bluuebunny/crossref_metadata_2025 huggingface dataset:
Petrochemistry, U–Pb (zircon) age, and palaeotectonic setting of the Lampang volcanic belt, northern Thailand
Authors: BARR S. M. , MACDONALD A. S. , DUNNING G. R. , OUNCHANUM P. , YAOWANOIYOTHIN W.
Published: June 2010

Two NE‐trending belts of mainly subaerial dacitic to rhyolitic flows and tuffs occur in the area between the towns of Lampang and Denchai in northern Thailand. In the western belt (Doi Ton), the rocks have been pervasively altered to quartz keratophyre; rocks in the eastern belt (Doi Luang) are generally less altered. Mobile chemical components such as Na
2
O and K
2
O show wide variation, particularly in samples from the Doi Ton belt. However, low Zr/TiO
2
ratios and low Nb and Ta contents support an origin at a convergent plate margin. A positive epsilon Nd value of +4.9 for rhyolite from the Doi Luang belt supports derivation from a primitive crustal source. A rhyolite sample from the Doi Luang belt yielded a U–Pb zircon age of 240 ± 1 Ma (early Mid‐Triassic).

The Doi Ton and Doi Luang belts are part of the Lampang volcanic belt, which can be traced to the north into the Lincang–Jinghong volcanic belt in southern China. Comparison with published petrological data from the Lincang–Jinghong belt shows strong similarity, including the widespread development of keratophyric mineralogy and chemistry. The Lampang–Lincang–Jinghong belt formed at an early Mid‐Triassic convergent plate margin, and is similar in age and tectonic setting to the more mafic Phetchabun volcanic belt on the east side of the Nan River suture zone. These data constrain the timing of final amalgamation between the Indochina and Shan‐Thai terranes to Mid‐Triassic or younger.
Post‐magmatic hydrothermal circulation and the origin of base metal mineralization, Cornwall, UK
Authors: GLEESON S. A. , WILKINSON J. J. , SHAW H. F. , HERRINGTON R. J.
Published: June 2010

A detailed fluid‐inclusion study of post‐Variscan quartz ± carbonate ± sulphide ± anhydrite ± fluorite veins hosted by Palaeozoic basement (Porthleven, Menheniot, Cornwall) and Permo‐Triassic sediments (Western Approaches Basin) has identified two broad fluid types. A high salinity (20–27 wt% NaCl), low temperature (80–150°C) brine is present in base metal mineralized veins hosted by Palaeozoic rocks onshore and in sulphate‐bearing veins within the Permo‐Triassic offshore succession. Microthermometric data indicate that saline fluids found in the Permo‐Triassic basinal sequences have similar compositions to the base metal mineralizing fluids and confirms that such basins are likely sources for the mineralizing fluids. A second, hotter (200°C) more dilute (0–5 wt%) fluid has been identified in fault‐hosted east–west‐trending veins in the Porthleven area. It is likely that the temperatures of both the dilute and saline fluids have been affected by the local high heat producing Cornubian granite batholith. There is also limited evidence for fluid mixing of these two fluids which may have been responsible for base metal precipitation.
Weathering and abrasion of Fe–Ti oxides during rock degradation and fluvial transport: implications for sedimentary provenance studies
Authors: MARTINEZ‐MONASTERIO E. , STEPHENS W. E. , WALDEN J. , DUCK R. W.
Published: June 2010

Physical and chemical degradation of individual grains of titanomagnetite and ilmenite during rock weathering and fluvial transport processes in the River Eden catchment, Eastern Scotland, have been traced using backscattered electron images and electron probe microanalysis. Magnetic characteristics have been used to detect differences in magnetic mineralogy concentration, paragenesis and grain size between rock samples showing different stages of weathering, and between different sources and sediment samples. Results have shown higher physical and chemical durability of ilmenite during this segment of the geological cycle than titanomagnetite, which is rapidly altered. During progressive subaerial weathering of a dolerite, the increasingly intensive and extensive oxidation and development of internal fractures in titanomagnetite are observed. However, under subaqueous conditions, titanomagnetite was found to be progressively replaced by titanite and Ti‐impoverished magnetite due to hydrocirculation. Neither the total physical nor the total compositional degradation of titanomagnetite is achieved under rock weathering and fluvial transport processes. Thus, the importance of titanomagnetite as a provenance indicator remains despite its degradation during the geological processes studied in the River Eden catchment.
Discriminating between tectonic and sedimentary burial in a foredeep succession, Northern Apennines
Authors: ZATTIN MASSIMILIANO , LANDUZZI ALBERTO , PICOTTI VINCENZO , ZUFFA GIAN GASPARE
Published: June 2010

An extensive apatite fission‐track survey has been carried out on the Marnoso‐arenacea foredeep succession in the Northern Apennines. The data show a general decrease of the maximum paleotemperature undergone by the sediments toward the foreland areas. The maximum burial calculated by using a geothermal gradient of 20°C km
−1
spans from more than 5 km to less than 2.5 km and indicates that the previously assessed total thickness of the Marnoso‐arenacea succession is not enough to justify the determined values. It is concluded that a now eroded Ligurian wedge, up to 5 km thick, was present on top of the Marnoso‐arenacea sediments.
Controls on kaolinite and dickite distribution, Highland Boundary Fault Zone, Scotland and Northern Ireland
Authors: PARNELL JOHN , BARON MARTIN , BOYCE ADRIAN
Published: June 2010

Kaolinite and dickite occur widely in central Scotland and Northern Ireland. Stable hydrogen and oxygen isotope compositions of both minerals are similar, suggesting that the formation of kaolinite occurred first at temperatures of <50°C from meteoric water, probably as a result of alteration of Lower Carboniferous volcanic rocks, and that dickitization followed locally as a result of local heating that accompanied the intrusion of dykes during Late Carboniferous–Permian times. This mechanism of dickite formation explains why the higher‐temperature polytype dickite occurs in a region from the Firth of Clyde to Perthshire, in association with dyke swarms, whilst kaolinite occurs elsewhere. The original kaolinite precipitation was focused along the high permeability fault zone now marked by the Highland Boundary Fault Zone and its presumed trace in Northern Ireland.
Enhanced productivity on the Iberian margin during glacial/interglacial transitions revealed by barium and diatoms
Authors: THOMSON J. , NIXON S. , SUMMERHAYES C. P. , ROHLING E. J. , SCHÖNFELD J. , ZAHN R. , GROOTES P. , ABRANTES F. , GASPAR L. , VAQUEIRO S.
Published: June 2010

The Portuguese margin is at a critical location for studies of the ocean’s behaviour during glacial/interglacial climatic changes, and the rapid accumulation rates of the sediments enable high‐resolution palaeoclimatic investigation. The sedimentary record of the past 350 ka has been investigated in a 35 m long core from 3.5 km water depth on the slope at 40°N by geochemical, isotopic and micropalaeontological techniques. The CaCO
3
content of this core as a function of time contains significant Milankovitch orbital frequencies of 18.8, 23.7, 38.0 and 100.6 ka, but these are driven primarily by dilution by clay‐flux variations rather than by CaCO
3
productivity variations. The largest signals in the productivity indicators C
org
, Ba/Al and diatom abundance are all observed as simultaneous peaks at the oxygen isotope stage boundaries 10/9 and 6/5, with the signal magnitude in the order 10/9>6/5 for all three indicators. Smaller coincident signals in C
org
, Ba/Al but not diatoms are also observed at the oxygen isotope stage 2/1 boundary. Other less prominent peaks in the C
org
and Ba/Al profiles occur elsewhere, including Heinrich Event horizons, but these are not always simultaneous and none contain evidence of the dissolution‐prone diatom microfossils. The 10/9, 6/5 and 2/1 oxygen isotope stage transitions represent the three most extreme glacial/interglacial sea level rises in the past 350 ky, possibly in the same sequence of magnitude, when sea level rose rapidly by 120+m from glacial low stands to interglacial low stands to interglacial high stands. The productivity signals at these transitions are contained within <5 ka (including bioturbation).
NE Atlantic benthic foraminifera: modern distribution patterns and palaeoecological significance
Authors: AUSTIN W. E. N. , EVANS J. R.
Published: June 2010

Microfaunal evidence is presented from a region in the NE Atlantic Ocean characterized by well‐constrained and very uniform physiochemical water mass properties, but a significant gradient in surface ocean productivity. Notable changes in the species composition of benthic foraminiferal assemblages can be directly related to surface productivity and particulate organic matter supply to the deep ocean floor. Because of the labile nature of much organic matter as it reaches the sea floor, it is argued that benthic foraminifera, which exhibit a high preservation potential in most marine sediments, provide a better proxy for estimating past fluxes than bulk sediment organic carbon (OC) content. Three distinct assemblage groups are recognized: a
Cassidulina laevigata
group which is dominated by infaunal species and a relatively high sediment OC content; a
Rhizammina
spp. group which is also dominated by infaunal species; and an
Epistominella exigua
group dominated by epifaunal taxa and falling sediment OC content. Significant faunal assemblage changes appear to be independent of grain size.
Pre-ocean opening compression of the Northwestern Atlantic margin: evidence from eastern North Greenland
Authors: MANBY GEOFF , LYBERIS NIKOS
Published: June 2010

The deformation of the Wandel Sea Basin of eastern North Greenland and the West Spitsbergen Fold Belt are the result of Late Cretaceous–Palaeocene Greenland–Barents Sea/Svalbard convergence following the opening of the Labrador Sea–Baffin Bay opening. The Tertiary rocks of the Wandel Sea Basin are undeformed while the Late Palaeozoic–Mesozoic are weakly folded and thrust faulted. Thrust fault movements in North Greenland ceased before Mid-Palaeocene time when the dextral motion separating Greenland and Svalbard began. The shortening was orthogonal to the continental margin and a transpressional origin for the deformation of the Wandel Sea basin is not confirmed.
Isotopic evidence for anoxic pyrite oxidation and stimulation of bacterial sulphate reduction in marine sediments
Authors: BOTTRELL S. H. , PARKES R. J. , CRAGG B. A. , RAISWELL R.
Published: June 2010

Pore-water sulphate concentrations show marked increases at depths >50 m at ODP sites 888 and 890/889 from the Cascadia Margin accretionary wedge. In the uppermost 10 m sulphate concentrations decrease with depth and sulphate δ
34
S and δ
18
O increase as sulphate is removed by bacterial sulphate reduction. Isotopic data show that sulphate formed below 50 m results from oxidation of early diagenetic pyrite and that oxygen in the sulphate molecules is derived from pore water. Fe
3+
in the sediment is the probable oxidizing agent. The increased sulphate concentrations stimulate bacterial sulphate reduction at depths of 70–250 m and are thus important in sustaining deep bacterial activity.
Ammonite faunal turnover tracing sea-level changes during the Jurassic (Betic Cordillera, southern Spain)
Authors: O’DOGHERTY L. , SANDOVAL J. , VERA J. A.
Published: June 2010

Ammonite faunal turnover has been used to trace changes in sea level during the Jurassic in the Betic Cordillera, southern Spain (i.e. westernmost Tethys). Major turnovers recorded in the Jurassic succession are interpreted as extinction phenomena, and as appearance, diversification and radiation bioevents of the various ammonite associations. They are explained as being due to falls and rises in sea level, respectively. The ten most abrupt diversification and radiation bioevents have been detected in the ammonite associations associated with pelagic Jurassic sedimentary rocks. All of these bioevents can be linked with sea-level rises, most coinciding with the eustatic increases of the same age expressed in the eustatic curves of Hallam and Haq
et al
. The relative sea-level falls, including eustatic ones coinciding with extinctions, are recorded as stratigraphic breaks and stratigraphic condensation phenomena in the Betic Jurassic succession. The seven most significant extinction events recognized in the Betic Jurassic are also largely attributable to eustatic falls. We conclude that the proposed faunal turnover curve is predominantly the expression of global changes in sea-level and it can be considered as a basis for plotting a Jurassic eustatic curve.
Evidence for Late Cretaceous (Late Turonian) climate cooling from oxygen-isotope variations and palaeobiogeographic changes in Western and Central Europe
Authors: VOIGT S. , WIESE F.
Published: June 2010

Trends of stable oxygen-isotope data through four European sections of Middle–Upper Turonian sediments show three phases of synchronous variations, each phase having a duration of about 250 ka. The isotopic variations are independent of local facies, sedimentary thickness and diagenetic history. Two positive δ
18
O shifts are associated with a southward spread of northern macrofaunas. This coincidence of geochemical and palaeontological data implies that the δ
18
O trends reflect a southward shift of cooler water masses. This southward extension of cooler waters was caused by changes in ocean circulation and was associated with a major regression in the early Late Turonian.
Mantle plume uplift in the sedimentary record: origin of kilometre-deep canyons within late Neoproterozoic successions, South Australia
Authors: WILLIAMS GEORGE E. , GOSTIN VICTOR A.
Published: June 2010

In South Australia, canyons 200–250 km long are incised to depths of
c
. 1.5 km in late Neoproterozoic (after
c
. 590 Ma) marine deposits of the Adelaide fold belt and canyons 90 km long and 700 m deep occur in correlative marine strata of the Officer Basin 1000 km to the NW. In the Adelaide fold belt, the isotopic signature of limestone veneering canyon walls, canyon sinuosity and sedimentary structures in canyon fill suggest that the canyons were cut subaerially and filled by shallow-water marine deposits during coastal onlap. Eustacy cannot account for the kilometre-scale change in sea level required for subaerial canyon erosion and chemostratigraphy and the lack of evaporites at that stratigraphic level in southern Australia argue against a Messinian-style drawdown. In each region, uplift and crustal extension preceding or coeval with canyon incision are indicated by a regional unconformity, turbidite or mass-flow deposition, and extensional faults. These features and canyon incision may be explained by regional uplift above a rising mantle plume over a distance of >1000 km in southern Australia. Flood basalt volcanism in the Officer Basin tentatively dated at 563±40 Ma may have followed this uplift. Mantle plume uplift is expressed in the sedimentary record by emergent trends in facies, regional thinning, regional unconformities, turbidites, gravity slides, normal faults and incised canyons and palaeovalleys.
Land–offshore tectonic links in western Norway and the northern North Sea
Authors: SMETHURST M. A.
Published: June 2010

Aeromagnetic and marine gravity data sets for the northern North Sea and western Norway have been interpreted in terms of land to offshore tectonic links. The data allow identification of linking-structures both in crystalline basement and overlying sedimentary rocks and consequently facilitate a more comprehensive interpretation of regional structural features and trends. With the help of bathymetric data in the inshore region, major fault structures can be traced between western Norway and the offshore region west of the Øygarden Fault Zone. In this way spatial and chronological links have been established between tectonic events recognized on land and the development of the North Sea Basin. An interpretation of basement geology is proposed for the region between western Norway and the Uer Terrace. This is complemented with a depth to top crystalline basement map covering the North Sea Basin between the Uer terrace and the East Shetland Basin. Two regional NW–SE lineaments were recognized offshore western Norway and given the names Marflo Lineament and Troll Lineament. The Marflo Lineament is interpreted to be a Caledonian or older zone of weakness that accommodated development of a 20–30 km offset in the Jurassic Viking Graben axis. The lineament can be traced into the North Atlantic where it parallels oceanic fracture zones and transform faults. The Troll Lineament relates to a deep geological discontinuity crossing the Uer and Lomre Terraces. A grouping of earthquake epicentres along part of the lineament suggests that the discontinuity is tectonically active.
A Miocene collisional belt in north Borneo: uplift mechanism and isostatic adjustment quantified by thermochronology
Authors: HUTCHISON CHARLES S. , BERGMAN STEVEN C. , SWAUGER DAVID A. , GRAVES JOHN E.
Published: June 2010

Subduction followed by underthrusting of continental lithosphere, driven by Oligocene–Early Miocene spreading in the South China Sea marginal basin, account for the tectonic features of Sabah. Isostatic rebound then caused Late Miocene uplift of the Western Cordillera. The strata were buried under 4–8 km of overburden then rapidly exhumed and cooled at >10°C Ma
−1
. A rate of exhumation of 0.5–0.7 mm a
−1
is deduced from thermochronology. The same order of uplift in the Labuk Highlands has exposed metamorphic rocks of the epidote-glaucophane facies. Rapid erosion of the Western Cordillera supplied abundant clastic sediments to the Miocene–Pliocene Baram Delta oil-bearing basin and to the Eastern Lowlands and Sulu Sea.

The Eastern Lowlands were affected by Miocene rifting of the Sulu Sea marginal basin. In contrast to the Western Cordillera, the strata contain apatite crystals whose fission track ages pre-date the containing rocks, indicating burial by only about 2–3 km of overburden. The terrain has been isostatically stable. Some apatite and all zircon crystals, extracted from Tertiary strata, yield Cretaceous fission track provenance ages.
U–Pb and
40
Ar/
39
Ar constraints on the Fjord Region Detachment Zone: a long-lived extensional fault in the central East Greenland Caledonides
Authors: HARTZ E. H. , ANDRESEN A. , MARTIN M. W. , HODGES K. V.
Published: June 2010

The high strain zone separating infracrustal ortho- and paragneisses from supracrustal cover rocks in the East Greenland Caledonides has been interpreted variously as (1) a combined Grenvillian and Caledonian thrust, (2) a Vendian extensional shear zone reactivated as a Caledonian thrust, (3) a Caledonian extensional detachment reactivated as a late Caledonian thrust or (4) a late Caledonian extensional detachment. In this study we present new kinematic and geochronological data (U–Pb and
40
Ar/
39
Ar) from a well-studied segment of the high strain zone in Kejser Franz Joseph Fjord, demonstrating top-to-the-east, normal-sense displacement. Syntectonic peraluminous granites in the infrastructure are interpreted to have formed by decompressional anatexis (
c
. 430–425 Ma) and were later deformed to ultramylonites, cataclasites and psudotachylites along the high strain zone. Extension related fabrics overprint earlier and are synchronous with contractional top-to-the-NW thrust faults and associated structures. Muscovite records progressively younger
40
Ar/
39
Ar cooling ages (from 408 to 388 Ma) downward in the extensional footwall, whereas feldspar from the mylonites yield a closure age of 349 Ma. Foreland-directed shortening in the East Greenland Caledonides lasted until at least Early Devonian times, while orogenic extensional collapse initiated along the zone of high strain during the Late Silurian in an overall collisional setting. Upper crustal thinning continued well into the Devonian along increasingly more narrow and brittle extensional faults.
New approaches to assessing the risk of groundwater contamination by pesticides
Authors: WORRALL F. , WOOFF D. A. , SEHEULT A. H. , COOLEN F. P. A.
Published: June 2010

Because of the large range of circumstances (such as soil-type, climatic zone, and local agricultural practice) in which pesticides are applied, it is impossible to test fully the environmental fate of a new pesticide being considered for registration. Thus, risk assessors should make best use of modern techniques and all relevant information to make their assessments. This paper discusses the use of statistical methods which use pesticide chemical properties to predict environmental fate. Using US data, a logistic regression approach can be used to estimate the probability that a compound leaches to groundwater based on adsorption (
K
oc
) and degradation (
DT
50
) parameters. An advantage is that both properties are already required to be measured as part of the present pesticide registration process. For UK groundwater monitoring, precise pesticide soil properties are not measured. However, further methods using UK data also indicate that polluting and non-polluting compounds may be distinguished on the basis of these chemical properties. The techniques presented can be used in conjunction with pesticide usage statistics to inform the selection of priority pollutants, to enable monitoring programmes to become more focused, to assess the risk associated with new compounds, and to identify those at high risk of contaminating groundwater.
The geometry of drag zones adjacent to salt diapirs
Authors: ALSOP G. I. , BROWN J. P. , DAVISON I. , GIBLING M. R.
Published: June 2010

Drag zones are highly strained regions developed adjacent to the flanks of salt diapirs, and are produced when the sedimentary overburden is folded or rotated into steeply dipping attitudes sub-parallel to the diapiric walls. This case study focuses on a diapiric province on Cape Breton Island, Nova Scotia, where five Visean-age salt diapirs penetrate Upper Carboniferous (Namurian–Stephanian) conglomerates, sandstones, shales and coal seams. 2D marine seismic coverage extends over several diapirs thus allowing the drag zones studied onshore to be located relative to the adjacent diapir. The width of diapiric drag zones within the case studies varies from 70 m up to 500 m, with narrow drag zones reflecting the low mean competence of shales and siltstones which may have been shallowly buried and poorly lithified at the onset of diapirism. Broader drag zones are dissected by two sets of extensional fractures together with major faults, suggesting that the overburden was semi-lithified and displayed greater flexural rigidity. Overburden displaying high competency contrasts results in strain localization and partitioning, with pervasive granulation seams and minor faults developed in sandstones and bedding-parallel shears in coal and shale horizons. Drag zones are segmented by steeply outward-dipping faults associated with decametric, asymmetric drag profiles. These faults facilitate the upward movement of material and effectively expand the diapiric process into adjacent overburden via a newly termed process of
lateral diapiric accretion.
Pre-emplacement structural history recorded by mantle peridotites: an example from the Lizard Complex, SW England
Authors: COOK C. A. , HOLDSWORTH R. E. , STYLES M. T. , PEARCE J. A.
Published: June 2010

The Lizard Complex of SW England includes thrusted units of peridotites that were initially exhumed from upper mantle (
c.
 52 km) to lower crustal (
c.
 24 km) depths during a period of Early Devonian rifting and break-up. This basin closed during the Late Devonian, when the Lizard Complex was thrust towards the NNW along a major low-angle detachment and became incorporated within a series of Variscan thrust nappes. In the peridotites, a primary high-
T
and high-
P
spinel lherzolite mineral assemblage (
c
. 1119°C and
c.
 15.7 kbar) was progressively exhumed and re-equilibrated to conditions of lower
T
and
P
(
c
. 991–1010°C and
c
. 7.5 kbar) during the development of kilometre-scale mylonitic plagioclase- and amphibole-bearing mantle shear zones. These fabrics demonstrably pre-date emplacement related structures. The new structural and geochemical evidence from the peridotites also strongly suggests that the Lizard Complex formed in a rifted, non-volcanic continental margin setting, possibly in a pull-apart basin, rather than at a mid-ocean ridge. The
P–T
and textural evolution of the Lizard peridotites supports growing evidence that shear zones in the lithospheric upper mantle may to some extent accommodate large-scale displacements associated with crustal extension and continental breakup.
Contrasting tectonic history of the arc–continent suture in the Southern and Middle Urals: implications for the evolution of the orogen
Authors: AYARZA P. , BROWN D. , ALVAREZ-MARRÓN J. , JUHLIN C.
Published: June 2010

The Main Uralian Fault has been considered the original arc–continent suture for 2000 km along the Uralide orogen. The symmetry of the tectonic units across it suggested a consistent east-dipping polarity for the palaeosubduction zone, which, together with its topographic and aeromagnetic signature, supported the idea of a single suture. However, several characteristics vary at different latitudes. In the Middle Urals, it is a strike-slip fault zone with moderately deformed and metamorphosed volcanic arc fragments in its hanging wall, and low-grade metamorphic rocks of the East European Craton in its footwall. Here, it has a prominent NNW-trending magnetic signature which cross-cuts north-trending anomalies in its hanging wall, and a pronounced reflection seismic signature that can be traced to the top of the middle crust at
c.
 5 s. TWT. In the Southern Urals, it is a serpentinite mélange zone of ambiguous kinematics, with a weakly deformed and metamorphosed volcanic arc in its hanging wall, and moderately metamorphosed to high pressure rocks of the East European Craton in its footwall. In this part of the orogen, it has a weak reflection seismic character, and a magnetic signature that parallels that of its hanging wall. On the basis of an integrated analysis of these different data sets, we suggest that the Main Uralian Fault, as it is currently defined, is not a single entity, but rather the original arc–continent suture in the south, and the western strand of a strike-slip fault system that reworked the original suture in the Middle Urals.
Tracking arc–continent collision subduction zone processes from high-pressure rocks in the southern Urals
Authors: BROWN D. , HETZEL R. , SCARROW J. H.
Published: June 2010

Subduction-related high-pressure metamorphic rocks in the southern Urals confirm material flux was active within the subduction zone. Suprasubduction zone ophiolitic material was tectonically eroded in an intraoceanic setting, metamorphosed under mantle conditions and exhumed. With the entrance of the East European Craton into the subduction zone, the upper continental crust was removed at a shallow level, whereas middle crustal material was subducted to mantle depths, metamorphosed under eclogite facies conditions and interacted with the mantle wedge. Eclogite-bearing rocks were exhumed to an upper mantle level and juxtaposed against material that was tectonically eroded from the fore-arc region of the upper plate.
Evidence of the proto-Iceland plume in northwestern Ireland at 42 Ma from helium isotopes
Authors: KIRSTEIN LINDA A. , TIMMERMAN MARTIN J.
Published: June 2010

Combined K–Ar and Ar–Ar dating of a xenolith-bearing alkaline dyke, previously considered to be of late Palaeozoic age, suggest a mid-Eocene age of
c.
 43 Ma, indicating that it is part of extensive rift-related Tertiary intrusive activity. High
3
He/
4
He ratios of 11–16
R
a
, potentially up to 23
R
a
(
R
a
=atmospheric ratio of 1.39×10
−6
) have been measured from mantle xenoliths in the dyke and are consistent with previous determinations of the helium isotope composition of Tertiary lavas in Greenland and Scotland linking the magmatism with the proto-Iceland mantle plume.
Equilibrium profile development in graded deep-water slopes: Eocene, Eastern Turkey
Authors: CRONIN BRYAN T. , HARTLEY ADRIAN J. , CELIK HASAN , HURST ANDREW , TÜRKMEN IBRAHIM , KEREY ERDAL
Published: June 2010

Recently published models for deep marine slopes provide a framework for understanding the sedimentary architecture and geometries of major correlative surfaces in this environment. These models use concepts which include: (i) the development of erosional and unconformable onlapping relationships in a slope-to-basin setting by processes other than changes in relative sea-level (e.g. earthquake induced gravity flows), (ii) the definition of genetic facies associations and (iii) the development of base-of-slope systems by repeated mass-wasting in order to establish an equilibrium slope profile. These models are based primarily on seismic data from present-day slopes or numerical simulation, and have not been tested in the field. An example from Turkey of a progradational Eocene basin-to-slope transition is presented to test these models. We found that most mass-wasting occurs at the top and not base of the slope, that this is likely to be earthquake-induced rather than related to changes in relative sea-level, and that seafloor topography continues to control sand transportation pathways and mass-wasting throughout slope apron deposition.
Impact of headwater river capture on alluvial system development: an example from the Plio-Pleistocene of the Sorbas Basin, SE Spain
Authors: MATHER ANNE E.
Published: June 2010

The Plio-Pleistocene sedimentary rocks of the Sorbas Basin, SE Spain are used to reconstruct the palaeogeography, palaeoclimate and active tectonics operative in the Late Pliocene–Early Pleistocene. The deposits are generated from two distinct source areas. These are (1) relatively larger catchments developed across a structural lineament situated in the foothills of the Sierra Alhamilla and (2) a more basinal, smaller catchment developed to the north of the structural lineament. The alluvial systems show evidence for sheet flooding, channelized flow, and overbank sedimentation in distal and marginal areas and are interpreted as fluvial distributary systems. The deposits were subjected to syn-sedimentary folding which exerted a strong control on the general topography at the time of alluvial system development. The balance between the accommodation space created by the tectonics operative over the Plio-Pleistocene, coupled with the sediment discharge, determined the alluvial system morphology and sedimentological architecture. The eventual cessation of deposition from the larger catchments is explained by their capture by an aggressive external drainage developing south of the structural lineament. The switching off of sediment supply from the larger catchments, coupled with high subsidence rates in the sediment dispersal area enabled the smaller alluvial system, still connected to its source area north of the lineament, to expand. Eventually the remaining catchment areas were also reduced by continued river capture. The study emphasizes the significance of river capture in re-routing both sediment and water discharge
between
sedimentary basins (the Sorbas Basin lost 15% of its original sediment and water budget to the Lucainena fan delta and associated coastal system of the Carboneras Basin to the south) and its subsequent effect on the pirated area (reduction in rates and changes in style of deposition). These latter factors outweighed the direct impact of tectonics and climate on the later development of the studied alluvial systems. The study emphasizes that to maximize the effects of sediment re-routing on actively aggrading alluvial systems (in the sedimentary basins) the positioning of the capture point is crucial and is most effective where (1) the sediment supply areas (mountain catchments) are pirated closest to their outlet (mountain front) into the receiving sedimentary basin and (2) the pirating drainages are external to the sedimentary basin.
Evidence for high-frequency cyclic fault activity from high-resolution seismic reflection survey, Rukwa Rift, Tanzania
Authors: MORLEY C. K. , VANHAUWAERT P. , DE BATIST M.
Published: June 2010

A high-resolution seismic survey of the Rukwa Rift has imaged the upper 300 m of the Pliocene–Holocene section. The sediments are characterized by aggradational deposition in shallow lacustrine conditions that episodically dried out. Overall the reflection package expands northeastwards towards the Lupa Fault (half-graben bounding fault). Isopach maps for nine intervals (6 m to 65 m thick) show four periods of marked expansion of the section towards the Lupa Fault, interpreted to represent times of fault activity or infilling of fault-created topography during the early stage of fault quiescence. There are three periods of little or much reduced expansion interpreted to represent infilling of the accommodation space between the lake floor and the lake surface during periods of fault inactivity. Cyclicity of such high frequency has not been widely reported for faults which penetrate the crust. The periods of activity show remarkably similar displacement patterns with no lateral migration of the main depocentre, implying that seismic and aseismic slip has persistently clustered in the same parts of the fault. Identification of high-frequency fault cyclicity has implications for sequence stratigraphy in tectonically active areas, since there is a tendency to assume faults do not have cyclic effects on the scale of tens of thousands of years.
Deformation mechanisms and rheology: why marble is weaker than quartzite
Authors: BRODIE K. H. , RUTTER E. H.
Published: June 2010

When deformed together in nature, calcite rocks invariably appear weaker and more ductile than quartz rocks. This can be reconciled with experimental flow data only by taking into account grain-size-sensitive (GSS) flow in calcite rocks, which is predicted to dominate even at grain sizes on the order of 1mm at middle metamorphic grades. Using new experimental data that demonstrate the transition between intracrystalline plastic and GSS flow of quartz rocks, we predict that unnaturally small grain sizes at temperatures of 700°C or higher are required for GSS flow of quartz in nature. Thus natural flow of quartzite is expected to occur by intracrystalline plastic processes, even after recrystallization to a fine grain size.
Cyclical summit collapse events at Ascraeus Mons, Mars
Authors: SCOTT EVELYN D. , WILSON LIONEL
Published: June 2010

The sequential development of multiple summit calderas of shield volcanoes gives clues about how the spatial location of shallow magma chambers evolves with time and how the magma supply into these chambers evolves. We re-interpret the sequence in which caldera collapse events took place at the Martian shield volcano Ascraeus Mons and argue that the formation of the central caldera, usually accepted to be the most recent, was followed by two further collapse events. We also present structural evidence for an early, large central caldera and, therefore, also an early large magma reservoir. This challenges the current hypothesis for Ascraeus Mons that successive magma reservoirs have increased in size as this volcano matured and that a reservoir occupied a central location within the volcano only at the end of its active lifespan. We propose that there has been a cyclical oscillation in the site of shallow storage of magma at Ascraeus Mons between central and peripheral magma reservoirs. The earliest reservoir formed centrally, but magma was subsequently redirected into peripheral reservoirs, over which the peripheral calderas formed. Later, the central location was utilized again, only to be followed once more by a development of peripheral storage reservoirs. This alternating pattern implies substantial variations with position and time in both the magma supply rate from the Martian mantle and the distribution of stresses within the volcanic edifice.
Kinematic history of a reactivated oceanic suture: the Mamonia Complex Suture Zone, SW Cyprus
Authors: BAILEY W. R. , HOLDSWORTH R. E. , SWARBRICK R. E.
Published: June 2010

The Mamonia Complex Suture Zone in SW Cyprus marks an arcuate tectonic suture between an Upper Cretaceous, oceanic microplate of supra-subduction zone origin (Troodos Complex) and a deformed Triassic passive margin sequence (Mamonia Complex). Mapping of the serpentinite-filled fault zones that define the suture zone, combined with microstructural studies of its constituent fault rocks, has revealed evidence of three main tectonic events of Upper Cretaceous age: (1) high temperature (
c
. 600°C), transform-related, dextral strike-slip and localized metamorphism of Mamonia Complex units (
c
. 90–83 Ma); (2) retrograde hydration (<400°C) during dextral transtension associated with the rotation of the Troodos microplate and the shallow-level emplacement of serpentinite (
c
. 83–73 Ma); (3) regional contractional reactivation at low temperatures, which ceased by the latest Maastrichtian (
c
. 65 Ma). The present day structural geometries are interpreted as the result of Maastrichtian contractional reactivation of a pre-existing, steep and irregular structural architecture that formed during transtension. The resultant orientation of finite strain axes and thrust displacements display a radial distribution, documenting near fault normal contraction along the whole length of the arcuate suture zone. This pattern of displacements suggests a model whereby the Troodos microplate impinged on the Mamonia Complex during westerly- to southwesterly-directed plate motion, contractionally reactivating the mechanically weak suture zone.
The Caledonian Orogeny redefined
Authors: McKERROW W. S. , MAC NIOCAILL C. , DEWEY J. F.
Published: June 2010

Recent advances in our understanding of Palaeozoic tectonics, and in the precise dating of tectonic events require exact definitions of terminology. The Caledonian Orogeny is here redefined to include all the Cambrian, Ordovician, Silurian and Devonian tectonic events associated with the development and closure of those parts of the Iapetus Ocean, which were situated between Laurentia (to the NW) and Baltica and Avalonia (to the SE and east). We suggest that the term ‘Caledonian Orogeny’ be restricted in this geographic sense, but that (as in modern usage) it continues to encompass a series of tectonic, or orogenic, phases (related to arc–arc, arc–continent and continent–continent collisions as Iapetus was closing). Many of these phases have been named; these and many more unnamed events are defined as orogenic phases (local components) of the Caledonian Orogeny. Some of these phases were synchronous over long distances, whereas others were diachronous. The whole Caledonian Orogeny occupied a time interval of around 200 Ma. Thus the term Caledonian should not be used to indicate age.
Volatile phase fluxed anatexis of metasediments during late Caledonian ophiolite obduction: evidence from the Sogneskollen Granitic Complex, west Norway
Authors: SKJERLIE KJELL P. , PEDERSEN ROLF B. , WENNBERG OLE P. , DE LA ROSA JESÚS
Published: June 2010

In the west Norwegian Caledonides minor granitic sheets were intruded during obduction of the
c.
 443 Ma Solund–Stavfjord Ophiolite Complex. The Sogneskollen Granitic Complex is the largest intrusive complex and consists of several minor lenses and one larger lens of granodiorite. The Sogneskollen Granitic Complex samples generally have high Ba, Sr and Na
2
O, very low Y values (<7 ppm), negative ϵ

Nd
420 Ma

values (
c.
 −7 to −10.1) and
87
Sr/
86
Sr
420 Ma
ratios of 0.70437–0.70705. The REE patterns are strongly HREE depleted and La/Yb
n
varies from 0.3 to 36. Most samples display small positive Eu anomalies, but those that are most fractionated have small negative anomalies. The main part of the Sogneskollen Granitic Complex is a white composite granodiorite which is intruded by a suite of grey biotite-granite dykes. It is suggested that this, and other similar granitic sheets in the area, most probably formed by melting of sediments in the presence of a H
2
O-bearing volatile phase during obduction of the ophiolite. The quartzofeldspathic source sediments most probably contained detritus from long-term Rb-depleted lower continental crust and from an island arc. The sediments were deposited in large amounts in the marginal basin now represented by the Solund–Stavfjord Ophiolite Complex. During obduction the sediments were buried beneath the hot overriding Ophiolite Complex and the associated island-arc, and yielded granitic magmas during partial melting.
Late Devensian glaciotectonic deformation at St Bees, Cumbria: a critical wedge model
Authors: WILLIAMS G. D. , BRABHAM P. J. , EATON G. P. , HARRIS C.
Published: June 2010

Glaciotectonic deformation of the Late Devensian sediments exposed at St Bees, Cumbria is represented by minor extensional faults resulting from ice-sheet loading of the unconsolidated sediments accompanied by thrusting and folding. The highly deformed northern part of the section has numerous thrust faults associated with fold structures that verge predominantly to the SE, but with some NW-vergent (backthrust) structures. A high-resolution seismic reflection survey confirms that the thrust structures form a linked fault system that detaches at, or slightly above bed rock, which is here composed of Triassic, St Bees sandstones. In the less deformed southern part of the section, the seismic survey has imaged bedding with a southerly component of dip in the St Bees sandstone cut by steep north-dipping extensional faults which, to some extent, control rockhead topography. An integrated approach combining structural geology and high-resolution seismic reflection surveying has enabled the construction of a balanced cross-section which estimates a minimum of 115 m (22%) cumulative shortening due to glaciotectonic processes. Minor structures observed in the St Bees cliffs and larger structures interpreted from the seismic profile are compatible with a critical wedge model for deformation caused by an overlying thick ice wedge with a SE-dipping surface slope.
Sediment provenance and dispersal in a deep marine foreland basin: the Lower Carboniferous Culm Basin, Czech Republic
Authors: HARTLEY A. J. , OTAVA J.
Published: June 2010

The Lower Carboniferous Culm Basin of the Czech Republic represents the most easterly and southerly part of the European Variscan foreland basin system. The NNE–SSW-trending basin is exposed along the eastern flank of the Bohemian Massif. It contains up to 7.5 km of deep marine sediment deposited as an axial turbidite system sourced from south/southwest of the basin. Heavy mineral data and clast types indicate that for much of the Viséan, sediment was sourced from a predominantly low-grade metamorphic terrane and Viséan limestones. In the latest Viséan, a progressive change in source material is recorded by an increase in high-grade metamorphic detritus. Studies of Variscan nappe pile emplacement along the eastern flank of the Bohemian Massif allow an assessment of the relationship between basin development and nappe emplacement. Basin initiation coincided with underthrusting of high grade metamorphic (Moldanubian) nappes at 340 Ma. Sedimentation was synchronous with nappe emplacement throughout the Viséan which resulted in uplift and erosion of a low grade metamorphic terrane. Moldanubian nappes were exhumed at approximately 330 Ma when high grade metamorphic detritus entered the basin. Two phases of northward-directed sediment progradation are recognized. Sediment progradation is considered to be related to changes in drainage basin size and/or climatic fluctuations within the Variscan Orogen, since sediment is inferred to have been supplied to the basin axially rather than laterally and subsidence curves show no significant change in subsidence rates. In contrast to many models of foreland basin sediment distribution, filling of the Culm Basin was largely independent of tectonic activity adjacent to the basin margin and/or of subsidence rate changes. Sedimentation in the Culm Basin commenced 10–15 Ma earlier than the rest of the Variscan foreland, and records the first impact of the northwardly propagating Variscan Orogen in northern Europe.
Sedimentology of the Indus Group, Ladakh, northern India: implications for the timing of initiation of the palaeo-Indus River
Authors: SINCLAIR H. D. , JAFFEY N.
Published: June 2010

The upper reaches of the Indus River form a longitudinal network that drains a large portion of the western Himalaya. It plays an important role as a sediment routing system, feeding the Indus Delta and submarine fan, and has played a controlling role in the denudational history of the western Himalaya. Given the rivers long-term significance, its timing of initiation remains poorly constrained. The facies, palaeocurrents and provenance of the post-early Eocene Indus Group preserved along the upper reaches of the modern Indus reveal a history of fluvial/deltaic and deep-water sedimentation in an intermontane basin dominated by internal drainage. Hence, the Indus Group is not considered to represent the deposits of a palaeo-Indus River as previously thought. Illite crystallinity values and apatite fission track dating of the Indus Group suggest that the succession was buried to temperatures of 155–280°C, and that unroofing started in early Miocene times and proceeded at 0.1–0.4 mm a
−1
to the present. The youngest sedimentary rocks preserved along the Indus Basin are early Miocene in age from the tectonostratigraphically equivalent deposits around Kargil to the west of the study area. The transition from sediment accumulation to erosional unroofing in early Miocene times coincides with accelerated regional unroofing of the High Himalayas to the south, and the initiation of the Indus Delta/submarine fan to the west. Differential uplift between the northward thrusting of the Zanskar and Indus sedimentary succession against the undeformed Ladakh Batholith provides a mechanism for post-early Miocene initiation of a major longitudinal river. Hence, early Miocene times is believed to represent the earliest possible age of initiation of the palaeo-Indus river following this course.
A sequence stratigraphy of the Kimmeridgian and Bolonian stages (late Jurassic): Wessex–Weald Basin, southern England
Authors: TAYLOR STEVE P. , SELLWOOD BRUCE W. , GALLOIS RAMUES W. , CHAMBERS MARTIN H.
Published: June 2010

A sequence stratigraphic framework for the late Jurassic Kimmeridgian and Bolonian stages of the Wessex–Weald Basin, southern England is proposed, based on the integration of sedimentological, geophysical and geochemical data. The NERC-funded Rapid Global Geological Events (RGGE) boreholes of Swanworth Quarry 1 and 2, and Metherhills 1, are used as reference sections. Eleven complete depositional sequences and their component systems tracts are recognized within the Kimmeridge Clay Formation, bounded by 12 sequence boundaries (Km1–12). Seventy-four boreholes have been used in this study. During the Kimmeridgian, a major transgression, associated with tectonic movements, led to a marked change in basin geometry. Major deepening of the sea during the late Kimmeridgian (Eudoxus Zone) led to a change from unconformities of basinwide extent to those confined to the basin margins. The progressive deepening of the basin towards a highstand in the mid-Bolonian (Wheatleyensis to Pectinatus zones) was associated with a broad-scale change in sedimentary, faunal and geochemical characters. The ‘layer-cake’ basin architecture and thickening of the Kimmeridge Clay Formation towards the basin centre suggests a dominantly aggradational system. The partially enclosed nature of the Kimmeridgian and Bolonian seas generated basin dynamics more analogous to those of modern day meromictic lakes. Consequently, sequence stratigraphic approaches derived from continental shelf-margins are inappropriate in epicontinental basins of this type.