bluuebunny/crossref_metadata_2025 huggingface dataset:
A quest to locate sites described in the world's first publication on trichloroethene contamination of groundwater
Authors: Rivett M.O. , Clark L.
Published: July 2007

‘Contamination of water by trichloroethylene’ by
Lyne & McLachlan (1949)
(
Analyst
, 74, 513) is believed to be the UK's and world's first publication documenting cases of groundwater contamination by trichloroethene (TCE). The paper on this now notorious contaminant appears to have been overlooked for half a century. The passage of over 55 years since publication, both authors being deceased, and the original text brevity including the omission of site identities makes uncovering the historical details surrounding the paper difficult. Our quest to identify the location of the two anonymous case study sites described by Lyne and McLachlan is reported. Literature and archive searches, consultations with relevant professionals, data matching to site descriptions and reconnaissance site visits were undertaken. Lyne and McLachlan were ‘public analysts’ providing certified analysis for local authority jurisdictions including Reading, Berkshire, Oxford and parts of London including the City of Westminster and Boroughs of Chelsea, Fulham and Marylebone. Such a large jurisdictional area has made identification of the case study sites challenging. Our search to date has focused upon Reading, based upon the affiliation address given by the authors and it being the most industrialized jurisdiction covered. Although some candidate sites were found, unfortunately none could be conclusively identified as Lyne and McLachlan's sites. It remains possible that the sites may still be located within Reading but were simply not recognized because of the paucity of both the site descriptions Lyne and McLachlan provided and historical site contamination records that now generally remain from the 1940s. Industrial areas of the other jurisdictions served are more limited, but remain to be searched. The paucity of relevant historical records suggests that ultimate proof of sites would require contact with personnel directly involved with the incidents. This has, however, become a very remote possibility.
Development of a digital geological compass
Authors: Zobl F. , Brunner F.K. , Wieser A.
Published: July 2007

The spatial orientation of a geological feature is commonly specified by the dip angle and azimuth of the fall line. Both angles are measured using a geological compass (GC). A conventional GC needs to be levelled before the magnetic azimuth can be read. We have developed a digital geological compass (DiGC) that does not require levelling; it can be manufactured small and lightweight, and yields accurate dip angle and azimuth measures within less than a second. We introduce the concept of such a DiGC, based on an assembly of three accelerometers and three magnetometers, discuss the computation of dip angle and azimuth, and present results from a series of test measurements confirming that a precision of better than 1° (1σ) can be obtained.
Discovery of the palaeo-Indus delta-fan complex
Authors: QAYYUM MAZHAR , LAWRENCE ROBERT D. , NIEM ALAN R.
Published: July 2007

The Indus River carries sediments from the western Himalaya and deposits some of these as channel and floodplain sediments or molasse. The rest of its load forms the Indus delta at the margin of the Indian Ocean. The Indus delta passes some of its sediments to be deposited as Indus submarine fan turbidites. Thus, as elsewhere, Himalayan molasse, delta, and fan deposition are related hi tune and space. However, when we examine fluvial and marine age-range data of the older Indus deposits, in terms of this sedimentary assemblage, a major portion of its marine record is missing. The oldest known molasse along the Indus suture zone, and hi the foredeep are middle Eocene and late Palaeocene hi age, respectively. A recent synthesis of sedimentation in the northern Indian Ocean, however, shows that turbidite sedimentation started around early Miocene in the modern Indus fan, and even later in the Bengal fan. Where are the Palaeogene Indus delta and fan sediments? We suggest herein that these are preserved as the Palaeogene siliciclastic Khojak Formation hi the Katawaz Basin and eastern Makran.

The modern Indus River is 2900 km long (Coumes & Kolla 1984) and has 30 000 m
3
s
− 1
discharge (Milliman
et al.
1984) in summer (Fig. 1), twice that of the Mississippi River. The annual suspended sediment load (Wells & Coleman 1984) varies between 395 and 435 x 10
3
t, almost equal to that of the Mississippi. The existence of the middle Eocene to middle Miocene Indus molasse along the
Late Proterozoic rift faults and basement—cover relationships within the Ben More thrust sheet, NW Scotland
Authors: BUTLER R. W. H.
Published: July 2007

Recently proposed models for the tectonic evolution of Northern Scotland, involving lithospheric extension during the late Precambrian, are supported by new discoveries and interpretations of early normal faults within the Moine Thrust Belt. Such structures control the preser­vation of Torridonian sediments beneath the sub-Cambrian unconform­ity. The Ben More thrust ramp from basement into the Cambrian cover may have been controlled by the early faults. Major synclines within the Ben More thrust sheet appear as tightenedhalf-grabens and thus are composite structures. This may require a re-examination of the field relationships between these folds and the apparently syn-tectonic alkaline intrusions that have been used to date thrust activity.

The Ben More thrust sheet of the Moine Thrust Belt contains the most easterly outcrops of Torridonian Supergroup (late Proterozoic) in Scotland (Fig. 1). These sediments and their Lewisian basement are unconformably overlain by the Cambrian quartzites of the Eriboll Sandstone Group. The stratigraphic relationships of these units, with the two un­conformities (Cambrian on Torridonian, Torridonian on Lewisian) discordant so that the Cambrian sediments overstep from Toridonian onto Lewisian basement, have been known for over a century. However, the nature of the overstep and its implications for the Precambrian arrangement of Torridonian and Lewisian rocks, is less established. Soper & Barber (1979) inferred the presence of major upright folds with wavelength in excess of 30 km so that Torridonian sediments lie preserved in synclines while the crests of the anticlines are eroded beneath the sub-Cambrian unconformity. This model for Precambrian basement–cover relationships has
Quantitative palaeoclimate GCM validation: Late Jurassic and mid-Cretaceous case studies
Authors: PRICE GREGORY D. , VALDES PAUL J. , SELLWOOD BRUCE W.
Published: July 2007

Using quantitative proxy models of peat and bauxite formation, based upon modern analogues, predictions of the distribution of peats (coals) and bauxites for both the Late Jurassic (Kimmeridgian) and mid-Cretaceous (Cenomanian) have been made using a General Circulation Model (GCM). The predictions have been compared with the known distribution of these deposits. Such an approach provides a means of identifying and isolating which components of the GCM accurately reflect palaeoclimate. The prediction of peats and bauxites for the Jurassic and Cretaceous show good correspondence with known coals and bauxites and provides otherwise elusive quantitative estimates of high latitude climate. The GCM is thus successfully replicating precipitation and mean annual temperatures for both the Kimmeridgian and Cenomanian.

Investigations of Mesozoic palaeoclimate using General Circulation Models (GCMs) have often focused on qualitative evaluation of results (e.g. Barron & Washington 1982;

Valdes
et al.
1995

;

Chandler
et al.
1992

). A number of recent studies have, however, highlighted the need for GCM predictions to be quantitatively validated against the sedimentological and palaeobiological record (e.g. Poore & Chandler 1994; Pollard & Schulz 1994;

Price
et al.
1995

). Quantitative estimates of terrestrial climate have been produced by physiognomic analysis of floras (e.g. Herman & Spicer 1996; Wolfe & Upchurch 1987), and have also been derived from organisms such as crocodiles (e.g.
Markwick 1994
). Comparable results have been used effectively for validating GCM predictions (e.g. Sloan & Barron 1992), but data tend to be restricted to North America and are often Latest Cretaceous, or younger, in age.
Estimates of the amount and rate of sea-level change across the Rhaetian—Hettangian and Pliensbachian—Toarcian boundaries (latest Triassic to early Jurassic)
Authors: HALLAM A.
Published: July 2007

An attempt is made to determine the amount and rate of sea-level change for two major events in the latest Triassic to early Jurassic, both of which are associated with mass extinctions, using the best available facies evidence and time scale. The amount of marine deepening across the Pliensbachian—Toarcian boundary, based on analysis of the excellent Yorkshire coast section, is likely to have been a few tens of metres, at a rate of between 1cm 1.2 ka
− 1
and 1cm 0.4 ka
− 1
. The change across the Rhaetian—Hettangian (Triassic—Jurassic) boundary was different in that the sea-level rise was immediately preceded by a sea-level fall, effectively a 'regression-transgression' couplet. The earliest Jurassic sea-level rise is likely to have been much more rapid than that across the Pliensbachian—Toarcian boundary, at a rate of at least 1 cm 0.2 ka
− 1
. Whereas the speed of Pliensbachian—Toarcian change is consistent with the growth of oceanic ridges, the appreciably more rapid Triassic—Jurassic change is suggestive of a different tectonoeustatic mechanism involving stress-induced changes in plate density.
Unusual rates and patterns of Holocene emergence, Ellesmere Island, Arctic Canada
Authors: ENGLAND JOHN
Published: July 2007

Substantial postglacial emergence (up to 150 m) characterizes the Canadian High Arctic following the last glacial maximum. Across northern Ellesmere Island, rapid emergence is not observed during the early stages of deglaciation as it is in other parts of Arctic Canada. Rather, the curves show an interval of slow emergence (
c.
1 m per century) during initial ice retreat. This is attributed to a slow rate of glacial rebound that was countered by a similar rate of eustatic sea-level rise.

Normally, isobases drawn on postglacial shorelines define broad cells of uplift that mimic centres of former maximum ice thickness. However, isobases on the 8 ka BP shoreline, surveyed throughout northern Ellesmere Island, indicate more complex patterns of crustal uplift that seem in congruent with reported ice thicknesses. On west-central Ellesmere Island, the isobases (110–150 m asl) trace a plunging ridge, aligned with geological structure, across an area considered to have had minimal ice cover during the last glacial maximum. The ridge may record an important structural influence associated with the geologically youthful Sverdrup Basin. Collectively, this evidence cautions against the view that postglacial emergence has a universally, predictable signature solely portraying former ice loads.
Climate change, loess and palaeosols: proxy measures and resolution in North China
Authors: DERBYSHIRE EDWARD , KEMP ROB A. , MENG XINGMIN
Published: July 2007

The Loess Plateau of North China is a key region for the study of records of Quaternary climatic change. Various techniques to abstract climatically sensitive data were first applied to the classic loess—palaeosol site at Luochuan, and current views on climatic change in Asia have been strongly moulded by results from this central part of the Loess Plateau. Data including the magnetic susceptibility, granulometry, mineralogy, geochemistry, micromorphology, fossil content, and inorganic and organic carbon content of Asian loess—palaeosol series have been used, singly and in combination, as surrogate measures of palaeoclimates to infer climatic changes with particular reference to changes in the Asian monsoon. Some of this work is reviewed and the status of a number of parameters as climatic proxies is discussed. Some lithostratigraphic sequences from which proxy measures of climate have been derived are incomplete, as shown by erosion surfaces, water-laminated zones and truncated palaeosol profiles, while others provide records of relatively low resolution. Most descriptions of Quaternary climatic changes based on studies of the loess emphasize alternations in the relative dominance of warm and moist v. cool, dry and dust-laden monsoons. Some recent studies of the much higher resolution loess—palaeosol successions on the western margins of the Loess Plateau have suggested that such changes may sometimes be out of phase, with the inference that the current climate model is too simple. Means of testing this hypothesis are proposed.
Cryptic trace-element variation as an indicator of reverse zoning in a granitic pluton: the Ricany granite, Czech Republic
Authors: JANOUŠEK V. , ROGERS G. , BOWES D. R. , VAÒKOVÁ V.
Published: July 2007

Cryptic variation recognized on the basis of trace-element patterns shows the Øíèany granite in the northeastern part of the Hercynian Central Bohemian Pluton to be a reversely zoned, high-level intrusion. Unlike many other reversely zoned plutons, there are no marked differences in modal composition between the margins and the centre of the intrusion.

The granite is generally peraluminous and geochemically evolved, as demonstrated by its restricted and high SiO
2
range and low K/Rb ratio, coupled with a
c.
two-fold variation in Ba and Sr concentrations. Modelling shows that the geochemical variations can be most readily explained by K-feldspar-dominated fractionation in a magma chamber below the present level of exposure. The reverse zoning is interpreted as the product of emplacement of an essentially single pulse of magma from a deeper level magma chamber in which fractionation has led to a vertical compositional gradient. The least evolved magma was emplaced in the centre of the high-level pluton with the more evolved magma around it.

Recognition of cryptic reverse zoning in granites has major implications for granite petrogenesis in that the magmatic evolution of such bodies has to be established before assessing potential mechanisms of emplacement.
Gravity gradients and upper-crustal tectonic fabrics, Ireland
Authors: READMAN P. W. , O’REILLY B. M. , MURPHY T.
Published: July 2007

Gravity gradients derived from an updated Bouguer anomaly map of Ireland reveal large-scale lineaments, many of which can be related to geological structures and tectonic development. First horizontal derivatives of the anomaly calculated at various azimuths accentuate linear trends in different directions, while the second derivative helps resolve near surface structure. The dominant NE–SW Caledonian-trending lineaments are interpreted as due to fault boundaries and folds in pre-Carboniferous basement and Caledonian fault reactivation during the Variscan Orogeny. Subsidiary NNE–SSW–trending lineaments are present, as well as weaker NW–SE-trending lineaments. The largest negative anomalies are produced by late Caledonian granites and widespread buried granitic rock in the middle to upper crust is proposed. Both exposed and inferred granites appear to be spatially related to intersections of NE–SW- with NNE–SSW- and NW–SE-trending lineaments. The orientation of the dominant gravity trend changes from NE–SW towards ENE–WSW going westwards across Ireland and forms part of a more regional change in the ‘Caledonian’ gravity fabric recognised throughout the northeast Atlantic region. ‘Variscan’ E–W gravity trends in the south of Ireland overlay the ‘Caledonian’ trends. Relationships between gravity lineaments and anomalies support a ‘thin-skinned’ model for the Variscan cover.
Umbers, ocean crust and the Irish Caledonides: terrane transpression and the morphology of the Laurentian margin
Authors: WILLIAMS D. M. , HARKIN J. , RICE A. H. N.
Published: July 2007

The Clew Bay Complex of western Ireland contains a variety of rock types. These include schists possibly of Dalradian association, amphibolites and serpentinites of unknown age, cherts, volcanic rocks and graded gabbros of mid to upper Ordovician age and shales and sandstones of Silurian age. Intercalated within the cherts of the complex on Clare Island are chocolate-brown horizons of a porous rock, geochemically comparable to hydrothermal mid-ocean ridge metalliferous sediments (e.g. umbers). These cherts overlie volcanic rocks of MORB affinities with an island arc influence. The association exposed on Clare island of graded gabbros, MORB volcanic rocks, discontinuous carbonaceous horizons, cherts, umbers and deep water shales suggest the presence of a mid- to late Ordovician spreading centre now preserved as a dismembered ophiolite.

The Clew Bay and Highland Border Complexes, both being parts of the Border Terrane, have many similarities including evidence of mid- to late Ordovician spreading, and it is suggested they formed in the same basin. However, they are dissimilar to both the South Mayo and Midland Valley Ordovician and Silurian rock associations, from which they are separated by a terrane boundary. The geochemical data and field associations do not indicate back-arc or intra-continental rifting. We suggest, therefore, that elements of older ocean crust became trapped inboard of a collided early Ordovician arc at re-entrants along the Laurentian margin. This trapped crust became the site of mid- to late Ordovician spreading. We also suggest that the site of this entrapment was to the northeast of the present positions of the Clew Bay and Highland Border Complexes and that they were emplaced into their present sites by end-Silurian transpression. This Laurentian margin morphology is compatible with that demonstrated for parts of the Newfoundland-Quebec sectors of the Appalachian sector of the orogen.
Early meteoric fluid flow in high-grade, low-
18
O gneisses from the Mallee Bore area, northern Harts Range, central Australia
Authors: MILLER JODIE A. , CARTWRIGHT I.A.N.
Published: July 2007

Granulite-facies ortho- and paragneisses from the Mallee Bore area, central Australia are depleted in
18
O by up to 10%o. The zone of
18
O depletion is elongate, not coincident with any lithological or structural feature, and covers an area of approximately 9 km
x
3 km. Within this zone, average 8
18
O values of paragneisses and orthogneisses are
c. 4.6%c
and
c. 4.1%c
respectively, and locally are as low as 2.7%o and 2.4%o, respectively. The lowering of δ
18
O values probably occurred due to isotopic exchange between the rocks and a surficial fluid at high temperatures. The preservation of high-temperature mineral oxygen isotope fractionations and the lack of gross retrogression of the Mallee Bore rocks, indicates that fluid flow after regional metamorphism was negligible. Furthermore, the difficulties associated with downward circulation of surface-derived fluids to depths in excess of 25 km, as well as the lack of wholesale melting in the rocks, suggest that fluid flow occurred prior to the peak of granulite-facies regional metamorphism. Hence, the
18
O depletion observed at Mallee Bore most likely occurred during early contact metamorphism, or during the prograde stages of regional metamorphism. The preservation of low δ
18
O values suggests that there was little pervasive fluid flow during or subsequent to regional metamorphism.
Morphology, seismic structure and tectonic development of the Powell Basin, Antarctica
Authors: COREN F. , CECCONE G. , LODOLO E. , ZANOLLA C. , ZITELLINI N. , BONAZZI C. , CENTONZE J.
Published: July 2007

The Powell Basin, located near the Scotia-Antarctica strike-slip plate boundary, is bounded on three sides by continental crustal blocks, and it separates the South Orkney microcontinent from the northeastern Antarctic Peninsula. On the basis of the entire geophysical data set available, the main structural and geological elements of the basin are identified. The northern domain is characterized by an oceanic-like environment, with a ridge axis in the centre of the basin. Two conjugate deep, restricted sedimentary basins are located at the base of the northeastern and northwestern margins, and filled by thick sedimentary sequences. The southern domain is mainly floored by transitional crust and presents rift-related basement graben. The margins surrounding the basin are different, with the northern and southern margins mainly transcurrent, whereas most of the eastern and western margins show passive margin characteristics. The sedimentary sequences filling the basin have been correlated to the main tectonic processes responsible for Powell Basin opening, and partially dated using marine magnetic anomaly identifications. Three main evolutionary phases are recognized that explain the geological setting of the Powell Basin. An early phase of separation between the Antarctic Peninsula and the South Orkney microcontinent produced stretching and progressive continental lithospheric thinning, with the creation of restricted pull-apart basins (proto-Powell phase). This phase was followed by a northward movement, possibly accomplished with a clockwise rotation, of the South Orkney microcontinent (drift phase), with consequent oceanic crustal accretion in the northern sector of the basin, and development of rift-related structures in the southern sector (phase spanning 27-18 Ma, as determined from the marine magnetic anomalies). A successive clockwise rotation of the South Orkney microcontinent determined the complete development of the northern sector of the basin, with spreading and final structuration of the margins encircling the basin plain.
Rb-Sr ages of micas from the Kathmandu complex, Central Nepalese Himalaya: implications for the evolution of the Main Central Thrust
Authors: JOHNSON M. R. W. , ROGERS G.
Published: July 2007

The Kathmandu complex, comprising the Bhimphedi and Phulchauki groups which range in age from Precambrian to Lower Palaeozoic, is situated in the frontal part of the Main Central Thrust sheet. Although it is likely that a tectonothermal event antedated the intrusion of early Ordovician granites, Rb-Sr dating of muscovites in deformed pegmatites suggests that the high-grade metamorphism in the Bhimphedi Group is of Tertiary age. These pegmatites cooled through
c.
500°C at 18–14 Ma. Biotite Rb-Sr data indicate cooling through
c.
300°C at 7.5 Ma. Thermobarometric and radiometric data from central Nepal suggest an evolutionary model for the emplacement history of the Main Central Thrust sheet involving cooling from a peak temperature
c.
660°C to
c.
500°C in 7 Ma, and loss by erosion or tectonic denudation of
c.
4–11 km of section.
Petrology and palaeoenvironmental significance of glaucony in the Eocene succession at Whitecliff Bay, Hampshire Basin, UK
Authors: HUGGETT J. M. , GALE A. S.
Published: July 2007

Following the investigations of Odin and others into the distribution of green granules, glaucony has been widely assumed to be a reliable indicator of a fully marine, open shelf environment with a low sedimentation rate. We have investigated the value of glaucony as a palaeoenvironmental indicator through an investigation of the pellets, and their distribution and reworking in the predominantly brackish to shallow marine Tertiary sediments of the Hampshire basin, together with a re-evaluation of the sedimentology.

Glaucony has apparently formed
in situ
in all lithofacies from shallow marine to estuarine. Of the three highest glaucony concentrations (all dominated by
in situ
glaucony) two occur within highstand system tracts, the third is at a sequence boundary. Several important surfaces do not have more than a few percent glaucony, with very variable proportions of mature and
in situ
pellets. The correlation between glaucony concentration and sequence stratigraphy is most obvious in the London Clay and Wittering Formations, where least reworking of pellets has occurred. In the Barton Group there are no major concentrations of glaucony at any of the important stratal surfaces, we believe this more random glaucony distribution is due to limited glaucony formation and reworking of older glaucony. In these sediments ideal conditions for glaucony formation are interpreted to have been: fully marine, 10–30 m water depth, a ‘warm’ temperature plus low sedimentation rate with periodic winnowing to concentrate the pellets. Although most of these conditions for glaucony formation occurred in the Selsey Formation and Barton Group, a factor or factors mitigated against glauconitization. We suggest that this was lowering of the water temperature. The London Clay and Wittering Formations were deposited relatively rapidly (50–60 m Ma
−1
) and include intervals of estuarine sedimentation, both factors that we believe inhibited glaucony formation.

Glaucony maturity reflects the minimum length of time spent in surface sediments, close to the oxic/sub-oxic interface. Point count data and chemical data for glaucony indicate widespread reworking and an overall increase in reworking with time, possibly due to uplift on the Isle of Wight monocline. The apparently wide range of conditions in which glaucony will form, and the frequency with which it is reworked, suggest that it is a less useful indicator palaeo-environmental indicator than is commonly supposed.
An Early Cretaceous forearc basin in the Golfo de Penas region, southern Chile
Authors: DIEMER J. A. , FORSYTHE R. D. , ENGELHARDT D. , PORTER C.
Published: July 2007

A 4000 metre thick fining-up succession of conglomerates, sandstones and mudstones on the northwestern edge of the Golfo de Penas, southern Chile, is defined as the Puerto Barroso Formation. It probably formed in a forearc basin where a fan delta built across a narrow coastal plain into a shallow marine environment during the Barremian to Aptian. The basin is situated to the west of contemporaneous arc, back are and epicratonic basins and is the only documented forearc basin of this age in southern South America.
Deep-sea sediments record the geophysiology of the late Ordovician glaciation
Authors: ARMSTRONG HOWARD A. , COE ANGELA L.
Published: July 2007

Sedimentological analysis of the Ordovician-Silurian international boundary stratotype section at Dob's Linn, Scotland shows systematic changes in muddy turbidite microfacies which are interpreted in terms of a four phase glaciation. This comprised: (1) a pre-glacial cooling of the deep sea in the early Ashgill (Cautleyan), (2) initiation of intense thermohaline circulation in the late Rawtheyan, predating, (3) the start of the glacial maximum near the end of the Rawtheyan, and (4) rapid de-glaciation in the mid- to upper Hirnantian (lower part of the
persculptus
Biozone). It is proposed that the glacial maximum was triggered by a combination of negative greenhouse effect (‘Monterey Hypothesis’) and increasing surface albedo. Cessation of thermohaline circulation and the expansion of anoxia mark the rapid end of the glaciation in this deep-sea environment.
Geochemical and isotopic constraints on subduction polarity, magma sources, and palaeogeography of the Kohistan intra-oceanic arc, northern Pakistan Himalaya
Authors: KHAN M. ASIF , STERN ROBERT J. , GRIBBLE ROBERT F. , WINDLEY BRIAN F.
Published: July 2007

Geochemical and isotopic data are presented for 18 representative samples from the intraoceanic phase of the Kohistan arc. A restricted range of initial
87
Sr/
86
Sr (0.7036–0.7066) and ºNd (+2.8 to +7.4) along with measured
206
Pb/
204
Pb (18.0–18.6) are consistent with formation of the arc complex in an intra-oceanic setting. The isotopic data demonstrate the involvement of enriched, DUPAL-type mantle, suggesting that the Kohistan arc formed at or south of the present equator. Subduction polarity inferred from geochemical and isotopic data indicate that the Chalt Volcanics and Kamila Amphibolites represent a forearc and backarc basin sequence, respectively. These inferences are most simply resolved with a tectonic model whereby the intra-oceanic Kohistan arc evolved over a south-dipping subduction zone, implying that Kohistan and India moved northwards on the same plate, although separated, during much of Cretaceous time. Collision of Kohistan with the Karakorum caused a new, north-dipping subduction zone to form on the south side of Kohistan, leading to collision with India in early Tertiary time.
Rifting Archaean lithosphere: the Eyasi-Manyara-Natron rifts, East Africa
Authors: EBINGER C. , DJOMANI Y. POUDJOM , MBEDE E. , FOSTER A. , DAWSON J. B.
Published: July 2007

Long (>50km) normal faults bound one or both sides of narrow basins within the East African Rift System, but the dimensions and internal geometry of individual basins vary along its length. We examine basins in N Tanzania that developed in Archaean and Late Proterozoic (Pan-African) crust, and the relationship of Neogene-Recent faulting and volcanism to pre-existing lithospheric structure. In northern Tanzania the
c
. 50 km-wide Eastern (Gregory) Rift splays into three seismically active arms, with active extension distributed across a 200 km wide zone. We use new gravity and aeromagnetic data, and existing seismic, gravity, heat flow, and geochemical data to model lithospheric structure beneath the Archaean craton and Proterozoic orogenic belts, and its influence on rift development in N Tanzania. Depths to source bodies determined from Euler deconvolution of aeromagnetic data (1 km grid) indicate that
c
. 40 km wide basins are less than 3.5 km deep, with basin depths decreasing to the south, consistent with depths estimated from gravity anomalies. Asymmetric basins in the Archaean and zone of reworked Archaean and Proterozoic nappes are bounded by unusually long (100 km) border faults associated with seismicity to depths >25 km. Estimates of flexural rigidity, or effective elastic thickness
(TJ,
suggest that the lithosphere beneath the Tanzania craton, including the western rift arm, is stronger (64 ± 5 km) than that beneath the Proterozoic belt and the transition zone (30 ± 4 km), with the lowest
T

e

values found beneath the central rift arm (23
+2
4
km). Heat flow, seismicity, and mantle xenolith data also indicate that the lithosphere beneath the Archaean craton was and is colder and stronger than the post-Archaean lithosphere. Geophysical and geochemical data suggest that (a) pre-existing heterogeneities in the Archaean crust influenced the orientation of border faults bounding basins, and (b) that topography at the base of the lithosphere guided the location of rifting in Tanzania, producing a broader rift zone. These results indicate the persistence of a deep cratonic root despite the impingement of a mantle plume in Cenozoic time.
The age and tectonic significance of dolerite dykes in western Norway
Authors: TORSVIK TROND H. , ANDERSEN TORGEIR B. , EIDE ELIZABETH A. , WALDERHAUG HARALD J.
Published: July 2007

Coast-parallel dykes in SW Norway, primarily of Permo-Triassic age, have been linked regionally to the early tectonic evolution of the Norwegian continental shelf. We demonstrate from palaeomagnetic data (mean declination = 206.1°, inclination = — 30.1°, a
95
= 11.8°) that dolerite dykes in the coastal Sunnfjord region of Western Norway and immediately west of the Devonian Basins are also of Permian (c. 250-270 Ma) age, and not lower- or pre-Devonian as previously advocated. The Sunnfjord dykes appear to be contemporaneous with dykes from SW Norway at Sotra (262 ± 6 Ma) and the oldest dykes from Sunnhordland (260–280 Ma), and geochemical data attest to a transition from sub-alkaline to alkaline magmatism at the dawn of the Mesozoic.

The Sunnfjord dykes are not simple records of E-W extension and magma intrusion, but instead represent significant mid-late Permian time markers within a complex zone of fault activation and rejuvenation. Late Mesozoic-Cenozoic magnetic overprinting (mean declination = 348.6°, inclination = + 68.9°,
a
95
=12°) and metamorphic alteration documented by these dykes are directly dependent upon proximity to major E-W brittle faults south of the Hornelen Devonian Basin, hence some motion and related fluid activity do post-date dyke intrusion. The E-W high-angle normal or oblique-slip faults can be regionally traced offshore to the Øygarden Fault Zone. Onshore, these faults truncate the Hornelen low-angle detachment, which in turn cuts folded D evonian strata. These observations, along with evidence for Permian and Late Jurassic-Cretaceous extension from the nearby Dalsfjord region, demonstrate important reactivation of a Late to post-Caledonian detachment and high-angle fault system in Western Norway.
Upper crustal fluid migration: an example from the Variscides of SW Ireland
Authors: MEERE PATRICK A. , BANKS DAVID A.
Published: July 2007

The density and composition of single generation fluids in quartz veins from two similar host lithologies located either side of the Irish Variscan front were investigated using fluid inclusion microthermometry and crush leach analysis. The front marks the northern boundary of a distinctive cleavage developed under sub-greenschist facies conditions and coincides with the margin of a fault-controlled inverted half graben, the Late Devonian Munster Basin. Trapped fluids in Variscan veins north of this basin have medium salinities (4–14 wt% NaCl eq.) and densities generally compatible with the expected
P—T
conditions of deformation in the area. Fluids in veins south of the half graben margin can be grouped into those in (a) syn-compressional veins with moderate salinities (8–16 wt%) and (b) late stage veins associated with post-orogenic extension which have trapped high salinity fluids (22–27 wt%). Fluid densities for both vein types are broadly compatible with estimated
P–T
conditions of both trapping events. Crush-leach analyses reveal that all the fluids analysed have Br/Cl ratios close to SMOW. Variations in I/Cl ratios and cation chemistry indicate significant water/rock interaction for medium salinity fluids on either side of the front.

The marked internal consistency in Br/Cl ratios from northern and southern fluids coupled with the broad ranges of cation to chloride ratios suggests that an early homogenous marine brine was subsequently modified by differing migration histories during the Late Palaeozoic tectono-sedimentary evolution of the area. It is contended that on a megascopic scale, gravity driven fluid flow controlled by megascopic fold geometries was the dominant mechanism of fluid migration associated with the buckling phase of the orogen, while expulsion of supra-hydrostatically pressurised fluids is associated with late stage orogenic extension.
Palaeomagnetic dating of sub-Torridon Group weathering profiles, NW Scotland: verification of Neoproterozoic palaeosols
Authors: WILLIAMS GEORGE E. , SCHMIDT PHILLIP W.
Published: July 2007

A palaeoplain that cuts across Lewisian Gneiss in the Cape Wrath area, northwest Scotland, is weathered to depths of 1–6 m beneath fluvial red conglomerates and sandstones of the Applecross Formation of the early Neoproterozoic Torridon Group. Weathered Lewisian rocks are enriched in K
2
O and Fe
2
O
3
, and contain hematite as an alteration product of biotite and magnetite. Palaeomagnetic analysis of the weathering profiles has been carried out to constrain the age of alteration. Thermal step demagnetization of 87 oriented core specimens of biotite-gneiss and amphibolite spanning four profiles at Poll a’ Mhurain and Sheigra reveal a stable, high-temperature component with a mean direction of remanence of
D=
149.1°,
I
=57.2° (α
95
= 5.0°) (corrected for dip of the overlying Applecross strata) that gives a pole at 9.8°S, 199.2°E (dp = 5.3°, dm=7.3°). This direction differs significantly from that for little-weathered Lewisian at those two localities and also from directions for the late Mesoproterozoic Stoer Group. The remanence direction for the weathered rocks is, however, near the dip-corrected high-temperature remanence direction
(D=
122.3°,
I
=50.5°, α
95
=10.8°) obtained by us from the thermal step demagnetization of 39 sandstone specimens of the Applecross Formation in the Cape Wrath area. Furthermore, the direction for the weathered rocks agrees closely with other dip-corrected results for the Torridon Group, such as the detrital remanent magnetization (DRM) mean direction
(D=
148.3°,
I
=59.9°, α
95
=13.8°) for the Applecross Formation on Rum and that for the main outcrop of the Aultbea Formation (
D
=139.7°,
I
=52.6°, α
95
= 14.5°).

The concordance of palaeomagnetic results for the sediments and weathered rocks implies that the weathering profiles in the Cape Wrath area acquired their remanence penecontemporaneously with deposition of the Applecross and Aultbea formations. The palaeomagnetic results therefore argue strongly that the weathering profiles are palaeosols of Applecross age (
c.
980 Ma) that formed at a palaeolatitude of 38° and constitute the oldest known palaeosols in the British Isles—views that the weathering is substantially older or younger than Applecross deposition cannot be sustained. Our findings carry implications for Applecross palaeoclimate and source and strengthen the conclusion that atmospheric oxygen was a substantial fraction of its present abundance by early Neoproterozoic time.
The geology of Hong Kong
Authors: FLETCHER C. J. N.
Published: July 2007

The eight papers included in this thematic set were presented at a meeting on the geology of Hong Kong held at the University of Hong Kong on 22 January 1997. The meeting reviewed the accomplishments of the Hong Kong Geological Survey and its co-workers since it was founded fifteen years ago, and coincided with the publication of the final geological memoir of the current series that describes the 1:20 000-scale geological maps of Hong Kong. The meeting also formed part of the 20th Anniversary celebrations of the establishment of the Geotechnical Engi­neering Office of the Hong Kong Government. A total of 112 registrants from consultant companies, academic institutions, researchers from China, and several Government departments attended the meeting. In addition, 40 students from the newly established Department of Earth Sciences of Hong Kong University were present.

Hong Kong is one of the world’s major urban communities, with a population of over six million and in common with most of eastern Asia is expanding rapidly. However, development is hindered by the rugged terrain and steep-sided islands, and engineers are tackling some of the world’s largest and technically most challenging civil engineering projects. This meeting highlighted the need for systematic and accurate geological information, and the importance of understanding geological processes. It brought together geologists, geotechnical engineers and engineering geologists with the common objective to sustain the effective and safe development of Hong Kong.

The meeting was opened by the Secretary for Works, H. S. Kwong, who described the significance of the
The significance of primary volcanic fabrics and clay distribution in landslides in Hong Kong
Authors: KIRK P. A. , CAMPBELL S. D. G. , FLETCHER C. J. N. , MERRIMAN R. J.
Published: July 2007

Most rain-induced landslides on Hong Kong’s volcanic rocks are shallow and small-scale. However, two major landslides that occurred on Hong Kong Island in 1995 highlight relationships between primary volcanic foliations and kaolin accumulations that may have general significance in determining loci of larger failures. In the first case, a bedding-parallel shear zone was the locus for kaolin concentration in a shallowly dipping tuff. This formed a weak, planar, low-permeability layer which acted as the surface of rupture of a translational failure. In the second case, steeply inclined fabrics (eutaxitic foliations) and subparallel, closely spaced joints occurred within a zone of syn-volcanic folding and shearing. Deep weathering developed along the zone, with kaolin concentrations present mainly above the soil-rock interface. The irregular and variably concave to planar rupture surface was closely associated with kaolin-infilled relict joints towards the base of the soil profile. Kaolin distribution is largely associated with the weathering profile, and may have been both physically and chemically redistributed within it. Halloysite is more abundant than kaolinite in most clay samples at and near both rupture zones, and may have developed from kaolinite in response to strain. Detailed mapping of volcanic fabrics around the major landslides suggests that kaolinized bedding-parallel shear zones are uncommon, but that deep weathering zones associated with shearing and faulting are common, mappable features.
Regional tectonic setting of Hong Kong: implications of new gravity models
Authors: FLETCHER C. J. N. , CAMPBELL S. D. G. , CARRUTHERS R. M. , BUSBY J. P. , LAI K. W.
Published: July 2007

Hong Kong lies on the SE margin of the Cathaysia Block and straddles the NE-trending Lianhuashan Fault Zone, one of the dominant structural features of SE China. Isotope signatures of the Mesozoic granites have indicated that the zone overlies a major crustal discontinuity. The proposed gravity model of Hong Kong consists of a heterogeneous upper crust underlain by middle to lower crust composed of a felsic Archaean segment, approximately 25 km wide, flanked by more mafic Proterozoic crust. The southern boundary of the felsic segment dips steeply to the north, whereas the northern boundary is subvertical. Euler gravity anomalies define the fundamental faults in the upper crust, and many of these can be correlated with faults that have been mapped at surface. The middle to lower crustal discontinuities are considered to be associated with a major shear zone within the Cathaysia Block that has similar dimensions to transcratonic structures in other Precambrian shield areas. The geological development of Hong Kong and neighbouring SE China has largely been controlled by periodic reactivation of this deep crustal shear zone since the late Neoproterozoic.
Quaternary sea-level change on the continental shelf of Hong Kong
Authors: FYFE J. A. , SELBY I. C. , SHAW R. , JAMES J. W. C. , EVANS C. D. R.
Published: July 2007

High-resolution seismic reflection profiles and continuously sampled boreholes have been used to investigate the Quaternary offshore sequence that overlies weathered bedrock in Hong Kong. Four formations have been recognized: the lowermost Chek Lap Kok Formation comprises dominantly fluvial sand and mud, much of which probably accumulated prior to 130 000 years BP, during sea-level lowstands of Middle Pleistocene (Oxygen Isotope Stage 6) age and earlier. The upper surface of the Chek Lap Kok Formation is defined by a fluvial/tidal entrenchment surface that is overlain by transgressive, fine-grained, marine sediments of the Sham Wat Formation. These were deposited during the Eemian interglacial (Stage 5c) at a time when sea level was similar to that of today. In southeastern Hong Kong waters, a late Weichselian (Stage 5c) ravinement surface is overlain by submerged shoreface sands, succeeded by a back-stepping wedge of marine sediments that comprise the Waglan Formation. Fluvial/tidal entrenchment of the top of this formation occurred prior to the deposition of the uppermost dominantly marine Hang Hau Formation, deposited during the Late Weichselian to Holocene transgression, the main phase of which is represented by a ravinement surface.
Structural control and tectonic setting of Mesozoic volcanism in Hong Kong
Authors: CAMPBELL S. D. G. , SEWELL R. J.
Published: July 2007

Middle Jurassic to Lower Cretaceous silicic volcanic rocks and granitoid plutons in Hong Kong form part of the broad, NE-trending Yanshanian tectonomagmatic belt, that extends through SE China. Pyroclastic deposits in Hong Kong are typically proximal and infill linear flared vents and ellipsoidal calderas. These pass down through elongate rift-like conduits into extensive multiple fault- and shear zone-hosted ('sheeted') dyke complexes and granitoid plutons. Dykes also emphasize the limits of calderas. The spatial distribution and geometry of the vents, calderas, dykes and plutons are structurally controlled during each of four temporally well-constrained periods of petrogenetically related volcanism and plutonism. E- and ENE-trending axes of extension, and transtension were dominant. NW-trending faults increased in importance with time, and their intersections with ENE-trending faults influenced the loci of volcanic centres. Nesting of the calderas confirms persistent reactivation of some faults. The loci of magmatism migrated over 25 Ma from NW to SE. Zones of silicic crust created during these magmatic episodes have a broadly tripartite crustal 'stratigraphy' (pluton, dyke, volcanic) reminiscent in very general terms of ophiolites. The zones were created during periods of unusually rapid extension, as the continental margin of SE China changed from an active margin, dominated by subduction, to a back-arc regime, and dextral strike-slip along ENE-trending faults gave way to sinistral strike-slip.
Geochemistry of coeval Mesozoic plutonic and volcanic suites in Hong Kong
Authors: SEWELL R. J. , CAMPBELL S. D. G.
Published: July 2007

Middle Jurassic to Lower Cretaceous intermediate to silicic plutonic and volcanic rocks of Hong Kong record a transition from calc-alkaline, through high-K calc-alkaline, to transitional shoshonitic compositions with time. Close spatial and temporal associations among comagmatic volcanic-plutonic pairs indicate that magmatism occurred in discrete episodes, mostly of less than one million years duration. Synchronous high-K calc-alkaline and transitional shoshonitic magmatic activity during at least one pulse suggests a relatively rapid transition from a subduction-related to an extension-related tectonic setting.

Geochemical signatures indicate that the magmatic suites have a mantle origin with a decreasing crustal contribution from two distinct sources. The earliest mantle-derived magmas interacted strongly with a dominantly Archaean crustal protolith. Younger magmas show evidence for interaction with a dominantly Proterozoic crustal protolith. The strongest mantle influence is shown by magmas which were intruded along the boundary between the two dominant crustal sources. This interface marks a deep crustal discontinuity which promoted the passage of magmas to the surface.
U-Pb dating of Mesozoic igneous rocks from Hong Kong
Authors: DAVIS D. W. , SEWELL R. J. , CAMPBELL S. D. G.
Published: July 2007

Twenty-two new zircon and monazite U-Pb ages have been obtained for Mesozoic plutonic and volcanic rocks of Hong Kong. These have revealed the existence of four distinct periods of Mid-Jurassic to Lower Cretaceous volcano-plutonism: 164.6 ±0.2 to 159.3 ±0.3 Ma, 146.6 ±0.2 to 146.2 ±0.2 Ma, 143.7 ±0.3 to 142.5 ±0.3 Ma, and 140.9 ±0.2 to 140.4 ±0.2 Ma. A concordant monazite age of 236.3 ± 0.8 Ma has also been obtained from one intrusive body representing the first known occurrence of a Mid-Triassic granitoid in the Territory. Among these rocks, discordant U-Pb data projected to the concordia curve have given a broad range of inheritance ages from early Phanerozoic to late Archaean. A xenocrystic zircon from one sample has yielded a concordant age of 1872 ±3 Ma. The new U-Pb ages have refined the results of recent Rb-Sr whole-rock age dating of the granitoid rocks and have considerably improved correlation between intrusive and extrusive units. The occurrence of inherited components in many of the analysed rocks indicates that they were derived from, or erupted through, older crust containing a wide variety of age components, either as primary igneous or detrital material.