bluuebunny/crossref_metadata_2025_split huggingface dataset:
The diagenetic and economic significance of composite grains of monazite and hydrocarbon in Western Australian arenites
Authors: RASMUSSEN BIRGER , GLOVER J. E. 
Published: December 2007

Composite grains consisting of detrital monazite and solid hydrocarbon, ranging up to 0.5 mm in diameter, have been found in Phanerozoic sedimentary rocks in three Western Australian basins. The most common form is a monazite core surrounded by a hydrocarbon envelope. The envelopes, which have conchoidal fracture and radial cracks, apparently congealed when hydrocarbons were polymerized and crosslinked by irradiation from the monazite. Some composite bodies contain fractured monazite grains within solid hydrocarbon and a few consist of a microbreccia of hydrocarbon and disseminated monazite fragments. The breakup of the monazite was probably a diagenetic chemical process that began when crosslinked hydrocarbons within cracks and open cleavages swelled as they were infiltrated by fluid hydrocarbons of low molecular weight.

Five microprobe analyses of the monazite reveal the following ranges in percent composition: La
2
O
3
, 10.88–13.66; Ce
2
O
3
, 25.58–28.78; Pr
2
O
3
, 3.03–5.38; Nd
2
O
3
, 9.15–12.11; ThO
2
, 7.0–11.49; U
3
O
8
, 0–1.44. 2V
γ
extends from 12.5–15.5°.

In the northern Perth Basin, the composite bodies, which contain cores of monazite derived from local gneissic basement rocks, formed after the growth of siderite cement but before extensive silicification. In the central Perth Basin, the composite bodies seem to have formed after the growth of kaolinite and before silicification. Textures associated with the bodies allow them to be slotted into the diagenetic sequence and they therefore show when the oil was present. Analysis of the bodies has indicated a contribution of oil from the Lower Triassic Kockatea Shale, but some may have grown from more than one generation of petroleum.
Given the ubiquity of detrital monazite, similar bodies are likely to be useful diagenetic and economic indicators elsewhere.
A multiple fluid history recorded in Alpine ophiolites
Authors: FRÜH-GREEN GRETCHEN L. , WEISSERT HELMUT , BERNOULLI DANIEL 
Published: December 2007

Petrographic and cathode luminescence studies of Alpine ophicalcites are combined with stable isotope data of pelagic sediments and associated ophiolite relicts, to document multiple phases of fluid-rock interaction related to sea-floor processes and Alpine orogeny. Internal sediments and primary carbonate microstructures in ophicalcites provide evidence for early sea-floor fragmentation, cementation and fluid activity in the Jurassic Tethys. Ca-carbonate cementation is comparable to cementation in modern transform setting analogues, where alkaline and Ca-enriched fluids are associated with serpentinites. Local mineralization and isotopic compositions of serpentine in ophicalcites are interpreted as signs of hydrothermal activity at temperatures of 100–150 °C.
Differences in the degree of oxygen isotope re-equilibration reflect differences in fluid/rock interaction during Alpine accretionary tectonics and continent-continent collision. Regional-scale homogenization of oxygen isotopes in carbonates and cherts indicate the presence of pervasive metamorphic fluids in the pelagic sediments during early Alpine recrystallization. In contrast, a lack of oxygen isotope re-equilibration in serpentine may reflect lower permeabilities and more limited fluid flow in serpentinites during Alpine metamorphism. Cathode luminescence and preliminary oxygen isotope data of late vein-forming phases suggest that late metamorphic fluids were channelled along discrete brittle fractures in a closed, rock-dominated system.
Geodynamic evolution of the northern and central Andes during early to middle Mesozoic times: a Tethyan model
Authors: JAILLARD ETIENNE , SOLER PIERRE , CARLIER GABRIEL , MOURIER THOMAS 
Published: December 2007

The early to middle Mesozoic sedimentary and magmatic history of the northern and central Andes (i.e. the NNE-trending Colombian-Ecuadorian segment, and the NW-trending Peruvian segment) exhibits a spatially contrasted evolution involving several successive tectonic and geodynamic settings.
The late Triassic to late Liassic period began with a widespread marine transgression. From the latest Triassic, the Colombian marine shelf was progressively destroyed by southward propagating extensional tectonic activity but marine sedimentation continued in Peru. During this time, no significant magmatic activity is recorded except in the emerging Colombian area. This period is interpreted as the result of rifting of a Tethyan oceanic arm which separated the Colombian and palaeo-Mexican margins.
From latest Liassic, an important calc-alkaline magmatic arc developed along the emergent Colombian segment. Further south, the north-Peruvian shelf probably emerged, but marine sedimentation continued in southern Peru. During middle and early Late Jurassic times, the Colombian segment was characterized by important magmatic activity and by coarse clastic continental sedimentation. Along the Peruvian segment, a turbiditic trough, emergent areas, and continental basins were created, and the scarcity of calc-alkaline magmatism suggests that only very local subduction took place. This period is regarded as one of the southeastward subduction beneath the Colombian segment, and of Tethyan oceanic crust originating in the newly formed ‘Colombian’ oceanic arm. This pattern would have induced a chiefly left-lateral transform motion along the Peruvian segment.
By Kimmeridgian-Tithonian times, the palaeogeographic framework had drastically changed. Along the Colombian segment, magmatic activity ceased, and continental accretions occurred along dextral strike-slip sutures. In Peru, tectonic activity was recorded by the creation of a new turbiditic trough and by the resumption of detrital sedimentation. In the coastal area, arc-related volcanism indicated that subduction took place beneath this segment. This geodynamic change is interpreted as the result of a sharp decrease in the spreading activity of the Tethyan ridges and replacement by Pacific spreading centres inducing a roughly northeastward convergence direction.
Exhumed lower crust in NW Ireland, and a model for crustal conductivity
Authors: SANDERS I. S. 
Published: December 2007

Granulite-facies gneisses within the Ox Mountains inlier, NW Ireland, are interpreted as an exhumed segment of sub-Dalradian lower crust, formed at 605 ± 37 Ma and later wedged upwards by crustal imbrication along the N-dipping Highland Boundary Fault-Clew Bay terrane boundary. A lower crustal provenance for the gneisses is suggested by evidence for eclogite decompression and for the later replacement of sillimanite by kyanite in response to slow cooling at depth.
Granulite-facies rocks are believed to be present throughout much of the lower continental crust. Granulites are electrically resistant in contrast to the lower crust, which is usually electrically conducting. This paradox may be resolved by inferring that the granulite-facies rocks form dry, kilometre-scale lenses (mega-augen) wrapped around by anastomosing, retrograded, brine-soaked, electrically-conducting shear zones.
Retrogressive hydration is believed (a) to seal the margins of the dry mega-augen with expanded reaction products, and (b) to concentrate the residual brine. Amphibolite-facies rocks associated with the lower crustal shear zones (above about 350°C) would equilibrate with strong, unsaturated brine and become electrically conducting. In the upper crust, similar rocks would concentrate the brine to the point of saturation, whereupon halite would precipitate, all water be consumed, and the rock would become an insulator.
Tethyan ferromanganese oxide deposits from Jurassic rocks in Hungary
Authors: CRONAN D. S. , GALÁCZ A. , MINDSZENTY A. , MOORBY S. A. , POLGARI M. 
Published: December 2007

Fossil manganese nodules and encrustations from ‘seamount’ and ‘basin’ localities in the Transdanubian Central Mountains of Hungary are lithologically, mineralogically and chemically similar to some modern marine ferromanganese oxide deposits, and show no evidence of postdepositional changes other than cementation. Five groups of deposits were encountered: Fe/Mn nodules, encrusted shells, pavements, stains, and Fe oxide encrusted intraclasts, the first three of which are specific to the 'seamount' environment and the last to the ‘basins’.
Optical and electron microprobe investigation of the samples shows them to exhibit many similarities with modern ferromanganese oxide deposits, and that many of the nodules are surrounded by a halo of dispersed ferromanganese oxides, strongly suggesting that they continued to accrete metals through the pore waters of unlithified sediments for a period after burial. By contrast, pavements which appear to have grown on hardgrounds at the sea floor show little or no evidence of derivation of metals from underlying sediments.
Geochemical investigations on the deposits show the ‘seamount’ varieties to be closer in composition to most modern nodules and crusts than the ‘basin’ varieties, and that the latter are essentially manganese and trace-element-poor ferruginous deposits. Nevertheless, all can be more or less compositionally equated with modern ferromanganese oxide deposits forming in marginal Atlantic environments, which would be in accord with the proposed depositional environment of the Transdanubian Central Mountains based on other evidence
Chalk porosity and Tertiary uplift, Western Approaches Trough, SW UK and NW French continental shelves
Authors: HILLIS R. R. 
Published: December 2007

Porosities have been derived from sonic logs for the Cenomanian–Maastrichtian Chalk of 22 hydrocarbon exploration wells in the Western Approaches Trough. Although the burial depth of the Chalk studied ranges from 40–1500 m below sea-bed, porosities are all within the range 0–45%. The most deeply buried Chalk sequences exhibit close to normal porosity/depth relations for offshore chalks. Abnormally low porosities in the remainder of the wells result from burial at greater depth than that presently observed. Low porosities were preserved during Tertiary, Alpine-related uplift of the area. For a given well the magnitude of uplift not reversed by subsequent subsidence (apparent uplift) equals the displacement of its porosity/depth relation from the normal relation along the depth axis. Apparent uplift in the Western Approaches Trough ranges from 0–1.3 km.
In the Western Approaches Trough, Chalk porosity data provide evidence of more widespread Tertiary uplift than do seismic reflection records. Alpine-related compression and uplift (fault-bounded basin inversion) is apparent only on seismic records in the southern part of the Trough (Brittany and South-West Channel Basins), whereas Chalk porosity data suggest regional uplift occurred throughout the Trough and adjacent highs.
Chalk porosity data were also used to quantify Tertiary uplift in the Cleethorpes-l well of the East Midlands shelf. The resultant value of 1.1km is considerably greater than that previously derived from shale sonic velocities (approximately 0.3 km) and slightly less than that based on apatite fission track analysis (1.3–1.7 km).
Ordovician bimodal volcanism in SW Wales: geochemical evidence for petrogenesis of the silicic rocks
Authors: BEVINS R. E. , LEES G. J. , ROACH R. A. 
Published: December 2007

Rhyolitic lavas, pyroclastic, and high-level intrusive rocks form an important component of a bimodal tholeiitic basalt-rhyolite association of early Ordovician (Llanvirn) age exposed in North Pembrokeshire, on Ramsey Island, in the Fishguard area, and on Mynydd Preseli.
In the same region, a 400 m thick tholeiitic layered differentiated sill, the St David's Head intrusion, considered to be co-genetic with this association, comprises a series of units ranging from basic (olivine + orthopyroxene-bearing gabbros) through intermediate (granophyric gabbro) to acidic (aplite) compositions. Consideration of the major and trace element concentrations in these various intrusive units suggests that they are related largely through a crystal fractionation process. The principal fractionating phases were clinopyroxene and plagioclase feldspar, with olivine and orthopyroxene in the more mafic compositions, substantial Fe-Ti oxide and minor apatite in the intermediate compositions, and minor apatite and titanite in the most evolved compositions.
A comparison between the composition of a typical aplite from the St David's Head intrusion and compositions of the various silicic rocks from the bimodal suites in North Pembrokeshire suggests these latter rocks have also been derived from a more basic tholeiitic magma via crystal fractionation. Potential parental magmas are the various basaltic lavas and related doleritic intrusions of the Fishguard Volcanic Complex. However, certain silicic lavas and intrusions from the Porth Maen Melyn area appear not to have been derived from a tholeiitic parental magma, but rather have a calc-alkaline type chemistry, similar to older lavas of the Trefgarn Volcanic Group exposed a short distance to the south of Fishguard.
These findings support the contention that large volume silicic units in bimodal associations can be derived by crystal fractionation, despite the obvious geochemical discontinuity, and the apparently anomalous volume relationships commonly present.
On the trace of the Iapetus suture in Ireland and Britain
Authors: TODD S. P. , MURPHY F. C. , KENNAN P. S. 
Published: December 2007

The Iapetus suture in Ireland and Britain is that line which separates Caledonian rocks of the Laurentian and Avalonian continents. The suture is cryptic: nowhere is there an exposed fault-zone containing ophiolite remnants, blue-schist melanges, or trench deposits. Instead a suture line may be traced with varying degrees of confidence through a series of faults that traverse the Iapetus suture zone, which contains two or more tectonostratigraphic terranes.
Several data sets are utilized to constrain this trace. The distribution of faunal provinces caused by oceanic separation can be used most reliably to define early Ordovician terranes. Fauna1 intermingling in the mid-Ordovician reduces provinciality and the confidence of terrane identification using faunal data. The late Ordovician and particularly Silurian tectonostratigraphic histories of terranes either side of the suture suggest that amalgamation of the terranes, elimination of the Iapetus Ocean and development of the suture zone had begun by the Ashgill. Therefore the resolution of the suture trace becomes unreliable where Ordovician rocks do not crop out, because Silurian turbidite fans of Laurentian provenance may have dispersed across a significant width of Avalonian crust. Similarly, the precision of structural identification of the suture zone, by correlating the suture with a major fold-facing confrontation, may be weakened by late overthrusting. Tectonic interleaving of crustal flakes in the zone is supported by geophysical evidence which suggests that some major boundaries in the lower crust do not always coincide with their inferred projections in outcrop. Tectonic and sedimentary mixing of crustal blocks and sediments in the zone is further reflected by Nd and Pb isotopic patterns; the Rb-Sr patterns of granites record a stronger distinction between north and south of the suture.
Despite these difficulties, we depict a possible suture trace in Ireland that departs significantly from the traditionally placed line by following a NE-SW-aligned trace through the Slane fault and the Navan-Tipperary lineament, and thence through a dog-leg to pass north of the Dingle Peninsula.
A mountain front model for the Variscan deformation of the South Wales coalfield
Authors: JONES JULIE A. 
Published: December 2007

Access to the considerable geological database of British Coal, together with seismic evidence of subsurface relationships, has enabled the development of a structural model for the South Wales coalfield. Detailed site investigations are used as key examples. The simple broad synclinal nature of the coalfield masks a more complex structural system. Thrusting of Variscan age is largely confined to the Lower and Middle Coal Measures and throughout the central and northern coalfield is dominantly a forethrust system. However, along the south-crop a major backthrust system is developed which in places penetrates the Upper Coal Measures. The south-crop shows features analogous with a mountain front and is interpreted as a triangle zone, in which pre-existing basement faults have facilitated uplift.
The lack of thrusting within the Upper Coal Measures, in contrast to the underlying Lower and Middle Coal Measures, suggests they have acted as a passive roof to the thrust system. Geographical variation in the intensity of the deformation can be related to the proximity of, and buttressing against, the Caledonian massif. Although broadly analogous with current models of foreland basin development and deformation, the South Wales coalfield demonstrates the importance of pre-existing massifs and lineaments in determining the precise evolution of an area.
Devonian extensional tectonics versus Carboniferous inversion in the northern Orcadian basin
Authors: SERANNE M. 
Published: December 2007

The Old Red Sandstone (Middle Devonian) Orcadian basin was formed as a consequence of extensional collapse of the Caledonian orogen. Onshore study of these collapse-basins in Orkney and Shetland provides directions of extension during basin development. The origin of folding of Old Red Sandstone sediments, that has generally been related to a Carboniferous inversion phase, is discussed: syndepositional deformation supports a Devonian age and consequently some of the folds are related to basin formation. Large-scale folding of Devonian strata results from extensional and left-lateral transcurrent faulting of the underlying basement. Spatial variation of extension direction and distribution of extensional and transcurrent tectonics fit with a model of regional releasing overstep within a left-lateral megashear in NW Europe during late-Caledonian extensional collapse.
Later inversion (probably during the Upper Carboniferous) is characterized by E–W to NE–SW contraction. It induced reactivation of extensional faults as thrusts, development of small-scale folds and thrusts, and right lateral transcurrent movement of the major faults such as the Great Glen and Walls Boundary faults.
Embaluh Group turbidites in Kalimantan: evolution of a remnant oceanic basin in Borneo during the Late Cretaceous to Palaeogene
Authors: MOSS STEVE J. 
Published: December 2007

Turbidites crop out in large parts of NW Borneo, including Kalimantan and Sarawak. The strata predominantly comprise the Embaluh Group in Kalimantan and lateral equivalents the Rajang Group in Sarawak (collectively known as the Rajang–Embaluh Group). Previous interpretation of these rocks as the product of deep marine deposition and deformation as part of an accretionary prism during Late Cretaceous to Palaeogene subduction implies south-dipping thrusts, northward stratigraphic younging, the existence of a complete arc to trench system, and significant deformation and metamorphism of the turbidites. However new fieldwork described here established consistent southward stratigraphic younging in Kalimantan, no evidence for southward-dipping thrusts and a lack of metamorphism and associated accretionary complex-related deformation features. Furthermore all available palaeontological and radiometric age data indicate that deposition of the bulk of the Rajang–Embaluh Group postdates in-board subduction-related magmatism and thus a complete arc-trench system cannot be demonstrated. Consequently the Rajang–Embaluh Group turbidites are re-interpreted as having formed in either a post-collisional foreland basin or a remnant ocean basin. The lack of a identifiable mountain belt and linked thrust system, and probable oceanic aYnity of crust beneath the Rajang–Embaluh Group basin favour the latter interpretation.
Borneo occupies a pivotal position within southeast Asia. This new model of a remnant oceanic basin setting for extensive turbidite units of Borneo therefore has far-reaching implications for the tectonic evolution of Borneo, the South China Sea and SE Asia. The new model is compared with older, Palaeozoic orogenic belts which also contain thick turbidites sequences.
Observations on the origins and ascent mechanisms of granitic magmas
Authors: CLEMENS J. D. 
Published: December 2007

This review presents a summary of most current beliefs about the origins of granitic magmas, together with calculations of some important properties of granitic melts and magmas. Turning attention to magma ascent mechanisms, diapirism and dyking represent two competing end-member models. The differences in processes and products between the two are fundamental, and the implications of the differences are profound for the evolution of the continental crust.
The weight of evidence favours dyke ascent for the majority of granitic magmas, and modelling shows that dyke ascent is both rapid and thermally effcient. Furthermore, the structural and petrological features expected in crust through which granitic diapirs have passed have not been discovered in nature. Granites in the upper crust commonly have forms and structures indicating that diapirism could not have been the emplacement mechanism. In contrast, granitic dykes are common, suggesting that it is reasonable to consider the ascent of granitic magmas through fracture systems. Many granitic batholiths are tabular and some have been fed by large dykes. The rate-limit in granitic plutonism is not magma ascent, but either the rate of melting and segregation (near the magma source) or the rate of deformation (at the emplacement site)
Palaeokarst systems in the Neoproterozoic of eastern North Greenland in relation to extensional tectonics on the Laurentian margin
Authors: SMITH M. P. , SOPER N. J. , HIGGINS A. K. , RASMUSSEN J. A. , CRAIG L. E. 
Published: December 2007

Palaeokarst, in the form of large, uncollapsed cave systems, is described from the Proterozoic of Kronprins Christian Land, eastern North Greenland. The endokarst, of entirely meteoric origin, is developed in dolostones of the Fyns Sø Formation (Hagen Fjord Group, Riphean). At one locality, Hjørnegletscher, shallow, sub-horizontal phreatic conduits are present below an unconformity surface and are infilled by the overlying Ediacaran Kap Holbæk Formation. In Sæfaxi Elv, the unconformity is overlain by the Wandel Valley Formation, an Early Ordovician carbonate sequence that is widely transgressive over northeastern Greenland. Vertical vadose fissures extend down towards the phreas, but the cave systems are again filled by Kap Holbæk Formation sediments. At Hjørnegletscher, channels up to 40 m wide incise the phreatic system, pointing to relative base-level lowering before, or during, deposition of the Kap Holbaek Formation.
Recognition of a depositional hiatus between the Fyns S0 and Kap Holbaek formations, in what was previously thought to be a continuous Vendian Hagen Fjord sequence, has implications for regional correlation and tectonics. The unconformity could represent most of Vendian time, accounting for the absence, in this area, of glaciogenic sedimentary rocks in the Hagen Fjord Group. This permits correlation of the Fyns SøFormation with other end-Riphean transgressive carbonate sequences developed in East Greenland, Svalbard and perhaps Scotland, that represent the culmination of a major pre-Iapetan rift-sag cycle.
Secondly, recognition of the scale of the sub-Wandel Valley unconformity points to regional uplift and tilting of northeastern Greenland in mid-Cambrian to earliest Ordovician time. This must represent a phase of renewed extension of the Iapetus passive margin that is unique to this corner of Laurentia, not terrane collision as previously suggested.