bluuebunny/crossref_metadata_2025_split huggingface dataset:
Coats Land dolerites and the generation of Antarctic continental flood basalts
Authors: Brewer T. S. , Hergt J. M. , Hawkesworth C. J. , Rex D. , Storey B. C. 
Published: September 2007

Abstract

On the basis of geochemical signatures, Mesozoic magmatism in Antarctica is divided into the Ferrar Magmatic Province and the Dronning Maud Land Province. The tholeiitic magmatism of the Ferrar Magmatic Province is distinguished by such features as low Ti/Y (< 200) and Zr/Y (< 5.0) ratios, negative εNd values (< −3) and relatively enriched initial
87
Sr/
86
Sr ratios (> 0.709). All of these geochemical features indicate a major contribution from the continental mantle lithosphere in the generation of these magmas. In contrast, the Dronning Maud Land magmatism has elevated trace element ratios and εNd values (Ti/Y 250–600; Zr/Y 3.0–9.0; εNd −2 to +3) and lower initial
87
Sr/
86
Sr ratios (< 0.707) relative to the Ferrar Magmatic Province. The trace element and isotopic correlations suggest that these magmas were derived by the mixing of an OIB like asthenospheric component with a continental lithosphere component. The transition between these two geochemical provinces is located in Coats Land.

In Coats Land, the Mesozoic tholeiitic magmatism is represented by doleritic sills and minor dykes which intrude Permo-Triassic sedimentary rocks. The dolerites can be subdivided into two series based on their TiO
2
contents. Series 1 dolerites (TiO
2
< 1.5%) can be further subdivided into three groups, which give Ar/Ar ages of 171±6 Ma (Group 1) and 193±7 Ma (Groups 2 and 3). It is only Group 2 magmas which have trace element and isotopic signatures akin to the Ferrar Magmatic Province. Group 1 dolerites have geochemical signatures which are transitional between the Ferrar Magmatic Province and Dronning Maud Land magma types.

The Ferrar Magmatic Province signature in Coats Land is confined to the early magmatic episode (193±7 Ma) and this appears to mark the initiation of rift related magmatism in this region. It is argued that extension was limited and that most of the melt was derived from the continental mantle lithosphere. In contrast, the younger rocks (176±5 Ma) have relatively lower initial
87
Sr/
86
Sr and higher trace element ratios relative to the Ferrar Magmatic Province, and this appears to be associated with the later stages of rifting and relatively enhanced crustal extension which allowed for the encorporation of a small asthenosphere component.
The granites of northern Patagonia and the Gastre Fault System in relation to the break-up of Gondwana
Authors: Rapela C. W. , Pankhurst R. J. 
Published: September 2007

Abstract
The transcurrent Gastre Fault System in central Patagonia, which is closely associated with subvolcanic granite emplacement, is recognized as a major dextral shear-zone and geological boundary. We propose its equivalence to a Late Triassic-Jurassic precursor of the Aghulas Fracture Zone, allowing dextral displacement of the Southern Patagonian Block relative to the rest of South America during the earliest rifting phase of Gondwana break-up. This model could explain some of the inferred movement of the Falkland/Malvinas Islands and alleviate geometrical problems inherent in reconstructions of the South Atlantic region. It can also explain unique geological features of southern Patagonia, such as the Upper Triassic to Lower Jurassic calc-alkaline granitoids of the North Patagonian Massif and the extensive silicic volcanism of Mid-Late Jurassic times. The magmatism is seen as a consequence of the mechanism of Gondwana disintegration and it is not necessary to invoke a relationship to deep mantle structure or plume activity.
Paraná magmatism and the opening of the South Atlantic
Authors: Hawkesworth C. J. , Gallagher K. , Kelley S. , Mantovani M. , Peate D. W. , Regelous M. , Rogers N. W. 
Published: September 2007

Abstract

New chemical and isotope results are presented on dyke rocks associated with the Paraná CFB, together with preliminary laser
40
Ar/
39
Ar analyses on selected Paraná basalts. Dyke rocks from the Ponta Grossa Arch are similar to the Pitanga and Paranapanema magma types in the Paraná lavas, but dykes from the Santos-Rio de Janeiro section include samples with compositions not observed in the overlying lavas. Rather their minor and trace elements are strikingly similar to basalts recently erupted on Tristan de Cunha, and thus these late stage dykes may represent the first direct evidence for the involvement of typical plume-related OIB in the Paraná province. Laser
40
Ar/
39
Ar analyses of two Gramado low Ti basalts have yielded preferred isochron ages of 132.4 ± 1.4 and 132.9 ± 2.8 Ma. These indicate a short eruption time for at least the Gramado magma type, and that magmatism took place several million years after the species extinction in the Tithonian (
c.
141 Ma).

The majority of basalts and basaltic andesites in the Paraná CFB have distinctive trace elements ratios (low Nb/La and Nb/Ba), and relatively enriched Sr, Nd, and Pb isotope compositions. Since such features are not commonly observed in oceanic basalts, and they occur in CFBs which have been screened for the effects of crustal contamination, they are typically attributed to old, incompatible element enriched source regions in the continental mantle lithosphere. In some models the minor and trace element ‘mantle lithosphere’ component was introduced in small degree melts (lamproites) added to asthenosphere derived magmas. However, such models appear to be inconsistent with the data from low Ti CFB, and they also require that the asthenosphere derived magmas have very low incompatible element contents, in marked contrast to the high Nb/La late stage dykes in the Paraná. Alternatively some CFBs may have been generated within the mantle lithosphere in the presence of small amounts of water. The results of preliminary calculations indicate that in the presence of a mantle plume up to 5 km of melt may be generated entirely from within the mechanical boundary layer, for
β
values of less than 1.2.
Magmatism and continental rifting during the opening of the South Atlantic Ocean: a consequence of Lower Cretaceous super-plume activity?
Authors: Wilson Marjorie 
Published: September 2007

Abstract
Two large-scale mantle plumes, whose present-day foci are close to the oceanic islands of Tristan da Cunha and St Helena, appear to have played a significant role in the initial stages of rifting between Africa and South America during the Early Cretaceous opening of the South Atlantic Ocean. They may represent the initial burst of a super-plume event which generated extensive oceanic plateaux in the Pacific and Indian oceans.
The recent volcanic products of Tristan da Cunha and St Helena have near endmember Sr-Nd-Pb isotopic characteristics (EM I and HIMU) in the spectrum of ocean basalt isotopic compositions. These isotopic signatures are recognised for more than 100 Ma in the plume-related magmatic products and therefore appear to be a long-lived feature of the plume source. The history of rifting and magmatism in West and Central Africa/NE Brazil and in southern Brazil, above the broad heads of the initial starting plumes between 145 Ma and 130 Ma, strongly suggests that there are different physical differences between the two plumes in addition to chemical ones. The St Helena plume appears to have been much weaker and cooler, with a smaller buoyancy flux. The hotter Tristan plume has generated voluminous flood basalts volcanism in the Paraná basin of Brazil and appears to be associated with continental break-up within a few million years of the plume head impinging on the base of the lithosphere. In contrast, in West and Central Africa, rifting above the St Helena plume, associated with small volumes of alkaline-transitional magmatism, spans an extended period of 30–40 Ma before break-up occurs in the Equatorial Atlantic.
New geophysical evidence for extensional tectonics on the divergent margin offshore Namibia
Authors: Light M. P. R. , Maslanyj M. P. , Banks N. L. 
Published: September 2007

Abstract
Over 14 000 km of high-resolution multifold seismic data together with gravity and magnetic data provide the opportunity to examine the mechanism and history of rifting on the Namibian continental margin. The region is a completely developed divergent margin containing a pre-rift megasequence of interior cratonic sag origin; two rift basin megasequences dominated by siliclastic deposition; a transitional megasequence and thermal sag megasequences dominated by overlapping progradational wedges. In the Orange Basin acid to intermediate volcanic rocks erupted at the end of the pre-rift phase in Mid- to Late Jurassic times and this was followed by regional uplift. Basaltic volcanic activity was associated with the synrift phases and widespread volcanic rocks developed during the second synrift event, related to the Tristan da Cunha-Walvis Ridge mantle plume. Regional seismic mapping indicates that rifting migrated from south to north with time. The geophysical data enable the recognition of major structural elements which include the Eastern Graben Province, the Medial Hinge Line, the Central Half Graben and the Marginal Ridge. The geometry of the rift basin is asymmetric and can be explained by a simple shear mechanism. South of Walvis Ridge extension was accommodated by movement along a major normal fault which is listric at depth. The basin depocentre represented by the Central Half Graben lies landward of this major fault and is offset from the area of thinnest crust as interpreted from the gravity data.
The timing of magmatism, uplift and crustal extension: preliminary observations from Yemen
Authors: Menzies M. A. , Baker J. , Bosence D. , Dart C. , Davison I. , Hurford A. , Al’Kadasi M. , McClay K. , Nichols G. , Al’Subbary A. , Yelland A. 
Published: September 2007

Abstract

The Red Sea and the Gulf of Aden form young, oceanic rift basins, situated between the diverging African and Arabian plates and bordered by highly elevated, volcanic margins. Yemen in the southeastern Red Sea, was once centred over the Afar plume/triple-junction (
c.
30 Ma) forming part of the Arabian ‘passive’ margin. The present high elevation of the Afro-Arabian rift-flanks (up to 3.6 km as in Yemen), is the combined result of a number of endogenic rift processes which served to generate both the initial crustal uplift and also preserve the elevated topography. A further isostatic response generating uplift is likely to have been driven by differential erosion of the rift-flanks. However, the sedimentary record of the pre-Jurassic to early Tertiary period provides little evidence for major changes in relief or elevation. Furthermore, structural and volcanological observations indicate that most of the crustal extension occurred during mid-late Tertiary. The voluminous Oligo-Miocene basalt-rhyolite magmatism of Yemen was not apparently associated with pre-volcanic (> 30 Ma) uplift despite the commonly held belief that the Afar plume existed beneath the region 30 Ma ago. Geological data point to an episode of uplift that occurred after the initiation of magmatism. Fission track data indicate that uplift related exhumation postdates magmatism by some 10–15 Ma, perhaps the amount of time needed to change the thermal character of the Pan-African lithosphere above the Afar plume. A sequence of magmatism followed by synchronous crustal extension and uplift for Yemen does not fit with the traditional categories of active (uplift-magmatism-rifting) and passive (rifting-uplift-magmatism) rifting. Clearly such end-member models do not simply apply to the Red Sea or the Great Basin of the western USA where a period of tectonic quiescence, followed by post-volcanic extension and uplift (1 km), post-dated the Oligo-Miocene ignimbrite flare-up.
Tectonism and magmatism during NE Atlantic continental break-up: the Vøring Margin
Authors: Skogseid Jakob , Pedersen Tom , Eldholm Olav , Larsen Bjørn T. 
Published: September 2007

Abstract
The temporal and spatial relationships of tectonic and magmatic features on the Vøring volcanic margin show that continental break-up occurred in association with significant magmatic activity about 18 Ma after initiation of lithospheric extension. From the distribution of extension across the margin and the volumes of melt produced, a thermal anomaly of 50–80°C is estimated, in agreement with predictions from recent plume models. A tectono-magmatic model is proposed in which the ascending proto-Iceland plume released the rifting, over a > 300 km wide zone, by uplift-induced extension of the NE Atlantic lithosphere already affected by tensional stresses. Initial rifting took place without decompressional melting when the plume, carrying the thermal anomaly, was still 600–700 km beneath the lithosphere. Subsequently, widespread magmatism occurred when the plume impinged on, spread out beneath and infilled the rift-defined relief at the base of the lithosphere. Break-up is suggested to be a consequence of melt-induced weakening of the lithosphere, whereas the anomalously thick igneous crust at the continent-ocean transition along the NE Atlantic margins is explained by melt focusing towards the uplifted break-up axis.
Tertiary picrites in West Greenland: melting at the periphery of a plume?
Authors: Gill R. C. O. , Pedersen A. K. , Larsen J. G. 
Published: September 2007

Abstract
The West Greenland/Baffin Island Tertiary volcanic province differs from other CFB provinces in containing an unusually high proportion (30–50% by volume) of magnesian picritic lavas and hyaloclastites. Olivine-liquid equilibrium considerations suggest the presence during the earlier stages of eruption of picritic melts with MgO contents as high as 20%. Calculations based on McKenzie-Bickle melting models point to high degrees of melting (24–30%) at depths of 60–90 km in the underlying mantle, and require potential temperatures of 1540–1600°C. Such high potential temperatures are inconsistent with reconstructions that attribute the West Greenland volcanism to melting on the margins of the incipient Iceland plume-head. The distribution of Tertiary volcanic activity in Greenland, in particular its relation to Mesozoic-Tertiary extensional basins, indicates that lithospheric structure plays a part in determining where the plume-head can undergo melting. But to explain the restriction of high-temperature picrites to West Greenland, together with their distinctive trace element geochemistry, it is necessary to invoke (a) either an elongated Icelandic plume initially extending as far as West Greenland or a short-lived precursory plume head that developed directly beneath West Greenland, and (b) an active extensional regime that allowed rapid access of picritic melts to the surface.
Sill-intrusion, flood basalt emplacement and deep crustal structure of the Scoresby Sund region, East Greenland
Authors: Larsen H. C. , Marcussen C. 
Published: September 2007

Abstract
The late Palaeozoic-Mesozoic Jameson Land basin in East Greenland was situated during early Tertiary break-up 300–400 km north of a presumed plume centre and 100–200 km landward of the initial line of North East Atlantic opening. The basin continues southward below Scoresby Sund fiord and the Scoresby Sund plateau basalts south of the fiord. By combining surface mapping with marine reflection and refraction seismics from Scoresby Sund and deep (6–12s) reflection seismics from the exposed part of the basin, it is possible to construct a composite image of the entire crustal structure in this region from the details of basalt stratigraphy at the top, through the basin fill, the foundation of the basin, and into the uppermost mantle. At the basin centre there is a very thin crystalline crust (6–8 km?) below as much as 16–18 km of basin fill. Virtually all crustal extension took place prior to mid-Permian time, and the post-rift Upper Permian to Cretaceous section contributes to only one third or less of the total thickness of the succession. During Tertiary break-up the basin was intruded by basaltic sills and dykes, and basaltic flood basalts flowed over the basin with an apparently decreasing thickness to the north. The sills are mainly exposed along the basin margins as rather thin (10–15 m) layers, but apparently increase in intensity and thickness at depth and towards the basin centre. It seems that magmas were intruded as sills up to 300 m thick in the deep (10–15 km) central parts of the basin, from where they ascended towards the basin margins and to much younger stratigraphic levels. Their geometry and possible volume make them potential candidates as mid-crustal magma chambers and crustal magma pathways for the flood basalts which show low-pressure fractionation. However, extension surface geological data and deep crustal reflection seismic data show no faulting or crustal extension associated with this intense break-up volcanism. In Scoresby Sund there is a general rather conformable relationship between the basin stratigraphy and the gross stratigraphy of the flood basalts, suggesting limited or no initial uplift prior to flood basalt volcanism. The present-day high elevation of the basalts is considered part of large regional margin uplift post-dating N Atlantic break-up by 20 Ma or more. The apparent guidance exerted by the basin on the break-up magmatic activity without renewed rifting of the basin itself, the apparent lack of a broad initial uplift during break-up, and the late regional margin uplift, all seem at odds with several current plume models.
Changes in moisture balance between glacial and interglacial conditions: influence on carbon cycle processes
Authors: Adams J. M. , Faure H. 
Published: September 2007

Abstract
During the arid Late Glacial and Last Glacial Maximum (between approximately 30 000 and 13 000 calendar years ago), vegetation cover retreated and large areas of the continents were occupied by desert and semi-desert vegetation. The result of this general decrease in biological activity would have been a decrease in the size of the land carbon reservoir, and a decrease in the rate of chemical rock weathering. By contrast, during the early-mid-Holocene, conditions in many areas seem to have been moister than today due to a more active hydrological cycle. All of these processes would have affected the global carbon cycle and altered the amplitude and timing of the climate fluctuations themselves. In effect, the climatic shift between glacial and interglacial conditions creates a very large ‘missing source’ of carbon, perhaps amounting to thousands of gigatonnes, to account for the carbon uptake by the land system during the present interglacial, and thus carbon cycle models of the late Quaternary may need to be revised extensively.
Human dimensions of palaeohydrological change
Authors: Brown A. G. 
Published: September 2007

Abstract
Because floodplains are ‘attractors’ of human activities and settlement, Late Pleistocene and Holocene palaeohydrological changes are an important part of archaeology. Indeed there has been a tradition of palaeohydrological writing within archaeology centring around topics such as river transport, drought/floods and floodplain farming, rivers as physical and cultural barriers, riverine resources, and the flood hazard. An agenda for continuing research in this inter-disciplinary area in a more quantitative and rigorous manner than in the past has been developed. This recognizes that the potential of palaeohydrological research to be applied to the study of past and future environmental change revolves around three areas: (i) the estimation of past frequency distributions and their relationships to climate; (ii) the past and future representations of risks; such as flooding; (iii) the uses and limitations of analogies (e.g. by using the Medieval climatic optimum as an analogy for future global warming).
Climatic or anthropogenic alluviation in Central European valleys during the Holocene?
Authors: Kalicki T. 
Published: September 2007

Abstract
Traces of increased river activity during the Late Glacial and Holocene can be identified in the river valleys of central Europe. This activity includes changes of river channel pattern and changes in the type and rate of floodplain sedimentation. A model of the sequence of events within a phase of increased river activity has been constructed as part of a detailed study of the Vistula valley. This analysis indicated that the evolution of the Vistula river valley has resulted primarily from climatic factors, although local factors (including human modification) contributed to the magnitude of changes which had already developed as a result of climatic controls.
Issues in scientific co-operation on information sharing: the case of palaeohydrology
Authors: Branson J. , Gregory K. J. , Clark M. J. 
Published: September 2007

Abstract
The hydrological cycle is interactively integral with climate, so that for an understanding of future environmental change it is important to have hydrological data accessible from previous times to use in both hydrological and climate change modelling of past, and also of present and future environments and also for the development and operation of surface water resources. A database has been developed as part of the research undertaken by the INQUA Global Continental Palaeohydrology Project (GLOCOPH) to facilitate the preservation and access of palaeohydrological data within the public domain, and through this the organization, facilitation, association and bisociation of the data.
Deviation from Red Queen behaviour at stratigraphic boundaries: evidence for directional recovery
Authors: Doran N. A. , Arnold A. J. , Parker W. C. , Huffer F. W. 
Published: September 2007

Abstract
Boundary-defining events influence the evolutionary behaviour of post-extinction survivors. The Cox proportional hazards model takes into account the varying background extinction rates characteristic of boundaries and enables survivorship analysis of post-boundary behaviour. Survivorship results from the Middle Cretaceous to recent planktonic foraminifera reveal two intriguing observations. First, they indicate significantly age-dependent extinction probabilities in populations of species following two boundaries: Cenomanian-Turonian (C-T) and Cretaceous-Tertiary (K-T); the survivors are short lived and show rapid turnover. Characteristics that might mediate this macroevolutionary behaviour are clearly distinct from those that precede the extinction. We hypothesize that the rapid taxonomic turnover during post-extinction macroevolutionary recovery is driven by the lingering expression of ‘passport’ characteristics, where the primary adaptive value was during the preceding extinction. Second, age-dependency of extinction oscillates through time. Many survivorship curves averaging long-term data have exponential or near-exponential form: suggesting a lack of age-dependence consistent with the Red Queen hypothesis. The boundary events discussed here, analysed in higher-resolution 15 Ma subsets, demonstrate perturbation of some post-extinction populations toward positive age-dependence, and are followed by long intervals suggestive of recovery. Red Queen behaviour, when measured over very long time-spans, appears to be the time-averaged result of these boundary-generated oscillations between short-term positive age-dependence and longer-term return to nearly age-independent Red Queen behaviour.