bluuebunny/crossref_metadata_2025_split huggingface dataset:
Neogene and Quaternary Volcanism of Southeastern Turkey
Authors: Arger Jan , Mitchell John , Westaway Rob W. C. 
Published: April 2008

Abstract

Potassium-argon dating indicates two episodes of basaltic magmatism in south eastern Turkey at
c.
19–15 and
c.
2.3–0.6 Ma. Each produced olivine-titanaugite basalts, whose chemical compositions are difficult to classify using any conventional model in both the Anatolian continental fragment and the Arabian Platform. It is proposed here that both episodes of volcanism, and the associated crustal thickening and surface uplift, result from heating of the mantle lithosphere by crustal thickening caused by inflow of plastic lower crust from adjoining regions. Thus, although this study region has remained in a plate boundary zone for tens of millions of years, its volcanism has no direct relationship to local plate motions. It is suggested instead that both episodes of volcanism are the result of loading effects caused by glacial to interglacial sea-level variations, which will cause net flow of lower crust from beneath the offshore shelf to beneath the land: the moderate glaciations of Antarctica which began in the Early-Middle Miocene, and the more intense lowland glaciations of the northern hemisphere which began around
c.
2.5 Ma.
Micromorphological analyses of microfabrics and microstructures indicative of deformation processes in glacial sediments
Authors: Menzies John 
Published: April 2008

Abstract
Various forms of sediment deformation can be detected within glacial sediments at the microscopic scale. Analyses of these forms leads to a preliminary classification of microfabrics and microstructures of brittle, ductile and polyphase modes of deformation in glacial sediments. With the development of a taxonomy of different microfabrics and microstructures these processes, once differentiated, permit insights into glacial sediments to a scale and level of detail hitherto unknown. Examples are presented that illustrate some of these different forms of deformation often within a single glacial sediment sample. This research suggests many of the past ideas with regard to details of glacial depositional processes, especially in terms of diamicton deposition and subsequent classifications, need to be re-evaluated.
Fluctuations in the carbonate production of Phanerozoic reefs
Authors: Kiessling Wolfgang , Flügel Erik , Golonka Jan 
Published: April 2008

Abstract
A comprehensive database on Phanerozoic reefs is used to evaluate the carbonate production of reefs through time. Net, gross and export carbonate productions of 2760 Phanerozoic reefs are calculated and the cumulative production for 32 time slices is evaluated. The total amount of carbonate produced in the reef ecosystem in a given time slice is a function of global reef abundance, average reef size and the relative amount of carbonate exported from the reefs. Carbonate production of reefs is usually low, but characterized by prominent peaks in the mid-Silurian Givetian-Frasnian, the Late Triassic, the Late Jurassic, the mid-Cretaceous and the Neogene.

The determinants of reefal carbonate production are correlated with a variety of intrinsic and extrinsic parameters such as palaeogeographic setting, dominant biota, reef type, bioerosion, petrographic composition, eustatic sea level, oceanic crust production rates, atmospheric CO
2
concentrations, and global nutrient level. The calculated carbonate production, however, is rarely correlated with particular Earth system parameters. This implies that either the controls on reefal carbonate production are too complex to allow reliable predictions, or biotic factors represent more important controls than physico-chemical parameters. The constructed curve of Phanerozoic reefal carbonate export production is also poorly correlated with proposed curves of global shallow-water carbonate production suggesting that reefs rarely contributed in a quantitatively significant way to the global carbonate budget.
The Late Palaeozoic relations between Gondwana and Laurussia
Authors: McKerrow W. S. , Mac Niocaill C. , Ahlberg P. E. , Clayton G. , Cleal C. J. , Eagar R. M. C. 
Published: April 2008

Abstract
Reconstructions based on biogeography, palaeomagnetism and facies distributions indicate that, in later Palaeozoic time, there were no wide oceans separating the major continents. During the Silurian and Early Devonian time, many oceans became narrower so that only the less mobile animals and plants remained district. There were several continental collisions: the Tornquist Sea (between Baltica and Avalonia) closed in Late Ordovician time, the Iapetus Ocean (between Laurentia and the newly merged continents of Baltica and Avalonia) closed in Silurian time, and the Rheic Ocean (between Avalonia and Gondwana and the separate parts of the Armorican Terrane Assemblage) closed (at least partially) towards the end of Early Devonian time. Each of these closures was reflected by migrations of non-marine plants and animals as well as by contemporary deformation. New maps, based on palaeomagnetic and faunal data, indicate that Gondwana was close to Laurussia during the Devonian and Carboniferous periods, with fragments of Bohemia and other parts of the Armorican Terrane Assemblage interspersed between. It follows that, after Early Devonian time, the Variscan oceans of central Europe can never have been very wide. The tectonic evolution of Europe during Devonian and Carboniferous time was thus more comparable with the present-day Mediterranean Sea than with the Pacific Ocean.
Review of Nd isotopic data and xenocrystic and detrital zircon ages from the pre-Variscan basement in the eastern Bohemian Massif: speculations on palinspastic reconstructions
Authors: Hegner Ernst , Kröner Alfred 
Published: April 2008

Abstract
Nd crustal residence ages combined with xenocrystic and detrital zircon ages of Neoproterozoic and early Palaeozoic granitoid gneisses and metasediments from the NE Bohemian Massif (West Sudetes and Erzgebirge) suggest an origin from a basement with significant Grenvillian and Svecofennian-Birimian-Amazonian age components. Large contributions from Archaean crust appear to be missing. Nd model ages of 1.4–1.7 Ga as well as Meso- to Palaeoproterozoic zircon xenocrysts ages for the Lugian Domain (Jizerské, Krkonoše, and Orlica-Sniezník Mountains) are interpreted as evidence for a predominantly Palaeoproterozoic basement that underwent rejuvenation during Meso- and Neoproterozoic-Ordovician magmatic events. Our interpretation of the Nd model ages may be relevant for the western part of the Variscan Belt, where a similar range of Nd model ages characterizes large crustal segments. Samples from the Silesian Domain (Desná Dome Staré Město Belt, Velké Vrbno Unit) of the Brunia Microcontinent, in thrust contact with the Lugian Domain, yielded Nd crustal residence ages of 1.1–1.3 Ga, which coincide with the oldest ages of xenocrystic zircons. Brunia is interpreted as a predominantly juvenile Grenvillian-age crustal segment, possibly constituting a former arc batholith outboard from the more ensialic setting of the Lugian Domain. Nd crustal residence ages for our 77 whole-rock samples, including 41 new data, as well as 185 xenocrystic and detrital zircon ages from the northern and northeastern Bohemian Massif agree with those of Neoproterozoic rocks from northern South America and support an origin from a northwest Gondwana palaeogeographical location.
Review of geochemical variation in Lower Palaeozoic metabasites from the NE Bohemian Massif: intracratonic rifting and plume-ridge interaction
Authors: Floyd P. A. , Winchester J. A. , Seston R. , Kryza R. , Crowley Q. G. 
Published: April 2008

Abstract

During early Palaeozoic time the Cadomian basement of the northern margin of Gondwana underwent extensive rifting with the formation of various crustal blocks that eventually became separated by seaways. Attenuation of the continental lithosphere was accompanied by the emplacement of anatectic granites and extensive mafic-dominated bimodal magmatism, often featuring basalts with an ocean crust chemistry. Intrusive metabasites in deep crustal segments (associated with granitic orthogneisses) or extrusive submarine lavas at higher levels (associated with pelagic and carbonate basinal sediments) show a wide range of chemical characteristics dominated by variably enriched tholeiites. Most crustal blocks show the presence of three main chemical groups of metabasites: Low-Titholeiitic metabasalts, Main Series tholeiitic metabasalts and alkalic metabasalt series. They differ in the degree of incompatible element enrichment (depleted to highly enriched normalized patterns), in selected large ion lithophile (LIL) to high field strength element (HFSE) ratios, and abundances of HFSE and their ratios. Both the metatholeiite groups are characterized by a common enrichment of light REE-Th-Nb-Ta. High Th values (or Th/Ta ratios) and associated low ε
Nd
values (especially in the Low-Ti tholeiitic metabasalts) reflect sediment contamination in the mantle source rather than at crustal levels, although this latter feature cannot be ruled out entirely. The range of chemical variation exhibited is a consequence of the melting of (a) a lithospheric source contaminated by a sediment component (which generated the Low-Ti tholeiites), and (b) a high-level asthenospheric mid-ocean ridge basalt (MORB)-type source that mixed with a plume component (which generated the range of enriched Main Series tholeiites and the alkali basalts). It is considered that a plume played an important role in the generation of both early granites and the enriched MORB-type compositions in the metabasites. Its significance for the initial fragmentation of Gondwana is unknown, but its presence may have facilitated deep continental crust melting and the fracturing into small crustal blocks. The early-mid-Jurassic plume-instigated break-up of the southern Gondwana supercontinent is considered to be a possible tectonic and chemical analogue for Early Palaeozoic Sudetic rifting and its magmatic products.
Passive margin detachment during arc-continent collision (Central European Variscides)
Authors: Oncken O. , Plesch A. , Weber J. , Ricken W. , Schrader S. 
Published: April 2008

Abstract
In the Rhenish Massif and Ardennes, the Rheno-Hercynian fold and thrust belt of the Mid-European Variscides exposes a telescoped complete Late Palaeozoic passive margin, which was detached from the lower crust during Carboniferous collision with a continental arc (Mid-German Crystalline High on the leading edge of Armorica). Geometric analysis and isostatically corrected balanced cross-sections show that the basal detachment propagated from the oceanic realm into the passive margin by repeated ductile footwall failure during lithospheric flexure of the weak lower plate (effective elastic lithospheric thickness <4 km) under the load of the advancing upper plate. Early collision was associated with offscraping of the uppermost slope sediments in frontal accretion mode. Subsequent detachment of the remaining passive margin cover was initiated after subduction of the ocean-continent transition to about 6 kbar depth. Rocks and fabrics from the detachment show that, at this pressure, they crossed the brittle-plastic transition at the fossil 300–400 °C isotherm. Newly failed segments of the basal detachment propagated along this isotherm and branched off towards the foreland by progressively downstepping from the passive margin sediments into the basement of the downflexed lower-plate crust. This evolution coincided with cyclic changes in accretion mode of the lower-plate upper crust to the advancing orogenic wedge (repeated changes from basal to frontal accretion) as well as with a related stepwise propagation of a narrow foreland basin. Propagation of the detachment segments and the related imbricate fans in the lower plate, moreover, was controlled by the geometry of the basin structure by localizing branch lines and ramps along earlier growth faults.
Syn-convergent high-temperature metamorphism and magmatism in the Variscides: a discussion of potential heat sources
Authors: Henk A. , von Blanckenburg F. , Finger F. , Schaltegger U. , Zulauf G. 
Published: April 2008

AbstractA period of pervasive high-temperature metamorphism and igneous activity from 340 to 325 Ma is a well-established characteristic of the Variscan Orogen of Central Europe. During this stage, the internal zone of the orogen was virtually soaked by granitic to granodioritic magmas. Petrological data point to temperatures of 600–850 °C at upper- to mid-crustal levels. These elevated temperatures occurred during the final convergence stage and may be comparable with similar processes inferred from geophysical evidence for the present-day Tibetan Plateau, in both regional extent and significance for the orogen’s evolution. We review various geodynamic scenarios that may have provided the heat for melting and metamorphism, and compare model predictions with field data from the Variscides. All lines of evidence point to a geodynamic scenario that led to thickening of the continental crust with increased internal radiogenic heating, but without simultaneous thickening of the mantle lithosphere. Possible mechanisms include convective removal of the thermal boundary layer, delamination of part of the lithospheric mantle, and subduction of the mantle lithosphere of the downgoing plate. However, with the present stage of knowledge it is virtually impossible to single out one of these three mechanisms, as their geological consequences are so similar.
The Svalbardian-Ellesmerian deformation of the Old Red Sandstone and the pre-Devonian basement in NW Spitsbergen (Svalbard)
Authors: Piepjohn Karsten 
Published: April 2008

Abstract
In NW Spitsbergen, the Late Silurian to Late Devonian infill of an Old Red Sandstone (ORS) basin was affected by west-vergent folding and west-directed thrusting during the Early Carboniferous (Tournaisian) Svalbardian deformation. The brittle, predominantly compressional structures of the Svalbardian Fold-and-Thrust Belt are concentrated along at least five narrow, more or less north-south-trending zones. Three zones are exposed in the Devonian infill of the ORS basin. The involvement of the post-Caledonian ?Late Silurian to Earliest Devonian Viggobreen weathering zone and deposits Early Devonian in two thrust zones within the basement of the western basin margin indicates that the Svalbardian deformation also affected the basement areas along the west coast of NW Spitsbergen. Structures of the Svalbardian Fold-and-Thrust Belt are exposed within an area at least 100 km wide between the Billefjorden Fault Zone in the east and the west coast of NW Spitsbergen. Therefore, the Svalbardian deformation represents a much more important fold belt than previously recognized. On the basis of the timing, the large extent and the orientation of the fold-and-thrust zones, the Svalbardian Fold-and-Thrust Belt appears to represent the eastern continuation of the Ellesmerian Fold Belt in North Greenland and the Canadian Arctic Archipelago.
Groundwater resources and vulnerability in the Cretaceous Chalk of Northern Ireland
Authors: Barnes S. 
Published: April 2008

Abstract
A confined Cretaceous Chalk aquifer underlies approximately one quarter of Northern Ireland, yet little is known about its groundwater resource potential. This issue has been addressed on the catchment scale by analysing spring discharge and hydrochemical fluctuations.
The Chalk springs are recharged by allogenic leakage and surface runoff from overlying Tertiary basalts. Sources connected to river-sinks show greater variation in flow and quality reflecting a much shorter residence time than those predominantly derived from the diffuse recharge. Discharge from the confined region becomes proportionally significant during prolonged dry spells, but is typically a minor component compared with groundwater circulation volumes in the unconfined region.
Spring flood recessions are rapid (recession coefficients up to 0.125 per day) and suggest that the Chalk has a high hydraulic conductivity and a low storage capacity. These characteristics together, with the essentially impermeable matrix, are consistent with an aquifer dominated by a dispersed fracture network.
Conceptual aquifer classification suggests that the outcrop region is a highly sensitive karst aquifer. The subcrop areas can only be exploited via boreholes and are likely to be less productive, although the water quality has been shown to be more stable and less vulnerable to contamination.
K-T boundary spherules from Blake Nose (ODP Leg 171B) as a record of the Chicxulub ejecta deposits
Authors: Martínez-Ruiz F. , Ortega-Huertas M. , Palomo-Delgado I. , Smit J. 
Published: April 2008

Abstract
The Cretaceous-Tertiary (K-T) boundary interval recovered by the ODP Leg 171 at Site 1049 (Blake Nose, NW Atlantic) contains a thick (9–17 cm) spherule bed marking the boundary. The spherules are mainly perfect spheres with a lesser proportion of oval spherules. They usually range from 100 to 1000 μm. This bed represent the diagenetically altered impact ejecta from Chicxulub and further supports this structure as the site of the K-T impact. Mineralogical and geochemical investigations indicate that impact-generated glass was altered to smectite. Transmission electron microscopy observations revealed in some spherules that smectite is forming from a Si-rich or Ca-rich material, which could suggest a precursor similar to Haitian glasses. The variable thickness and the presence of some Cretaceous planktonic foraminifera and clasts of Cretaceous chalk suggest reworking of the ejecta material. However, the spherule bed confirms that a large volume of the Chicxulub ejecta material reached the Blake Nose Plateau.
Pervasive Pan-African reactivation of the Grenvillian crust and large igneous intrusions in central Dronning Maud Land, East Antarctica
Authors: Paech H.-J. 
Published: April 2008

AbstractThe geological history of central Dronning Maud Land (cDML) is described on the basis of age data, recent observations, and published data. The ages of both the protoliths of the metamorphic rocks of cDML and their primary metamorphism are Grenvillian (1200 to 1000 Ma). Following a long hiatus for which geochronological data are lacking, the Grenvillian crust of cDML was intruded by abundant Pan-African partly charnockitic granitoids and anorthosites of the Dronning Maud Land igneous province. These intrusions occurred predominantly in two Pan-African igneous episodes. The early igneous episode (about 600 Ma), in which the Grubergebirge anorthosite intruded, was followed by Pan-African high-grade metamorphism, intense ductile deformation and then medium-grade retrogression during later Pan-African events (570 to 520 Ma). The Grenvillian structures and metamorphic signature were pervasively overprinted or completely eradicated. The Pan-African metamorphism and tectonism were completed prior to the late Pan-African igneous episode (500 Ma), in which predominantly post-kinematic granitoids, as well as a small anorthosite, intruded. Thus, the present tectonic structure of the crust in cDML was formed during Pan-African events by overprinting of Grenvillian basement and intrusion of granitoids/syenites and anorthosites.
Regional till geochemical surveys in the Canadian Cordillera: sample media, methods and anomaly evaluation
Authors: Levson Victor M. 
Published: April 2008

Abstract
Basal tills have become a widely used regional geochemical sampling medium in recent years in the Canadian Cordillera. They reflect the primary composition of the source bedrock and contrast with B-horizon soil that can be developed on a variety of glacial and non-glacial surficial sediment types. Detailed sedimentological data are critical to collect and they are used to differentiate basal tills from other visually similar sediments including englacial and supraglacial tills, colluvial debris flow deposits, and very poorly sorted, glaciofluvial or glaciolacustrine sediments (e.g. diamictons or gravelly muds). The variable transport and depositional processes that form these different sediments make interpretation of geochemical data difficult. Deep (usually >0.75 m) C-horizon sampling of basal till minimizes the complicating effects of pedogenesis, weathering, surface washing and gravity remobilization of the tills. The latter processes, particularly pronounced in the wet, steep terrain, typical of much of the Canadian Cordillera, lead to depleted concentrations of heavy minerals (notably Au) and hydromorphic dispersion of mobile elements in the near surface sediments. Also, elements that are preferentially concentrated in the fine fraction can be selectively removed by surface waters.
Offset sampling lines, oriented perpendicular to the dominant ice-flow direction, are most effective for detecting regional geochemical anomalies which are typically narrow and elongated parallel to ice-flow. Erratics trains and till anomalies are usually a few to several kilometres long and up to one or more kilometres wide. For some metals such as Au, anomalies are generally larger and more readily detected in till than in B-horizon soil. Surface till anomalies reflect up-ice sources and not the immediately underlying bedrock; down-ice displacements of > 500m often occur in areas of thick till. Basal till anomalies usually can be traced to source along linear transport paths reflecting topographically controlled valley-glacier flow in mountainous areas and unidirectional ice-sheet flow in many plateau areas, chiefly representative of the last glacial event. Interpretations of till geochemical data are enhanced with a clear understanding of the surficial and bedrock geology, Quaternary stratigraphy, ice-flow history and down-ice dispersal characteristics around known mineral deposits.