bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sidewall differentiation in an alkalic magma chamber: evidence from syenite xenoliths in tuffs of the Latera caldera, Italy
Authors: Turbeville B. N. 
Published: May 2009

AbstractFeldspathoidal and quartz-bearing syenite xenoliths in c. 235 to 155 ka tuffs surrounding the Latera caldera have textures and mineral assemblages that indicate an origin from the crystalline margins of a shallow magma chamber. This lithic suite exhibits a diversity of plutonic fabrics; unaltered, glass-bearing nodules with undeformed sanidine frameworks coexist with completely crystallized clasts, many of which show evidence of subsolidus modification. The syenites comprise eutectic mineral assemblages with high percentages of titanite, apatite, and melanite garnet as accessory minerals. Ubiquitous reaction textures in syenite accompany progressive changes in mineral assemblages, and they show the decreasing influence of limestone contamination with distance from the contact of syenite and skarn wallrock. Diagnostic mineral assemblages include nepheline rich in calcite inclusions, coexisting titanite and metamorphic perovskite, zircon with baddeleyite inclusions, fluorapatite mantled by a possible carbonate-bearing apatite (francolite), melanite garnet intergrown with clinopyroxene, and interstitial haüyne rich in pyrrhotite inclusions.At Latera, pumice fragments in the same deposit can exhibit up to ten-fold differences in vesicularity and crystal content (from < 5 to > 50 vol. % phenocrysts). These clasts, in conjunction with glass-bearing syenite and skarn xenoliths, may represent a range of progressively crystallized magmas that were quenched at the instant of their eruptive entrainment. The major element abundances of pumices and syenite reflect the fractionation of plagioclase and sanidine, with lesser amounts of fassaitic diopside, leucite, biotite, apatite, and alkali amphibole. Trace element ratios (e.g. Rb/Sr, Nb/Ta, Zr/Hf, LREE/HREE), on the other hand, are highly variable for crystalline and pumiceous ejecta, and some element variations (e.g. Li, Ta, Nb, Th) cannot be entirely reconciled with simple crystal-liquid fractionation. The syenite clasts span a range of compositions from strongly fractionated assemblages rich in accessory minerals to compositions that more closely approximate quenched reservoir liquids. These features reflect processes that range from pure fractional crystallization to in situ crystallization where fractionated liquid was trapped in the pores of sidewall cumulates along the chamber roof and walls.
A basement culmination in the Scandinavian Caledonides formed by antiformal stacking (Bångonåive, northern Sweden)
Authors: Greiling R. O. , Gayer R. A. , Stephens M. B. 
Published: May 2009

AbstractThe Bångonåive basement culmination, a doubly plunging antiform trending SW-NE in its southern part and SSW-NNE in the north, is part of a major Caledonian antiform in north-central Scandinavia. Crystalline, Proterozoic basement rocks (mainly syenite) are unconformably overlain by a sedimentary cover including tillites at the base, passing up into arkoses, quartzites and shales, capped by black phyllites. This sequence is correlated with the Varangian to Cambrian succession of the Baltoscandian platform farther east. Detailed mapping revealed a succession of five basement-cover horses, which represent the accessible part of an antiformal stack exposed beneath the Middle and Upper Allochthons and taken here as the Lower Allochthon structural level.Caledonian deformation varies in intensity from penetrative near thrusts and in pelitic rocks to very weak in the more internal parts of the horses. A penetrative foliation is associated with the growth of white mica and rare biotite. This early fabric is overprinted by a mylonitic foliation related to localized shear zones, which separate the structural units within the Lower Allochthon. Stretching and mineral lineations trend WNW-ESE and related shear-sense criteria indicate transport (top) towards the ESE. Structural units (horses) are thrust into an antiformal stack and folded around the lowermost horse exposed, which is itself folded into an anticlinal lift-off fold. Towards the northeast, the antiformal stack is overprinted by a pop-up and an out-of-sequence thrust. The latter breached the roof of the Lower Allochthon and transported part of it over the Middle and Upper Allochthons. Further folds are associated with lateral and oblique ramps in the Lower Allochthon. These structures relate very well with the complex fold pattern previously observed in the higher structural units and thrust tectonics provides a straightforward genetic explanation for these folds. Therefore, earlier genetic models of the Bångonåive basement culmination as a simple imbrication of basement into higher units, as a buckling structure or as a gravitational dome structure are rejected here. The structural information, supported by gravimetric data, is consistent with an essentially flat regional detachment surface (2° dip) extending from the present external Caledonian margin to the base of the Bångonåive antiformal stack.
Crustal structure of the London–Brabant Massif, southern North Sea
Authors: Rijkers Richard , Duin Ed , Dusar Michiel , Langenaeker Vital 
Published: May 2009

AbstractIn 1991 a deep seismic line, MPNI-9101, was acquired in the southern North Sea. The line runs from the Mesozoic Broad Fourteens Basin in the north, across the West Netherlands Basin, onto the London–Brabant Massif in the south. The London–Brabant Massif is a WNW–ESE trending stable structure located beneath southeastern England, the southern North Sea and Belgium. The London–Brabant Massif represents the most easterly part of the Anglo-Brabant Massif. At the northern margin of the London-Brabant Massif, Devonian and Carboniferous siliciclastic and carbonate rocks onlap the massif. Farther south, shallow parts of the seismic line in the vicinity of the axial zone of the London–Brabant Massif are almost completely devoid of primary reflections. This zone is composed of strongly folded Lower Palaeozoic sedimentary units which have been mapped in the onshore part of Belgium. Numerous seismic reflection multiples from the base of the Cretaceous are observed on this part of the section. The southern limit of the zone is very abrupt and may correspond to a fault belt delimiting an area of magmatic rocks known in the onshore part of Belgium. Unusually the deeper parts of the seismic line show a strongly reflective lower crust beneath the London-Brabant, a phenomenon which has not been observed on other deep seismic sections across the massif. Two-way travel times to the base of the lower crustal reflective zone (corresponding to the Moho), increase from 10 seconds beneath the West Netherlands Basin in the north to 12 seconds beneath the London–Brabant Massif, suggesting a thickening of the crust.
Post-Palaeozoic cooling and uplift of the Brabant Massif as revealed by apatite fission track analysis
Authors: Vercoutere C. , Van Den Haute P. 
Published: May 2009

AbstractA fission track study has been carried out on apatite from the igneous rock belt running along the southern border of the Brabant Massif. The study includes age determinations and a length analysis of both surface tracks and confined tracks. Apatite fission track ages vary between 146 Ma and 209 Ma. Confined track length distributions and the projected length age spectra indicate that the rocks cooled relatively rapidly from above 100 °C to ambient temperatures. The fission track ages therefore date a cooling phase of the Brabant Massif which is interpreted as reflecting an important uplift during the major part of the Jurassic, related to the Cimmerian tectonism which affected the North Sea basin and adjacent areas. Two apatite samples from the southerly Dinant Basin yield fission track ages around 200 Ma, similar to the oldest ages observed in the Brabant Massif, and with comparable track length characteristics. This indicates that the uplift was not limited to the Brabant region but also affected the Hercynian basement to the south.
Latest Middle Cambrian metazoan reef from northern Iran
Authors: Hamdi B. , Rozanov A. Yu. , Zhuravle A. Yu. 
Published: May 2009

AbstractMiddle and Late Cambrian reefs were built mainly by cyanobacterial communities. A few reefs with a metazoan as well as an algal component, however, are known from this interval. A Middle Cambrian reef formed primarily by spicular demosponges is described here from the Mila Formation in the Elburz Mountains, northern Iran. The reef is enclosed within calcareous grainstones which contain terminal Middle Cambrian (late Mayan) trilobites. The Mila Formation reef was constructed by sponges of the family Anthaspidellidae and bacterial (algal?) sheaths, and is the earliest metazoan reef to be documented from the interval after the demise of archaeocyath sponges. The reefal community is typical of subsequent reefal communities of Early–Middle Ordovician age. The Ordovician examples differ only by the incorporation of additional metazoan elements.
Bahamian giant stromatolites: microbial composition of surface mats
Authors: Riding Robert , Awramik Stanley M. , Winsborough Barbara M. , Griffin Karen M. , Dill Robert F. 
Published: May 2009

AbstractSubtidal columnar stromatolites up to 2.5 m high near Lee Stocking Island in the Exuma Cays, Bahamas, have surface mats approximately equally composed of algae and cyanobacteria. The stromatolites are composed of fine–medium oöid and peloid sand. This sediment is supplied to the growing stromatolite surfaces by strong tidal currents which lift grains into suspension and sweep migrating dunes over the columns. The algae include an unidentified filamentous chlorophyte, and numerous diatom species mostly belonging to Mastogloia, Nitzschia and Navicula. The dominant cyanobacteria are two oscillatoriacean species, both probably belonging to Schizothrix. Trapping of sediment is mainly effected by the unidentified chlorophyte which is veneered by epiphytic diatoms. Grains are bound into a mucilaginous mat composed of diatoms and cyanobacteria. Cyanobacteria alone would not be able to trap and bind coarse sediment so effectively in this environment. In being coarse-grained and having a significant eualgal component to their mats, these stromatolites are similar to subtidal columnar stromatolites at Shark Bay, Western Australia. The Lee Stocking stromatolites are physically stressed by high velocity tidal currents and mobile sediment. The Shark Bay stromatolites are stressed by hypersalinity. In both cases stress deters grazers, encrusters and bioeroders. These coarse-grained eualgal stromatolites contrast with micritic and predominantly prokaryotic stromatolites of most Recent marine environments, and are not analogues for most pre-Phanerozoic stromatolites. They appear to be a response to changing stromatolitic mat components in the Cenozoic.
The Wedza–Mimosa platinum deposit, Great Dyke, Zimbabwe: layering and stratiform PGE mineralization in a narrow mafic magma chamber
Authors: Prendergast M. D. 
Published: May 2009

AbstractThe Wedza–Mimosa platinum deposit is a loosely stratiform PGE-rich sulphide zone (MSZ) set within a complexly layered, shallow synclinal sequence of pyroxenites and gabbros. Both the MSZ and its host rocks display systematic stratigraphic, lithological and compositional variations between the margins and the axis of the deposit. A well preserved marginal facies is characterized by discordant layering, stratigraphic complexity, evidence of non-equilibrium crystallization, magmatic erosion and extensive pegmatoids, as well as by irregular MSZ development and metal contents. The principal transverse variations and marginal phenomena are interpreted in terms of the high transverse heat flux and heat gradient caused by the narrow trumpet-like cross-sectional structure of the original magma chamber, the magma replenishment process, the angular relationship between the chamber floor and the stratified magma, and the increase in magma density caused by the onset of plagioclase crystallization.
On the origin of Grunty Fen and other landforms in southern Fenland, Cambridgeshire
Authors: West R. G. 
Published: May 2009

AbstractDepressions and embayments of the southern Fenland margin and islands are ascribed to periglacial processes in the Devensian Stage (last cold stage) of the Pleistocene. The processes, which may be included in the general term thermokarst, include thermal erosion as an important element. The age of the active landscape evolution appears to be Late Devensian. The Crowland Bed of the Fenland Pleistocene succession is a product of these processes.
Proterozoic Mn-oxide precipitation by planktonic plant protists (acritarchs)
Authors: Morad S. , Vidal G. 
Published: May 2009

AbstractMicrofossils of plant protists called acritarchs occur embedded in, mostly, authigenic chlorite cement in sandstones of the Visingsö Group (Upper Proterozoic; southern Sweden). These microfossils are commonly encrusted by a Mn-oxide layer. Similar Mn-oxide was not observed elsewhere in the sandstones, thus suggesting that certain acritarchs have played a role in the transfer and precipitation of Mn in ancient sedimentary environments. In the light of available information on the role of extant protists in biomineralization, possible mechanisms for the precipitation of Mnoxide in the Visingsö Group are discussed.
Fe-enrichment in tholeiitic pyroxenes: complex two-pyroxene assemblages in Mesozoic dolerites, southern Tasmania
Authors: Hall R. P. , Hughes D. J. , Joyner L. 
Published: May 2009

AbstractThe pyroxene assemblages of four samples of ferrodolerite from the Mesozoic Mount Wellington sill of southern Tasmania are described. The pyroxenes of each sample define an Fe-enrichment trend equivalent to almost half of a Skaergaard-type pyroxene evolution trend. The calcic pyroxenes range from augite to ferroaugite (Ca30–40Mg40–17Fe15–45) and late-stage hedenbergite (Ca45 Mg5Fe50), and the pigeonites from intermediate to ferriferous types (Ca13Mg55–15Fe32–70). XMg numbers (Mg/(Mg + Fe)) of the calcic pyroxenes vary from 0.8 to 0.1, and of the calcium-poor pyroxenes (pigeonites) from 0.62 to 0.17. The chemical variation in the pyroxenes within individual samples is far greater than between the different samples. One sample contains an extremely wide range of pyroxenes which include some of the most ferriferous pigeonites ever recorded (Ca14Mg15 Fe71). Ti and Al contents are also highly varied, Ti:Al ionic ratios ranging from 1:15 to 1:2 with decreasing XMg. The augites have higher Ti and Al contents than pigeonites with corresponding XMg. The hedenbergites have erratic but generally low Ti contents, due to their late precipitation together with ulvospinel. The presence of such highly variable pyroxenes within individual samples and in some cases as single, complex grains makes the recognition of coexisting pyroxene pairs in such dolerites very difficult, but graphical pyroxene thermometers suggest a crystallization temperature range of 1100 to 850 °C.The range of pyroxene compositions in such dolerites is strongly influenced by the oxygen fugacity (fO2) of the liquid from which they derive. The primary Fe-Ti oxide phase in these Tasmanian dolerites is ulvospinel (now oxidized to ilmenite ‘oxidation-exsolution’ lamellae in titanomagnetite hosts) clearly demonstrating the originally low fO2 of the parental tholeiitic magma of the Mount Wellington sill.
Inter-related plutonism and deformation in South Victoria Land, Antarctica
Authors: Cox Simon C. 
Published: May 2009

AbstractThe Lower Palaeozoic Bonney Pluton is a regionally extensive coarse-grained, variably megacrystic, monzodioritic to granitic body that crops out over 1000 km2 in South Victoria Land. It intruded upper amphibolite facies Koettlitz Group metasediments and interlayered orthogneisses. Magmatic fabrics are developed in the centre of the pluton by flow alignment of K-feldspars before the majority of phases had crystallized, whereas solid-state fabrics developed in the pluton margins by ductile–plastic deformation. Structures developed in the host-rocks vary around this elongate northwest–southeast-trending pluton. Upright, tight northwest–southeast-trending macroscopic folds are developed at the sides of the pluton, with axis-parallel stretching lineations and boudinage indicating strong northwest–southeast extension. Broad warps of tight macroscopic folds, and mesoscopic refolded folds, sheath folds and complicated interference patterns characterize areas at the ends of the pluton. Emplacement of the pluton involved radial expansion in a regional northeast–southwest compression, and growth predominantly in the northwest–southeast direction. Superposition of the radial expansion and regional compression resulted in an inhomogeneous strain field at a regional scale, with coaxial strain at the sides of the pluton and non-coaxial strain at the ends. Upright folds developed at the pluton's sides, and became tighter with continued coaxial deformation. Non-coaxial structures developed at the ends of the pluton and were pushed aside by the growing pluton into areas of coaxial deformation, resulting in complex folding, re-folding and sheath folds. Metamorphism of the host-rocks and migmatite development was more intense at the sides of the pluton than near the ends, possibly due to different P-T-t paths of host-rocks around syntectonic plutons.
Geochemistry and eruptive environment of metavolcanic rocks from the Mona Complex of Anglesey, North Wales, U.K
Authors: Thorpe R. S. 
Published: May 2009

AbstractThe late Precambrian–early Palaeozoic Monian Supergroup of the Mona Complex is a thick sequence of flysch-type sediments and metavolcanic rocks which were deposited during the late Precambrian–early Palaeozoic and deformed during the late Precambrian and Caledonian (Ordovician/Silurian) orogenies. The Monian Supergroup includes tectonically emplaced, geographically separated outcrops of metabasalt/andesite, gabbro and serpentinized ultramafic rocks all of ophiolite affinity. The major units of the Mona Complex are separated by important faults/fault zones which may represent terrane boundaries. New chemical analyses, together with existing ones, show that the metabasalts and meta-andesites from the older New Harbour Group of north Anglesey have characteristics of suprasubduction zone arc eruptives whereas the metabasalts from the younger Gwna Group of south Anglesey and Lleyn have MORB geochemistry. It is suggested that these volcanic rocks were produced during the late Precambrian–early Palaeozoic development of the lapetus Ocean and emplaced as separate terranes during its closure.
Evidence for temperate soil development during the Early Devensian in Gower, South Wales
Authors: Case D. J. 
Published: May 2009

AbstractInvestigations into the micromorphology of the Pwll Du Red Beds in Gower, South Wales, have revealed pedo-features in the form of compound void coatings. Overlying marine deposits dated to the Ipswichian (Oxygen Isotope Substage 5e), the Red Beds are interpreted as the product of sedimentation and pedogenesis during Early Devensian time.
Chemical correlation of Moinian rocks in the northern Highlands of Scotland
Authors: Winchester J. A. , Lambert R. St J. , Holland J. G. 
Published: May 2009

SummaryComparison is made between the semipelitic and psammitic schists of the Morar and Glenfinnan Division in their type areas and the succession in the Fannich district of Northern Ross-shire. The tentative lithological correlation of the Morar Pelite with the Sgurr Mor Pelite is confirmed, while the Meall an t-Sithe Pelite and the semipelites of the Glenfinnan Division likewise have a similar geochemistry. In establishing these similarities, ratios involving Sr, Nb, Y, Zr and P2O5 have been found to be most useful, particularly Sr/Y. Other ratios (Ca/Y, K/Rb, K2O/(Na2O+CaO) and K/Ba) can also yield useful information regarding correlation and sedimentary history. Sr/Y decreases stratigraphically upwards in these successions and also towards the north east, suggesting a palaeogeography for the Morar Division involving increasing remoteness from the source area with time and in a northeasterly direction.
Occurrence of the ophiolitic complexes along the Indoburman orogenic belt
Authors: Duarah R. , Saikia M. M. , Bhattacharjee C. C. 
Published: May 2009

SummaryThe ophiolitic complexes within the Indoburman orogenic belt form a conspicuous N-S line along the eastern margins of Manipur and Nagaland. The rock assemblages consisting of mafic-ultramafics are associated with deep sea pelagic sediments of the Disang Group (Lower Cretaceous-Eocene). The ultramafics in part, represent the oceanic crust and upper mantle material that formed the basement on which the radiolarites and other pelagic sediments were deposited. The fossil radiolaria present in the cherts suggest that the orogen took its foundation during late Jurassic-Lower Cretaceous time. The westward obduction of the flysch ophiolites in the form of large thrust sheets was possible during underthrusting of the Indian plate beneath the Burmese. The position of the ophiolitic belt defines the Indoburman suture zone.
The (?) mid Triassic volcanic rocks of Lakonia, Greece
Authors: Pe-Piper G. , Panagos A. G. , Piper D. J. W. , Kotopouli C. N. 
Published: May 2009

SummaryThick subaerial volcanic sequences of probable mid Triassic age rest unconformably on Permo-Carboniferous limestones in the ‘Phyllite Series’ within the Gavrovo-Tripolitsa zone of the external Hellenide nappes. The volcanic rocks are varied in character. Pyroclastic rocks (often reddened) predominate, but minor basalt or andesite and rhyolitic hypabyssal intrusions and flows are also found. The rocks have experienced low-grade metamorphism and the only relict primary minerals are pyroxene and rare plagioclase in basic rocks and potash feldspar in acid rocks. The most important metamorphic phases are albite, chlorite, potassium mica, epidote, hematite, quartz and pumpellyite. Twenty-seven whole-rock major-element analyses suggest that there has been some exchange of Na2O and K2O for CaO during metamorphism, but that other elements have been relatively stable. A genetic interpretation of the rocks is attempted using published geochemical discriminator diagrams. The basic rocks are tholeiitic in major element chemistry and pyroxene composition. Trace element (Hf, Ta, Th, Ce, Yb) distribution suggests magma generation at a destructive plate margin.
A late Caledonian breccia dyke swarm in Glen Creran, near Glen Coe in the Grampian Highlands
Authors: Platten I. M. 
Published: May 2009

SummaryA series of late Caledonian breccia dykes composed of Dalradian schist fragments are emplaced in the Leven Schists. The form and extent of the breccia dykes are described, and dilational and nondilational components identified as contributing to the space occupied by individual breccias. Fabrics and textures of the breccia material are related to transport mechanisms and later compaction. The breccias are considered to have evolved as fluidized systems.
A Miocene submarine volcano at Low Layton, Jamaica
Authors: Wadge G. 
Published: May 2009

SummaryA submarine fissure eruption of Upper Miocene age produced a modest volume of alkaline basalt at Low Layton, on the north coast of Jamaica. The eruption occurred in no more than a few hundred metres of water and produced a series of hyaloclastites, pillow breccias and pillow lavas, massive lavas, and dikes with an ENE en échelon structure. The volcano lies on the trend of one of the island's major E–W strike-slip fault zones: the Dunavale Fault Zone. The K–Ar age of the eruption of 9.5 ± 0.5 Ma. B.P. corresponds to an extension of the Mid-Cayman Rise spreading centre inferred from magnetic anomalies and bathymetry of the Cayman Trough to the north and west of Jamaica. The Low Layton eruption was part of the response of the strike-slip fault systems adjacent to this spreading centre during this brief episode of tectonic readjustment.