gneiss samples provide estimates of the timing of igneous protolith emplacement and granulite facies metamorphism in the Gruinard Bay, Badcall Bay and Lochinver areas of the mainland Lewisian Gneiss Complex of north-west Scotland. Zircons from the gneisses contain complex zoning patterns making them amenable to SHRIMP ion microprobe analysis, with inherited zircon distinguishable from magmatic growth and metamorphic recrystallisation. From Gruinard Bay, a tonalitic granulite yielded a protolith age of 2,825±8 Ma for oscillatory-zoned zircon cores, with recrystallised low-U rims preserving an age of 2,733±12 Ma. An inherited 2,905±15 Ma age component was recognised in a sample of trondhjemitic gneiss, the protolith of which is estimated to have been emplaced at 2,858±11 Ma. Low-U rims yielding an age of 2,729±20 Ma are also present, which together with the rim age from the granulite are considered to date granulite facies metamorphism in the Gruinard region. For comparison with the Gruinard Bay gneisses, a trondhjemitic partial melt and trondhjemite sheet were analysed from the granulite facies rocks at Badcall Bay in the Assynt terrane. Age data do not show definitive relationships with zoning patterns in the zircons, and show a spread along concordia typical of previous ion microprobe age data from the Scourie gneisses. Both samples do, however, show a significant isotopic disturbance at 2,480 Ma, the most recent estimate for the Badcallian metamorphism. Protolith ages for components of the Assynt terrane range between ca. 2,900 and 3,030 Ma, and appear to be older than the 2,860–2,825 Ma gneiss protoliths from the Gruinard Bay area. The timing of granulite facies metamorphism also appears to be different between the two areas, suggesting that the two granulite regions of the mainland may not be related as previously thought. Instead, they are interpreted in terms of a terrane accretion model whereby the two areas evolved as separate blocks prior to their juxtaposition during the Palaeoproterozoic. The boundary between the two terranes is thought to lie to the south of Lochinver, corresponding with the Strathan Line, because of the observed 2,480 Ma age signature to the north and 2,730 Ma signature to the south. By defining a new mainland terrane, the Gruinard Terrane, the number of mainland blocks, which includes the Assynt (central), Rhiconich (northern) and Southern terranes, has been expanded.

Thermotectonic evolution of the churchill province in Northern Saskatchewan

Grenvillian basement and a major unconformity within the Caledonides of Nordaustlandet, Svalbard

Fingerprinting W-Sn mineralization processes in the East Greenland Caledonides using scheelite and cassiterite U-Pb dating and trace element composition

The geological development of Greenland spans a period of nearly 4 Ga, from the earliest Archaean to the Quaternary. Greenland is the largest island in the world with a total area of 2 166 000 km2, but only c. 410 000 km2 are exposed bedrock, the remaining part being covered by an inland ice cap reaching over 3 km in thickness. The adjacent offshore areas underlain by continental crust have an area of c. 825 000 km2. Greenland is dominated by crystalline rocks of the Precambrian shield, which formed during a succession of Archaean and early Proterozoic orogenic events and which stabilised as a part of the Laurentian shield about 1600 Ma ago. The shield area can be divided into three distinct types of basement provinces: (1) Archaean rocks (3100-2600 Ma old, with local older units) almost unaffected by Proterozoic or later orogenic activity; (2) Archaean terraines reworked during the early Proterozoic around 1850 Ma ago; and (3) terraines mainly composed of juvenile early Proterozoic rocks (2000-1750 Ma old). Subsequent geological developments mainly took place along the margins of the shield. During the later Proterozoic and throughout the Phanerozoic major sedimentary basins formed, notably in North and North-East Greenland, and in places accumulated sedimentary successions which reached 10-15 km in thickness. Palaeozoic orogenic activity affected parts of these successions in the Ellesmerian fold belt of North Greenland and the East Greenland Caledonides; the latter also incorporates reworked Precambrian crystalline basement complexes. Late Palaeozoic and Mesozoic sedimentary basins developed along the continent-ocean margins in North, East and West Greenland and are now preserved both onshore and offshore. Their development was closely related to continental break-up with formation of rift basins. Initial rifting in East Greenland in latest Devonian to earliest Carboniferous time and succeeding phases culminated with the opening of the North Atlantic in the late Paleocene. Sea-floor spreading was accompanied by extrusion of Tertiary plateau basalts in both central West and central and southern East Greenland. During the Quaternary Greenland was almost completely covered by ice sheets, and the present Inland Ice is a relic of the Pleistocene ice ages. Vast amounts of glacially eroded detritus were deposited on the continental shelves offshore Greenland. Mineral exploitation in Greenland has so far mainly been limited to one cryolite mine, two lead-zinc deposits and one coal deposit. Current prospecting activities in Greenland are concentrated on the gold, diamond and lead-zinc potential. The hydrocarbon potential is confined to the major Phanerozoic sedimentary basins, notably the large basins offshore East and West Greenland. While proven reserves of oil or gas have yet to be found, geophysical data combined with extrapolations from onshore studies have revealed a considerable potential for offshore oil and gas. The description of the map has been prepared with the needs of the professional geologist in mind; it requires a knowledge of geological principles but not previous knowledge of Greenland geology. Throughout the text reference is made to the key numbers in the map legend indicated in square brackets [ ] representing geological units (see Legend explanation, p. 79), while a Place names register (p. 83) and an Index (p. 87) include place names, geological topics, stratigraphic terms and units found in the legend. The extensive reference list is intended as a key to the most relevant information sources.

Leucogranites are common in the East Greenland Caledonides. Most granites cut across Caledonian contractional structures and have been interpreted as decompression melts related to late to post-orogenic collapse. To constrain the timing of the collisional event responsible for crustal thickening, zircon, monazite and xenotime were extracted from syn-contractional magmatic rocks from André Land, NE Greenland (73°N) and analysed using the U–Pb isotope dilution thermal ionization mass spectrometry method. The resulting ages range between 429 and 425 Ma. An age of 424 Ma on monazites from a kyanite–garnet–mica gneiss (granite melt source rock) is interpreted as dating late-stage metamorphism and migmatization in the area. A large syn-extensional granite pluton yielded an age of 429 ± 1 Ma. These ages, combined with field observations, demonstrate that subhorizontal upper crustal extension was contemporaneous with mid- to lower crustal subhorizontal contraction, and that the upper crustal strain field is not necessarily representative of the coeval strain fields in the middle and lower crust. The presence of 429–425 Ma migmatites and related intrusive rocks structurally above low-grade metasediments demonstrates that the late and post-tectonic leucogranites are not late orogenic but related to a separate early Caledonian tectonomagmatic phase predating Early Devonian nappe translation.

The close spatial relationship between Devonian high-pressure rocks (eclogites) and Ordovician–Silurian calc-alkaline plutonic rocks, as observed in Liverpool Land, NE Greenland, is not easily explained by existing tectonic models for the Caledonide orogen. New field studies and isotope dilution–thermal ionization mass spectrometry U-Pb geochronology demonstrate, however, that the association is just coincidental, because the two rock groups are located within distinct terranes separated by a composite structure. The major element is the Gubbedalen shear zone, a N-dipping shear zone dominated by a penetrative top-up-to-the-S ductile fabric. Superimposed brittle-ductile top-down-to-the-N shear zones are typical of the structurally uppermost part of the shear zone. The contact against the hanging wall is the N-dipping, brittle Gubbedalen extensional detachment fault. A zircon age of 399.5 ± 0.9 Ma for an eclogite body is interpreted to represent the time of high-pressure metamorphism of the footwall. The host gneiss was migmatized between ca. 388 Ma and ca. 385 Ma, as constrained by the ages of a pegmatite predating migmatization and crosscutting granites. Coeval synkinematic granites intrude along amphibolite-grade, top-to-the-S high-strain zones in the Gubbedalen shear zone. Juxtaposition of the Ordovician–Silurian plutonic terrane (hanging wall) against the Early to mid-Devonian eclogite terrane (footwall) is best explained by a tectonic model involving early mid-Devonian buoyancy-driven exhumation followed by late mid-Devonian syncontractional extension related to thrusting on the Gubbedalen shear zone in a dextral strike-slip zone. Subsequent exhumation through the brittle-ductile transition occurred by extension on early semiductile structures and the overprinting Gubbedalen extensional detachment fault, and erosion.

Development of an integrated information resource base for 4D/VR construction processes simulation

A computational fluid dynamics software (DynamFluid) based on the application of the finite element method with the characteristic-based-split algorithm is presented and validated. The software is used to numerically integrate the steady and unsteady Navier–Stokes equations for both constant-density and Boussinesq non-isothermal flows. Benchmark two-dimensional computations carried out with DynamFluid show good agreement with previous results reported in the literature. Test cases used for validation include (i) the lid-driven cavity flow, (ii) mixed convection flow in a vertical channel with asymmetric wall temperatures, (iii) unsteady incompressible flow past a circular cylinder, and (iv) steady non-isothermal flow past a circular cylinder with negligible buoyancy effects. The new software is equipped with a graphical user interface that facilitates the definition of the fluid properties, the discretization of the physical domain, the definition of the boundary conditions, and the post-processing of the computed velocity, pressure and temperature fields.

The SoilExp software: An open-source Graphical User Interface (GUI) for post-processing spatial and temporal soil surveys

This paper introduces a dependability assessment tool (WSsDAT) for Web Services monitoring and testing. It allows users to evaluate dependability of Web Services from the point of view of their clients by collecting metadata representing a number of dependability metrics. This Java-based tool can be deployed in diverse geographical locations to monitor and test the behavior of a selected set of Web Services within preset time intervals. The graphical user interface of the tool provides real-time statistical data describing dependability of the Web Services under monitoring. The tool makes it possible for the users to identify typical patterns of dependability-specific behavior depending on the time of the day, days of the week or the client locations. In addition, WSsDAT can collect and analyze service dependability measurements during long periods of time, as well as obtaining dependability-related information about current service behavior. The paper reports on a successful series of experiments using this tool for investigating the dependability of two BLAST Web Services which are widely used in the bioinformatics domain. The paper shows how the tool can be employed by e-scientists in making informed choices of the distributed services being used in an in silico experiment and thereby improving their overall dependability.KeywordsService-oriented architecturereliabilitymonitoringBLAST services

The structure and features of a software package for 3D inversion of geophysical data are considered. The presented software package is focused on solving direct and inverse problems of electrical exploration and engineering geophysics. In addition to the parameters that determine physical properties of the medium, the software package allows you to restore the geometry parameters of the geophysical model, namely layer reliefs and boundaries of three-dimensional inclusions. The inclusions can be in the form of arbitrary hexagons or prisms with a polygonal base. The software package consists of four main subsystems: an interface, subsystems for solving direct and inverse problems, and a client-server part for performing calculations on remote computing nodes. The graphical interface consists of geophysicist-oriented pre- and postprocessor modules that allow you to describe the problem and present the results of its solution in user-friendly terms. To solve direct problems, the finite element method and the technology for dividing the field into normal and anomalous components are used. At the same time, special methods of discretization of the computational domain are used, which make it possible to take into account both the complex three-dimensional structure of the environment and the presence of man-made objects (wells) in the computational domain. To increase the efficiency of solving direct problems, nonconforming grids with cells in the form of arbitrary hexahedrons are used. Methods for efficient calculation of derivatives (with respect to these parameters) necessary for solving inverse problems by the Gauss-Newton method are also described for the geometry parameters. The main idea for efficient derivatives computation is to identify the effect of changing the value of the parameter (used to compute the value of the generalized derivative) on the problem. The main actions performed by the subsystem for solving inverse problems and the features associated with the processing of geometry parameters are described.

Halogens are important elements for a range of geological processes during metamorphism from stabilizing mineral phases to being important ligands for mass transfer. Halogens are highly incompatible in most minerals, which makes it difficult to unravel their presence in the past. Minerals useful for understanding halogen behaviour during metamorphism include: scapolite, apatite, titanite, biotite, and amphibole. However, their ability to incorporate halogens depends on parameters such as bulk rock composition, fluid properties, and water-rock ratios. Comprehensive studies of halogens in regional metamorphic rocks and minerals, such as the Clearwater Region, Idaho, USA or the Mary Kathleen Fold Belt, Mt Isa Inlier, Australia, show that halogen contents are highly variable on a bulk rock- and rock layer-scale, reflecting protolith variations. Where low fluid-rock ratios occurred during regional metamorphism, pre-exisiting variations in halogen compositions and ratios across individual layers were not eliminated, resulting in large differences between halogen concentrations on a mineral- and rock-layer scale. Research on F and Cl in apatite in siliceous marbles from five classic aureoles highlights the use of this mineral regarding rock or fluid buffering, and in establishing fluid sources. Chlorine enrichment in biotite and amphibole, associated with regional albitization observed in Cloncurry, Australia or the Bamble Sector Norway, demonstrate advection of saline fluids during albitization and K-feldspar metasomatism that occur in association with regional mineralization. Chlorine-bearing fluids are capable of mobilizing large amounts of metals during large-scale metamorphism on a regional, whole rock, and mineral scale. Consequently, fluid flow could be an essential prerequisite to actively discharge metals from the metamorphic rocks. Recent analytical advancements allow for more routine analyses of halogen contents in minerals and fluid inclusions. For instance, in situ LA-ICP-MS analyses of Cl and Br allow for the reconstruction of the interaction of halogen-bearing fluids with crustal rocks in complex geological settings that have undergone multiple hydrothermal events. In such cases, scapolite can be used as an archive for fluid properties during metamorphism. For example, within the Mount Isa Inlier, it was found that the fluids, which interacted with calc-silicates in the Mary Kathleen Fold Belt, were of bittern brine derivation contrasting with the Cloncurry Region, where the fluids show evidence of dissolved halite. Magmatic fluid interaction with calc-silicate rocks was found to be localized.