bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

AbstractInternal 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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract
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

Abstract
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

Abstract

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.