bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sand-rich turbidite system of the Late Oligocene Northern Apennines foredeep: physical stratigraphy and architecture of the ‘Macigno costiero’ (coastal Tuscany, Italy)
Authors: Cornamusini Gianluca 
Published: April 2008

Abstract
The ‘Macigno costiero’ turbidite system characterized the oldest foredeep clastic wedge of the Northern Apennines during the Late Oligocene collisional phase. The cropping-out thickness is about 500 m. The features of the ‘Macigno costiero’ indicate a sand-rich, low-efficiency turbidite system. The system developed within a partially confined basin, which was part of a complex foredeep system. The stacking pattern of the turbidite system was determined through the analysis of facies and physical stratigraphy. It consists of a succession organized in sedimentary units, which are characterized by particular associations of facies linked to distinct depositional environments. Several architectural elements are seen: (1) unchannelized and channelized lobes; (2) distributary channels with channel-fill, overbank and channel-margin deposits; (3) main channel with channel-fill, channel-margin and interchannel deposits. Five turbidite stages were identified. From the bottom up they consist of four lobe stages and one proximal channel stage. The lobe stages are characterized by thickening-coarsening upward trends, from distal lobes to proximal lobes up to the channel-lobe transition zone. The uppermost, fifth stage is linked to a main channel complex with stacked channel-fill, channel-margin and interchannel deposits. This final stage also marks the maximum progradation of the system up to its closure due to the synsedimentary overthrusting of the orogenic wedge.
Diachronous Variscan late-orogenic collapse as a response to multiple detachments: a view from the internides in France to the foreland in the Irish Sea
Authors: Praeg Daniel 
Published: April 2008

Abstract

Models of the collapse of orogenic belts imply diachronous tectonism in which crustal uplift and extension may be compensated by peripheral compression. This first-order prediction is tested against published data on Varsican late-orogenic extensional and compressive structures along a 1500 km transect from the Variscan central internides in France to the foreland in the Irish Sea area. The collapse of the orogen is shown to have expanded northward over time, via three main stages: (i)
collapse of the central internides
(late Visean-mid-Westphalian,
c.
335–310 Ma) — crustal thinning took place by NW-SE extension within a relatively narrow (< 500 km) central axis, accompanied to the north by passive infill of basins spanning a broad seaway inherited from extension during closure of the Rheic Ocean; (ii)
reorientation and expansion of collapse
(mid-Westphalian-late Stephanian,
c.
310–300 Ma) — in the mid-Westphalian, a 90° rotation to NE-SW extension in the central internides was accompanied by changes across the northern internides (episodic basin formation and deformation), the externides (onset of thrust propagation) and the foreland (Westphalian C inversion), while from the early Stephanian, basins began to form in the central internides and expanded to the externides, coeval with final nappe emplacement along the orogenic front; and (iii)
collapse of the foreland
(late Stephanian-Early Permian,
c.
300–290 Ma) — km-scale uplift and erosion of the foreland took place, prior to widespread basin formation in the Early Permian (<290 ± 5 Ma). These three stages are argued to support a model of Variscan late-orogenic collapse in response to three successive detachments of negatively buoyant lithospheric material: of a collisionally thickened orogenic root, and of two (Rheic) oceanic slabs subducted, previously, southward (beneath the orogen) and northward (beneath the foreland). Multiple detachments are a predictable consequence of ocean closure and continental collision, so that episodic collapse may be a common process in the rise and fall of orogenic belts and the tectonic evolution of their forelands.
New constraints on the timing of late Carboniferous-early Permian volcanism in the central North Sea
Authors: Heeremans Michel , Timmerman Martin J. , Kirstein Linda A. , Faleide Jan Inge 
Published: April 2008

Abstract

The Permo-Carboniferous evolution of the central North Sea is characterized by three main geological events: (1) the development of the West European Carboniferous Basin; (2) a period of basaltic volcanism during the Lower Rotliegend (latest Carboniferous-early Permian); and (3) the development of the Northern and Southern Permian Basins in late Permian times. The timing of the late Carboniferous-Permian basaltic volcanism in the North Sea is poorly constrained, as is the timing of extensional tectonic activity following the main phase of inversion during the Westphalian, due to the diachronous propagation of the Variscan deformation front. Results of high precision Ar-Ar dating on basalt samples taken from a core from exploration well 39/2-4 (Amerada Hess) in the UK sector of the central North Sea suggests that basaltic volcanism was active in the late Carboniferous, at
c.
299 Ma. The presence of volcanics below the dated horizon suggests that the onset of Permo-Carboniferous volcanism in the central North Sea commenced earlier, probably at
c.
310 Ma (Westphalian C). This is contemporaneous with other observations of tholeiitic volcanism in other parts of NW Europe, including the Oslo Graben, the NE German Basin, southern Sweden and Scotland. Interpretations of available seismic data show that main extensional faulting occurred after the volcanic activity, but the exact age of the fault activity is difficult to constrain with the data available.
Carboniferous and Permian magmatism in Scotland
Authors: Upton B. G. J. , Stephenson D. , Smedley P. M. , Wallis S. M. , Fitton J. G. 
Published: April 2008

Abstract
Extensional tectonics to the north of the Variscan Front during the Early Carboniferous generated fault-controlled basins across the British Isles, with accompanying basaltic magmatism. In Scotland Dinantian magmatism was dominantly mildly alkaline-transitional in composition. Tournaisian activity was followed by widespread Visean eruptions largely concentrated within the Scottish Midland Valley where the lava successions, dominantly of basaltic-hawaiitic composition, attained thicknesses of up to 1000 m. Changing stress fields in the late Visean coincided with a change in the nature of the igneous activity; subsequently, wholly basic magmatism persisted into the Silesian. As sedimentary basin fills increased, sill intrusion tended to dominate over lava extrusion. In the Late Carboniferous (Stephanian) a major melting episode, producing large volumes of tholeiitic magma, gave rise to a major dyke swarm and sills across northern England and Scotland. Alkali basaltic magmatism persisted into the Permian, possibly until as late as 250 Ma in Orkney. Geochemical data suggest that the Carboniferous-Permian magmas were dominantly of asthenospheric origin, derived from variable degrees of partial melting of a heterogeneous mantle source; varying degrees of interaction with the lithosphere are indicated. Peridotite, pyroxenite and granulite-facies basic meta-igneous rocks entrained as xenoliths within the most primitive magmas provide evidence for metasomatism of the lithospheric mantle and high-pressure crystal fractionation.
40
Ar/
39
Ar geochronology of Carboniferous-Permian volcanism in the Midland Valley, Scotland
Authors: Monaghan A. A. , Pringle M. S. 
Published: April 2008

Abstract

Twenty-one new
40
Ar/
39
Ar step-heating experiments on mineral separates from intrusive and extrusive Carboniferous and Permian igneous rocks in the Midland Valley of Scotland yielded 17 concordant experiments with a relative age precision better than 1% (2σ). These ages resolve inconsistencies between existing K-Ar dates on the same samples and their stratigraphical constraints correlated to recently published timescales. The precise
40
Ar/
39
Ar dates are stratigraphically constrained to stage level and can contribute to Carboniferous timescale tie points at the Tournaisian-Visean boundary, within the Visean and at the Carboniferous-Permian boundary. Situated in the extending Variscan foreland, two distinct phases of extension-related transitional-alkaline volcanism have been resolved in the Dinantian: the Garleton Hills Volcanic Formation in the eastern Midland Valley near the Tournaisian-Visean boundary, 342.1 ± 1.3 and 342.4 ± 1.1 Ma; and the Clyde Plateau Volcanic Formation in the western Midland Valley during the mid-Visean, 335 ± 2–329.2 ± 1.4 Ma. Alkaline basic sills near Edinburgh, previously thought to be Namurian, appear to be coeval with the Clyde Plateau Volcanic Formation at 331.8 ± 1.3–329.3 ± 1.5 Ma. The new ages allow correlation between these short-lived Dinantian magmatic pulses and extensional and magmatic phases in the Northumberland-Solway and Tweed basins to the south. After late Westphalian, end-Variscan, compression and a regionally important tholeiitic intrusive phase at
c.
301–295 Ma, alkaline magmatism related to post-Variscan extension occurred in the central and western Midland Valley during the latest Carboniferous or Permian from 298.3 ± 1.3 to 292.1 ± 1.1 Ma. This correlates well with post-Varsican extension and magmatism observed across the NW European foreland from 300 to 280 Ma.
Helium isotope signature of lithospheric mantle xenoliths from the Permo-Carboniferous magmatic province in Scotland — no evidence for a lower-mantle plume
Authors: Kirstein L. A. , Dunai T. J. , Davies G. R. , Upton B. G. J. , Nikogosian I. K. 
Published: April 2008

Abstract

Noble gas studies of well-characterized spinel-peridotite-facies lithospheric mantle xenoliths and garnet megacrysts from Scottish Permo-Carboniferous dykes, sills and vents demonstrate that the mantle beneath Scotland during the late Palaeozoic was more radiogenic than the source of mid-ocean ridge basalts (MORB). The samples were collected from the Northern Highland Terrane and the Midland Valley Terrane, which vary from Archaean-Proterozoic to Proterozoic-Palaeozoic in age. Helium isotope ratios of between 3
R
a
and 6
R
a
(
R
a
= atmospheric ratio) indicate that there has been time-integrated U-Th enrichment of the subcontinental mantle. This enriched mantle was preferentially melted following the transition from early Palaeozoic compression to late Palaeozoic extensional tectonics. Helium isotope ratios provide no clear evidence for the presence of undegassed plume-type mantle beneath this part of Scotland during the Permo-Carboniferous. The measured helium ratios do not discount the presence of a low-helium plume similar to those of the European Cenozoic volcanic province. A passive origin, however, is preferred for the Permo-Carboniferous magmatism due to the protracted activity, relatively small-extruded volumes of mafic magma and the low-helium isotope ratios measured.
Permo-Carboniferous extension-related magmatism at the SW margin of the Fennoscandian Shield
Authors: Obst K. , Solyom Z. , Johansson L. 
Published: April 2008

Abstract

Permo-Carboniferous rifting in Europe was accompanied by the widespread emplacement of mantle-derived magmas forming regional dyke swarms and sills in northern England, Scotland, Norway and southern Sweden during the late Stephanian and early Autunian. The trends of the dyke swarms intersect at a focal point in the Kattegat south of the Oslo Graben, and are probably all related to a single magmatic centre that could be plume-related. The WNW- to NW-trending dyke swarm at the SW margin of the Fennoscandian Shield in southern Sweden is composed mainly of tholeiitic dolerites, with lesser amounts of alkaline mafic rocks (camptonites, alkali basalts and spessartites) and trachytes. The alkaline mafic rocks are enriched in Ba, Sr, Nb, P and CO
2
, implying a metasomatic enrichment of their upper-mantle source prior to melting. After generation of alkaline melts by relatively small degrees of partial melting, increased extension was accompanied by the formation of subalkaline tholeiitic magmas. Whole-rock compositions (Mg-numbers between 55 and 30) and mineral chemistry (olivine Fo
60
-Fo
40
; clinopyroxene approximately Wo
30
En
45
Fs
15
; plagioclase An
70
-An
50
) indicate relatively evolved melts that have undergone crystal fractionation of olivine and clinopyroxene. Two groups of dolerites can be distinguished on the basis of bivariate element plots, e.g. Zr-TiO
2
and La-Sm. Although both groups show enrichment in the whole range of incompatible trace elements, slight differences in mantle-normalized trace-element patterns and different Nb/La ratios suggest that they were generated from two different sources. Group I dolerites were formed from a (re-)enriched, but isotopically mildly depleted, sublithospheric garnet-bearing mantle source (Nb/La mostly >0.9, ɛNd
i
= +4 to +3, where ɛNd
i
is the initial Nd isotope ratio), whereas group II dolerites seem to indicate mixing of the asthenospheric-derived magmas with lithospheric mantle melts (Nb/La mostly <0.9, ɛNd
i
= 0 to −1). Increasing Th/Ta ratios together with decreasing U/Nb ratios from group I towards group II dolerites further reflect progressive crustal contamination.
Post-Variscan evolution of the lithosphere in the Rhine Graben area: constraints from subsidence modelling
Authors: Ziegler P. A. , Schumacher M. E. , Dèzes P. , Van Wees J.-D. , Cloetingh S. 
Published: April 2008

Abstract
In the area of the Cenozoic Rhine rift system, crustal and lithospheric thicknesses range between 24 and 35 km, and 60 and 120 km, respectively. This rift system transects the deeply truncated Variscan Orogen and superimposed Permo-Carboniferous wrench-induced troughs, and Late Permian and Mesozoic thermal sag basins. At the time of its Westphalian consolidation, the Variscan Orogen was probably characterized by 45–60 km deep-crustal roots that were associated with its Rheno-Hercynian-Saxo-Thuringian, Saxo-Thuringian-Bohemian and Bohemian-Moldanubian sutures, all of which are transected by the Cenozoic Rhine rift system. During the Stephanian-Early Permian wrench-induced disruption of the Variscan Orogen, subducted lithospheric slabs were detached causing upwelling of hot mantle material. During the resulting thermal surge, partial delamination and/or thermal thinning of the continental mantle-lithosphere induced regional uplift. At the same time the Variscan orogenic roots were destroyed and crustal thicknesses reduced to 28–35 km in response to the combined effects of mantle-derived melts interacting with the lower crust, regional erosional unroofing of the crust and, on a more local scale, by its mechanical stretching. Towards the end of the Early Permian, the potential temperature of the asthenosphere returned to ambient levels. With this, regional, long-term thermal subsidence of the lithosphere commenced, controlling the development of a new system of Late Permian and Mesozoic thermal sag basins. However, the evolution of these basins was repeatedly overprinted by minor short-term subsidence accelerations that reflect the build-up of far-field stresses related to rifting in the Tethyan and Atlantic domains. Comparison of observed and modelled subsidence curves suggests that in the area of the Rhine rift system the lithosphere had equilibrated with the asthenosphere at the end of the Cretaceous at depths of 100–120 km, before it became thermally destabilized again by Cenozoic rifting and plume-related magmatism. Modelled subsidence curves indicate that by the end of Early Permian times the thermal thickness of the remnant mantle-lithosphere ranged between 10 and 50 km in areas that were later incorporated into Mesozoic thermal sag basins; this corresponds to mid-Permian thermal lithosphere thicknesses of 40–80 km.
Timing of Upper Carboniferous-Permian horst-basin formation and magmatism in the NW Thuringian Forest, central Germany: a review
Authors: Zeh Armin , Brätz Helene 
Published: April 2008

Abstract

During Late Carboniferous-Early Permian times dextral transtensional movements along the NW-trending Franconian Fault System and parallel faults caused complex block faulting in the Thuringian Forest region, Germany, accompanied by intense magmatism. This is well constrained by geochronological data (
207
Pb/
206
Pb single zircon, SHRIMP,
40
Ar/
39
Ar mica, zircon fission-track ages), field relations, and the sedimentary record from the Ruhla Crystalline Complex (RCC) and surroundings. The combined dataset indicates that the Ruhla Crystalline Complex was faulted into three nearly N-S-trending segments, which underwent different exhumation histories during Late Carboniferous-Permian times. The central segment of the RCC was exhumed by several kilometres as a horst block, while the eastern and western segments subsided simultaneously, forming the basement to the Oberhof and Eisenach molasse basins, respectively. Late Carboniferous-Permian uplift of the central segment is constrained by
40
Ar/
39
Ar cooling ages of 311 ± 3 (muscovite) and 294–288 ± 3 Ma (biotite), a weighted zircon fission-track age of 272 ± 7 Ma and overlying Zechstein sediments. In contrast, the eastern segment shows much older
40
Ar/
39
Albiotite cooling ages between 336 ± 4 and 323 ± 3 Ma, was exposed at
c.
300 Ma, and subsequently covered by molasse sediments and volcanic rocks between 300 and
c.
275 Ma. A similar Late Carboniferous evolution is inferred for the western segment, as it is also overlain by Lower Permian volcanic rocks and has a 297 ± 29 Ma single zircon fission-track age. Simultaneous horst and basin formation is additionally constrained by granite pebbles in conglomerates of the Oberhof and Eisenach basins. These pebbles can partly be derived from granites in the central segment of the RCC.

Age data and the orientation of granitoid bodies and dykes in the Ruhla Crystalline Complex and its surroundings provide evidence for the opening of NE-trending structures between 300 and 294 Ma, and formation or reactivation of W- to NW-trending structures between 290 and 275 Ma. Magmatic activity in the Thuringian Forest region may have been caused by widespread mantle upwelling in central Europe during the Late Carboniferous-Early Permian.
Permian magmatism and basin dynamics in the southern Pyrenees: a record of the transition from late Variscan transtension to early Alpine extension
Authors: Lago M. , Arranz E. , Pocoví A. , Galé C. , Gil-Imaz A. 
Published: April 2008

Abstract
Permian magmatism in the Pyrenees is characterized by two compositionally different and temporally consecutive magmatic episodes: a calc-alkaline-transitional phase (andesites) and a midly alkaline phase (basalts and dolerites). These two magmatic episodes were related to the attenuation of late Variscan transtensional tectonics and the onset of extension related to regional rifting. The strike-slip fault systems that affected the Pyrenees in late Variscan times initially controlled the development and morphology of the sedimentary basins. These were periodically affected by phases of extension, which controlled the subsidence of the basins, and, in addition, the emplacement of magmas. The whole-rock trace-element and isotopic signature of the andesites suggests that they were derived from the upper mantle and variably hybridized with late orogenic crustal melts, whereas the alkali basalts could have been derived from a lithospheric mantle source, enriched as a consequence of Variscan subduction processes with the contribution, in some areas, of an enriched (asthenospheric) component.
Lower Permian magmatism of the Iberian Chain, Central Spain, and its relationship to extensional tectonics
Authors: Lago M. , Arranz E. , Pocoví A. , Galé C. , Gil-Imaz A. 
Published: April 2008

Abstract

Late Variscan magmatism in the Iberian Chain (Central Spain) is recorded by the presence of both pyroclastic units and high-level intrusions (sills and dykes). This magmatism encompasses a variety of subalkaline igneous rocks, from basalt to rhyolite; andesitic rocks are, however, dominant. The pyroclastic units contain plant fossils and pollen that suggest an Autunian age, which is consistent with the available K-Ar radiometric age data (283–292 Ma) obtained for the hypabyssal intrusions. Earlier amphibole-rich andesite, rich in crustal xenoliths (metapelite, granitoid and quartzite fragments) and xenocrysts (e.g. garnet) suggest the occurrence of significant crustal assimilation in the petrogenesis of the intermediate magmas, whereas later intrusions (pyroxene-rich andesites, basalts and some rhyolites) lack any crustal xenoliths or xenocrysts. Crustal assimilation is also suggested by the radiogenic
87
Sr/
86
Sr
290
and negative ɛNd
290
values for all the studied rocks. The cross-cutting relationships between the different rock types provide evidence for a multi-stage magmatic evolution, coeval with the post-orogenic transtensive evolution of the southern Variscan belt in Europe. A significant hiatus, covering the Middle Permian and most of the Upper Permian, separates this Lower Permian magmatism from the subsequent Triassic and Jurassic alkaline magmatism that represents different rifting events that affected the Iberian Chain, progressively thinning the Variscan crust as the Alpine cycle began.
Instability and localization of deformation in lower crust granulites, Minas fault zone, Nova Scotia, Canada
Authors: White Joseph C. 
Published: April 2008

Abstract
Blocks of granulite from within the megabreccia at Clarke Head, Nova Scotia, Canada contain extremely well preserved mylonitic and ultramylonitic textures developed in mineral assemblages for which thermobarometic calculations have indicated temperatures and pressures between 700–860 °C and 750–950 MPa. Deformation within these rocks is characterized by localization at several discrete length scales associated with the development of new microstructures comprising finer-grained material. Mylonitized granulite exhibits dislocation creep microstructures, with development of intense S-C fabrics and shear bands during the transition to ultramylonite. Dynamically recrystallization of plagioclase can be followed through progressive grain size reduction to about 5 μm, but there remain extensive zones with grains less than 1 μm in diameter. Localization of the these finest-grained ultramylonites occurs by transient frictional events associated with the introduction of partial igneous melts and formation of pseudotachylyte which produces abrupt decreases in grain size that cannot arise during dislocation mediated grain size reduction.
The heterogeneous response of these rocks demonstrates the importance of considering characteristic length scales when assigning evidence from the rock record (e.g. palaeopiezometry) to bulk behaviour of the lithosphere. Associated with the localization of strain and subsequent strain softening is the observation that microstructures formed during the event that initiated the instability can be an obliterated by ductile flow. In instances where critical components of the microstructural evolution are known to have been largely overprinted, it becomes possible to reconcile contradictions in the rock record, such as production of ultra-fine-grained superplastic aggregates in what otherwise appears to be a dominantly dislocation creep regime.