bluuebunny/crossref_metadata_2025 huggingface dataset:
Fermor lecture: The influence of life on the face of the Earth: garnets and moving continents
Authors: Nisbet E. G.
Published: April 2008

The Hadean Earth (before
c.
4 Ga) was abiotic, possibly sterring a bumpy course between brief periods of hot inferno after meteorite impacts, and long episodes of Norse icehell. The earliest Archaean life would probably not have been planet-altering, but restricted to particular habitats. One of the first may have been hot regions around hydrothermal systems where redox contrasts between ocean water and magmatic fluids could be exploited. Molecular evidence suggests that with the evolution of anoxygenic photosynthesis, life became able to occupy wider regions, although focused in the vicinity of hydrothermal systems. Oxygenic photosynthesis by cyanobacteria allowed life fully to occupy the planet, not only forming coastal microbial mats but also possibly inhabiting the broad oceans with abundant photosynthetic bacterial picoplankton, underlain by deeper archaeal picoplankton. In the Belingwe belt, Zimbabwe, textural and isotopic evidence suggests that a complex microbial ecology existed in the late Archaean (2.7 Ga), which was essentially modern in its biochemical abilities and which sequestered into the biosphere the same fraction of primitive carbon emitted from mantle as today. To do this, by the late Archaean the biological productivity must have been significant; not necessarily as large as today, but capable of managing the global carbon budget. When this began is unknown, possibly earlier than 3.5 Ga ago. The controls on the oxidation state of the late Archaean atmosphere—ocean system are not self-evident. Although inorganic controls dominate the long-term balance, short-term biological management of the air may have been crucial. Methane may have played a major role in the pre-metazoan biosphere. The modern atmosphere is a biological construct: oxygen and its reverse, carbon dioxide, are managed by rubisco; nitrogen, its oxides and hydrides mainly by nitrifying and denitrifying bacteria, with a small input from lightning in an oxygen-rich atmosphere; and water (itself the most important greenhouse gas) by its complex interdependence with other greenhouse gases and albedo, including clouds. Earth’s air is highly improbable. In controlling surface temperature a subtle interplay between organic and inorganic controls has operated, perhaps to the extent that it is invalid to ask which was the dominant factor. But there is a reasonable uniformitarian argument that life has constructed the air in the past as now, and that, within the broad constraints of the physical setting, this biologically shaped atmosphere has been the dominant control on the planet’s surface temperature. In turn, the surface temperature has been one of the various controlling factors on the tectonic evolution of the planet. Thus to a significant extent life has helped shape the physical evolution of the planet.
The metamorphic history of the Isua Greenstone Belt, West Greenland
Authors: Rollinson Hugh
Published: April 2008

New geological investigations in the
c.
3.7–3.8 Ga Isua Greenstone Belt in West Greenland have revealed that the belt comprises a number of separate structural domains. Five such domains have been identified on the basis of lithological and structural differences. This study uses the morphology and compositional zoning of garnet porphyroblasts in pelites to investigate the extent to which the various domains within the greenstone belt preserve contrasting deformational and metamorphic histories. Up to three episodes of garnet growth have been identified in a single domain and significant differences in garnet growth history are noted between domains. A distinction is drawn between the relatively simple metamorphic history of a low-strain zone in the NE of the greenstone belt and other domains where more complex histories are preserved. Combining this result with existing geochronology suggests that in the south and west, the greenstone belt was metamorphosed twice, at
c.
3.74 Ga and at
c.
2.8 Ga, whereas in the NE there was a single event at 3.69 Ga. Preliminary garnet-rim thermometry indicates that some rocks experienced an early metamorphism in which temperatures exceeded 610°C. Kyanite is thought to have been in equilibrium with these assemblages, indicating pressures of at least 6 kbar. A later prograde metamorphic event shows a temperature rise from 480 to 550°C. The high pressures indicate a crustal thickness of at least 20 km at 3.7 Ga.
Palaeozoic amalgamation of Central Europe: an introduction and synthesis of new results from recent geological and geophysical investigations
Authors: Winchester J. A. , Pharaoh T. C. , Verniers J.
Published: April 2008

Multidisciplinary studies undertaken within the EU-funded PACE Network have permitted a new 3-D reassessment of the relationships between the principal crustal blocks abutting Baltica along the Trans-European Suture Zone (
TESZ
). The simplest model indicates that accretion was in three stages: end-Cambrian accretion of the Bruno-Silesian, Łysogóry and Małopolska terranes; late Ordovician accretion of Avalonia, and early Carboniferous accretion of the Armorican Terrane Assemblage (
ATA
), which had coalesced during Late Devonian — Early Carboniferous time. All these accreted blocks contain similar Neoproterozoic basement indicating a peri-Gondwanan origin: Palaeozoic plume-influenced metabasite geochemistry in the Bohemian Massif in turn may explain their progressive separation from Gondwana before their accretion to Baltica, although separation of the Bruno-Silesian and related blocks from Baltica during the Cambrian is contentious.

Inherited ages from both the Bruno-Silesian crustal block and Avalonia contain a 1.5 Ga ‘Rondonian’ component arguing for proximity to the Amazonian craton at the end of the Neoproterozoic: such a component is absent from Armorican terranes, which suggests that they have closer affinities with the West African craton.

Models showing the former locations of these terranes and the larger continents from which they rifted, or to which they became attached, must conform to the above constraints, as well as those provided by palaeomagnetic data. Hence, at the end of the Proterozoic and in the early Palaeozoic, these smaller terranes, some of which contain Neoproterozoic ophiolitic marginal basin and magmatic arc remnants, probably occurred within the end-Proterozoic supercontinent as part of a ‘Pacific-type’ margin, which became dismembered and relocated as the supercontinent fragmented.
The
40
Ar/
39
Ar ages from the West Sudetes (NE Bohemian Massif): constraints on the Variscan polyphase tectonothermal development
Authors: Marheine D. , Kachlík V. , Maluski H. , Patočka F. , Żelaźniewicz A.
Published: April 2008

The West Sudetes (NE margin of the Bohemian Massif) consist of a complex mosaic of several tectonometamorphic units juxtaposed during the Variscan orogeny. The polyphase Variscan tectonothermal development of the West Sudetes was determined by
40
Ar/
39
Ar ages of single grains and mineral concentrates. Late Famennian (359 Ma) mica ages from the high-grade Góry Sowie Block suggest continuous uplift after a Late Devonian high temperature-low pressure (HT-LP) event contemporaneous with the end of subduction-related high pressure-low temperature (HP-LT) metamorphism in the East Krkonoše Complex.

Mid-Late Devonian high pressure events in the Krkonoše-Jizera Terrane and Orlica-Śnieżnik Dome are followed by coeval high temperature events between 345 and 335 Ma (Viséan). The latter are interpreted as consequence of uplift, and decompression during overthrusting of both complexes on their forelands. Subsequent small- to large-scale shear movements dated at around 325–320 Ma (early Namurian) affected the Orlica-Śnieżnik Dome, Krkonoše-Jizera Terrane, including the Intra-Sudetic Fault, and also the eastern Lusatian Granitoid Complex. They were accompanied by contemporaneous emplacement of the Krkonoše-Jizera pluton. The upper limit of the tectonometamorphic and magmatic activity is dated at 314–312 Ma (Namurian/Westphalian boundary). The final juxtaposition of the diversified tectonometamorphic units, which constitute the West Sudetes, took place in early Namurian times.
Palaeozoic terrane amalgamation in Central Europe: a REE and Sm-Nd isotope study of the pre-Variscan basement, NE Bohemian Massif
Authors: Crowley Quentin G. , Timmermann Hilke , Noble Stephen R. , Holland J. Grenville
Published: April 2008

The West Sudetes, NE Bohemian Massif, comprises several suspect terranes accreted to the margins of Laurussia during Variscan orogenesis. Whole rock REE and Sm-Nd isotope data for seven separate provinces (Izera, Kaczawa, Rudawy Janowickie and Kłodzko complexes; Fore-Sudetic and Góry Sowie Blocks; Slęża Ophiolite) suggest involvement of a variety of crustal and mantle sources. Felsic metasedimentary rocks (ɛNd(t) = −8.3 to −5.0) have two stage T
DM
ages of 1.9 to 1.5 Ga, whereas acidic metavolcanic rocks and granite gneisses (ɛNd(t) = −5.4 to +0.8) have two stage T
DM
ages of 1.5 to 1.0 Ga. A range of sources is implicated: predominantly Archaean and Palaeoproterozoic sources for the metasedimentary rocks, and Archaean. Palaeoproterozoic and Neoproterozoic to early Palaeozoic sources for the meta-igneous felsic lithologies. LREE depleted tholeiitic metabasites ((Ce/Yb)
N
= 0.8 to 3.4) generally have ɛNd(t) = +4.0 to +9.1, indicating derivation from depleted mantle asthenosphere. LREE enriched meta-alkali basalts ((Ce/Yb)
N
= 4.6 to 10.1) with ɛNd(t) between +3.1 and +7.0 implicate utilization of enriched mantle asthenosphere.

Analogous lithologies from elsewhere in the Sudetes, North Bohemian Massif and the Armorican Terrane Assemblage have similar REE abundances, ɛNd values and T
DM
ages. Complexes previously considered to have had disparate Neoproterozoic to early Palaeozoic histories may be integrated into a unifying geodynamic model of derivation from the North Gondwanan (North African) margin during a widespread episode of continental margin break-up.
The Mariánské-Lázně Complex, NW Bohemian Massif: development and destruction of an early Palaeozoic seaway
Authors: Crowley Quentin G. , Floyd Peter A. , Štědrá Veronika , Winchester John A. , Kachlík Vaclav , Holland J. Grenville
Published: April 2008

The Mariánské-Lázně Complex is a Cambro-Ordovician terrane of oceanic affinity tectonically emplaced between the Saxothuringian Zone and Teplá-Barrandian Unit, NW Czech Republic. It forms a SE-dipping allochthonous body that comprises the largest contiguous exposure of metamorphosed basic and ultrabasic lithologies in the Bohemian Massif. Petrographic evidence indicates that a significant proportion of protoliths underwent eclogite facies metamorphism (570 to 720°C, 1.44 to 2.10 GPa), followed by an increase in temperature (up to around 800°C) and a subsequent widespread retrograde amphibolite facies event (550 to 680 °C, 0.75 to 1.20 GPa). New major and trace element geochemical analyses of metamorphosed basic and ultrabasic lithologies indicate that they exhibit geochemical characteristics attributable to a sea floor origin. The metabasites were generated at a spreading centre that interacted with deep-seated upwelling mantle asthenosphere. Separate, independently fractionating basic melt batches existed: these were derived from depleted and enriched asthenosphere and depleted sub-continental lithosphere sources. Geochemical correlation of the Mariánské-Lázně Complex with other early Palaeozoic metabasic provinces facilitates comparison of metabasic lithologies occurring in tectonically dislocated nappe pile thrust sheets, and allows delineation of important suture zones in the European Variscides.
Coronitic metagabbros of the Mariánské Lázně Complex and Teplá Crystalline Unit: inferences for the tectonometamorphic evolution of the western margin of the Teplá-Barrandian Unit, Bohemian Massif
Authors: Štědrá V. , Kachlík V. , Kryza R.
Published: April 2008

Bodies of coronitic metagabbro occur in the SW Mariánské Lázně Complex (MLC) and the adjacent Teplá Crystalline Unit (TCU) on the western margin of the Teplá-Barrandian Unit (TBU), Bohemian Massif. The characteristic structural, geochemical, petrographic, and metamorphic features of five groups of metagabbros and related rocks are presented, compared with other metabasites of the MLC and Zone of Erbendorff-Vohenstrauss (ZEV), and used to constrain the tectonometamorphic evolution of the western part of the TBU. The metagabbros are considered to be a younger intrusive member of the complicated lower crustal tectonic stack of Upper Proterozoic to Early Palaeozoic age which is formed by the Mariánské Lázně Complex and the Teplá Crystalline Unit together. It is proposed that a significant part of the metamorphic evolution of some parts of these units took place before the emplacement of metagabbros and granitoids at around 496–516 Ma. The sequence of metamorphic events is interpreted to have been as follows. Deep burial of primitive MORB type tholeiitic rocks (a) metamorphosed up to eclogite facies, followed by (b) uplift to lower crustal levels so that the partially exhumed rocks were juxtaposed with other lower/middle crustal rocks. Thermal relaxation (c) followed, with an episode of extension recorded in L-tectonites of amphibolite facies. Once this lithologically variegated stack was welded together, it was intruded by the Upper Cambrian-Lower Ordovician granitoids and gabbros (d). This pre-Variscan metamorphic event may be expressed at the supracrustal level by an unconformity between Upper Cambrian and Lower Ordovician rocks in the Barrandian. The final configuration of the units was established during the Variscan collision of the Teplá Barrandian terrane with Saxothuringia (e) in which the rocks of the MLC and TCU were thrust to the NW over the Saxothuringian para-autochthon. The accompanying metamorphic event reached upper amphibolite facies. The thermally relaxed rocks cooled rapidly, and pre-existing thrust planes were re-activated during the final extensional collapse.
Basement structure in the southern North Sea, offshore Denmark, based on seismic interpretation
Authors: Scheck M. , Thybo H. , Lassen A. , Abramovitz T. , Laigle M.
Published: April 2008

Seismic reflection data from the Danish North Sea are interpreted to map the structure of the Palaeozoic basement in the area of the MONA LISA deep seismic lines. Based on a characteristic near-basement reflection, the upper crystalline crust of Baltica of offshore Denmark is traced to the south into the southern Horn-Graben, and to the west to the eastern shoulder of the Central Graben. A two-way-traveltime map of the near-basement horizon and several interpreted seismic sections reveal that three main tectonic events influenced the topography of the basement: (1) a compressional event which could be Caledonian in age; (2) a Palaeozoic extensional event postdating the compressional deformation and expressed in a system of WSW-ESE to W-E striking Palaeozoic half-grabens; and (3) the Permo-Triassic rifting that led to the formation of NNW-SSE to NNE-SSW trending Mesozoic faults of the Horn Graben and the Central Graben which are oriented sub-perpendicular to the Palaeozoic system. Compressive deformation is localized in a narrow zone around and south of the hitherto interpreted Caledonian Deformation Front and foreland deformation on Baltica is suggested as its origin. The seismic image of the Palaeozoic halfgrabens indicates that the East North Sea High is an inverted Palaeozoic rift which subsequently was cut by younger Late Palaeozoic to Mesozoic rifts of the Horn and Central Grabens. The timing of the first extensional phase remains speculative, but it predates the Rotliegend unconformity. Some of the older Palaeozoic normal faults may have been reactivated as transfer zones between the different graben segments during the Permo-Mesozoic extension.
On the architecture of high-latitude continental margins: the influence of ice-sheet and sea-ice processes in the Polar North Atlantic
Authors: Dowdeswell J. A. , Ó Cofaigh C. , Taylor J. , Kenyon N. H. , Mienert J. , Wilken M.
Published: April 2008

The presence of ice during the Late Cenozoic distinguishes the nature and rates of processes on high-latitude margins from those elsewhere. Ice sheets terminating in marine waters deliver icebergs, meltwater and debris to high-latitude seas. Sea ice influences ocean salinity structure and downslope water and sediment transfer, and also transports fine-grained sediments over long distances. These cryospheric processes have led to the development of a distinctive sedimentary architecture on modern high-latitude continental margins. Large submarine fans made up almost entirely of stacked debris flows are present around the Norwegian-Greenland Sea. Large slides are located in a variety of settings relative to rates of sediment delivery from Quaternary ice-sheet margins, but no large slides have been mapped on the East Greenland margin. However, extensive channel systems and sediment-wave fields are present in the Greenland Basin, probably related to intermittent downslope flow of dense water and turbidity currents. The extensive NE Greenland shelf was not innundated by ice-sheet advance during recent full-glacial conditions, allowing sea-ice and deep-water production during both interglacials and full-glacials. Changes in the nature and rate of sedimentation within the Greenland Basin should provide clues on the rate of dense-water production, with implications for thermohaline circulation in the North Atlantic. Other erosional and depositional features on the Norwegian-Greenland Sea margins include canyons and contourite drifts. High-relief tectonic features influence sediment reworking by turbidity currents at abyssal depths. A simple conceptual model for glacier-influenced marine sedimentation summarizes the role of cryospheric processes in high-latitude margin sedimentary environments.
Large-scale morphological evidence for past ice-stream flow on the mid-Norwegian continental margin
Authors: Ottesen D. , Dowdeswell J.A. , Rise L. , Rokoengen K. , Henriksen S.
Published: April 2008

The Norwegian continental margin has been affected by several cycles of growth and decay of the Fennoscandinavian Ice Sheet. Evidence for this former ice-sheet activity is found in the seismic stratigraphy of the shelf and slope, and in the morphology of seafloor sediments. The regional bathymetry of the mid-Norwegian shelf (63°N to 68°N) comprises a series of cross-shelf troughs, separated by shallower banks. In Trænadjupet and Suladjupet, streamlined, elongate sedimentary bedforms (known as mega-scale lineations) are found, aligned along trough long-axes. Spacing between ridge-tops is 400–500 m, and ridge width and height are about 250 m and less than 10 m, respectively. Streamlined bedforms are not present on the intervening shallow banks, and terminate abruptly at the trough margins, marking the former boundary of fast glacier flow. On northwestern Trænabanken and on either side of Trænadjupet, lateral ridges are inferred to mark the shear margin of ice streams in Sklinnadjupet and Trænadjupet. The Skjoldryggen Moraine records the seaward limit of Late Weichselian ice-sheet growth, and ridges inshore result from deposition in still-stands during ice retreat. The streamlined bedforms in Trænadjupet and Suladjupet are similar in morphology and scale to streamlined Antarctic bedforms, linked to the former presence of fast-flowing ice streams on the continental shelves of Antarctica. Several geomorphological criteria, identified as diagnostic of past ice-stream flow, are observed in our geophysical studies of the mid-Norwegian shelf. Using these criteria, we identify several fast-flowing ice streams on the western margin of the former Fennoscandinavian Ice Sheet. Numerical ice-sheet model predictions of fast-flowing ice coincide closely with the inferred locations of past ice streams based on the distribution of such suites of diagnostic bedforms.
Grain-size characteristics and provenance of ice-proximal glacial marine sediments
Authors: Andrews John T. , Principato Sarah M.
Published: April 2008

This paper addresses the issue of the characteristic grain-size spectra of glacial and glacial marine sediments, an important topic because of the increasing emphasis on the use of specific sand-size fractions as indicators of iceberg rafting. Different methods of IRD identification can lead to different palaeoclimatic interpretations. We use three methods of grain-size analyses, with examples from the Labrador Sea, East Greenland, North Iceland, and the Ross Sea, Antarctica. The first method illustrates the ‘real’ grain size of glacial marine sediments by an examination of X-radiographs by image analysis and the sizing of clasts larger than 2 mm. Typically, grain-size analyses only apply to the matrix fraction of the sediment (smaller than 2 mm), and ignore the larger size clasts. The mean grain size appears to be between 8 to 10 mm. The second method includes counting the number of clasts larger than 2 mm from X-radiographs, and counts of particles (106–1000 μm). These latter counts show that diamictons from the North Iceland shelf indicate a dominance of glacially abraded basaltic grains, but they also contain a small, consistent proportion of angular volcanic glass shards of various compositions. The third method is to examine grain-size spectra of surface samples from East Greenland and the Ross Sea region of Antarctica and compare these data with down-core data from neoglacial-age glacial marine sediments from Nansen Fjord, East Greenland, and with late glacial diamictons from the North Iceland shelf. These sediments have a mode in the silt fraction, but they frequently have secondary peaks in the coarse sand and fine sand/coarse silt areas, and a trough in the range of 100 to 500 μm (medium to coarse sand). Most of the sediment samples analysed in this study contain 20–50% in the below 1 μm grain size, which reinforces the importance of examining this fraction in provenance studies in glacial marine sediments.
Sediment reworking on high-latitude continental margins and its implications for palaeoceanographic studies: insights from the Norwegian-Greenland Sea
Authors: Cofaigh Colm Ó , Taylor Justin , Dowdeswell Julian A. , Rosell-Melé Antoni , Kenyon Neil H. , Evans Jeffrey , Mienert Jürgen
Published: April 2008

Geological evidence indicates that sediment reworking is common around the continental margins and abyssal depths of the Norwegian-Greenland Sea, a high-latitude setting with glacier-influenced margins. Detailed analysis of 22 cores up to 5 m long, placed in context by accompanying geophysical data including high resolution sub-bottom profiles, swath bathymetry and backscatter maps, indicates that reworking is variable and ranges from debris flows and turbidity currents, to bottom-current activity, as well as iceberg scouring. Reworking by debris flows appears to be restricted mainly to the main trough-mouth fans and sediment slides. Elsewhere, turbidity-current activity frequently dominates, although iceberg ploughing down to 600 m depth and current winnowing assume increasing significance on continental shelves. Reworking in the Norwegian-Greenland Sea reflects variations in ice-sheet dynamics that, in turn, influence the rate of sediment delivery and location of depocentres. Spatial variations in the style of reworking may also reflect the influence of continental slope gradient and bedrock geology on continental shelves. The widespread nature of sediment reworking has important implications for palaeoceanographic investigations in the region, as reworking can result in erosion and disturbance of the sediment column. It is estimated that less than 7% of material delivered to the Norwegian-Greenland Sea since the Late Weichselian is derived from hemipelagic and pelagic sedimentation. This problem is significant where continuous, high-resolution records of hemipelagic and pelagic sedimentation are required, and attempts are made to correlate with other high-resolution proxy records, such as ice cores, at sub-millennial scales. Bioturbation results in the smoothing of high-resolution records and imposes a maximum resolution for sediment-core time-slices of generally 400 years or more. In the Norwegian-Greenland Sea, areas of high sedimentation such as trough-mouth fans or contourite drifts are commonly associated with extensive reworking. Identification of reworking is particularly important where attempts are made to link records of iceberg-rafted debris to past ice-sheet dynamics, as bottom-current winnowing and mass-flow processes can increase the concentration of coarse-grained iceberg-rafted debris. Such localized accentuation of the iceberg-rafted debris signal may lead to erroneous palaeo-environmental interpretations. It is therefore critical that palaeoceanographic interpretations are firmly underpinned by an explicit sedimentological assessment of reworking.
Correlating magmatic-hydrothermal ore deposit formation over time with geodynamic processes in SE Europe
Authors: Lips Andor L. W.
Published: April 2008

Numerous magmatic-hydrothermal metal deposits in SE Europe occur in relatively narrow belts of magmatic rocks that have been classically related to subduction. In contrast to the hundred million years of convergence and consumption of lithosphere at the subduction zones in the region, the belts have been produced in discrete time intervals. It has also become recognized that the dominant phases of mineralization in the belts were accompanied by extension. Research focusing on the evolution of the lithosphere at convergent margins identifies secondary thermal and mechanical processes that accompany the primary process of subduction. Such secondary processes have been identified as the possible trigger of the magmatism, regional crustal extension, and enhanced flow of heat and circulation of fluids. The lithosphere dynamics may thus have played a vital role in the formation and localization of the mineralization. Roll-back of the subducted lithosphere, or restoration of the orogenic wedge geometry by changes in internal friction, set by variations in rates of the Africa-Eurasia convergence; and gravitational collapse (e.g. involving slab detachment or root delamination), are the scenarios that favour extension and the transfer of heat to relatively shallow lithospheric levels. Analysis of the temporal and spatial constraints of these geodynamic processes, together with a refining of the timing of the main phases of mineralization is the first step to discriminate between the geodynamic causes, and to determine their effects in relatively short-lived regional igneous and hydrothermal activities and the formation of related mineralization.
Contrasting Late Cretaceous with Neogene ore provinces in the Alpine-Balkan-Carpathian-Dinaride collision belt
Authors: Neubauer Franz
Published: April 2008

Internal sectors of the Alpine-Balkan-Carpathian-Dinaride (ABCD) orogen comprise fundamentally different ore deposits along strike in three temporally and spatially distinct belts. These were formed by several short-lived, late-stage collisional processes (including slab break-off) during the Late Cretaceous and Oligocene to Neogene times. Reconstruction of Late Cretaceous (c.92–65 Ma) collisional structures, magmatic features and mineralization reveals contrasting variations along strike, including the following.

(1a)

The Late Cretaceous ‘banatite’ magmatic belt, which extends from the Apuseni mountains to the Balkans, associated mainly with porphyry Cu-Au, massive sulphide and Fe-Cu skarn mineral deposits. In respect to their country rocks and geodynamic setting, the magmatism is interpreted to represent either post-collisional or Andean-type calc-alkaline due to continuous subduction or break-off of the subducted lithosphere.

(1b)

The Alpine-West Carpathian sector, which is characterized by strong Late Cretaceous metamorphic/deformational overprint, lack of magmatism and both syn- and late-orogenic formation of metasomatic and metamorphogenic talc, magnesite, siderite and vein- and shear zone-type Cu and As-Au due to the exhumation of metamorphic core complexes.

(2a)

The Oligocene-Miocene Serbomacedonian-Rhodope metallogenic zone extends across several structural units from the Bosnian Dinarides to the Rhodopes and to Thrace. It includes both a belt with volcanic-hosted and vein-type Pb-Zn deposits and a belt of porphyry Cu-Au-Mo and epithermal Au mineralization, which is more common in the south. Both belts appear to relate to microcontinent collision and associated subsequent magmatism, again possibly due to slab break-off.

(2b)

Different types of mineralization were also formed along the internal Inner Carpathian and Alpine sectors during Late Oligocene to Miocene collision. In the Alps, mineralization formed due to eastward extrusion of fault-bounded blocks into the Carpathian arc. Associated mineral deposits are always related to exhumation of metamorphic core complexes and include: sub-vertical mesothermal Au-quartz veins and replacement As-Ag-Cu ore bodies within the metamorphic core complex, fault-bounded mineralization (Pb-W-Au) along low-angle ductile normal faults along the upper margins of the metamorphic core complex, mineralized (Sb-Au) strike-slip faults and sub-vertical Au-Ag-Sb-bearing tension veins.

(2c)

In contrast, nearly all Miocene ore deposits within the Carpathians are related to volcanic activity contemporaneous with the invasion of fault-bounded blocks into the Carpathian arc. These have been related to slab break-off and cessation of subduction. Mineral deposits include structurally controlled Au-Sb-Cu-Pb-Zn ore bodies within shallow volcanic edifices, with a preference for steep tension veins parallel to the motion direction of laterally escaping crustal blocks.
The Elatsite porphyry copper deposit in the Panagyurishte ore district, Srednogorie zone, Bulgaria: U-Pb zircon geochronology and isotope-geochemical investigations of magmatism and ore genesis
Authors: Von Quadt Albrecht , Peytcheva Irena , Kamenov Borislav , Fanger Lorenz , Heinrich Christoph A. , Frank M.
Published: April 2008

Single zircons from several porphyry dykes bracketing the time of formation of the Elatsite porphyry Cu-Au deposit (Bulgaria) were dated by high-precision U-Pb isotope analysis, using thermal ionization mass spectrometry (TIMS). On the basis of cross-cutting relationships, and the mineralogy and geochemistry of igneous and altered rocks, five dyke units are distinguished. The earliest porphyry dyke is associated with, and overprinted by, the main stage of ore-related veining and potassic alteration. U-Pb analyses of zircons yield a mean
206
Pb/
238
U age of 92.1 ± 0.3 Ma, interpreted to reflect the time of intrusion. Zircons of the latest ore forming dyke, crosscutting the main stage veins but still associated with minor potassic alteration and veining, give an intrusion age of 91.84 ± 0.3 Ma. Thus, ore mineralization is confined by individually dated igneous events, indicating that the entire time span for the ore-forming magmatism and high temperature hydrothermal activity extended over a maximum duration of 1.1 Ma, but probably much less. Zircon analyses of a late ore dyke cutting all ore veins and hosting pyrite as the only sulphide mineral give a concordant
206
Pb/
238
U age of 91.42 ± 0.15 Ma. Based on a spatial relationships of the magnetite-bornite-chalcopyrite assemblage with coarse-grained hydrothermal biotite and K-feldspar, a Rb-Sr age of 90.55 ± 0.8 Ma is calculated using the two K-rich minerals. This age is interpreted as a closing date for the Rb-Sr system at T ≈ 300 °C consistent with published K-Ar data. Therefore the entire lifespan of the magmatic-hydrothermal system is estimated to have lasted about 1.2 Ma. Soon after, the Cretaceous complex was exposed by erosion, as shown by palaeontologically dated (Turonian; 91–88.5 Ma) sandstones containing fragments of porphyry dykes.

Geochemical discrimination ratios suggest a mixed mantle and crustal source of the Cretaceous magma. Isotope analyses of Sr, Nd and Hf confirm the conclusion that all porphyry rocks within and around the Elatsite deposit originate from an enriched mantle source at Cretaceous times, with crustal contamination indicated by moderately radiogenic Pb.
The relationship between ore deposits and oblique tectonics: the SW Iberian Variscan Belt
Authors: Tornos Fernando , Casquet César , Relvas Jorge M. R. S. , Barriga Fernando J. A. S. , Sáez Reinaldo
Published: April 2008

The Ossa Morena and South Portuguese Zones of the Variscan Belt of Iberia are interpreted to represent continental fragments that collided during the Variscan orogeny. Oblique northward subduction of an oceanic realm beneath the Ossa Morena Zone and subsequent collision induced thrusting and left-lateral transcurrent motion of crustal blocks and formation of a variety of ore deposits in both terranes. Most of the mineralization is related to dilational openings within thrusts and shear zones, extensional faults and pull-apart basins. A discontinuous diachronous vertical section from exhalative to deep mesozonal hydrothermal systems of Variscan age can be inferred. Volcanic-hosted massive sulphides are formed in third order pull-apart basins, but deeper related extensional structures are the
loci
for epithermal Hg, fluorite and Pb-Zn vein systems, Cu-Ni magmatic mineralization and iron-rich calcic skarns. Dilational regions along major shear zones also host mesozonal gold-bearing quartz veins. The overall Variscan mineralization pattern is inferred to be representative of an oblique collisional, (transpressional) geodynamic regime.
Permo-Mesozoic multiple fluid flow and ore deposits in Sardinia: a comparison with post-Variscan mineralization of Western Europe
Authors: Boni M. , Muchez P. , Schneider J.
Published: April 2008

The post-Variscan hydrothermal activity and mineralization in Sardinia (Italy) is reviewed in the framework of the geological and metallogenic evolution of Western Europe. The deposits can be grouped into (a) skarn, (b) high- to low-temperature veins and (c) low-temperature palaeokarst. The structural, stratigraphical and geochemical data are discussed. The results suggest three hydrologically, spatially, and possibly temporally, distinct fluid systems.
System 1
(precipitating skarn and high-temperature veins) is characterized by magmatic and/or (?) magmatically heated, meteoric fluids of low-salinity. The source of metals was in the Variscan magmatites, or in the Palaeozoic/Precambrian basement.
System 2
(low-temperature veins and palaeokarst) is represented by highly saline, Ca-rich (formation or modified meteoric) fluids. Sources of the metals were the pre-Variscan ores and carbonate rocks.
System 3
is characterized by low-temperature, low-salinity fluids of meteoric origin.

The hydrothermal deposits related to Systems 1 and 2 can be framed in a ‘crustal-scale hydrothermal palaeofield’, characterizing most of the post-orogenic mineralization in Variscan regions of Western and Southern Europe, allowing for local age differences of each single ore district and background effects. The suggested timing for the hydrothermal events in Sardinia is: (1) Mid-Permian (270 Ma), (2) Triassic-Jurassic. It is suggested that the Mesozoic events were related to the onset of Tethys spreading.
The timing of W-Sn-rare metals mineral deposit formation in the Western Variscan chain in their orogenic setting: the case of the Limousin area (Massif Central, France)
Authors: Cuney M. , Alexandrov P. , Le Carlier de Veslud C. , Cheilletz A. , Raimbault L , Ruffet G. , Scaillet S.
Published: April 2008

New
40
Ar/
39
Ar dating performed on Rare Metal Granites and W ± Sn deposits in the northern Limousin has provided evidence of two metallogenic episodes. An Early Namurian episode (
c.
325 Ma) was contemporaneous with the emplacement of the large peraluminous leucogranite bodies, which are associated with small W ± Sn deposits, but also with some larger deposits, at Puy-les-Vignes (323.4 ± 0.9 Ma) and Moulin-Barret (323.7 ± 0.8 Ma) formed at a shallower level above cryptic granite plutons. These new data indicate that the metallogenic potential of the Namurian leucogranites might have been underestimated. Most other W ± Sn deposits in the northern Limousin area are attributed to a Mid-Westphalian episode (
c.
310 Ma), and are contemporaneous with the emplacement of all the Rare Metal Granites. Both episodes were related to leucogranite emplacement and associated fluid circulations, but in two different geodynamic contexts. The Early Namurian episode may be related to syncollisional extension of the Variscan belt, whereas the Mid-Westphalian one occurs during generalized extension and rapid exhumation of the belt associated with the granulite-facies metamorphism of the lower lithosphere probably related to the delamination of the lower lithosphere. Thus, W ± Sn and rare metals (Ta, Nb, Be, Li) deposits are clearly temporally and probably genetically related to leucogranitic magmatism.
The Baikalide-Altaid, Transbaikal-Mongolian and North Pacific orogenic collages: similarity and diversity of structural patterns and metallogenic zoning
Authors: Yakubchuk Alexander
Published: April 2008

The Baikalide-Altaid, Transbaikal-Mongolian and North Pacific orogenic collages consist of several oroclinally bent magmatic arcs separated by accretionary complexes and ophiolitic sutures located between the major cratons. The tectonic and metallogenic patterns of these collages are principally similar as they were formed as a result of rotation of the surrounding cratons and strike-slip translation along the former convergent margins.
Role of Pan-African events in the Circum-East Antarctic Orogen of East Gondwana: a critical overview
Authors: Yoshida Masaru , Jacobs Joachim , Santosh M. , Rajesh H. M.
Published: April 2008

Recent studies of Pan-African events in East Gondwana are critically reviewed, particularly recent models of amalgamation of East Gondwana during the Pan-African period. It is pointed out that critical data are insufficient to constrain the newly proposed models and so the classical model of the Grenvillian Circum-East Antarctic Orogen cannot yet be replaced. Grenvillian tectonothermal events with a peak between 1.0 and 1.2Ga assembled different crustal blocks of the East Antarctic Shield with different geohistories. Pan-African tectonothermal reworking took place over wide but selected areas of the orogen. Careful geochronological studies, including SHRIMP dating associated with structural and petrological investigations to correlate ages with those events, are shown to be important, since fluid-rich and/or deformational conditions are equally effective as temperature conditions for mineral recrystallization and resetting of isotopic systematics. Pan-African suture zones, one extending from the Mozambique Belt to the Shackleton Range and another connecting the Mozambique Belt to the Zambezi Belt, are equally possible, although the width of the southern Mozambique Ocean is poorly understood. The extent of Pan-African sutures in the Prydz Bay area is enigmatic, although they represent definite orogens. Palaeomagnetic studies may provide critical constraints in evaluating the sutures, provided that the age of magnetization is well established.
Palaeomagnetic constraints on the Proterozoic tectonic evolution of Australia
Authors: Wingate Michael T. D. , Evans David A. D.
Published: April 2008

Recent plate tectonic models advocate assembly of Proterozoic Australia by tectonic processes that involved large-scale horizontal motions, whereas previous models suggested that the continent evolved as an essentially intact block of lithosphere. Geological and geochemical observations alone are insufficient to test whether the major cratonic blocks of Australia were together or widely separated during the Proterozoic; only palaeomagnetism can provide quantitative constraints on relative plate motions during the Precambrian. Despite deficiencies in the palaeomagnetic record for Proterozoic Australia, groups of overlapping palaeopoles for 1.7–1.8 and 1.5–1.6 Ga permit the North and West Australian cratonic assemblages to have occupied their present relative positions since at least
c.
1.7Ga, and to have been joined to the South Australian cratonic assemblage since at least
c.
1.5Ga. Nonetheless, additional geological, geochronological and palaeomagnetic data are required to test whether large oceans closed between any of the continental blocks.
Proterozoic basement provinces of southern and southwestern Australia, and their correlation with Antarctica
Authors: Fitzsimons I. C. W.
Published: April 2008

Three Precambrian basement provinces extend from the southern coast of Australia into East Antarctica when reconstructed in a Gondwana configuration. These are, from east to west, the Mawson Craton, and the Albany-Fraser and Pinjarra Orogens. The Mawson Craton preserves evidence for tectonic activity from the late Archaean until the earliest Mesoproterozoic. It is exposed in the Gawler Craton of South Australia, the Terre Adélie and King George V Land coastline of East Antarctica, and the Miller Range of the central Transantarctic Mountains. It may form a significant part of the ice-covered East Antarctic Shield, although insufficient data are available to constrain its lateral extent. The Mawson Craton underwent late Palaeoproterozoic tectonism along its eastern margin (the Kimban Orogeny) and the occurrence of
c.
1700Ma eclogites in the Transantarctic Mountains implies that this was, in part, a collisional event, although elsewhere it was characterized by low
P/T
metamorphism. The western margin of the Mawson Craton collided with a continental fragment comprising the Nawa Domain of the Gawler Craton, the Coompana Block and the Nornalup Complex of Western Australia at
c.
1560Ma during the Kararan Orogeny. The western edge of the Nornalup Complex later collided with the Biranup and Fraser Complexes and Yilgarn Craton to form the Albany-Fraser Orogen during two stages of tectonism at
c.
1350–1260 and 1210–1140Ma. The Pinjarra Orogen truncates the western margin of the Yilgarn Craton and Albany-Fraser Orogen, and contains allochthonous 1100–1000Ma gneissic blocks transported along the craton margin during at least two stages of Neoproterozoic transcurrent movement. It divides East Gondwana into Australo-Antarctic and Indo-Antarctic domains, which are distinct continental fragments with different Proterozoic histories that were juxtaposed by oblique collision at 550–500Ma during the assembly of Gondwana. The path taken by the Pinjarra Orogen beneath the Antarctic ice sheet is unknown, but it is of similar width and length to the East African Orogen, and must have been a fundamental Neoproterozoic boundary of critical importance to supercontinent assembly and breakup.
Pan-African events in Prydz Bay, East Antarctica, and their implications for East Gondwana tectonics
Authors: Zhao Y. , Liu X. H. , Liu X. C. , Song B.
Published: April 2008

Decompression, anatexis and the clockwise granulite-grade
P-T
evolution of high-grade rocks of Prydz Bay reflect late collisional extension that occurred
c.
530 Ma in the Prydz Belt. Rapid cooling of the mid-crust high-grade terranes of the Prydz Belt was achieved during
c.
517-486 Ma by tectonically driven exhumation along dextral ductile shear zones in which late tectonic partialmelt bodies were emplaced. Instead of a model of polyphase metamorphism and deformation for the basement-and-cover sequences in Prydz Bay, we apply an accretionary one, i.e. an accretionary wedge with allochthonous blocks, to interpret the tectonic history in the Late Neoproterozoic of the Prydz Belt. SHRIMP U-Pb dates and Nd isotopic data available for both Prydz Bay and the Grove Mountains are used to explain amalgamation of the high-grade terranes in the Prydz Belt. This demonstrates that the assembly of the East Antarctic Craton was completed in the Pan-African event, and the East Antarctic Craton is a Pan-African-age collage rather than a keystone of East Gondwana during the Neoproterozoic.
Tracing tectonic deformation using the sedimentary record: an overview
Authors: McCann Tom , Saintot Aline
Published: April 2008

Tectonic activity, on a range of scales, is a fundamental control on sedimentary activity. The range of structural deformation within a region extends from the plate tectonic scale, governing, for example, rift initiation, to the basin scale, with the formation of basinbounding faults. Internal basin configuration is also strongly influenced by tectonic activity. However, the relationship between tectonic activity and sedimentation is a complex one, given the many additional factors which can also influence sedimentary activity, including erosion, sediment transport, source area lithology, groundwater chemistry, range of depositional environments, climate, eustasy, and the relative location of an area and its distality to marine influences. In this paper we provide a selective overview of the issues associated with the interlinked themes of tectonics and sedimentation, examining the main basin types forming in both extensional and compressional plate settings. We then review the various models of sedimentation in the selected basins, both on a local and a basinal scale. Finally, we look to the future — providing a series of possible research areas, almost exclusively multidisciplinary, which would help to improve existing models of interlinked sediment-tectonics systems.
Evaluation of controlling factors on facies distribution and evolution in an arid continental environment: an example from the Rotliegend of the NE German Basin
Authors: Rieke H. , McCann T. , Krawczyk C. M. , Negendank J. F. W.
Published: April 2008

About 3 km of core material from 14 wells together with additional data from several hundred wells across the NE German Basin (NEGB), have been investigated in order to reconstruct the facies architecture and the evolution of the Upper Rotliegend II. Special attention has also been given to the verification of various controlling factors and their influence on sedimentation in an arid continental environment. The facies architecture within the logged profiles comprises five main environments, namely braided plain, ephemeral stream floodplain, sand flat, mudflat and playa lake. The evolution can be subdivided into four distinct basin-wide correlatable periods — Parchim, Mirow, Dethlingen and Hannover formations — with each of them being characterized by a specific basin geometry and interplay of controlling factors. The deposition of the basal Parchim Formation largely took place within a tectonically created basin, whereas the facies evolution displayed an initial less-arid climatic period and later shift to an arid climate. The succeeding Mirow Formation marks the beginning of thermally induced basin subsidence. However, sedimentation itself clearly reflects a period in which the climate was relatively less arid. The overlying Dethlingen Formation was largely controlled by the increasing thermal subsidence of the basin, leading to broad extension towards the south and east. Internally, the strata can show the effects of climatic variability, depending on their position within the basin. The uppermost Hannover Formation was the product of ongoing basin subsidence, a reduction in sediment supply and an increasingly peneplaned topography. In summary, evolution of the Upper Rotliegend II within the NEGB reveals a variety of factors which have a significant influence on sedimentation, such as climate variations, the creation rate and amount of accommodation space, wind direction, sediment budget and source area lithology. An understanding of how these various factors interlink in controlling basin infill is of great significance in understanding the complex depositional history of arid continental successions.