bluuebunny/crossref_metadata_2025_split huggingface dataset:
The structural age and possible origin of the Vagastie Bridge granite and associated intrusions, central Sutherland
Authors: Holdsworth R. E. , Strachan R. A. 
Published: May 2009

AbstractThe Vagastie Bridge granite, central Sutherland, belongs to a regional suite of igneous intrusions within Moine psammites adjacent to the base of the east Sutherland migmatite complex. An isotopic date of 405 ± 11 Ma, obtained using U–Pb determinations on zircon and sphene taken from the granite, has previously been interpreted as an intrusion age. However, a reassessment of the field relationships demonstrates that intrusion was syn-tectonic with respect to the later stages of ductile Caledonian deformation affecting the Moine rocks. It is suggested that the granite suite magmas originated at depth and that they were channelled into the still active Caledonian ductile thrust zone (the Naver Thrust) which forms the tectonic base of the Naver Nappe. On regional grounds, the interpretation of the c. 405 Ma date as an intrusion age is untenable, which implies that the isotope systematics of the Vagastie Bridge granite require re-investigation.
Beaches and beach-related facies, Holocene barrier islands of Georgia
Authors: Frey R. W. , Howard J. D. 
Published: May 2009

AbstractThe mesotidal coast of Georgia encompasses diverse sedimentary features and depositional environments, most of which typify major facies of the entire Georgia Bight – a broad embayment on the southeastern U.S. shelf. Barrier island strandline environments especially include tidal inlets and shoals, the beach shoreface, foreshore, and backshore, and dunes and washover fans. Low energy beach segments may grade directly into small seaside tidal flats. Relict salt marsh deposits crop out on erosional beaches. All deposits are in dynamic equilibrium with fluctuating coastal conditions and a gradual rise in sea level.Most of these facies are important in interpreting ancient epeiric transgressive/regressive coastal sequences. Pronounced local variations in the overall sequence result from complex latero-vertical relationships between (1) the shoreface, foreshore, and shoals, and (2) the shoals, low energy beaches, and beach-related tidal flats. Washover fans and relict deposits on erosional beaches cause perturbations within present day lateral relationships but are normal in transgressive facies tracts along such coasts. Close stratigraphic control of outcrops or cores would be necessary for detailed reconstructions of, or correlations among, ancient analogs.
The origin of Variscan kink bands: a study from the Dungarvan Syncline, southern Ireland
Authors: Murphy F. X. 
Published: May 2009

AbstractKink bands formed due to the rotation of cleavage are very common within the Irish Variscides. A detailed examination of those within the Dungarvan Syncline has enabled the recognition of three categories based on kink fold axis orientation; the subvertical, those parallel to first or second order fold axes and those with subhorizontal randomly trending axes. The subvertical variety were formed by strike-parallel compression within a hinge depression in the Dungarvan Syncline and modified by later north–south dextral shear stresses to produce cataclasis of the kink-band boundaries, tension-gashes within the kinked segment and over-rotation. Those, whose axes are parallel to major or minor fold axes, formed as accommodation structures during folding due to extension in the be plane. Those, with subhorizontal randomly trending axes formed due to a relaxation in the northward compression which allowed a reorientation of the principal stress directions, σ1 became vertical and kink bands were generated as a consequence of the increased overburden due to fold tightening and thrusting. It is considered that kink bands throughout the Irish Variscides may be divisible into similar categories.
An initial continental margin plutonism — Cretaceous Older Ryoke granitoids, southwest Japan
Authors: Kutsukake Toshio 
Published: May 2009

AbstractThe emplacement of the Older Ryoke granitoids took place in the Mid-Cretaceous Period in the outermost side of the Inner Zone of southwest Japan, which was located at the eastern margin of the Eurasian Continent before the opening of the Japan Sea. The Ryoke Belt constitutes a long segment of the Cretaceous to Palaeogene felsic magmatic belt of Pacific Asia. The Older Ryoke granitoids represent its initial magmatism, related to the subduction of an oceanic plate underneath the Eurasian plate in that time. Their magmas were generated in the lower to middle crust beneath the Ryoke Belt in the subduction regime. They were emplaced during the Ryoke regional metamorphism and converted to orthogneisses.
Biostratigraphy of the Vendian-Cambrian beds and the lower Cambrian boundary in Siberia
Authors: Khomentovsky V. V. , Karlova G. A. 
Published: May 2009

AbstractGeneral agreement exists that the position of the base of the Cambrian (Precambrian–Cambrian boundary) should coincide with a biostratigraphic marker that can be widely traced and is linked to the evolution of the small shelly fauna. On the Siberian platform the presence of distinct facies during the Vendian–Cambrian interval has made biostratigraphic correlation based on palaeontological data highly contentious. A solution to this problem appears to exist with the recognition of an almost uninterrupted profile in the Aldan–Uchur watershed where key sections expose the eastern and transitional facial region. On this basis we present a general biostratigraphic scheme for the Vendian–Cambrian across the southern Siberian platform that connects separate facies. Further correlation with key sections in northern Siberia leads to the recognition of three biostratigraphic zones for the Vendian–Cambrian interval. These are: Anabarites trisulcatus Zone; Purella antiqua Zone; Aldanocyathus sunnaginicus Zone. The abundance of Chinese-type small shelly fossils in the region of the eastern facies suggest correlation of the A. sunnaginicus Zone with the Siphogonuchites–Paragloborilus Zone of China, and the P. antiqua Zone with the Circotheca–Anabarites–Protohertzina Zone. In places, at the base of the Circotheca–Anabarites–Protohertzina Zone in China, analogies to the A. trisulcatus Zone can be identified. It is proposed that in Siberia the base of the A. sunnaginicus Zone (= base of Tommotian Stage) be taken as the base of the Cambrian. This would correspond with Marker B of the Meishucunian in China
Flow direction and groundmass shear zones in dykes, Shimane Peninsula, Japan
Authors: Smith J. V. , Miyake Y. , Yamauchi S. 
Published: May 2009

AbstractThe groundmass of andesitic dykes at Sezaki, southwest Japan, has trachytic texture and contains microscopic shear zones. The shear zones comprise a conjugate pair formed by flattening of the solidifying dyke rock, probably caused by the magma pressure of the still molten part of the dyke. This pressure shortened the solidifying rock perpendicular to the dyke margins and caused it to extrude parallel to the magma flow direction. The groundmass shears indicate that locally the magma flowed 60° upward in the dykes. It is concluded that while groundmass shears are a useful indicator of flow direction in dykes, phenocryst alignment in dykes is strongly influenced by magma-pressure flattening and thus may be a poor indicator of flow direction
The petrogenetic significance of chemically related plutonic and volcanic rock units
Authors: Wyborn D. , Chappell B. W. 
Published: May 2009

AbstractComagmatic granitic and volcanic rocks are divided into two types depending on whether or not the primary magma contains restite crystals. Examples of both of these types are discussed from the Lachlan Fold Belt of southeastern Australia.Volcanic rocks containing restite phenocrysts are chemically identical to the associated plutonic rocks containing the same amount of restite. The more mafic granitic rocks correspond in composition to the most phenocryst-rich volcanics (up to 60% phenocrysts), and thus cannot be cumulate rocks produced by fractional crystallization, but must represent true magma compositions. These restite-bearing magmas result from partial melting in a source region up to the rheological critical melt percentage, which we estimate to be about 40% in the S-type Hawkins Suite of volcanics.Melts which escape their restite at the source, before the critical melt percentage is reached, are able to undergo fractional crystallization in high level magma chambers by heterogeneous crystallization on chamber walls. In this case volcanic products from the top of the chamber are more felsic than the plutonic products, the plutonics are crystal cumulates and the volcanics are composed of the complementary fractionated liquid. Those phenocrysts present in the volcanics were probably eroded from the chamber walls and are less abundant (< 20%) than in the restite-retentive volcanic products.
Ordovician volcanism in the Welsh Borderland
Authors: Leat P. T. , Thorpe R. S. 
Published: May 2009

AbstractBasaltic, andesitic and rhyodacitic/rhyolitic volcanism was widespread during Ordovician time in the Welsh Basin. New chemical data are presented for Llanvirn to Caradoc lavas and tuffs from the Welsh Borderland which, during Ordovician time, formed the southeastern margin of the Welsh Basin. In view of the observed chemical alteration, immobile elements are used in the interpretation of the original geochemical character. The data indicate that the Llanvirn Stapeley volcanic group of the Shelve inlier was a bimodal basalt/basaltic andesite – rhyodacite/rhyolite association. The basalts have trace element contents of tholeiitic associations with a subduction-related character. The Caradoc Whittery and Hagley volcanic groups of the Shelve inlier comprise lavas and tuffs of calc-alkaline andesite. Blocks sampled from the Breidden Hills show that these were also derived from a calc-alkaline volcano. Associated Caradoc pumice- and ash-flow deposits from the Breidden Hills are probably of altered calc-alkaline rhyodacite/rhyolite composition. The Sibdon Carwood basalt flow, the only known example of Ordovician volcanism east of the Pontesford–Linley and Church Stretton lineaments, has transitional tholeiitic to alkaline character, with trace element contents influenced by subduction-related processes. The overall tholeiitic to calc-alkaline nature of the magmatism is consistent with the view that, during Llanvirn to Caradoc time, the Welsh Basin was an ensialic marginal basin.
Trace fossils from the Precambrian–Cambrian boundary candidate at Meishucun, Jinning, Yunnan, China
Authors: Crimes T. P. , Zhiwen Jiang 
Published: May 2009

AbstractThe Precambrian–Cambrian boundary candidate section at Meishucun, China, has yielded trace fossils which are abundant at some horizons. The earliest occur in Unit 3 of the Zhongyicun Member approximately 8 m above the lower selected stratotype reference point for the boundary and includeArenicolitessp.,Asteriacitessp.,Neonereites biserialis, N. uniserialisandSellaulichnus meishacunensis. The next trace-fossil-bearing horizon is in Unit 6 of the Zhongyicun Member whereCochlichnussp.,Monomorphichnussp.,Neonereites biserialisandN. uniserialisoccur. Immediately above, in Unit 7, areCruzianasp.,Didymaulichnus miettensis, Monomorphichnussp. andRusophycussp. In the Badaowan Member at the top of the section there areDidymaulichnussp. andTaphrhelminthopsis circularisin Unit 9,Arenicolitessp.,Diplocraterionsp.,Gordia molassica, Skolithossp. andT. circularisin Unit 11, andGordia meandria, ?Plagiogmussp.,Skolithossp. andT. circularisin Unit 12.Comparison of this trace-fossil distribution with that in key Precambrian–Cambrian boundary sections in other countries indicates that the ranges of a few trace fossils cross the boundary (e.g.Didymaulichnus, Neonereites, Planolites) but most appear only in the Cambrian. Different ichnogenera seem to appear at various levels above the boundary.ArenicolitesandAsteriacitesare among the first, whileTaphrhelminthopsis circularisis only encountered higher in all sequences. Some have only been recorded at much higher levels and relatively close to the first appearance of trilobites (e.g.Cruziana, Diplocraterion, Rusophycus). This suggests that the first appearance of specific trace fossils or groups of trace fossils may be valuable for locating the boundary in some sections and for correlating late Precambrian and early Cambrian strata.
Mid-Palaeozoic metamorphism and polyphase deformation of the Forland Complex, Svalbard
Authors: Manby G. M. 
Published: May 2009

AbstractThe Forland Complex of Prins Karls Forland has been subjected to mid-Palaeozoic greenschist facies metamorphism and polyphase deformation. Metamorphism was initiated prior to D1 deformation and gave rise to a parallelism of stratigraphic and metamorphic reaction surfaces. D1 gave rise to imbricately thrust, southwest-directed fold nappes which have not noticeably disturbed the isograd surfaces. D2, interpreted as belonging to the mid-Cenozoic West Spitsbergen Orogeny (WSO) which was coaxial but not coplanar with D1, produced crenulation folds and pressure solution cleavages and some thrusting. D3 structures are related to the formation of the Prins Karls Forland–Forlandsundet–Oscar II horst and graben system which is a late expression of the WSO. The rejuvenation of the Prins Karls Forland horst along NNW–SSE faults, the large scale E–W flexures and ENE–WSW faults in the Forland Complex and Tertiary graben deposits are assigned to D3.
Carbonated melilitites and calcitized alkalicarbonatites from Homa Mountain, western Kenya: a reinterpretation
Authors: Clarke M. G. C. , Roberts B. 
Published: May 2009

AbstractHoma Mountain is a well developed ijolite/carbonatite complex of Miocene to Quaternary age. Late stage olivine melilitite occurs as a satellite plug, parts of which show strong deuteric alteration to carbonate resulting in complete pseudomorphing of the melilite.A second satellite centre exposes a grey carbonate tuff and accompanying dykes, all of which exhibit relic textures after an elongate, rectangular mineral also formerly believed to be melilite. Comparison with other recently described occurrences indicates however that the second centre erupted alkali-carbonatite and that the chief mineral originally present was nyerereite (Na2Ca(CO3)2). The field relationships and petrographic characters of both rock types are described and criteria are given which permit distinction between carbonated melilite and calcitized nyerereite. It is concluded that olivine melilitite and alkalicarbonatite are closely related in space and time.
A note on Lower Jurassic magmatism in the Coastal Cordillera of Atacama, Chile
Authors: Naranjo J. A. , Puig A. , Suárez M. 
Published: May 2009

AbstractRadiometric dates on specimens of plutons of the Coastal Cordillera of Atacama span the period 300–110 Ma. A group of dates cluster around 190 Ma and evidence is presented which strongly suggests that they represent near crystallization ages. The geographic distribution of these plutons, adjacent to Liassic tuffs and lavas (Pan de Azúcar and Posada de los Hidalgo formations), suggests a genetic relationship between them, and that the plutons were the roots of the Lower Jurassic volcanic chain. The location of these granitoids to the west of the Liassic volcanic rocks, favours a previous idea that the Liassic basin extended eastwards as a back-arc or intra-arc basin. The host rocks to the Lower Jurassic plutons include Palaeozoic granitoids and metasedimentary rocks, indicating that the volcanic chain was founded on continental crust. The distance from the Liassic plutons to the present-day trench is less than 100 km, which indicates the possibility that part of the arc-trench system of that time is missing.
Cambrian and late Precambrian basaltic igneous activity in the Scottish Dalradian: a review
Authors: Graham C. M. , Bradbury H. J. 
Published: May 2009

SummaryIn the evolution of the Scottish Dalradian basin, the climax of widespread tholeiitic magmatism pre-dated or coincided with major basement faulting and the onset of deep marine sedimentation in Lower Cambrian times. Earlier basin-deepening and precursory igneous activity had already occurred. Major and trace element chemistry of low-grade metabasites indicates their affinity with basalts from ocean-spreading centres, or transition to ‘within-plate’ types. Geological evidence favours a tectonic setting for this igneous suite and the Highland Border Series on the NW margin of an actively evolving Lower Cambrian ocean basin, possibly a marginal basin to the Iapetus Ocean System.
Plagiogranites in the Coolac ophiolite suite, New South Wales, Australia
Authors: Ashley P. M. , Franklin B. J. , Ray A. S. 
Published: May 2009

SummaryPlagiogranites occur mainly as intrusive bodies and tectonic inclusions within mafic and ultramafic members of the Coolac ophiolite suite. Quartz diorites and trondhjemites appear to represent localized late-stage felsic differentiates of subalkaline tholeiitic magma, with their formation dominantly controlled by fractionation of hornblende and plagioclase. Albitites are interpreted as altered equivalents of quartz diorites and trondhjemites. Chemical data, while emphasizing the similarity of these rocks to ‘oceanic plagiogranite', also indicate that variation in the latter may be broader than previously defined. The Coolac rocks show less marked Fe-enrichment, higher Ni and Cr, and lower Y and Zr than many ophiolitic plagiogranites. These data are consistent with weak calc-alkaline tendencies demonstrated in the Coolac ophiolite suite.
Surface and subsurface structural study of the Wadi El Rayan area, Southwest Fayoum, Egypt
Authors: Youssef M. M. , El Khashab H. M. 
Published: May 2009

SummaryThe surface geologic map of the Wadi El Rayan area, based on the study of aerial photographs and field observations, is correlated with seismic structural two-way time maps for the basement, the top of Cenomanian and the base of Tertiary horizons. Major structural features comprise a northeasterly faulted plunging anticlinal stretch traversing the NW-SE Wadi El Rayan depression. Three sets (ENE-WSW, NW-SE and NE-SW) of faults dissect the area. Folding movement was still active at least to the end of Middle Eocene epoch. ENE-WSW faults affecting the basement, and traced in higher levels, have the same trend as the fold axes. It is thus possible that compressional features appearing on the surface and subsurface horizons are in part due to thrusting in deeper levels that took place parallel to folding.
The Phanerozoic cover sequences preserved as xenoliths in the kimberlite of eastern Sierra Leone
Authors: Hubbard F. H. 
Published: May 2009

SummarySedimentary and volcanic rocks, now unrepresented in surface exposure, occur as xenoliths in the kimberlite of the Koidu District of eastern Sierra Leone. The sedimentary rocks prove, on micropalaeontological evidence, to have Lower Palaeozoic stratigraphic age. An eastern extension of the Ordovician/Silurian marine transgression on to the Leo Uplift of the West African Craton of some 200 km is indicated. The volcanic rocks may belong to the same cycle of surface rock generation or relate to the younger, widespread, Triassic magmatic event.
Precambrian-Cambrian Boundary candidate, Aldan River, Yakutia, U.S.S.R.
Authors: Cowie J. W. , Rozanov A. Yu. 
Published: May 2009

SummaryThe current situation in 1982 regarding the status and validity of the Ulakhan-Sulugur section on the Aldan River as a candidate for the global stratotype section and point for the Precambrian-Cambrian (PC-C) Boundary is reviewed with details of new work since 1973 and consequent revisions of views on controversial topics on a regional, continental and intercontinental scale of stratigraphic correlations with a short note regarding accessibility.
The petrochemistry of the basic volcanic rocks of the South Connemara Group (Ordovician), western Ireland
Authors: Ryan P. D. , Max M. D. , Kelly T. 
Published: May 2009

Summary16 samples of Ordovician basic volcanic rocks of the South Connemara Group, which abut the southern side of the metamorphic rocks of the Connemara massif in western Ireland, have been analysed for both major and trace elements. Although subject to low grade regional metamorphism and subsequently hornfelsed by the Galway Granite (400 Ma), their immobile element contents do not appear to be significantly disturbed. These elements characterise the metabasites of the South Connemara Group as ocean floor basalts having their origins in a marginal basin. The Skird Rocks Fault, separating the South Connemara Group from high grade metamorphic rocks of the Connemara massif, is consequently regarded as the northern margin of the vestiges of the lapetus Ocean which can be traced into, and along, the Southern Uplands Fault.
The South Harris gravity anomaly
Authors: Durrance E. M. , Grainger P. , Kearey P. 
Published: May 2009

SummaryThe results of a gravity survey of South Harris show that a residual gravity anomaly of + 220 g.u. occurs towards the southeast of the anorthosite-gabbro-tonalite igneous suite, with a minor low of + 150 g.u. over the anorthosite outcrop and a minor high of + 170 g.u. over the main gabbro outcrop. The distribution of the maximum positive anomaly and the minor anomalies is interpreted as due to interbanding of gabbro and anorthosite. The tonalites do not produce a local anomaly and are interpreted as extending to only limited depth. North of the igneous suite the residual gravity anomaly falls to - 10 g.u. over a hidden granite within migmatitic gneisses. It is suggested that the igneous suite was formed when a large body of gabbroic-anorthositic magma was injected into older continental crust, causing melting and the formation of contemporaneous tonalites, with complex fractionation producing gabbro and anorthosite layering. The sequence of events is interpreted as relating to an igneous episode that was a prelude to continental rifting which predated later phases of metamorphic/orogenic activity.
The Portland-Purbeck junction (Portlandian-Berriasian) in the Weald, and correlation of latest Jurassic-early Cretaceous rocks in southern England
Authors: Wimbledon W. A. , Hunt C. O. 
Published: May 2009

SummaryAmmonites and palynology are described at the Portland-Purbeck junction in the Weald. A major disconformity exists between glaucolithus Zone Portland Beds and the overlying basal Purbeck facies, the basal Purbeck Beds of the Weald are correlated with the Middle Purbeck strata of Dorset. The Cinder Bed of Dorset and Wiltshire is described as one of several marine incursions entering Wessex from further south in the Anglo-Paris basin, not from the Spilsby basin. The use of Cinder Bed as a convenient Jurassic-Cretaceous (Portlandian-Ryazanian) boundary is critically reviewed, as is the placing of the base of the Berriasian Stage in the type Purbeck section. The rival biostratigrahic schemes based on ostracods and palynology are discussed and the discrepancies between the two schemes in southern England are examined.