bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cretaceous granitoids in SW Japan and their bearing on the crust-forming process in the eastern Eurasian margin
Authors: Nakajima Takashi 
Published: November 2011

ABSTRACT:The Cretaceous granitic rocks and associated regional metamorphic rocks in SW Japan were formed by a Cordilleran-type orogeny. Southwest Japan is regarded as a hypothetical cross-section of the upper to middle crust of the Eurasian continental margin in the Cretaceous, comprising (1) high-level granitoids (called San-yo type) and weakly to unmetamorphosed accretionary complexes that are exposed on the back-arc side and (2) low-level (Ryoke type) granitoids with high-grade metamorphites up to migmatitic gneisses on the forearc side. All these granitoids are of the ilmenite series, and predominantly I-type, with a subordinate amount of garnet- or muscovite-bearing varieties in the Ryoke zone, but none of these contains cordierite. These mineralogical variations are likely to depend more on their slightly peraluminous chemistry rather than the pressure differences during crystallisation.In the eastern part of SW Japan, the granitoids of both levels give K–Ar biotite ages of approximately 65 Ma, whereas the magmatic age of high-level granitoids is approximately 70 Ma, 15 Ma younger than the nearly 85 Ma old lower level granitoids. This implies that the formation of the middle crust started approximately 15 Ma before that of the upper crust. The middle crust material was kept over 500°C for 15–20 Ma after solidification, then it cooled together with the upper crust to 300°C, 6–7 Ma after the formation of the upper crust. The coincidence of cooling history below 500°C of the upper and middle crust may reflect the regional uplift of the crust.The low-level granitoids have higher 87Sr/86Sr initial ratios than those of high-level granitoids in the middle-western part (Chugoku district), but the relationship appears to be opposite in the eastern part. This may imply that the two plutonic series formed by separate magmatic pulses at an interval of c. 15 Ma, even though they are not independent, but rather part of a larger episode of crustal growth.
Petrogenesis of slab-derived trondhjemite–tonalite–dacite/adakite magmas
Authors: Drummond M. S. , Defant M. J. , Kepezhinskas P. K. 
Published: November 2011

ABSTRACT:The prospect of partial melting of the subducted oceanic crust to produce arc magmatism has been debated for over 30 years. Debate has centred on the physical conditions of slab melting and the lack of a definitive, unambiguous geochemical signature and petrogenetic process. Experimental partial melting data for basalt over a wide range of pressures (1–32 kbar) and temperatures (700–1150°C) have shown that melt compositions are primarily trondhjemite–tonalite–dacite (TTD). High-Al (> 15% Al2O3at the 70% SiO2level) TTD melts are produced by high-pressure (≥ 5 kbar) partial melting of basalt, leaving a restite assemblage of garnet + clinopyroxene ± hornblende. A specific Cenozoic high-Al TTD (adakite) contains lower Y, Yb and Sc and higher Sr, Sr/Y, La/Yb and.Zr/Sm relative to other TTD types and is interpreted to represent a slab melt under garnet amphibolite to eclogite conditions. High-Al TTD with an adakite-like geochemical character is prevalent in the Archean as the result of a higher geotherm that facilitated slab melting. Cenozoic adakite localities are commonly associated with the subduction of young (<25 Ma), hot oceanic crust, which may provide a slab geotherm (≍9–10°C km−1) conducive for slab dehydration melting. Viable alternative or supporting tectonic effects that may enhance slab melting include highly oblique convergence and resultant high shear stresses and incipient subduction into a pristine hot mantle wedge. The minimumP–Tconditions for slab melting are interpreted to be 22–26 kbar (75–85 km depth) and 750–800°C. ThisP–Tregime is framed by the hornblende dehydration, 10°C/km, and wet basalt melting curves and coincides with numerous potential slab dehydration reactions, such as tremolite, biotite + quartz, serpentine, talc, Mg-chloritoid, paragonite, clinohumite and talc + phengite. Involvement of overthickened (>50 km) lower continental crust either via direct partial melting or as a contaminant in typical mantle wedge-derived arc magmas has been presented as an alternative to slab melting. However, the intermediate to felsic volcanic and plutonic rocks that involve the lower crust are more highly potassic, enriched in large ion lithophile elements and elevated in Sr isotopic values relative to Cenozoic adakites. Slab-derived adakites, on the other hand, ascend into and react with the mantle wedge and become progressively enriched in MgO, Cr and Ni while retaining their slab melt geochemical signature. Our studies in northern Kamchatka, Russia provide an excellent case example for adakite-mantle interaction and a rare glimpse of trapped slab melt veinlets in Na-metasomatised mantle xenoliths.
Granitic magmatism and metallogeny of southwestern North America
Authors: Barton Mark D. 
Published: November 2011

ABSTRACT:In southwestern North America, late Palaeozoic through Cenozoic granitoids and their related mineral deposits show consistent patterns that can be interpreted in terms of combined provincial, exposure and process controls. Voluminous Cordilleran magmatism began in the Permian and continued with few major interruptions through the Mesozoic and Cenozoic, reaching maximum fluxes in the mid-Jurassic, Late Cretaceous and Oligocene. Two distinctive types of broad-scale igneous suites formed. The first type consists of calc-alkaline to alkaline suites that vary regularly with time from early intermediate-mafic centres to late felsic centres over intervals lasting 20–50 Ma. These suites formed during periods of stable convergence and compressional tectonics, most notably in the late Mesozoic and early–mid-Cenozoic. The second type is compositionally varied, but shows no obvious secular variation in composition. This type formed during neutral to extensional tectonics in the mid-Mesozoic and the mid- to late Cenozoic. Regional (west to east) and secular (old to young) changes from calcic to alkalic compositions do not correspond to basement types; they point to tectonic rather than crustal controls on magmatic evolution, although basement signatures are clearly transmitted in isotopic systematics. Contrasting types of intrusive centres formed in the same lithospheric columns, suggesting that variability reflects thermal and stress regimes, subcrustal magma flux and crustal thickness. Simple thermal and mechanical models of limits on assimilation and magma uprise are broadly consistent with these patterns.Igneous-related mineralisation is ubiquitous where epizonal environments are preserved, thus preservation (and exposure) form the first-order filter on metallogeny. Mineralisation includes porphyry, skarn, epithermal, replacement and syngenetic deposits of widely varying styles, metal contents and links to magmatic heat and materials. Metal contents and alteration styles correlate closely with igneous compositions and are broadly independent of setting, although systematic regional variations in metal ratios are documented. Ore element suites vary from Cu–Au–Fe associated with (quartz) dioritic to monzonitic intrusive centres through Cu–Zn–Mo–Pb–Ag–W–Au associated with broadly granodioritic centres, and finally to F–Mo–Zn–W–Ag–Be associated with metaluminous to strongly peraluminous granitic centres. A model that includes both composition and process controls rationalises this igneous correlation and the lack of strong regional control. Key features are (1) mineralogical controls on fluid compositions and (2) the efficacy of magmatic processes in producing voluminous ore-forming aqueous fluids. This interpretation is supported by field relationships, igneous petrographic and isotopic data, and theoretical considerations.
Exsolved magmatic fluid and its role in the formation of comb-layered quartz at the Cretaceous Logtung W-Mo deposit, Yukon Territory, Canada
Authors: Lowenstern Jacob B. , Sinclair W. David 
Published: November 2011

ABSTRACT:Comb-layered quartz is a type of unidirectional solidification texture found at the roofs of shallow silicic intrusions that are often associated spatially with Mo and W mineralisation. The texture consists of multiple layers of euhedral, prismatic quartz crystals (Type I) that have grown on subplanar aplite substrates. The layers are separated by porphyritic aplite containing equant phenocrysts of quartz (Type II), which resemble quartz typical of volcanic rocks and porphyry intrusions. At Logtung, Type I quartz within comb layers is zoned with respect to a number of trace elements, including Al and K. Concentrations of these elements as well as Mn, Ti, Ge, Rb and H are anomalous and much higher than found in Type II quartz from Logtung or in igneous quartz reported elsewhere. The two populations appear to have formed under different conditions. The Type II quartz phenocrysts almost certainly grew from a high-silica melt between 600 and 800°C (as β-quartz); in contrast, the morphology of Type I quartz is consistent with precipitation from a hydrothermal solution, possibly as α-quartz grown below 600°C. The bulk compositions of comb-layered rocks, as well as the aplite interlayers, are consistent with the hypothesis that these textures did not precipitate solely from a crystallising silicate melt. Instead, Type I quartz may have grown from pockets of exsolved magmatic fluid located between the magma and its crystallised border. The Type II quartz represents pre-existing phenocrysts in the underlying magma; this magma was quenched to aplite during fracturing/degassing events. Renewed and repeated formation and disruption of the pockets of exsolved aqueous fluid accounts for the rhythmic banding of the rocks.
Granitic pegmatites
Authors: London David 
Published: November 2011

ABSTRACT:The primary focus of this review is onP-Tconditions, mineralogical indicators of melt or fluid composition and textural evolution; lesser treatment is given to pegmatite sources or to pegmatite-wallrock interactions. Investigations of stable and radiogenic isotopes have revealed that the source materials for pegmatites are likely to be more heterogeneous or varied than previously thought, especially for peraluminous pegmatites, but that overall pegmatites bear a clear intrusive relationship with their hosts, as opposed to an originin situ. TheP-Tconditions of crystallisation of some lithium-rich pegmatites have been constrained by lithium aluminosilicate stability relations in combination with stable isotope or fluid inclusion methods. Experimental studies have elucidated the effects of components such as Li, B, P and F, which are common in some classes of pegmatites, to liquidus relations in the hydrous haplogranite system. Experimentation has also provided corroboration of an old concept of pegmatite crystallisation—that pegmatites owe their distinctive textures and mineral/chemical zonation to relatively rapid crystallisation of melt from the margins inwards at conditions far from the equilibrium (i.e. from supercooled liquids). The origin of aplites, whether alone, layered, or paired with pegmatites, remains an active area of research. Studies of fluid inclusions, crystal-vapour equilibria and wallrock alteration have helped to define the timing and compositions of vapour phases in pegmatites and to aid in the economic evaluation of deposits.
Evidence of heterogeneous crustal sources: the Harney Peak Granite, South Dakota, U.S.A.
Authors: Krogstad Eirik J. , Walker Richard J. 
Published: November 2011

ABSTRACT:The Early Proterozoic (1715 Ma) Harney Peak Granite (Black Hills, SD, U.S.A.) is a complex of hundreds of dykes and sills. Earlier studies of Nd, O and Pb isotope variations demonstrated that the complex was not derived from a single source, or even different sources of a single age. Instead, the granites can be divided into a group with sources probably dominated by Early Proterozoic sediments and a group with sources probably dominated by Archean sediments. New results on the Nd isotopic variations of many additional samples indicate that there is considerable overlap between Nd isotopic compositions within the complex. Values of εNd (1715 Ma) of the Harney Peak Granite suite (n = 20) range from −2·0, indicating an Early Proterozoic (2300-2200 Ma) crustal source, to −13·4, indicating a Middle to Late Archean (3200-3100 Ma) protolith. These results suggest that the Early Proterozoic source may have included rocks such as the c. 2200-1900 Ma metasedimentary rocks that occur in the southern Black Hills. The Archean sources might have included rocks such as those exposed on the periphery of the Black Hills. The range in Nd model ages negates the usefulness of the concept of the ‘average’ age of the crust in this part of the craton. Because such heterogeneity is present in the magmatic compositions of the Harney Peak Granite, it can be inferred that at least as much heterogeneity was present in the sources. In this granite system, melts were evidently derived from isolated, heterogeneous zones and did not have the opportunity to coalesce into large magma bodies. In systems where coalescence does occur, the evidence for such highly heterogeneous sources may be lost. These results emphasise that inferences drawn from a few samples of plutonic rocks in which magma mixing and homogenisation occurred can lead to erroneous conclusions about the age and nature of protoliths and, consequently, the development of continental crust.
Ontogeny of the trilobiteParabolina spinulosa(Wahlenberg, 1818) from the upper Cambrian Alum Shales of Sweden
Authors: Clarkson Euan N. K. , Taylor Cecilia M. , Ahlberg Per 
Published: November 2011

AbstractThe ontogeny ofParabolina spinulosais described on the basis of material from Andrarum (Skåne) and Jämtland in Sweden. Protaspides are rare, and indifferently preserved, but well-preserved isolated tagmata and complete specimens from the early meraspid stages onwards were available for study. Whereas the ontogeny is broadly similar to that of the earlierOlenus wahlenbergi, there are subtle differences, notably in a greater spinosity from the earlier stages and a gradual, rather than a sudden, change of surface sculpture in the early holaspid.P. spinulosaat all stages of growth is much more variable than isOlenus. Meraspides have larger articulating halfrings anteriorly and the first thoracic segments are of greater sagittal length than in the adult; these were adaptations which enabledParabolinato undergo cylindrical enrollment from an early stage.Parabolinais considered to have arisen from the earlier genusOlenus, and on the basis of comparative ontogeny many, though not all, features ofParabolinaappear to be of paedomorphic origin. These include the reduction of the preglabellar field, retention of the visual surface, position of the eyes set close to the glabella, retention of a conterminant hypostome, yoking of the librigenae, spinosity of the thorax and pygidium, more numerous glabellar furrows and reduction in number of thoracic segments.Olenus attenuatushas several features intermediate between those of earlierOlenusspecies andParabolina, and the origin of the latter genus is best considered in terms of a mosaic paedomorphocline.
Carboniferous dykes as monitors of post-Caledonian fluid events in West Connacht, Ireland
Authors: Jenkin Gawen R. T. , Mohr Paul , Mitchell John G. , Fallick Anthony E. 
Published: November 2011

AbstractThe causes of hydrothermal alteration in dolerite dykes intruding Caledonian rocks of W Connacht are investigated using stable isotope, water content and K–Ar data for whole rocks and mineral separates. Using an isochron approach the Logmór dyke in the north is re-dated to 308±4 Ma; previously determined older whole-rock ages reflect excess 40Ar. The ∼ 305 Ma age previously proposed for the Teach Dóite suite in the south is reinforced by a 305 Ma age on a pyroxene separate, although the severe resetting of most samples is emphasised by other pyroxene and plagioclase ages of ∼210 Ma. Pyroxene δ18O values for these Upper Carboniferous dykes are mostly 5·5 to 6·1%, indicating negligible crustal contamination. Logmór whole-rock samples have water contents of 1·7–2·1 wt.%, δ5D= 59 to –47‰ and δ18O = 9·4 to 9·6‰; plagioclase shows little mineralogical alteration but its δ18O is 9·7‰. Hydrothermal alteration involving a local formation or metamorphic water took place at high fluid/rock ratios and high temperature during cooling after intrusion, most probably in a thermally-driven convection system. Teach Dóite dykes have water contents of 2·0–4·2 wt.%. δD= –58 to –38‰ and δ18O = 3·6 to 9·2‰, and were mostly altered in two stages; hydration upon intrusion to ∼ 2 wt.% water by contemporaneous meteoric water at low fluid/rock ratios was followed by extensive chemical and isotopic alteration at ∼210 Ma (Upper Triassic) by surface waters. This latter event could also have caused the extensive alteration observed in the host rocks.
On the nature of the parental magma of the Palaeogene Staffa Magma sub-type, Isle of Mull, Scotland
Authors: Kerr Andrew C. 
Published: November 2011

AbstractThe tholeiitic, columnar (Staffa type) lavas found at, and near, the base of the Tertiary lava succession on the Isle of Mull contrast markedly with overlying transitional tholeiiticalkalic Mull Plateau Group lavas, and as a result previous workers have classed the Staffa type lavas as a distinct group. The Staffa type lavas are among the most contaminated in the British Tertiary Igneous Province and have equilibrated and fractionated at shallow depths within the crust (relative to the overlying Plateau Group lavas), so obscuring the chemical identity of their parental magma. However, Staffa type lavas which are more basic than examples hitherto reported help in the elucidation of the parental magma. It is demonstrated that the Staffa type lavas were derived from a parental magma which was compositionally similar to that of Plateau Group lavas. The primary reasons for the distinctive features of the Staffa type are related to post-mantle melt generation processes, i.e. to extensive crystal fractionation and to crustal contamination at shallow crustal depths. The lavas are compositionally and temporally unrelated to the Hebridean tholeiitic magma types, the Central Mull Tholeiite type and the Skye Preshal More type.
Depositional controls on Early Cambrian microbial carbonates from the Montagne Noire, southern France
Authors: Álvaro J. Javier , Vennin Emmanuelle , Vizcaïno Daniel 
Published: November 2011

AbstractLower Cambrian shallow-water carbonates enclosing microbial structures are documented for the first time from the upper Lastours Member of the Montagne Noire (southern France). Microbial organisms constructed self-supported boundstones resulting in the formation of exclusively microbial-accreted buildups, which exhibit three main types of non-skeletal microbialites: planar stratiform stromatolites, dome-shaped stromatolites and nonlaminated (thrombolitic) biostromes. In addition, thrombolitic boundstones display four distinct microbial microstructures: clotted andRenalcis-like forms, branching bushy forms, clusters of unbranching straight filaments and crustose forms.The upper member of the Lastours Formation records an upward transition from a shalydominant open shelf to a protected shelf environment bounded by a surface representing a major subaerial exposure. Initially, at the inception of the highstand systems tract, flat stratiform stromatolites formed on open sea subtidal shaly substrates, while stacked domal stromatolites developed in peritidal areas which record subaerial exposure. In contrast, prograding shoal barriers of the transgressive systems tract favoured the establishment of thrombolitic boundstones in protected (back-shoal) environments.
Karoo tupilakosaurid: a relict from Gondwana
Authors: Warren Anne 
Published: November 2011

AbstractA new temnospondyl, Thabanchuia oomie gen. et sp. nov., is described from three skulls and associated postcranial elements from the Early Triassic Lystrosaurus Zone of South Africa. T. oomie is the best-preserved member of the Tupilakosauridae, a temnospondyl taxon previously known only from disarticulated material from Russia and Greenland, but shown here to include Kourerpeton bradyi, an articulated specimen with no locality data but presumed to be from North America. Tupilakosaurids are the only Mesozoic survivors of the dvinosaurian radiation, the sister group to the archegosaurs of the Permian plus the stereospondyl clade. It is postulated that their occurrence in Russia, Greenland and North America represents a reinvasion from Gondwana, where they survived the Late Permian extinctions along with the stem of the stereospondyl clade. T. oomie is probably immature but, like other members of the dvinosaurian clade, was fully aquatic, had ossified ceratobranchials and most likely an increased number of vertebrae and reduced limbs. Like Tupilakosaurus, T. oomie had diplospondylous centra.
A new chasmataspid (Chelicerata: Chasmataspida) from the Lower Devonian of the Midland Valley of Scotland
Authors: Dunlop Jason A. , Anderson Lyall I. , Braddy Simon J. 
Published: November 2011

AbstractA new chasmataspid (Chelicerata, Chasmataspida) is described as Forfarella mitchelli gen. et sp. nov. from the Lower Devonian of Scotland. This species is problematic in that it was catalogued under the name Forfarella mitchelli Waterston (no date), but was never formally described. Furthermore, its type locality is uncertain. Chasmataspids are a poorly known taxon within Chelicerata which appear to be closely related to eurypterids. F. mitchelli is only the fourth chasmataspid species to be described. Though poorly preserved, it shows affinities with other Devonian chasmataspids and supports the hypothesis that this group may have been more geographically widespread in the Devonian than has previously been recognised.
A study of the new samples of the Pliocene Hipparion (Equidae, Mammalia) from Spain and Bulgaria
Authors: Alberdi Maria T. , Alcalá Luis 
Published: November 2011

AbstractThe Pliocene Hipparion from La Gloria 4, La Calera, Orrios 1 and 3, Villalba Alta Río 1, Villalba Alta (Teruel basin) and Layna (Soria province), all in Spain, and Dorkovo (Sofia, Bulgaria), are described and tested by multivariate analysis. These Spanish and Dorkovo forms are compared with the specimens from Pavlodar (large-sized) and Kalmakpai (both in Kazakhstan), Çalta (large-sized, Turkey), the Roussillon (France) and Alcoy (Spain). The faunal assemblages indicate an Early and Late Alfambrian age (Ruscinian, MN14 and MN15) for the Spanish Hipparion and Early Alfambrian (MN14) for Dorkovo specimens. Hipparion remains from Pliocene Spanish localities show a very similar structure. They are referred to Hipparion fissurae, except Orrios 1 assigned to Hipparion aff. H. fissurae and Villalba Alta classified as Hipparion cf. H. fissurae. Despite certain relationships between Hipparion from Layna and Pavlodar, the multivariate analysis confirms the independence of both forms: H. fissurae in Layna, and H. longipes in Pavlodar. The specimens from Kalmakpai present many features close or intermediate to Layna and Pavlodar forms. Finally, Hipparion from Dorkovo is determined as Hipparion cf. H. crassum. These remains have a great morphological resemblance to H. crassum from Roussillon.