bluuebunny/crossref_metadata_2025 huggingface dataset:
Geochemical characteristics of the Abor volcanic rocks, NE Himalaya, India: nature and early Eocene magmatism
Authors: SENGUPTA S. , ACHARYYA S. K. , DE SMETH J. B.
Published: December 2007

The Abor volcanic rocks. exposed in the Siang window, NE Himalaya. occur as dismembered thrust-hound packages interbanded with fossiliferous shelf sediments of Upper Palaeocenc to Middle Eocene age. Their age is broadly contemporaneous with the age of collision between the Indian and Tibetan continents. They were. therefore, erupted in a convergent setting through channel ways in the leading edge of the Indian continent. The volcanic rocks occur beneath the Lesser Himalayan thrust sheets and were transported with them during their southward propagation. The Abor volcanic rocks were erupted in an early Palaeogene shallow basin located within marginal parts of the Himalayan fold-thrust belt south of the collision zone. They may thus represent foreland basin magmatism.

The abundances of some major and large-ion-lithophile elements have been affected by alteration of the samples. Ti and some other trace elements remain unaffected however, and their abundances indicate that the volcanic rocks form a chemically coherent group of tholciites and alkalinc basalts. The tholeiitic and alkaline basalts reflect different degrees of melting, and low-pressure fractional crystallization involving olivine and plagioclase has played a significant role in the evolution of the basalts. On the basis of ratios of strongly incompatible elements, the two basalt types appear to have been generated from sources having similar character. This source is inferred to he enriched sub-continental mantle.
Clastic dykes in east Belgium: evidence for upper Pleistocene strong earthquakes west of the Lower Rhine rift segment
Authors: DEMOULIN A.
Published: December 2007

Fissures of seismic origin are described from terrace deposits of the Meuse river in the Liège-Maastricht area, west of the Lower Rhine–Roer rift segment. Though associated with hydroplastic deformation of the sediments, they are not injection structures. They are interpreted as tension cracks resulting from local deformation of susceptible layers inferred to be due to cyclic loading by seismic waves: the fissures have been tilled afterwards from above by vertically laminated sands and silts. The distribution of the fissured areas and the special features of some ground cracks suggest that they could be linked to more than one earthquake between 650 and l00 ka bp. By comparison with liquefaction phenomena described in relation to actual earthquakes, the failure of the Meuse terrace deposits could have been produced by seismic events of
M
L
> 6.5.
Precise
40
Ar/
39
Ar age for the initiation of Palaeogene volcanism in the Inner Hebrides and its regional significance
Authors: PEARSON D. G. , EMELEUS C. H. , KELLEY S. P.
Published: December 2007

Sanidine crystals from two tuff layers at the base of the Palaeocene Eigg Lava Formation on the Isle of Muck, Inner Hebrides, yield step-wise Ar release plateau ages of 62.8 ± 0.6 (2 σ
)
and 62.4 ±0.6 Ma using the laser
40
Ar/
39
Ar dating technique. These determinations, which are in accord with, but significantly more precise than earlier results, provide a definitive age for the inception of igneous activity in the Small Isles. From stratigraphical inferences, the Muck ages provide precise, maximum constraints on the possible age of Skye magmatism and possibly most of the British Tertiary Volcanic Province. The new ages significantly predate the oldest ages determined so far for Tertiary magmatism in NE Greenland but are similar to ages obtained from W Greenland and offshore SE Greenland and support the concept that the initiation of regional volcanism was primarily controlled by lithospheric thin spots. The Muck sanidine age appears to precisely date the first manifestation of the impingement of the Iceland mantle plume on the lithosphere beneath NW Scotland.
Primary lithological variation in the kaolinized St Austell Granite, Cornwall, England
Authors: MANNING D. A. C. , HILL P. I. , HOWE J. H.
Published: December 2007

Geological mapping of existing and redundant kaolin workings within the St Austell Granite has identified a suite of granitic rocks which show evidence of complex late-stage magmatic and hydrothermal processes. Coarse porphyritic biotite granites, like those which predominate in southwest England, occur much more widely than previously acknowledged, and are intruded by an apparently cogenetic suite of lithium-mica granites and tourmaline granites. The tourmaline granites characteristically exhibit very variable textures, with coarse quartz grains set within a fine grained, tourmaline-rich matrix. A highly evolved fine-grained tourmaline granite represents the most evolved of this suite. Topaz granites intrude the earlier granite varieties, and all are intruded by rhyolite porphyry dykes (elvans).

Major and trace element chemical data suggest that the biotite granite–lithium-mica granite–tourmaline granite suite represents the product of crystallization of a granitic magma within which B (but not F) became progressively enriched until water saturation was achieved. Water exsolution effectively quenched any remaining granitic melt, resulting in the very variable textures shown by the tourmaline granites. The topaz granites are chemically distinct from their predecessors, showing marked enrichment in F, Li and P
2
O
5
(but not B). Instead of being products of differentiation of biotite granite magma, the topaz granite melts may have been derived separately in a later episode of partial melting of the same source.

Kaolinization is widespread throughout the western part of the St Austell Granite, and deposits worked at present tend to be located in granite varieties other than biotite granite. The geochemical parameters used to distinguish the primary granite types (particularly Nb v. Zr and Ga–Nb–Zr plots) are sufficiently robust to permit the parent granitic rock type to be identified for heavily kaolinized material.
The Pinal Schist, southeast Arizona, USA: contraction of a Palaeoproterozoic rift basin
Authors: KEEP MYRA
Published: December 2007

The Palaeoproterozoic Pinal Schist of southeast Arizona comprises mainly greenschist facies turbiditic metasedimentary rocks with associated volcanic rocks. The deformation history of the Pinal Schist includes foliation and elongation-lineation development within sedimentary protoliths during early basin contraction, followed by gentle warping of the metamorphosed sediments into upright, regional-scale horizontal folds with 10 km wavelengths. Continued contraction caused development of shear zones approximately parallel to anticlinal axial surfaces, and syn-kinematic granitic rocks intruded into anticlinal cores. Such shear zones occur throughout southeast Arizona in the turbiditic rocks of the Pinal Schist as well as in rocks of more continental character associated with the Tonto Basin Supergroup in the Mazatzal Mountains. It is proposed that shear zone distribution in both the Pinal Schist and the adjacent Tonto Basin Supergroup, reflects control by a pre-existing rift margin. The Pinal Schist and Tonto Basin Supergroup therefore represent distal and proximal rift-margin facies, respectively. Reactivation of early extensional faults as reverse shear zones during margin contraction controls shear zone distribution in southeast Arizona with deformation character changing from ductile to brittle with shallowing crustal level. This model explains shear zone and lithological distribution and deformational style in southeast Arizona, and it also implies a continuum of sediment deposition and deformation throughout this part of the Mazatzal orogeny.
Strike-slip fault reactivation in the Cardigan Bay basin
Authors: TURNER JONATHAN P.
Published: December 2007

Fault kinematics in Cardigan Bay during the Cretaceous/Tertiary are problematic. In spite of abundant evidence of basin inversion across the region, there are few recognized examples of typical inversion-type structural geometry. Sub-surface structural mapping of the southern part of the Cardigan Bay basin reveals evidence of sinistral oblique-reactivation of an Early Palaeozoic fault during the Tertiary. A new kinematic scheme depicts Cardigan Bay as one part of a structurally compartmentalized Irish Sea–Cardigan Bay–Celtic Sea basin system. In this model, pre-existing NE-trending faults in Cardigan Bay exhibit sinistral displacement within a larger, NW-trending dextral shear couple. The geometry and magnitude of Tertiary inversion within this basin system was largely dependent on the relative orientation of the Early Tertiary palaeostress to the basement lineaments within each sub-compartment. Some of the implications of strike-slip fault reactivation for hydocarbon exploration and production are discussed.
Sediment supply as a control on the variability of sequences: an example from the late Namurian of northern England
Authors: CHURCH KEVIN D. , GAWTHORPE ROBERT L.
Published: December 2007

Currently, variations in accommodation space are seen as the major control on facies stacking patterns and stratal geometries. This paper emphasizes the importance of the sediment supply variable through the use of a regional, stratal surface-based interpretation of the late Namurian stratigraphy of northern England. Late highstand palaeogeographies and stacking pattern variations highlight spatial and temporal variations in sediment supply, which promote the contemporaneous development of prograda-tional, aggradational and retrogradational stacking patterns. This questions the derivation of relative sea-level curves from specific stacking patterns and highlights the potential for miscorrelation in areas with major sediment supply variations.
The influence of basement reactivation on the extensional and inversional history of the Kutai Basin, East Kalimantan, SE Asia
Authors: CLOKE I. R. , MOSS S. J. , CRAIG J.
Published: December 2007

The Kutai basin, East Kalimantan, is one of several large extensional basins formed in the Middle to Late Eocene. Formed above an orogenic complex of Late Cretaceous/Early Tertiary age, basement fabrics oriented NW–SE and NE–SW strongly influenced basin extension and inversion. Remote sensing data and fieldwork show basement fabric on the margins and Tertiary cover are dominated by NE–SW, NW–SE and NNE–SSW-trending structures. Similarly, on a larger scale, NW–SE narrow linear gravity lows cut NNE–SSW highs on the gravity data within the basin. Reconstruction of the basin architecture shows NNE–SSW basin-bounding faults overlapping in a right stepping en-echelon manner. These overlaps (relay ramps) were breached by faults oriented NE–SW through reactivation of the basement fabric. Opposing antithetic and synthetic half-grabens were linked by highly oblique NW-SE transfer faults. Inversion utilized extensional faults as reverse faults; however, NW–SE-oriented structures were reactivated as zones of lateral offset along the fold-thrust belt, whilst fault kinks oriented NE–SW were reactivated as oblique-slip reverse faults. The Kutai Basin provides an example of the controls that basement heterogeneities play on both extension and inversion.
New discoveries of mud volcanoes on the Eastern Mediterranean Ridge
Authors: CRONIN B. T. , IVANOV M. K. , LIMONOV A. F. , EGOROV A. , AKHMANOV G. G. , AKHMETJANOV A. M. , KOZLOVA E. ,   SHIPBOARD SCIENTIFIC PARTY TTR-5
Published: December 2007

Data from two mud volcanoes discovered on the eastern Mediterranean Ridge are presented, showing that these features have erupted episodically within historical time. Both volcanoes mark the site of active gas and fluid venting from deep within the sedimentary pile. Large volumes of mud breccia have been extruded onto the volcano slopes. For the first time, clasts up to
c.
1 m in size have been recovered from sea-floor mud volcanoes. The submarine clasts show lithologies ranging from shallow water bioclastic sandstones to marls and limestones, dated using microfauna as Oligocene, Miocene and perhaps Cretaceous in age. Deep-towed video footage of one of the volcanoes shows clasts up to several metres across within the crater area. Deep-towed, high resolution side-scan sonar data and core data are presented to compare the two examples. The paper documents the discovery of the two volcanoes: the Dublin mud volcano and the Stoke-on-Trent mud volcano, the clasts that have been recovered from them, the intermittence of the eruptions as interpreted from gravity-core data, and how the volcanoes contrast with other mud volcanoes further to the west.
Compositional and microtextural zoning in alkali feldspars from the Shap granite and its geochemical implications
Authors: LEE M. R. , PARSONS I.
Published: December 2007

Alkali feldspar phenocrysts in the Lower Devonian Shap granite are compositionally and microtexturally zoned. Most of each phenocryst has exsolved to form microperthite with an approximate bulk composition of Or
72
Ab
28
An
<1
, but sub-millimetre wide zones within the phenocrysts with an approximate bulk composition Or
69
Ab
30
An
1
, have exsolved to cryptoperthite. The sub-optical scale of exsolution microtextures in the narrow An-rich zones is due to Ca–Al coupling, which slows rates of interdiffusion during exsolution relative to An-poor volumes of feldspar. This form of coupled compositional-microtextural zoning has not been described previously from Or-rich alkali feldspars using electron microscopy but we have seen other examples and predict that it is common. Cryptoperthite zones are of particular importance because they will have trace element and isotopic compositions least altered, subsequent to growth in the magma, of any microtextures in alkali feldspars and so will be the most rewarding targets for chemical analysis.
Continental eclogites and the Wilson Cycle
Authors: RYAN P. D. , DEWEY J. F.
Published: December 2007

The Wilson Cycle, the repeated opening and closing of oceans, commonly along roughly the same lines, is here attributed to the presence of eclogite-facies roots of partially collapsed orogens. We present a finite-element thermal model that suggests that such roots will weaken the orogenic lithosphere relative to that of the adjacent foreland for hundreds of millions of years and make it a preferred site for later rifting.
The onshore record of passive margin evolution
Authors: GALLAGHER KERRY , BROWN RODERICK
Published: December 2007

The onshore region of passive margins has been relatively neglected because there is no unambiguous record of the denudation chronology and processes. However, apatite fission track data are sensitive to temperatures <150°C, appropriate to the cooling interval relevant during denudation of passive margin topography. In order to understand the meaning of the measured fission-track age, it is crucial to consider the track-length distribution as this is where most information concerning the thermal history is available. Over the last 10 years or so, apatite fission-track analysis studies have been undertaken from a variety of passive margins and we consider data from southern Africa, Brazil, Yemen, western India and southeast Australia. These data suites are consistent with greater amounts of section removed on what is now the low elevation coastal plain, with less material lost from the hinterland. In general there is little evidence remaining of the break-up process because of protracted denudation during the subsequent evolution of the margin. Each passive margin shows different morphologies and amounts of denudation reflecting both local geomorphic and geodynamic conditions. In addition, regional structures (e.g. shear zones) show evidence of reactivation long after break-up, but still related to large-scale plate processes.
Tectonics and magmatism associated with Mesozoic passive continental margin development in the Middle East
Authors: LAWS EWAN D. , WILSON MARJORIE
Published: December 2007

Early Triassic-Cretaceous rifting and magmatism occurred along the western edge of the Arabian Peninsula from Egypt in the south to Syria in the north, associated with the development of the Neotethyan passive continental margin which is preserved in the present-day Eastern Mediterranean. A change in the direction and rate of extension during the Early Cretaceous had a profound effect upon the developing continental margin and controlled the pattern of rifting, magmatism and sedimentation.

Extensive Late Jurassic-Early Cretaceous volcanism occurred throughout the region and is clearly rift-related. Major and trace element (including rare earth element) and Sr–Nd isotopic compositions suggest derivation of the most primitive mafic magmas from an enriched mantle source with minimal evidence of crustal contamination. The magmas appear to have ascended rapidly to the surface through large-scale faults.

Isopach maps have been constructed for a series of time intervals during the Mesozoic, using well data from Egypt, Israel, Iraq, Jordan, Lebanon and Syria. These reveal the distribution and orientation of the main depocentres. The main tectonic feature from the Late Triassic until the Late Jurassic was a basin which extended northeastwards from northern Israel to the Palmyrides in central Syria. By the Early Cretaceous, however, deposition switched to a N–S oriented basin in central and northern Israel and Lebanon. The distribution of Late Jurassic-Early Cretaceous magmatism coincides with this new basin and indicates the location of the major extensional fault zones.
Wide and narrow margins of the Brazilian South Atlantic
Authors: DAVISON I.A.N.
Published: December 2007

Two contrasting end-members of passive continental margins, here referred to as wide and narrow margins, are present in the South Atlantic, although some margin segments are intermediate between these two styles. Narrow margins are characterized by a large bounding fault (>4 km throw) near the shelf edge; a sharp transition zone (10–20 km wide) from normal thickness to substantially thinned continental crust or oceanic crust; where the total width of extended continental crust is usually less than 100 km. Wide continental margins are characterized by a broad continental shelf and a wide zone (50–600 km) of thinned crust with an even distribution of faults. Wide margins usually have a more gentle continental shelf and slope. Narrow–narrow, wide–wide, and wide–narrow conjugate margin pairs exist in the South Atlantic and are suggested to be controlled mainly by the opening kinematics and the thermal structure of the lithosphere during rifting. Basement structure and strain rate appear to have exerted little control on the style of margin extension. Although basement architecture appears to control the trend of the initial rifts, the positions of fracture zones which separate narrow and wide segments, and the rate of lateral rift propagation.
The structure of the Rockall Trough imaged by deep seismic reflection profiling
Authors: ENGLAND R. W. , HOBBS R. W.
Published: December 2007

WESTLINE is a 450 km long near-normal-incidence seismic reflection profile crossing the Rockall Trough from the Rockall Bank to the Irish coast. Beneath Rockall Bank and the Irish shelf unreflective upper crust overlies reflective lower crust and upper mantle. Crustal reflectors beneath the Irish shelf are interpreted as Caledonian. The NW slope of the trough is dissected by a series of east dipping faults forming small sediment filled half grabens. The steep SE slope is formed by the Erris Ridge. The floor of the trough is formed from rotated blocks separated by mainly east-dipping faults. Wedges of sediment fill half grabens formed by this faulting. There is no evidence for oceanic crust or a 'reflection Moho' within the trough. The floor and slopes of the trough are blanketed by
c.
4 km of parallel-bedded sediments. The lower part of the parallel-bedded sequence is intruded by sills and dykes that do not extend above a minor unconformity. It is suggested that the bulk of the sediment preserved in the Rockall Trough accumulated during and following a major rifting event in the early or mid-Cretaceous.
Mid- to late Cenozoic sedimentation on the continental margin off NW Britain
Authors: STOKER M. S.
Published: December 2007

The present morphological expression of the continental margin off NW Britain is a mid- to late Cenozoic phenomenon, initiated by a major phase of rapid subsidence in the Rockall Trough and Hatton-Rockall Basin during the early late Eocene. This led to a deepening of the basins and the onset of bottom-current activity in this region. On seismic-reflection profiles, this basin-subsidence event is manifest in the form of a widespread deep-water unconformity caused by bottom-current erosion. This boundary is particularly enhanced at the basin margins and adjacent to the axial seamounts of Rosemary Bank and Anton Dohrn, where the downwarped and eroded surface of lower upper Eocene and older strata is onlapped by middle to upper Cenozoic sediments. The latter comprise two megasequences of late Eocene to mid-Miocene and mid-Miocene to Holocene age, which consist predominantly of deep-marine contourites both in the Rockall Trough and the Hatton-Rockall Basin, although a clastic wedge has built out along the Hebridean shelf-margin since the mid-Miocene. These megasequences reflect a gross, two-stage, depositional history; a response to intra-plate tectonism which modified sedimentation patterns and palaeoceanographic circulation. The development of the bounding unconformities (early late Eocene and mid-Miocene) was coincident with major phases of regional tectonism.
Gravity anomalies and magmatism along the western continental margin of the British Isles
Authors: WATTS A. B. , FAIRHEAD J. D.
Published: December 2007

Seismic data show that the western margin of the British Isles in the region of the Hatton Bank comprises a thin wedge of sediments, an extrusive volcanic sequence, stretched continental crust, and a thick high-velocity lower-crustal body. The sediments represent a load on the surface of the stretched crust, which should subside under their weight. The extrusive volcanic rocks defined by a seaward-dipping reflector sequence, were emplaced in the crust during the later stages of rifting. The lower-crustal body has been interpreted as underplated material which re-thickens the crust and causes uplift. Backstripping techniques have been used to evaluate the contribution of sediment loading and underplating to the observed crust and mantle structure and isolate the initial rift configuration of the margin. The contribution of these processes depends, however, on the elastic thickness,
T

e

of stretched lithosphere. We have constrained
T

e

by computing the combined gravity anomaly of rifting, sedimentation and underplating and comparing it to the observed free-air gravity anomaly. Underplating gives rise to a distinct pattern of gravity anomaly 'highs' and flanking 'lows': the highs reflect the relatively dense uplifted crust and the lows less dense underplated material. The best fit between observed and calculated anomalies is for a model in which the
T

e

of stretched lithosphere is low (<5 km) and the width of the initial rift is narrow (<75 km). Since
T

e

is low, isostatic anomalies at the margin would be expected to be of small-amplitude and this is indeed the case at the Hatton Bank margin. Sensitivity studies show that large-amplitude isostatic anomalies would be expected, however, if
T

e

is high—with negative anomalies of up to 30 mGal over the underplated region and positive anomalies of up to 10 mGal in flanking regions. Such anomaly patterns are seen west of Ireland and Scotland suggesting that underplating may be a widespread feature of the British Isles margin.
Tracing short cycles in long records: the study of inter-annual to inter-centennial climate change from long sediment records, examples from the Santa Barbara Basin
Authors: SCHAAF MICHAEL , THUROW JÜRGEN
Published: December 2007

We present a review of digital imaging techniques to obtain highest resolution colour/greyvalue time-series from geological material. From suitable sediments these methods can yield time-series with subannual resolution. They can be utilized for the detection of high-frequency (< 300 years) climate change over long periods of time. Automated laminae counting produces a high-precision stratigraphy and data on the laminae thickness. The application of the methods to drill cores from the Santa Barbara Basin demonstrates the power of the techniques in detecting rapid climate change. El Niño/Southern Oscillation cycles as well as solar and lunar cycles could be detected from both, the greyvalue and the laminae thickness time-series. Evolutionary power spectra, calculated from the colour/greyvalue time-series, reveal dramatic variations in the power and frequency of rapid climate oscillations during the Holocene.
Genesis of ‘hummocky moraines’ by thrusting in glacier ice: evidence from Svalbard and Britain
Authors: HAMBREY MICHAEL J. , HUDDART DAVID , BENNETT MATTHEW R. , GLASSER NEIL F.
Published: December 2007

Irregular mounds of glacial debris, commonly referred to as 'hummocky moraine', until recently were linked to ice stagnation during rapid climatic amelioration. However, recent work in Scotland has demonstrated that some hummocky moraine, dating from the Younger Dryas event (
c.
10 000 years

BP

), was the product of deposition at active ice margins. Observations at modern high–arctic glacier margins in Svalbard (76–80°N) indicate that some moraines of this type form under a dynamic glaciological regime, mainly by thrusting in active polythermal ice undergoing strong longitudinal compression. This situation is particularly common where there is a transition from warm–based ice in the interior of a glacier to cold–based ice at the margins or snout. From their morphological similarity (rectilinear slopes facing up–glacier and irregular downglacier faces), and apparent stacking of slabs of sediment of subglacial derivation, it is concluded that some assemblages of British moraines are also the product of thrusting. This process appears to be most dominant in polythermal glaciers, rather than in temperate glaciers. On this basis, it is tentatively suggested that the Younger Dryas in Britain was characterized by a climatic regime similar to that in Svalbard today (mean annual temperature − 5°C; 400–1000 mm precipitation), and that the associated glaciers may have been of polythermal character.
Using high-resolution stratigraphy to date fold and thrust activity: examples from the Neogene of south-central Sicily
Authors: BUTLER R. W. H. , LICKORISH W. H.
Published: December 2007

The integration of structural and stratigraphic data is fundamental for determining rates of deformation in the uppermost continental crust. The high temporal resolution provided by Neogene marine sediments is used here to examine deformation rates in part of a thrust belt chosen from the Maghrebian orogen of Sicily. Conventional biozonal stratigraphy, calibrated against the geomagnetic polarity time scale, shows that individual thrust-fold structures grew steadily over many millions of years. Structures across the thrust belt were active at the same time and accommodated bulk shortening rates of
c.
0.5 mm a
-1
. In contrast the basal detachment operated about ten times faster. These results are in broad agreement with some theoretical models for orogenic wedge kinematics. Shore-line carbonate successions, calibrated with precession cycles of sea-level change, provide a very high-resolution, temporal scale with which to chart tilt rates on fold limbs (1°/27.6 ka = 0.036° ka
-1
). These show that fold amplification was continuous although the rates may have varied with time. Incremental tilting of limbs during fold amplification is not predicted by popular models of fault-bend and 'fault-propagation' folding. Geometric modelling suggests that folding occurred by limb rotation, with minor hinge migration during buckling above buried thrusts. Thus stratigraphic data may be used to examine the kinematic evolution of thrust-fold systems along regional cross-sections, and of local structures. However, the types of structural models that can be tested using estimates of deformation rates depend upon the chrono-stratigraphic resolution available for the syn-tectonic sediments.
Application of palynological data to the chronology of the Palaeogene lava fields of the British Province: implications for magmatic stratigraphy
Authors: BELL B. R. , JOLLEY D. W.
Published: December 2007

New high-precision ages, determined from palynomorph assemblages within intercalated sedimentary deposits, are presented for the Palaeogene lava fields (Skye, Mull and Antrim) of the British Province. These data reveal very rapid averaged eruption rates (1 m/200 years) and the non-synchronous formation of the lava fields. Eruption of the volumetrically dominant transitional to mildly alkaline lavas of the Skye (58.25-58.0 Ma) and Mull (post 55 Ma) lava fields (the Skye Main Lava Series, and the Plateau Group of Mull, respectively) is separated by the eruption of the MORB-like Preshal More flows of olivine tholeiite found at the top of the preserved sequence on Skye and at the base of the Mull Lava Field. The Lower Formation of the Antrim Lava Field correlates with the Skye Lava Field and the Upper Formation correlates with the Preshal More flows. The new ages indicate that the eruption of the Preshal More flows was synchronous with the main ocean floor spreading event which occurred 500 km to the NW, at
c.
55 Ma, during Chron 24r. A combined thinspot and channelized plume model may best explain the temporal and spatial distributions of the lava fields and associated subvolcanic complexes of the British Province.
On the presence of
Allosaurus fragilis
(Theropoda: Carnosauria) in the Upper Jurassic of Portugal: first evidence of an intercontinental dinosaur species
Authors: PÉREZ-MORENO B. P. , CHURE D. J. , PIRES C. , MARQUES DA SILVA C. , DOS SANTOS V. , DANTAS P. , PÓVOAS L. , CACHÃO M. , SANZ J. L. , GALOPIM DE CARVALHO A. M.
Published: December 2007

The species
Allosaurus fragilis,
from the Morrison Formation of North America (Kimmeridgian–Tithonian, Upper Jurassic), is one of the best known members of the Theropoda, the group including all predatory non-avian dinosaurs and birds. Here, we report on the first diagnostic theropod remains discovered from the Jurassic of the Iberian Peninsula. The specimen is the first evidence of
A. fragilis
outside North America. Thus, this taxon represents the first dinosaur species found on two different continents, and suggests the existence of a ‘land bridge’ between North America and Europe during the Late Jurassic.
Lazarus taxa and fossil abundance at times of biotic crisis
Authors: WIGNALL P. B. , BENTON M. J.
Published: December 2007

Mass extinctions are often followed by intervals in which taxa disappear from the fossil record only to reappear again later. This ‘Lazarus effect’ is often attributed to a poor-quality fossil record or migration to refuges. Testing these alternatives, with examples from the end Permian and late Triassic extinctions, reveals that there is no link with the abundance of fossiliferous sites and the proportion of Lazarus taxa nor are missing taxa encountered in potential refuges. Therefore, the abundance of Lazarus taxa in the aftermath of these extinctions is probably a reflection of the extreme rarity of organisms at this time.
Late Archaean felsic alkaline igneous rocks in the Eastern Goldfields, Yilgarn Craton, Western Australia: a result of lower crustal delamination?
Authors: SMITHIES R. H. , CHAMPION D. C.
Published: December 2007

Numerous felsic alkaline intrusions were emplaced in the granite-greenstone terrain of the Eastern Goldfields, Yilgarn Craton, between
c.
2650 and 2630 Ma. Intrusion coincided with the waning stages of voluminous regional granitic magmatism. The alkaline rocks are localized along and adjacent to major crustal structures that separate lithostratigraphic greenstone terranes and are divided into four geographically and compositionally distinct suites;
viz.
the Mount Monger, Emu, Claypan and Ninnis suites. The rocks have features in common with A-type granites, including high total alkalis, an anhydrous primary mineralogy, an apparent anorogenic setting, and enrichment in some HFSE, although they also have low concentrations of Nb and Y. They show a range of features that, together, point to a crustal source; e.g. the alkaline rocks are not associated with voluminous mafic magmatism, they have high LILE concentrations, they carry zircon xenocrysts of similar age to whole-rock Sm–Nd model ages, they show evidence for regional source heterogeneity, suites have constant and distinct La/Y and Nb/Y ratios and the rocks show many compositional similarities to the slightly older, voluminous, crust-derived granites. Extreme enrichments in Sr and Ba in the Mount Monger Suite, however, suggests that their source may have been metasomatized before or during melting. Intrusion of the alkaline rocks heralds a poorly recognized third tectonothermal event in the evolution of the eastern part of the Yilgarn Craton, and was broadly synchronous with the intrusion of voluminous felsic fractionated granites, crustal extension and widespread Au-mineralization. The Late Archaean geology of the Eastern Goldfields shows many features in common with Phanerozoic collisional belts thought to be profoundly influenced by processes of lithospheric delamination or convective thinning. This newly recognized third tectonothermal event in the Eastern Goldfields, may relate to the delamination or convective thinning of a dense, garnet-rich, lower crust, that resulted from extraction of earlier voluminous granite magma, and it is possible that such processes have had a greater influence on Late Archaean crustal evolution than previously recognized.
Movement and mineralization in the Tyndrum Fault Zone, Scotland and its regional significance
Authors: TREAGUS J. E. , PATTRICK R. A. D. , CURTIS S. F.
Published: December 2007

Major and minor fracture analysis of the Tyndrum Fault Zone, Scotland, reveals a late Silurian history of transtensional deformation with opening across the zone as well as left-lateral strike-slip movements. The extensional phases are characterized by hydrothermal quartz veins and breccias associated with the early stages of precious-metal mineralization. The strike-slip movements are characterized by cataclastic textures and are associated with the later stages of the precious-metal mineralization. Further transtensional deformation in the Carboniferous is indicated by right-lateral strike-slip movements, associated with fractures throughout the zone containing both cataclastic and extensional hydrothermal quartz veins: the quartz veins are associated with base-metal mineralization. The pre-Devonian, WSW–ENE-directed, transtensional deformation of the zone is extrapolated to the whole Dalradian Terrane, the driving force being the gravitational collapse of the orogenic welt parallel to the tectonic trend. The necessary area increase is signified by the intrusion of the end-Caledonian granitic magmas and quartz-veins. The Carboniferous right-lateral movements resulting from N-S extension are related to similar movements, also transtensional, on the Great Glen Fault Zone and in the Midland Valley; the associated mineralization is related to a broader Dinantian base-metal mineralizing event.
Distinguishing climatic and tectonic forcing of turbidite sedimentation, and the bearing on turbidite bed scaling: Palaeocene-Eocene of northern Spain
Authors: WINKLER W. , GAWENDA P.
Published: December 2007

Mineral composition and carbon isotope signals of pelagic limestones and hemipelagic marlstones reveal the driving processes of interbedded turbidites. The Palaeocene to lower Eocene lower bathyal Zumaia series in northern Spain between Zumaia and Getaria (W of San Sebastian) offers this opportunity. This deep-marine series records the transition from a carbonate system (Palaeocene) to a siliciclastic system (early Eocene), mainly controlled by the initiation of Pyrenean uplift in the latest Palaeocene. During the tectonically quiet Palaeocene, varying carbonate turbidite deposition was controlled by climate-dependent production of (foramol association) carbonate debris on the carbonate shelves bordering the basin. The late Palaeocene period was characterized by a cycle of increasing and then decreasing turbidite sedimentation. Increased carbonate production was driven by comparably cool/dry climates in the late Palaeocene Atlantic region, and global marked temperature gradients which enhanced wind-driven Ekman-upwelling of nutrients. In contrast, during warm/perennially humid periods (early Palaeocene and the Palaeocene-Eocene transition) the dynamics of the carbonate turbidite deposition was sluggish, due to decreased carbonate production. In the carbonate system, frequency-size statistics of bed thicknesses show that turbidite generation occurred non-scale invariant. From the earliest Eocene, increasing siliciclastic input from the rising and west advancing Pyrenean chain is observed. After a transitional period, the highly dynamic lower Eocene siliciclastic system evolved on a prograding deep-sea fan under a perennially humid and seasonally wet climate. Several periods of increased tectonic activity and sediment input are recognized by clay mineral assemblages in interturbidite beds. Turbidite bed frequency-size statistics show a power-law distribution, implying that during such periods (particularly NP 12), the depositional system temporarily reached a self-organized critical state. The evolution of the system to critical state appears to be mainly driven by siliciclastic sediment input.
Search for signs of ancient life on Mars: expectations from hydromagnesite microbialites, Salda Lake, Turkey
Authors: RUSSELL MICHAEL J. , INGHAM J. KEITH , ZEDEF VEYSEL , MAKTAV DERYA , SUNAR FILIZ , HALL ALLAN J. , FALLICK ANTHONY E.
Published: December 2007

The 'White Rock', constituting a portion of what may be a lacustrine sedimentary sequence near the margin of a crater
c.
90 km across in Sabaea Terra, Mars, measures 18 × 15 km × 180–540 m high. It is re-interpreted as a lens of magnesium carbonate precipitated where ground waters seeped into an ancient evaporating crater lake. Were life to have emerged on Mars, as seems feasible, then the 'White Rock' might be expected to comprise a complex of stromatolitic mounds. Salda Gölü (Lake) in Turkey, is taken as an analogue. This enclosed lake is nearly surrounded and underlain by partially serpentinized harzburgite. Hydromagnesite stromatolites (microbialites) up to 7 m high coalesce to form a group of small islands 200 m across. The microbialites are seen to be growing near the mouth of the usually dry Salda River in the southwestern sector. Smaller developments of hydromagnesite encircle the lake and image processing of satellite data reveals a second extensive zone beneath the lake surface over a delta in the southeast. Individual columns a few centimetres high constitute bulbous mounds which are about 2 m in diameter. These columns terminate in domes a centimetre or so across. The domes are often annulated and are covered with a green biofilm a few millimetres thick comprised of cyanobactrial filaments. The columns consist of alternating fine and coarse hydromagnesite layers differentiated on a millimetric scale. The coarser layers near the surface still contain traces of the biofilm.

Fossil microbialites were also discovered in the friable hydromagnesite cliffs shoreward of the main developments, though the structures of the individual microbes have not survived. Instead the vestiges of microbialites are easily recognized and delineated by their coarse grain size and high porosity. Annular structures on their upper surfaces can be seen in places. The intervening and overlying material, also comprised of hydromagnesite, is a semi-lithified mud.

Bulbous megascopic structures, separated by finer grained magnesium carbonate mudstone, within strata in the 'White Rock', would be strong evidence of a photosynthetic microbial genesis. Another deposit of white rock on the western margin of Juventae Chasma could have a similar origin.
Mesozoic dolerite dykes of the Falkland Islands: petrology, petrogenesis and implications for geochemical provinciality in Gondwanaland low-Ti basaltic rocks
Authors: MITCHELL C. , ELLAM R. M. , COX K. G.
Published: December 2007

The dolerite dykes of central West Falkland provided the first palaeomagnetic evidence of the near-180° rotation of the islands during the break-up of Gondwanaland. Here we present the results of a petrological and geochemical study of those dolerites. Most of the dykes sampled can be assigned to one of two suites named north-south and east-west respectively in recognition of their dominant strike. E–W dykes have compositional affinities with magmas such as the Rooi Rand dolerites of SE Africa whose geochemical characteristics (e.g.
87
Sr/
86
Sr<0.704) are suggestive of predominantly asthenospheric mantle derivation. N–S dykes, which are the most numerous, resemble the Ferrar magma type of Antarctica and the rare Hangnest and Kraai River magma types of the Karoo. The N–S dykes evolved by assimilation and fractional crystallization (AFC), most likely at crustal levels, leading to initial
87
Sr/
86
Sr=0.708–0.712, but there is no compelling evidence for initial
87
Sr/
86
Sr<0.708, perhaps suggesting an enriched lithospheric mantle source. Dykes from Lively Island and Mount Alice appear to be correlatives of other Karoo magma types. All the Falklands dykes are low-Ti in character. However, within this one small area a variety of Karoo low-Ti magma types coexist with the Ferrar magma type of Antarctica. This overlap in space of different low-Ti magma types resembles the situation in Coats Land, Antarctica and enables us to propose an extension of the boundary of the Ferrar province parallel to the subducting margin of Gondwanaland.
Age and thermal evolution of the Mesoproterozoic Cape Meredith Complex, West Falkland
Authors: JACOBS JOACHIM , THOMAS ROBERT J. , ARMSTRONG RICHARD A. , HENJES-KUNST FRIEDHELM
Published: December 2007

U-Pb SHRIMP zircon and
40
Ar/
39
Ar mineral ages are reported for rocks of the Cape Meredith Complex, West Falkland. Felsic gneisses of the oldest Big Cape Formation give a zircon date of 1118 ± 8 Ma, interpreted as the time of extrusion of the rhyolitic protoliths. The three phases of granitoid which intrude the Big Cape Formation, namely granodiorite orthogneiss (Gl), syntectonic granite gneiss (G2) and post-tectonic granite (G3), gave U–Pb dates of
c.
1090, 1067 ± 9 and 1003 ± 16 Ma respectively. Metamorphic overgrowths on zircons from the felsic gneisses were dated at
c.
1000 Ma, coeval with the G3 granite, whereas a date of 1135 ± 11 Ma from inherited cores in G2 zircons were probably derived from a slightly older component of the Big Cape Formation.
40
Ar/
39
Ar hornblende ages from amphibo-lites of the Big Cape Formation (1009 ± 14 and 1015 ± 6 Ma), along with muscovite (989 ± 3 Ma) and biotite (989 ± 7 Ma) from G3 pegmatites show that the complex cooled relatively rapidly to below 350°C, with no evidence of any Pan-African (
c.
500 Ma) thermal overprinting. These data show that the older rocks of the Cape Meredith Complex are significantly younger than the equivalent rocks of the Natal Metamorphic Province, SE Africa (
c.
1200 Ma), though they are comparable in age to those of Western Dronning Maud Land (East Antarctica), areas which Gondwana reconstructions place west and east of the Falkland Microplate respectively. The older rocks of the Cape Meredith Complex may therefore represent younger outboard arc terranes relative to those exposed in Natal. However, the syn- to post-tectonic granites of the Cape Meredith Complex are comparable in age in all three areas (1070–1000 Ma), suggesting similar collisional and post-collisional histories throughout the entire region. The lower temperature history of the Cape Meredith Complex is comparable to data from Natal, but does not show the Pan-African (
c.
500 Ma) overprint which is characteristic of much of western Dronning Maud Land. This situation is consistent with the proposed position of the Falkland Microplate between SE Africa and East Antarctica in Gondwana, where a general eastward increase in the intensity of the Pan-African thermal effects has been recorded.
Photang thrust sheet: an accretionary complex structurally below the Spontang ophiolite constraining timing and tectonic environment of ophiolite obduction, Ladakh Himalaya, NW India
Authors: CORFIELD RICHARD I. , SEARLE MIKE P. , GREEN OWEN R.
Published: December 2007

The pre-collisional tectonic evolution of the north Indian continental margin is best recorded in the few ophiolite complexes preserved, the largest of which occurs in the Spontang area of the Himalayas. Structural, sedimentological, palaeontological and geochemical work on the ophiolite and associated allochthonous thrust sheets has been carried out to constrain the timing and tectonic environment of ophiolite obduction. A distinct thrust sheet of accretionary complex rocks has been identified immediately underlying the ophiolite. Accreted units include thrust slices of tectonic melanges and alkaline basaltic lavas capped by limestones ranging from late Permian to late Cretaceous in age, interpreted as remnants of former seamounts. The accretionary complex formed above a north dipping intra-oceanic subduction zone during the Cretaceous, the Spontang ophiolite located in the hanging wall. Beneath the Photang thrust sheet, two further distinct, allochthonous thrust sheets of sedimentary melanges and continental slope deposits have been recognized. The structural relations of the allochthonous thrust sheets with the sediments of the north Indian margin have been mapped in detail and show clear evidence that obduction occurred in the late Cretaceous. At this time the Dras-Kohistan intra-oceanic arc had already collided with the southern Asian margin, over 1500 km to the north. Obduction of the Spontang ophiolite therefore records a separate tectonic episode in the Ladakh Himalaya.
Permian and Mesozoic extensional faulting within the Caledonides of central south Norway
Authors: ANDERSEN TORGEIR B. , TORSVIK TROND H. , EIDE ELISABETH A. , OSMUNDSEN PER TERJE , FALEIDE JAN I.
Published: December 2007

Palaeomagnetic data from fault rocks along major faults in the Laerdal-Gjende Fault System cutting the Caledonian structure in the Jotunheimen area of central south Norway reveals a multi-component remanence pattern. Sample and site-mean directions from the fault rocks obtained by thermal cleaning demonstrate a simple pattern of normal polarity low blocking components and reverse polarity high-blocking directions. The magnetic signature of the Laerdal-Gjende Fault System fault rocks is identical to that observed on breccias on late faults along the west coast of Norway. Based on available palaeomagnetic reference data, we assign ages of mid-late Permian and late Jurassic-early Cretaceous for important phases of faulting and breccia formation along the Laerdal–Gjende Fault System in central south Norway. Structural windows, partly exposing basement along the axis of the Caledonides in southern Norway were exhumed by footwall uplift on major faults in the Laerdal–Gjende Fault System. The consanguinity of fault rock data from the Laerdal–Gjende Fault System and fault rocks in western Norway, and comparison with displacement on the offshore continuation of the Laerdal–Gjende Fault System along the Hardangerfjorden Shear Zone, indicate that the main tectonic events responsible for the development of the North Sea basin also significantly affected the geology of central south Norway.