bluuebunny/crossref_metadata_2025 huggingface dataset:
End-Carboniferous fold-thrust structures, Oxfordshire, UK: implications for the structural evolution of the late Variscan foreland of south-central England
Authors: PEACE G. R. , BESLY B. M.
Published: December 2007

Interpretation of commercial seismic reflection data from the west of Banbury, south-central England, has provided information on the late Carboniferous structural evolution of the Oxfordshire Syncline. End-Carboniferous structures are preserved in the footwall of the main basin-bounding faults of the Permo-Triassic Worcester Graben. Restoration of major pre-Triassic normal faults has allowed reconstruction of earlier compressional structures. In contrast to the WNW-ESE trend of structures to the south, in the Variscan foreland fold-thrust belt, major faults and folds in Oxfordshire are approximately N-S trending. The structures seen to deform Westphalian D-Stephanian-aged sequences on the seismic profiles are a combination of steep (30-40° dip) fault-bounded uplifts and less dominant thin-skinned tectonics, apparently showing transport to the east. In the south, some thin-skinned structures are present, and in the north cover sequences are uplifted in a narrow zone of deformation on reactivated basement faults. The amount of shortening also changes along strike, from
c.
1600 m in the south to
c.
950 m in the north. Reactivation of major basement faults with differential basement shortening accounts for the main structures. Localized detachment in the young and weak sediments close to the palaeo-land surface explains the thin-skinned structures seen on some of the seismic lines. These end-Carboniferous structures in Oxfordshire and structures in the Malvern-Abberley Hills represent the structural limits of a large N-S-striking intra-Stephanian uplift in the late Variscan foreland. It is suggested that the structures formed during a discrete phase of intra-Stephanian E-W-directed regional shortening prior to the final phase of movement in the Variscan belt.
Regional Neogene exhumation of Britain and the western North Sea
Authors: JAPSEN PETER
Published: December 2007

Tertiary exhumation of Britain and the western North Sea is interpreted to have taken place in two episodes, each with amplitudes of about 1 km: a Palaeogene phase that principally affected the present onshore Britain (west of the present extent of the Late Cretaceous-Danian Chalk Group), and a Neogene phase that affected both onshore areas and the western North Sea. Consequently maximum burial of Mesozoic and older rocks in the present onshore areas generally occurred in the Palaeocene (
c
. 60 Ma). In the western North Sea, the preservation of the Chalk Group today suggests relatively stable conditions prevailed immediately after its deposition rather than substantial Palaeocene exhumation. In this area, maximum burial is interpreted to have occurred in the Neogene. The proposal is consistent with published exhumation estimates based on studies of sediment compaction (offshore) and of fission tracks (onshore). It also does away with unlikely high burial rates which are implied in the latest Cretaceous-earliest Tertiary if removal of overburden from the Chalk is assumed to have occurred in the Palaeocene.
Oligocene and Pliocene interglacial events in the Antarctic Peninsula dated using strontium isotope stratigraphy
Authors: DINGLE R. V. , McARTHUR J. M. , VROON P.
Published: December 2007

Strontium isotope stratigraphy is used to date two interglacial-marine deposits in the Antarctic Peninsula region. On King George Island, interglacial pectinid-rich sediments in the Low Head Member of the Polonez Cove Formation give a strontium isotope stratigraphy age of 29.0
+0.7
−0.6
to 29.8
+0.8
−0.7
Ma (mid-Oligocene), which, in conjunction with previous K–Ar dating of volcanic rocks, indicates a glacial episode in the Antarctic Peninsula between middle Eocene (42.0 ±1.0 Ma) and mid-Oligocene time. In addition, an inter-glacial deposit
(Pecten
Conglomerate) from tectonically-elevated exposures on Cockburn Island is dated as Pliocene (3.5–5.3 Ma). Published data suggest these latter sediments were deposited under shallow marine conditions, which were warmer than those of present-day Antarctica.
Isotopic studies in palaeontology
Authors: HUDSON J. D. , MARSHALL J. D.
Published: December 2007

The tenth Lyell Meeting of the Geological Society was held at Burlington House on Tuesday 27 February 1996. The intention was to focus on examples in which isotopic data on fossils are used to help answer questions in palaeobiology, evolution or palaeoenvironment, rather than those in which fossils are used simply as a convenient source of dated biominerals for global-scale palaeotemperature or chemostratigraphic studies. The meeting included nine talks and five poster contributions and was attended by over 60 participants.

The enormous impact of isotopic data on palaeoenvironmental research in the broadest sense is plain for all to see, perhaps most obviously in the revolution of the last quarter century in understanding of the late Cenozoic ice ages; much of it foreshadowed by Emiliani's classic work of 1955. It seems as remarkable now as it did 20 years ago, that 'the most powerful method of assessing the waxing and waning of the Northern Hemisphere ice sheets should be nothing to do with tracing moraines or measuring raised beaches, but making extremely accurate isotopic analyses of the shells of tropical marine animals' (
Hudson 1977
). This refers to oxygen isotopes in foraminiferal shells as reflecting the combined influence of ice accumulation and temperature of growth, both of which increase the
18
O/
16
O ratio in the shell carbonate. A break­through came with Shackleton and co-workers' success in resolving the partitioning between the two effects by comparing surface-living planktonic foraminifera with deep-dwelling benthic species that experience almost constant temperatures during glacial-interglacial cycles on a scale
Holocene palaeolimnology of Kajemamm Oasis, Northern Nigeria: an isotopic study of ostracodes, bulk carbonate and organic carbon
Authors: HOLMES J. A. , STREET-PERROTT F. A. , ALLEN M. J. , FOTHERGILL P. A. , HARKNESS D. D. , KROON D. , PERROTT R. A.
Published: December 2007

A high-resolution 5500 year palaeolimnological record from Kajemarum Oasis, a closed basin in the Manga Grasslands of northern Nigeria, provides evidence of environmental change in Subsaharan Africa during the Holocene. Palaeohydrological variations, mainly changes in the balance between precipitation and evaporation, are recorded by stable oxygen isotope ratios in bulk carbonate and ostracod calcite and by the Sr/Ca ratio in ostracode shells. Variations in the carbon isotope ratios in carbonates indicate changes in primary productivity in the lake, whereas the carbon isotope composition of organic carbon reflects ecophysiological processes within the lake and its surrounding catchment. Results indicate that there have been marked environmental changes in the Manga Grasslands over the last 5500 years. A more variable climate set in around 1500 cal. a BP. A prolonged drought between 1200 and 1000 cal. a BP, with reduced aquatic productivity, was followed by a switch to a wetter, but still unstable climate: moist conditions prevailed during the Little Ice Age. The results indicate that drought has affected the Sahel episodically over the last 1500 years and is not solely a twentieth-century phenomenon.
New isotopic data solving an old biostratigraphic problem: the age of the upper Ordovician brachiopod
Holorhynchus giganteus
Authors: BRENCHLEY P. J. , MARSHALL J. D. , HINTS L. , NÕLVAK J.
Published: December 2007

Recent work has shown that there is a pronounced positive late Ordovician excursion in both δ
13
C and δ
18
O which appears to be global and identifies a clear chemostratigraphic interval that is confined to part of the Hirnantian Stage. Pre-Hirnantian (Rawtheyan) brachiopod carbonate values of δ
13
C are typically in the range – 1 to + 1‰ PDB and lower Hirnantian values are typically in the range of +4 to +7%o PDB. This contrast in isotopic values has been used to assess the age of the distinctive late Ordovician brachiopod
Holorhynchus giganteus.
The age of the
Holorhynchus
association is important in terms of its relationship to the major late Ordovician extinction that was initiated at the start of the Hirnantian. The species, which traditionally was regarded as uppermost Ordovician (Hirnantian) in age has been shown on stratigraphic evidence to be pre-Hirnantian at many locations. If this is so it predates the first phase of extinction and is not associated with the
Hirnantia
fauna, which characterizes the interval between the two main episodes of late Ordovician extinction. However, at its type locality in the Asker district of Norway the stratigraphic evidence has pointed to it being Hirnantian in age. To resolve this ambiguity, analyses have been made on
Holorhynchus
at three locations, (1) in the east Baltic region where
Holorhynchus
occurs below demonstrable Hirnantian rocks, (2) in the Boda Limestone of central Sweden where
Holorhynchus
occurs high on a carbonate mud mound where its age is unclear and (3) in the type area of the species in Norway. At all three locations the δ
13
C values are low, indicating a pre-Hirnantian, pre-extinction, age for
Holorhynchus.
The re-assessment of the age of the Asker sequence in Norway implies the presence of a cryptic unconformity there and suggests uplift rather than subsidence during the latest Ordovician. This study emphasizes the value of chemostratigraphy in high-resolution stratigraphy.
A geochemical framework for the application of stable sulphur isotopes to fossil pyritization
Authors: RAISWELL R.
Published: December 2007

Pyrite formation is associated with fossils where the organic material decays by sulphate reduction, or where the carbonate skeleton acts either as a nucleation substrate or induces iron sulphide precipitation by dissolution. These requirements define specific combinations of porewater chemistry and saturation state with respect to carbonates and iron sulphides. A review of modern marine sediments suggests that near-surface porewaters are always over-saturated, or close to saturation, with iron sulphides but are alternately rich in either dissolved iron or dissolved sulphide. However, significant variations in carbonate saturation state may occur, with porewaters being undersaturated in the early stages of sulphate reduction, but subsequently becoming oversaturated until the later stages of methanogenesis. Here undersaturation may return if there is a substantial input of carbon dioxide, and if little alkalinity has arisen from iron reduction.

Organic matter pyritization requires that soft-tissue material decays by sulphate reduction to release dissolved sulphide, with dissolved iron supplied by the surrounding porewaters. The modern sediment studies therefore suggest that organic matter pyritization can occur only during the earliest stages of sulphate reduction, where there are iron-rich porewaters which are saturated with iron sulphides. Pyrite replacement of carbonate shell material requires porewater undersaturation with respect to carbonates and analogy with modern sediments suggests that these conditions occur either during the earliest stages of sulphate reduction, or when methanogenesis produces undersaturation. Between these periods porewaters are saturated with respect to carbonates and pyrite of different morphologies can precipitate on carbonate shells. Sulphur isotope data provide support for these associations of porewater chemistry and style of fossil pyritization. The best-described examples are for soft tissue pyritization in Beecher's Trilobite Bed (Ordovician) and the Hünsruck Slate (Devonian), where the isotopic data are consistent with rapid, early pyritization in iron-rich porewaters. More data are needed on shell pyritization with the range of isotopic compositions indicating formation through all stages of diagenesis.
Geochemistry and U-Pb and
40
Ar-
39
Ar geochronology of the Man of War Gneiss, Lizard Complex, SW England: pre-Hercynian arc-type crust with a Sudeten-Iberian connection
Authors: SANDEMAN H. A. , CLARK A. H. , STYLES M. T. , SCOTT D. J. , MALPAS J. G. , FARRAR E.
Published: December 2007

The Man of War Gneiss is a variably deformed meta-igneous body that ranges in composition from gabbro to tonalite and comprises part of the basal structural slice of the Lizard ophiolite complex, SW England. U-Pb dating of zircon demonstrates that the parental magmas crystallized in the earliest Ordovician (499t.+
s
3
Ma), but
40
Ar-
39
Ar step-heating analysis of amphiboles suggests that at least the northernmost zone of the gneiss was subjected to an amphibolite-grade metamorphic event at
c.
374 Ma, probably associated with thrust emplacement of the ophiolite. The gneiss exhibits major, trace and rare earth element variations in conformity with an origin through partial melting of an amphibolitic source containing hornblende and plagioclase, probably with minor garnet and zircon. The elemental abundances and variations are characteristic of granitoids formed in supra-subduction zone environments. A granitoid sill within the adjacent Old Lizard Head Series schists, previously inferred to be related to the Man of War Gneiss, is trondhjemitic and exhibits higher SiO
2
, TiO
2
and MgO, but lower Zr, V, Ba, and Sr contents, and therefore is probably not genetically related to the latter. The sill may record local melting during ophiolite emplacement. The Man of War Gneiss probably represents a structural inlier of pre-Hercynian basement incorporated in the Hercynian nappes of SW England during NNW-directed thrusting. We emphasize the geological and geochronological similarities between variably deformed granitoid units of the Lizard complex, the Sudeten Massif of southern Poland, and the allochthonous complexes of northern Portugal and NW Spain. These granitoid rocks may represent dispersed remnants of Tremadoc arcs that formed oceanward from the northern margin of Gondwana. This is further convincing evidence that at this time Eastern Avalonia was separated from northern Gondwana by an ocean basin that may have been connected with the Tornquist Sea.
Tectonic, magmatic and depositional processes at passive continental margins
Authors: ROBERTS ALAN M. , KUSZNIR NICK J.
Published: December 2007

The papers presented in this thematic collection all derive from a meeting on geological processes at passive margins, held at Burlington House in February 1996. The meeting was co-hosted by the Geological Society, The Norwegian Geological Society and The Norwegian Petroleum Society. We would like to thank our colleagues Bjørn Larsen and Olav Eldholmfor ensuring the strong Norwegian participation at the meeting and Mike Daly for organizing contributions from the UK hydrocarbon industry.

The formation of passive continental margins during continental rifting to form new oceans is a fundamental component of the plate tectonic process yet many aspects of the formation of passive margins are still poorly understood. Passive margins are amongst the more difficult areas of the earth's surface to study, because of their great water depths and the difficulty of acquiring data. Much of the current upsurge of attention to passive continental margins, which is particularly strong for the Irish, UK and Norwegian Atlantic margins, arises from the increased interest in their hydrocarbon potential resulting from advances in deep water exploration and production technology. This renewed interest has led to the collection of new data and the increased exchange of ideas between industry and academia, some of the results of which are presented here.

The successful geological analysis of passive margins calls for the integration of many different disciplines. The papers presented here show how we need to understand the link between tectonics, depositional systems and magmatic processes in order to understand margin evolution. In addition much of
The Erris Ridge: a major geological feature in the NW Irish Offshore Basins
Authors: CUNNINGHAM G. A. , SHANNON P. M.
Published: December 2007

The Erris Ridge is a narrow structural high that separates the Erris and Rockall Troughs. It has a composite internal character and its orientation is thought to be controlled by a pre-Caledonian structural fabric which was frequently reactivated during Caledonian to Cenozoic time. In the north it is fault-bounded and probably contains rocks of Palaeozoic and older age. It formed a positive topographic feature which was progressively onlapped during Permo-Triassic to Cretaceous times. Fault reactivation occurred along its western boundary in Tertiary times and it was submerged by approximately latest Miocene times. Further south the Ridge is more complex. The Palaeozoic and older core is flanked to the SE by interpreted Permo-Triassic to Lower Jurassic strata which constitute a fault-controlled, uplifted, remnant of a half-graben basin. This composite structure was probably inverted during Late Jurassic times and remained as a topographic feature until Cretaceous times. It was progressively onlapped during Cretaceous and Tertiary times, with a minor phase of fault reactivation during the Early Tertiary. The Ridge acted as a rigid block which facilitated the focusing of several phases of crustal extension in the Erris Trough and in the Rockall Trough.
Subsidence of the Vøring Basin and the influence of the Atlantic continental margin
Authors: ROBERTS ALAN M. , LUNDIN ERIK R. , KUSZNIR NICK J.
Published: December 2007

The post-Cretaceous subsidence history of the Vøring Basin, part of the Atlantic passive margin offshore mid-Norway, has been investigated. Extension and β -factors related to rifting and continental break-up during the Palaeocene have been quantified using both forward and reverse basin-modelling techniques. In the preferred geological model it is assumed that rifting occurred in the Vøring Basin during the Palaeocene (prior to break-up), following an earlier rift event during the Late Jurassic. During Palaeocene rifting the basin may have been dynamically uplifted by the Iceland mantle plume. In the east of the basin there was no Palaeocene extension. Subsidence analysis shows that in the centre of the basin forward and reverse models converge to predict a modest Palaeocene stretching factor (β) of
c.
1.15. In the west of the basin, closest to the Atlantic margin, forward models of upper-crustal faulting also predict a β of
c.
1.15, but reverse (backstripped) models of subsidence predict a β of up to 1.75. We suggest that lower-crustal and mantle-lithosphere thinning close to the margin were greater than the extension accommodated by upper-crustal faulting and that some lower-crustal/mantle-lithosphere stretching associated with continental separation was partitioned below the Vøring Basin, up to 150 km landwards of the margin.
Structural evolution of the Vøring Basin, Norway, during the Late Cretaceous and Palaeogene
Authors: BJØRNSETH H. M. , GRANT S. M. , HANSEN E. K. , HOSSACK J. R. , ROBERTS D. G. , THOMPSON M.
Published: December 2007

The Vøring Basin forms an integral part of the passive margin off central Norway. Three phases of extension and three phases of compression record the transition from rifting to sea-floor spreading between Norway and Greenland. The first regional extensional event is of Early Cenomanian age, causing relative uplift of the Gjallar Ridge and development of a regional depocentre in the Rås Basin. A second extensional event is represented by Late Campanian faulting on the Nyk High and along the Fles Fault Complex. A compressional event in the Late Maastrichtian led to inversion of the Râs Basin. This was followed by a regional extensional event in Late Palaeocene, leading to the continental break-up between Norway and Greenland in Earliest Eocene. After the onset of sea-floor spreading, the Vøring Basin has remained in overall compression, with two major compressional events identified in Early Eocene and Mid-Oligocene.
Structure and stratigraphy of the Early Tertiary basalts of the Blosseville Kyst, East Greenland
Authors: PEDERSEN A. K. , WATT M. , WATT W. S. , LARSEN L. M.
Published: December 2007

The central part of the 65 000 km
2
lava plateau in East Greenland between Kangerlussuaq and Scoresby Sund has been investigated by multi-model photogrammetry and profile sampling, and a three-dimensional framework for the lava plateau has been established. Post-volcanic movements have divided the region into several structural blocks with dips varying from 1–2° N-NE in the inland areas to 12°SE at the coast. A major N-S-trending fracture zone may reflect an underlying Caledonian structure. Early volcanic and sedimentary rocks are overlain by widespread plateau basalts, locally with an angular unconformity of 8°. The basalt stratigraphy established in the Scoresby Sund area has been extended over most of the region. The plateau basalts were erupted over a zone more than 150 km wide, from the present coast and inland. The succession attains a vertical thickness of more than 5.5 km in the central coastal areas and thins inland to 2–3 km. A differential sagging of the coastal areas by at least 2.3 km took place during the emplacement of the lavas, accelerating with time. The features suggest increasing focusing of the magmatic production into a developing rift zone close to the present coast.
The continental margin off southern Greenland: along-strike transition from an amagmatic to a volcanic margin
Authors: CHALMERS J. A.
Published: December 2007

The southern part of the continental margin off southern West Greenland is an amagmatic margin that may have taken at least 30 and possibly more than 60 million years to form during the Cretaceous at an average extension rate of between 8.7 and 4.4 mm a
-1
. To its northwest and east are volcanic continental margins formed in the Early Tertiary when sea-floor spreading started above the hot North Atlantic plume head. The survival of the amagmatic margin means that plume head material could never have been present under it and therefore the plume head could not have had the circularly symmetric shape commonly depicted in the literature.
Vedde Ash layer discovered in a small lake basin on the Scottish mainland
Authors: LOWE J. JOHN , TURNEY CHRIS S. M.
Published: December 2007

A thin layer of micro-tephra particles has been discovered in a lake sediment sequence from Sutherland, Scotland. The tephra is attributed to the Vedde Ash on the basis of ash geochemistry. The Vedde Ash, which has been dated to
c.
10 300 radiocarbon years BP and which was thus deposited during the Younger Dryas chronozone, has previously been reported from lake sequences in Norway, from sediment cores from the NE North Atlantic and from Greenland ice cores, but this is the first reported record from the British mainland. It is likely that this ash layer also occurs in other lake sediment sequences in northern Britain, thus providing the potential for more precise correlations of Younger Dryas sequences than has hitherto been the case. The way in which correlation by tephrochronology may revolutionize approaches to reconstructing the sequence of events in theNE Atlantic region during the last glacial-interglacial transition is briefly considered.
Late Quaternary faulting and neotectonics, South Victoria Land, Antarctica
Authors: JONES SARAH
Published: December 2007

Three Quaternary fault traces in Hidden and Garwood Valleys, South Victoria Land, provide direct evidence for neotectonic activity in the Transantarctic Mountain rift shoulder of the West Antarctic Rift system. The faults trend NE-SW and all show a large component of sinistral strike-slip displacement. The late Quaternary faults lie parallel to Palaeozoic brittle structures, suggesting that inherited anistropy has governed younger fault orientations. Sinistral displacement on NE-SW-striking Quaternary faults appears to be inconsistent with the predicted Cenozoic NW-SE dextral oblique extensional regime in South Victoria Land but can be accommodated by minor clockwise rotation of crustal blocks.
Mesozoic-Cenozoic evolution of the intraplate Euphrates fault system, Syria: implications for regional tectonics
Authors: LITAK ROBERT K. , BARAZANGI MUAWIA , BEAUCHAMP WELDON , SEBER DOGAN , BREW GRAHAM , SAWAF TARIF , AL-YOUSSEF WASIF
Published: December 2007

A lack of dramatic surface geological structures along the Euphrates River in Syria belie a complex tectonic history revealed by newly released seismic reflection and well data. We document the intraplate Euphrates fault system, characterize the variation in structural style along its 350 km length in Syria, and infer its Mesozoic-Cenozoic tectonic and deformational history. We then relate the deformation of the Euphrates system and other proximate intraplate structures to nearby Arabian plate boundary processes in order to develop a new model for the tectonic evolution of the northern Arabian plate.

Throughout most of Mesozoic time, the Euphrates area experienced minor deposition compared to the Palmyride trough to its southwest, and the Sinjar trough to its northeast. During latest Cretaceous time, however, significant sinistral transtension occurred along the length of the Euphrates fault system in Syria, with graben formation especially noteworthy in southeastern Syria. This episode was probably related to events at nearby plate boundaries, and may have reactivated a zone of weakness formed during Pan-African accretion of the Arabian plate. A Palaeogene sag basin formed over the graben system in southeastern Syria. Neogene continental collision along the northern and eastern Arabian plate boundaries caused minor reactivation of the Euphrates fault system in a dextral transpressional sense, in concert with significant inversion and the main phase of uplift of the nearby Palmyride and Sinjar mountains.
Syn-convergent exhumation implied by progressive deformation and metamorphism in the Valle dell’Orco transect, NW Italian Alps
Authors: INGER SIMON , RAMSBOTHAM WILL
Published: December 2007

Structural, metamorphic and geochronological data from the Valle del'Orco are best explained by an orogenic wedge model in which crustal slices from continent and ocean acted as passive blocks at different times in the Alpine orogeny. Deformation generally migrated westwards in this section, and metamorphic recrystallization at any given point was largely controlled by the pervasiveness of strain. The data suggest a dynamic crustal stacking system lasting from 70 to 35 Ma, rather than continental collision following long-lived B-type subduction, and offer a relevant and simple model for eclogite exhumation that requires exhumation of ductile shear-bounded slices within the orogenic wedge.

The easternmost, internal unit of the Sesia-Lanzo Zone, the Eclogitic Micaschist Complex, was subducted and pervasively recrystallized under eclogite facies conditions during the early stages of convergence in the late Cretaceous. During the development of the major preserved structures, the eastern Eclogitic Micaschist Complex was undergoing general non-coaxial shear with an overall top-down to the east vorticity, suggesting a potential mechanism of exhuming an eclogitic 'pip'. Slices of pre-Alpine basement, the Vasario-Sparone Subunit, were incorporated into the lower (western) parts of this unit during the latest part of this phase, but do not show penetrative effects of the early Alpine deformation. They were passively folded during the early decompressional part of the
P—T
history, prior to the unit being juxtaposed against the underlying Gneiss Minuti Complex under blueschist-greenschist facies conditions. The Gneiss Minuti Complex itself was then recrystallized at high strain in the greenschist-facies in the latest Eocene. Fabrics developed at this stage indicate top-down-to-east extension which may have accommodated the exhumation of eclogitized Piemont oceanic material and the European continental material of the Gran Paradiso massif. Evidence of northwest-directed thrusting within the Gran Paradiso unit at the same time suggests again that the crustal block was transported on a deeper reverse-sense shear zone that presumably links to the more external thrusts now exposed to the west. High-pressure mineral lineations within the Piemont zone cannot be unequivocally assigned to either the burial or exhumation paths, but are consistent with the generally east-west transport directions observed in the structurally higher units.
Thrusting and strike-slip tectonics in the Alto Molise region (Italy): implications for the Neogene-Quaternary evolution of the Central Apennine orogenic system
Authors: CORRADO S. , DI BUCCI D. , NASO G. , BUTLER R. W. H.
Published: December 2007

The Alto Molise area belongs to the Apennine orogenic belt, which has been developing since the Late Cretaceous as a result of the Europe–Africa collision. This area is characterized by the complex superposition of different palaeogeographic domains that developed during the Mesozoic along the passive southern margin of Tethys Ocean. These domains have been subdivided into four main structural units; from shallowest to deepest they are: the Sannio pelagic basin, the Latium-Abruzzi carbonate platform, the Molise pelagic basin and the Apulia carbonate platform Units. Until the present study, the tectonic relationship among these units was thought to have been mainly determined by Early Messinian to Late Pliocene thrusting. This paper reports the results of a new geometric and kinematic analysis of the Alto Molise area. This new interpretation of the Alto Molise structural style indicates that strike-slip tectonics played a primary role during post-Pliocene times, greatly modifying the previous Alto Molise thrust structures. Two main tectonic events are recorded, consisting of the Pliocene thrusting of the Molise domain onto the Apulia platform followed by the post-Pliocene disruption and rotation of the pre-existing compressional structures by N–S-oriented, high-angle, right-lateral strike-slip faults. These faults are manifest in the Apulia platform as narrow shear zones, but propagate towards the surface into wider belts of strike-slip and oblique-slip deformation. We have compared our results with published structural, palaeomagnetic and anisotropy of magnetic susceptibility (AMS) data from the Central Apennines. This comparison suggests that the superposition of the younger strike-slip tectonic deformation on the older fold and thrust structures in the Alto Molise area is consistent with block-rotation of a segmented orogen, applied to the whole Apennine system.
Tectonic development of the northern Taiizaiiian sector of the East African Rift System
Authors: FOSTER A. , EBINGER C. , MBEDE E. , REX D.
Published: December 2007

The Eastern Branch of the East African Rift System diverges from a single,
c.
50 km wide rift in southern Kenya to a
c.
200 km wide zone in northern Tanzania, where it is comprised of three distinct rifts with different orientations. The western part of this zone contains two rift branches: the Natron-Man yara-Balangida and Eyasi-Wembere rifts. Each rift contains individual basins that are defined here on the basis of structural and geophysical interpretations. These basins are shallow (<3km) and total extension across the bounding faults is small. New K/Ar age determinations on basalts from the western rift basins show that volcanism and sedimentation began in the area at
c.
5 Ma. Major fault escarpments were present by
c.
3 Ma and the present-day rift escarpments developed later than
c.
1.2 Ma. Pre-rift volcanism produced large shield volcanoes of a basalt-trachyte-phonolite association that now lie on the rift flanks. Volcanism after the main phase of rift faulting produced volatile- and alkali-rich explosive centres which are active today, and have no equivalent in southern Kenya. The change in morphology of the Eastern Branch of the East African Rift System, and the style of volcanism in northern Tanzania, may be the result of the transition from the rifting of Proterozoic Mozambique Belt lithosphere to the rifting of cratonic Archaean lithosphere.
Multiphase reddening and weathering events in Upper Carboniferous red beds from the English West Midlands
Authors: JOHNSON S. A. , GLOVER B. W. , TURNER P.
Published: December 2007

Sediments of the Halesowen and Salop Formations (Westphalian D-Stephanian) in the West Midlands were deposited on the southern margin of the Pennine Basin during a period of relative tectonic quiescence during the Variscan Orogeny. The clastic framework of the predominantly red sandstones and mudstones in the Salop Formation includes large detrital hematite grains; these yield a primary component of magnetization indicating that sediments were deposited close to the Carboniferous palaeo-equator. Variscan uplift, erosion and subsequent deep oxidation in an arid climate during the Permian resulted in the precipitation of finer hematite in rocks of both formations (which are now found at depths of over 150 m below the present-day ground level). These grains carry secondary magnetizations which indicate formation at palaeolatitudes of between 5° and 15°N, the position that Britain occupied during the Permian.

The pattern of Permian remagnetization (particularly in borehole samples) suggests that the secondary fine-grained hematite was precipitated as a result of lateral flow of meteoric water through connected, permeable sandstone units, rather than downward percolation through the entire succession. Present-day surface weathering has resulted in the dissolution of the finer grains of hematite and, in some cases, where permeabilities are relatively high, it has also affected the coarser fraction. Consequently, the record of late Carboniferous and Permian magnetization events is commonly incomplete in strata close to the present day ground level.
Timing of formation of forebergs in the northeastern Gobi Altai, Mongolia: implications for estimating mountain uplift rates and earthquake recurrence intervals
Authors: OWEN LEWIS A. , CUNNINGHAM DICKSON , RICHARDS BENEDICT W. M. , RHODES EDWARD , WINDLEY BRIAN F. , DORJNAMJAA DORJ , BADAMGARAV JALBUUGIN
Published: December 2007

Bedrock and Quaternary alluvial fans in the forelands of the northern Gobi Altai have been faulted and warped by foreland-propagating thrust faults to form elongate hills known as forebergs. Forebergs near Bogd town, north of Arsta Bogd, and at Ih Hetsüü, north of Baga Bogd were mapped and their formation constrained using luminescence dating of lacustrine and fanglomerates sediments to give localized uplift rates ofc.0.05 m ka−1, and betweenc.1.6 and 4.1 m ka−1, respectively. Comparisons between vertical surface rupture during the 1957 Gobi Altai earthquake with the age and amount of uplift of lacustrine sediments provide a tentative estimate of between 1288±382 to 497±120 years for the average recurrence interval of great earthquakes in the Baga Bogd region. These localized uplifts rates support the view that the Gobi Altai Mountains probably took between 50 and 25 million years to form and were, therefore, coeval with the uplift of the Himalayas and the Tibetan Plateau.
Shoreline displacements in southern-central Sweden and the evolution of the Baltic Sea since the last maximum glaciation
Authors: LAMBECK KURT
Published: December 2007

During late- and post-glacial times the Baltic basin has been periodically isolated from the Atlantic and freshwater and saline conditions have alternated. This is a consequence of the interactions between the spatially variable glacial rebound of the region and the simultaneous eustatic sea-level rise in the adjacent Atlantic. Observations of the timing of these isolations and of the location of the barriers therefore provide constraints on the rebound models. High resolution numerical models of rebound of southern Sweden, the Danish straits, and the Baltic have been developed and tested against observations of lake-level change as well as against the observed elevations of the Last Baltic Ice Lake shoreline which formed before about 10.3 ka bp. Predictions of sea- and lake-levels are used to test two alternative hypotheses about the ice thickness over Scandinavia and to estimate parameters that describe the Earth’s response. Optimum values for the latter are: lithospheric thickness of 60 ± 20 km, upper-mantle viscosity of 3.3 × 10
20
Pa s, and lower-mantle viscosity of 10
22
Pa s. The rapid lake-level fall at the end of the Baltic Ice Lake stage is estimated to be 30 ± 5 m. The optimum ice model for Scandinavia is one in which the ice thickness over southeastern and southern Scandinavia was relatively thin compared with the ice thickness over Sweden and Norway: the ice thickness in the southeast and south changes slowly with distance inwards of the ice margin whereas over Sweden and Norway the ice thickness profiles are considerably steeper. The earth and ice models have been combined with high-resolution digital terrain data to develop a comprehensive model for the evolution of the Baltic basin since the time the area last became ice free. The reconstructions predict the occurrence of barriers at certain times which impede free flow between the Atlantic and Baltic and confirm that the Baltic lake levels are controlled by rebound at four localities; Degerfors in the Närke region of southern-central Sweden, the Vänern outlet through the Göta Älv, Öresund, and the Darss–Langelands–Store bælts in Denmark.
Calculable fluid–rock interactions
Authors: CRAMPIN STUART
Published: December 2007

This paper introduces a model of rock deformation (anisotropic poro-elasticity or APE), where the response of fluid-saturated rock to changing conditions, prior to fracturing, can be calculated. The driving mechanism for deformation is fluid migration along pressure gradients between neighbouring intergranular microcracks and pores at different orientations to the stress field. The parameters that control changes to microcrack geometry also control the splitting (birefringence) of seismic shear-waves, so that changes in deformation can be directly monitored by analysing the shear-wave splitting which is observed in almost all rocks. Analysis of shear-wave splitting in the Earth's crust and APE-modelling show that distributions of, mostly intergranular, cracks in the crust are always geometrically close to fracturing with the implication that shear-wave splitting is sensitive to comparatively minor changes of stress and minor changes of
in situ
conditions. This has important implications for the state of criticality of the rockmass and, as a consequence, changes in shear-wave splitting have been observed before larger earthquakes on those few occasions when suitable source–receiver geometry coincides with appropriate seismic activity. APE also has implications for monitoring changing conditions in reservoirs during hydrocarbon recovery.
Mineralogy, geochemistry and the development of ductile shear zones in the Grampian Slide zone of the Scottish Central Highlands
Authors: HYSLOP E. K. , PIASECKI M. A. J.
Published: December 2007

The Grampian Slide zone comprises a system of shear zones characterized by strain-induced, syn-tectonic muscovitization, growth of porphyroblasts of plagioclase, garnet and muscovite, concordant quartz veinlets, and by later-tectonic sillimanite and late- to post-tectonic kyanite. Traverses across shear zones in the Central Highland division show progressive modification of original gneissic fabrics, demonstrating that metamorphism and gneissification preceded the shearing event. Mylonitization involved bulk mobilization of alkalies (Na, Ca, K) and trace elements (Ba, Rb, Sr, Ni, Cr, Zr), accompanied by decreasing Fe oxidation ratios; and increasing shearing progressively changed the mineral chemistry of reversely zoned plagioclase, zoned garnet and micas. Advanced syn-shearing blastesis produced a suite of lenticular pegmatitic segregation veinlets in the mylonites. A coeval suite of larger, intrusive pegmatites represents more mobile material that has migrated through the shear zones. The pegmatites and the mylonite matrices yield U-Pb monazite ages of
c.
806 Ma, corresponding to the Precambrian Knoydartian event in the Moine rocks of the Northern Highlands. The shear zones record compressional(?) transport directed towards the NNE, and in the northern sector of the Central Highlands were reactivated by later (Caledonian?) extensional SE-directed movement. The presence of the
c.
806 Ma event in the Grampian Group challenges recent proposals that early deformation across the entire Dalradian Supergroup can be correlated with the
c.
590 Ma Tay Nappe.
Evidence from the Gediz graben for episodic two-stage extension in western Turkey
Authors: KOÇYIĐIT ALÝ , YUSUFOĐLU HALÝL , BOZKURT ERDÝN
Published: December 2007

Western Turkey falls within a wide belt of NNE–SSW-directed, active continental extension, generally similar to the Basin and Range Province of the USA. It comprises a zone of WNW–ESE-trending major grabens. Detailed study of the Gediz graben reveals two contrasting infills that represent two distinct extensional stages, separated by a short phase of compression. The older infill consists of an 800 m thick, folded and exhumed continental sedimentary sequence with intercalated calc-alkaline volcanics. It accumulated in a basin formed in the northern hanging wall of a detachment fault during Miocene–early Pliocene times. The younger infill rests on the older infill with angular unconformity and consists of about 170 m of undeformed, terraced continental sediments and basaltic lavas. It accumulated during Plio-Quaternary times in an asymmetric graben bounded by step-like normal faults. This later extension was probably triggered by the commencement of sea-floor spreading along the Red Sea in early Pliocene times and has persisted to the present. Almost all the grabens in western Turkey are best explained by this episodic, two-stage graben model with an intervening phase of short-term compression, which differs from the progressive evolution inferred for the Basin and Range Province of the USA.
Mantle plumes and Antarctica-New Zealand rifting: evidence from mid-Cretaceous mafic dykes
Authors: STOREY BRYAN C. , LEAT PHILIP T. , WEAVER STEPHEN D. , PANKHURST ROBERT J. , BRADSHAW JOHN D. , KELLEY SIMON
Published: December 2007

Ocean floor magnetic anomalies show that New Zealand was the last continental fragment to separate from Antarctica during Gondwana break-up, drifting from Marie Byrd Land, West Antarctica, about 84 Ma ago. Prior to continental drift, a voluminous suite of mafic dykes (dated by Ar–Ar laser stepped heating at 107 ± 5 Ma) and anorogenic silicic rocks, including syenites and peralkaline granitoids (95–102 Ma), were emplaced in Marie Byrd Land during a rifting event. The mafic dyke suite includes both high- and low-Ti basalts. Trace element and Sr and Nd isotope compositions of the mafic dykes may be modelled by mixing between tholeiitic OIB (asthenosphere-derived) and alkaline high- to low-Ti alkaline magmas (lithospheric mantle derived). Pb isotopes indicate that the OIB component had a HIMU composition.

We suggest that the rift-related magmatism was generated in the vicinity of a mantle plume. The plume helped to control the position of continental separation within the very wide region of continental extension that developed when the Pacific–Phoenix spreading ridge approached the subduction zone. Separation of New Zealand from Antarctica occurred when the Pacific–Phoenix spreading centre propagated into the Antarctic continent. Sea floor spreading in the region of the mantle plume may have caused an outburst of volcanism along the spreading ridge generating an oceanic plateau, now represented by the 10–15 km thick Hikurangi Plateau situated alongside the Chatham Rise, New Zealand. The plateau consists of tholeiitic OIB-MORB basalt, regarded as Cretaceous in age, and similar in composition to the putative tholeiitic end-member in the Marie Byrd Land dykes. The mantle plume is proposed to now underlie the western Ross Sea, centred beneath Mount Erebus, where it was largely responsible for the very voluminous, intraplate, alkaline McMurdo Volcanic Group. A second mantle plume beneath Marie Byrd Land formed the Cenozoic alkaline volcanic province.
Deformed A-type granites in northern Malawi, east-central Africa: pre- or syntectonic?
Authors: RING U. , KRÖNER A. , LAYER P. , BUCHWALDT R. , TOULKERIDIS T.
Published: December 2007

Metamorphosed and deformed A-type granites ranging in age from 1087 to 1119 Ma occur in strike-slip and reverse-slip shear zones of the Ubendian and Irumide belts of northern Malawi. Peak metamorphic conditions in the granites and their wallrocks reached about 12–13 kbar and 680–740°C. Microstructures reveal that the granites experienced a seemingly progressive deformation from magmatic to solid state. Magmatic deformation is manifested by the coexistence of aligned magmatic potassium feldspar, plagioclase, amphibole, biotite and ilmenite with undeformed quartz and schlieren structures. High-temperature solid-state deformation is characterized by widespread grain-boundary migration, dynamic recrystallization and myrmekitic potassium feldspar replacement. The tectonic foliation is generally subparallel to the magmatic foliation in the granites and also subparallel to the borders of the plutons and to the foliation in the wallrock. Kinematic indicators in both granite and wallrock reveal sinistral movement in the Ubendian-belt shear zones and top-to-the-ESE thrusting in the Irumide-belt shear zones.

The overall parallelism of magmatic and tectonic foliations would suggest syntectonic emplacement of the granites with respect to a
c.
1100 Ma Irumide orogeny. However, similar deformation patterns of granite-related dykes and some Pan-African pegmatites and geochronologic work suggests that the first deformation of the granites, their related dykes and some of the pegmatites occurred during the Pan-African orogeny. This study implies that a purely structural approach to distinguish syn- and pretectonic granites is rendered difficult when post-emplacement deformation occurred under high-grade metamorphic conditions. Strongly heterogeneous deformation with a pronounced degree of coaxial flattening in the granites allows magmatic structures to be preserved in low-strain zones and to be passively rotated into parallelism with penetrative deformation structures. Our work also implies that there was no Irumide orogen in northern Malawi.
Numerical age control for the Miocene-Pliocene succession at Lothagam, a hominoid-bearing sequence in the northern Kenya Rift
Authors: McDOUGALL I.A.N. , FEIBEL CRAIG S.
Published: December 2007

Lothagam, located west of Lake Turkana in northern Kenya, is an uplifted fault block comprising a gently westward-dipping sequence of volcanic and sedimentary rocks. The lower part of the sequence, lavas and coarse volcaniclastic sediments of the Nabwal Arangan beds, was deposited mainly between 14 Ma and 12 Ma (Mid-Miocene), although the uppermost basalt has a K-Ar age of 9.1 Ma. The overlying fluvial sediments of the lower Nawata Formation have yielded ages on five tuffaceous horizons ranging from 7.4 ±0.1 to 6.5 ±0.1 Ma, Late Miocene. A tuffaceous horizon in the overlying Apak Member of the Nachukui Formation, yields an age of 4.22 ± 0.03 Ma;
40
Ar-
39
Ar age spectra on the succeeding Lothagam Basalt indicate an age of 4.20 ± 0.03 Ma for its eruption. Much of the rich faunal assemblage from the Nawata Formation derives from the tightly dated lower intervals. Two hominoid teeth from higher in the formation can only be constrained to lie between 6.5 and 5 Ma old. The hominoid mandible, KNM-LT 329, from the lower Apak Member is older than 4.2 Ma and younger than 5.0 Ma.