bluuebunny/crossref_metadata_2025 huggingface dataset:
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

The 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

Lower 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

A 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

A 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

The 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.
Biometrical trends in the Tetraconodontinae, a subfamily of pigs
Authors: van der Made J.
Published: November 2011

The Tetraconodontinae Lydekker, 1876 are a subfamily of pigs (Suidae) with a great variety of dental adaptations, such as greatly enlarged or reduced premolars, enlarged posterior molars, hypsodonty, enlarged incisors etc. The essence of most of these adaptations can be described very well by simple biometry. Size increase of the last molars has proved to be of importance in African biostratigraphy. However, it appears that members of different lineages have been mixed up.

Tendencies in relative premolar size indicate that the 21 species known can be grouped in three tribes: (1) the Tetraconodontini, with very large or even extremely enlarged premolars and, in one of the lineages, a tendency to enlarge the posterior molars; (2) the Nyanzachoerini new tribe, characterised by moderately enlarged or even reduced premolars and with a tendency to increase the length of the posterior molars by the addition of distal cusps; and (3) the Parachleuastochoerini new tribe, with relatively long but narrower premolars. Both Nyanzachoerini and Tetraconodontini include species that were placed previously inConohyusandNyanzachoerus.

A very long gradually evolving lineage in the Nyanzachoerini, spanning 13 Ma, is documented. In the last 5 Ma of this lineage, M3 length increased at such a rate that a (sub)species can be recognised about every 0·7 Ma. Slightly lesser rates of evolution are found in some other lineages, but still others experienced apparently long periods of stasis or very slow evolution. In a single case there is a period of stasis combined with a sudden evolutionary jump as in the punctuated equilibria model.

In the cases of intercontinental dispersal events combined with cladogenesis, where the ancestor in the continent of origin could be identified, the cause of cladogenesis seems to have been geographical isolation. Two tetraconodont lineages were restricted to Eurasia for about 5 Ma. During the Late Miocene, members of these lineages dispersed repeatedly to Africa. The Vallesian is a period of profound climatic changes which are reflected in changes in biogeography of many taxa. It is assumed that these and later climatic changes enabled the dispersal of Tetraconodontinae to Africa.
A tetraconodontine pig from the Upper Miocene of Turkey
Authors: van der Made Jan , Tuna Vahdet
Published: November 2011

Two species of Tetraconodontinae dispersed in the early Late Miocene from Eurasia into Africa. Tetraconodontinae then became the dominant pigs in the African Late Miocene and Pliocene. Although the dispersal to Africa must have come from SW Asia, no Tetraconodontinae were known from the area dating from the time of this dispersal.

In this paper, a tetraconodontine tooth from the Nuri Yamut locality near AlÇitepe in European Turkey is described. In morphology, size and in geographical and stratigraphical position this tooth is close to a form that is ancestral to part of the African Tetraconodontinae. The tooth is assigned to cf. Conohyus giganteus, one of the species that dispersed to Africa.

The dispersals of these Tetraconodontinae seem to be more or less coeval with that of Hipparion and are assumed to be allowed for by a change in global climate.
Appendicular myology of the hadrosaurian dinosaur Maiasaura peeblesorum from the Late Cretaceous (Campanian) of Montana
Authors: Dilkes David W.
Published: November 2011

Musculature of the pectoral and pelvic appendages and girdles of adult and nestling Maiasaura peeblesorum (Dinosauria: Ornithischia: Hadrosauridae) from the Late Cretaceous of Montana is restored according to a phylogenetically based methodology. This methodology uses an explicit, independently derived phylogenetic hypothesis of the fossil taxon and related extant taxa to generate a series of inferences regarding the presence of a muscle, its number of components, and the origin(s) and insertion(s) of these components. Corroborative osteological evidence is sought on the fossil in the form of scars and processes that fulfill the criteria for muscular attachment according to generalisations based upon extant vertebrates. A total of 46 muscles are restored, although separate attachment sites for numerous muscles cannot be discerned on the fossils. Osteological evidence for several muscles can be found in nestlings of Maiasaura despite their skeletal immaturity. Results of the phylogenetically based approach and new hypotheses for homologies of deep dorsal thigh muscles suggest that it is more parsimonious to restore the femoral insertions of M. iliofemoralis on the greater trochanter and M. puboischiofemoralis internus on the anterior (lesser) trochanter, a reversal of the traditional interpretation. The often-cited osteological specialisations of birds for flight are not accompanied in all instances by profound myological transformations, and birds must be included in any attempt to restore the myology of extinct dinosaurs.
The ontogeny ofTaihungshania miqueli(Bergeron, 1893) from the Arenig of the Montagne Noire, southern France
Authors: Berard Pierre , Clarkson Euan N. K. , Taylor Cecilia M.
Published: November 2011

The very large trilobiteTaihungshania miquelioccurs abundantly in siliceous nodules in the Ordovician of the Montagne Noire, southern France, but in these, larval individuals are not preserved. At a new locality at Peret, near Cabrières, protaspid and early meraspid growth stages occur in great abundance, together with a few complete specimens belonging to meraspid degrees 1, 2, 3, 5 and 7, and a single young holaspis. Although this material is largely flattened, and the originally globular protaspides crushed, it is still possible to establish the development of several axial rings before the transitory pygidium becomes liberated. In the degree 0 meraspis, the cephalon and transitory pygidium are about the same size, and the presence of a partially enrolled degree 3 meraspis indicates that protective coiling was possible by this early stage. Palpebral lobes are incipient in degree 2 meraspides, and fully formed by degree 7, otherwise the morphology of the cephalon becomes quite adult-like by degree 4. The pygidial spines begin to appear in degree 5, at which stage there are about 10 axial rings; there are about 13 in a degree 7 meraspis, and in the adult, where the posterior contour is semi-elliptical, there are some 22. The smallest hypostomes present belong to a degree 6 meraspis, and these are morphologically similar to those of adults. Observations on the later growth stages were made on material from another locality (Caramaou), as well as that from Peret. In the eye the upper lenses are large and slightly separated, but those towards the base are much diminished in size; this is a function of an unusual growth geometry.

At Peret, all stages of development, at least as far as young adults, are represented, albeit often in a fragmentary state. As with other asaphines, the protaspides are assumed to be planktic, andT. miquelipresumably left the plankton and became benthic between the protaspid and meraspid periods.
Micro structural and mineralogical evidence for limited involvement of magma mixing in the petrogenesis of a Hercynian high-K calc-alkaline intrusion: the Kozárovice granodiorite, Central Bohemian Pluton, Czech Republic
Authors: Janoušek Vojtěch , Bowes D. R. , Braithwaite Colin J. R. , Rogers Graeme
Published: November 2011

Textural and mineralogical features in the high-K calc-alkaline Kozárovice granodiorite (Hercynian Central Bohemian Pluton, Bohemian Massif) and associated small quartz monzonite masses imply that mixing between acid (granodioritic) and basic (monzonitic/monzogabbroic) magmas was locally petrogenetically significant.

Net veining, with acicular apatite and numerous lath-shaped plagioclase crystals present in the quartz monzonite, and abundant mafic microgranular enclaves (MME) in the granodiorite, indicate that as the monzonitic magma was injected into the granodioritic magma chamber, it rapidly cooled and was partly disintegrated by the melt already present. Evidence from cathodoluminescence suggests that the two magmas exchanged early-formed plagioclase crystals. In the quartz monzonite, granodiorite-derived crystals were overgrown by narrow calcic zones, followed by broad, normally zoned sodic rims. In the granodiorite, plagioclase crystals with calcic cores overgrown by normally zoned sodic rims are interpreted as xenocrysts from the monzonite. After thermal adjustment, crystallisation of the monzonitic magma ceased relatively slowly, forming quartz and K-feldspar oikocrysts.

Although the whole-rock geochemistry of the quartz monzonite and the MME support magma mixing, major- and trace-element based modelling of the host granodiorite has previously indicated an origin dominated by assimilation and fractional crystallisation. Magma mixing therefore seems to represent a local modifying influence rather than the primary petrogenetic process.
Origin of heterogeneous mafic enclaves by two-stage hybridisation in magma conduits (dykes) below and in granitic magma chambers
Authors: Collins W. J. , Richards S. R. , Healy B. E. , Ellison P. I.
Published: November 2011

Field, petrographic and geochemical evidence from the K-feldspar megacrystic Kameruka pluton, Lachlan Fold Belt, southeastern Australia, suggests that complex, multicomponent, mafic microgranular enclaves (MME) are produced by two-stage hybridisation processes. Stage 1 mixing occurs in composite dykes below the pluton, as mafic and silicic melts ascend through shared conduits. Pillows formed in these conduits are homogeneous, fine-to medium-grained stage 1 MME, which typically range from basaltic to granitic compositions that plot as a sublinear array on Harker diagrams. Stage 2 hybridisation occurs in the magma chamber when the composite dykes mix with the resident magma as synplutonic dykes. The stage 2 hybrids also form linear chemical arrays and range from basaltic to granodioritic compositions, the latter resembling the more mafic phases of the pluton. Stage 2 MME are distinguished from stage 1 types by the presence of K-feldspar xenocrysts and a more heterogeneous nature: they commonly contain stage 1 enclaves. Subsequent disaggregation and dispersal of stage 2 hybrid synplutonic dykes within the magma chamber produces a diverse array of multi-component MME.

Field evidence for conduit mixing is consistent with published analogue experimental studies, which show that hybrid thermo-mechanical boundary layers (TMBL) develop between mafic and silicic liquids in conduits. A mechanical mixing model is developed, suggesting that the TMBL expands and interacts with the adjacent contrasting melts during flow, producing an increasing compositional range of hybrids with time that are mafic in the axial zone, grading to felsic in the peripheral zones in the conduit. Declining flow rates in the dyke and cooling of the TMBL zones produce a pillowing sequence progressing from mafic to felsic, which explains the general observation of more MME in more silicic hosts.

The property of granitic magmas to undergo transient brittle failure in seismic regimes allows analogies with fractured solids to be drawn. The fracture network in granitic magmas consists of through-going ‘backbone’ mafic and silicic ± composite dykes, and smaller ‘dangling’ granitic dykes locally generated in the magma chamber. Stage 1 hybrids form in composite backbone dykes and stage 2 hybrids form where they intersect dangling dykes in the magma chamber. With subsequent shear stress recovery, the host magma chamber reverts to a visco-plastic material capable of flow, resulting in disaggregation and dispersal of these complex, hybrid synplutonic dykes, and a vast array of double and multicomponent enclaves potentially develop in the pluton.
Grain-scale and outcrop-scale distribution and movement of melt in a crystallising granite
Authors: Sawyer E. W.
Published: November 2011

The distribution of melt has been mapped in a granite pluton deformed whilst it contained melt. At the outcrop scale, leucomonzogranite melt was segregated from hornblende monzogranite when the rigid crystal framework was tectonically compacted. The melt collected in well-defined, structurally controlled sites that formed during dextral, non-coaxial, strike-slip shearing. The segregations are generally isolated, but locally they link to form extensive branched arrays which drained larger volumes of granite in a two-step process. First, melt drained from the compacting matrix through the array and pooled along dilatant foliation planes; later, the melt moved farther away when a single planar melt-transfer channel formed.

Thin section maps show that most melt was distributed in the foliation plane and along the lineation in the crystallising matrix. The location of melt at the grain scale is primarily controlled by the feldspar-dominated shape fabric of the crystal framework, and not by tectonic stresses as at the outcrop scale. Tectonic stresses account for the relatively small proportion of melt films located in grain boundaries normal to the lineation. The distribution of melt-bearing grain boundaries outlines larger domains in the thin sections that form a linked three-dimensional network through which melt moved within the crystallising framework.
Dyke widths and ascent rates of silicic magmas on Venus
Authors: Petford Nick
Published: November 2011

The ascent of silicic magmas in dykes and diapirs on Venus is investigated using magma transport models for granitic melts on Earth. For fixed planetary thermal and melt properties, differences in critical minimum dyke widths, and hence magma ascent rates, are controlled by gravitational strength alone. For density contrasts of 200–600 kg/m3 and a solidus temperature of 1023 K, minimum critical dyke widths (wc) on Venus range from c. < 1–1200 m for a transport distance of 20 km. Dyke widths are especially sensitive to small changes in the far-field lithospheric temperature at values close to a critical Stefan number (S∝crit) of 0·83 where dyke magma temperatures are equal to the mean surface temperature. Typical magma ascent rates range from 0·02m/s (ηm = 105 Pa s) to 10−9 m/s (ηm = 1017 Pa s) giving transport times of between 12 days and c. 105 years. Dyke ascent velocities for highly viscous melts are compared with diapiric rise of a hot Stokes body of radius comparable with the pancake dome average (c. 12 km), and require dyke widths of the order of 100 times the average width of low viscosity flows to prevent freezing. In both cases, magma flow is characterised by Péclet numbers between 1 and 4, although even at high viscosities (> 1014 Pa s), dyke ascent is still 100 to 1000 times faster than diapiric rise. At a melt viscosity of 1017 Pa s, critical dyke widths are between c. 1% and 5% the diameter of an average width pancake dome on Venus, indicating that even for extreme melt viscosities, domes can easily be fed by dykes. Given the abundance of dome structures and associated surface features related to hyperbasal magmatism, batholithic volumes of silicic rocks may be present on Venus. Intermediate to high silica melts formed by partial melting of the Venusian crust should be compositionally more akin to Na-rich terrestrial adakites and trondhjemites than calc-alkaline dacites or rhyolites.
Age and origin of coeval TTG, I- and S-type granites in the Famatinian belt of NW Argentina
Authors: Pankhurst R. J. , Rapela C. W. , Fanning C. M.
Published: November 2011

Three granitoid types are recognised in the Famatinian magmatic belt of NW Argentina, based on lithology and new geochemical data: (a) a minor trondhjemite–tonalite–granodiorite (TTG) group, (b) a metaluminous I-type gabbro-monzogranite suite, and (c) S-type granites. The latter occur as small cordieritic intrusions associated with 1-type granodiorites and as abundant cordierite-bearing facies in large batholithic masses. Twelve new SHRIMP U-Pb zircon ages establish the contemporaneity of all three types in Early Ordovician times (mainly 470-490 Ma ago). Sr- and Nd-isotopic data suggest that, apart from some TTG plutons of asthenospheric origin, the remaining magmas were derived from a Proterozoic crust-lithospheric mantle section. Trace element modelling suggests that the TTG originated by variable melting of a depleted gabbroid source at 10-12kbar, and the I-type tonalite-granodiorite suite by melting of a more enriched lithospheric source atc.5 kbar. The voluminous intermediate and acidic I-types involved hybridisation with lower and middle crustal melts. The highly peraluminous S-type granites have isotopic and inherited zircon patterns similar to those of Cambrian supracrustal metasedimentary rocks deposited in the Pampean cycle, and were derived from them by local anatexis. Other major components of the S-type batholiths involved melting of deep crust and mixing with the I-type magmas, leading to an isotopic and geochemical continuum.
Granitoids of the Central Asian Orogenic Belt and continental growth in the Phanerozoic
Authors: Jahn Bor-ming , Wu Fuyuan , Chen Bin
Published: November 2011

The Central Asian Orogenic Belt (CAOB), also known as the Altaid Tectonic Collage, is characterised by a vast distribution of Paleozoic and Mesozoic granitic intrusions. The granitoids have a wide range of compositions and roughly show a temporal evolution from calcalkaline to alkaline to peralkaline series. The emplacement times for most granitic plutons fall between 500 Ma and 100 Ma, but only a small proportion of plutons have been precisely dated. The Nd-Sr isotopic compositions of these granitoids suggest their juvenile characteristics, hence implying a massive addition of new continental crust in the Phanerozoic. In this paper we document the available isotopic data to support this conclusion.

Most Phanerozoic granitoids of Central Asia are characterised by low initial Sr isotopic ratios, positive εNd(T) values and young Sm—Nd model ages (TDM) of 300-1200 Ma. This is in strong contrast with the coeval granitoids emplaced in the European Caledonides and Hercynides. The isotope data indicate their ‘juvenile’ character and suggest their derivation from source rocks or magmas separated shortly before from the upper mantle. Granitoids with negative εNd(T) values also exist, but they occur in the environs of Precambrian microcontinental blocks and their isotope compositions may reflect contamination by the older crust in the magma generation processes.

The evolution of the CAOB is probably related to accretion of young arc complexes and old terranes (microcontinents). However, the emplacement of large volumes of post-tectonic granites requires another mechanism, probably through a series of processes including underplating of massive basaltic magma, intercalation of basaltic magma with lower crustal granulites, partial melting of the mixed lithologic assemblages leading to generation of granitic liquids, followed by extensive fractional crystallisation. The proportions of the juvenile or mantle component for most granitoids of Central Asia are estimated to vary from 70% to 100%.
Bimodal magmatism as a consequence of the post-collisional readjustment of the thickened Variscan continental lithosphere (Aiguilles Rouges-Mont Blanc Massifs, Western Alps)
Authors: Bussy François , Hernandez Jean , Von Raumer Jürgen
Published: November 2011

High Precision U-Pb zircon and monazite dating in the Aiguilles Rouges–Mont Blanc area allowed discrimination of three short-lived bimodal magmatic pulses: the early 332 Ma Mg–K Pormenaz monzonite and associated 331 Ma peraluminous Montées Pélissier monzogranite; the 307 Ma cordierite-bearing peraluminous Vallorcine and Fully intrusions; and the 303 Fe-K Mont Blanc syenogranite. All intruded syntectonically along major-scale transcurrent faults at a time when the substratum was experiencing tectonic exhumation, active erosion recorded in detrital basins and isothermal decompression melting dated at 327-320 Ma. Mantle activity and magma mixing are evidenced in all plutons by coeval mafic enclaves, stocks and synplutonic dykes. Both crustal and mantle sources evolve through time, pointing to an increasingly warm continental crust and juvenile asthenospheric mantle sources. This overall tectono-magmatic evolution is interpreted in a scenario of post-collisional restoration to normal size of a thickened continental lithosphere. The latter re-equilibrates through delamination and/or erosion of its mantle root and tectonic exhumation/erosion in an overall extensional regime. Extension is related to either gravitational collapse or back-arc extension of a distant subduction zone.
Nature and longevity of hydrothermal fluid flow and mineralisation in granites of the Bushveld Complex, South Africa
Authors: Robb L. J. , Freeman L. A. , Armstrong R. A.
Published: November 2011

The Lebowa Granite Suite of the Bushveld Complex is a large, 2054 Ma old, A-type batholith, characterised by numerous relatively small magmato-hydrothermal, polymetallic ore deposits. The mineralisation is represented by a three-stage paragenetic sequence: early magmatic Sn-W-Mo-F ores (600°C > T > 400°C), followed by a Cu-Pb-Zn-As-Ag-Au paragenesis (400°C > T > 200°C) and then late-stage Fe-F-U mineralisation (< 200°C). The first stage of mineralisation (typified by the endogranitic Zaaiplaats tin deposit) is related to incompatible trace element concentration during crystal fractionation and subsequent fluid saturation of the magma. Evolution of the late magmatic fluids as they were channelled along fractures, as well as mingling with externally derived connate or meteoric fluids, resulted in the deposition of the second stage of mineralisation (typified by the fracture-related, endogranitic Spoedwel and Albert deposits and the exogranitic, sediment-hosted Rooiberg mine) which is dominated by polymetallic sulphide ores. As the externally derived fluid component became progressively more dominant, oxidation of the polymetallic sulphide assemblage and precipitation of hematite, pitchblende and fluorite occurred generally along the same fracture systems that hosted the earlier sulphide paragenesis.

Small hydrothermal zircons trapped along quartz growth zones from the Spoedwel deposit yield a U-Pb concordia age of 1957 ± 15 Ma. Whole-rock Rb-Sr age determinations from the Lebowa Granite Suite fall in the range 1790 ± 114 Ma to 1604 ± 70 Ma and are interpreted to reflect alkali element mobility and isotopic resetting during exhumation of the Bushveld granite. In contrast to thermal modelling which indicates that hydrothermal activity should have ceased within 4 my of emplacement, isotopic evidence suggests that mineralisation was long-lived, but episodic, and that fluid flow events were linked to major periods of Palaeo- and Mesoproterozoic orogenic activity along the margins of the Kaapvaal Craton. During these orogenic episodes, fluid flow was enhanced by tectonically induced fluid over-pressuring and/or exhumation of the Bushveld Complex.
The Disappointment Hill complex: Proterozoic granulites in southwestern Newfoundland
Authors: Owen J. V. , Currie K. L.
Published: November 2011

The Steel Mountain terrane of the southern Long Range Mountains forms a fault-bounded massif of (meta)plutonic rocks including the Disappointment Hill complex (DHC), a sequence of granulite-facies lithologies containing charnockite emplaced at 1498 Ma (U-Pb, zircon). Quartzofeldspathic gneiss of the DHC contains garnet + biotite + orthopyroxene ± cordierite assemblages indicative of metamorphic P–T conditions of ca 750°C and 400 MPa. The relatively high thermal gradient (ca 70°C km−1) inferred for the DHC is attributed to a magmatic heat source.

On grounds of lithology, age and metamorphic grade, the DHC correlates to granulites of the Long Range Inlier (LRI) exposed farther north. Both complexes occur in blocks thrust westward over Taconic allochthons capped by ophiolite nappes. The block containing the DHC, however, preserves younger cover rocks, suggesting that it originated at a higher structural level than the LRI. This model is supported by lower pressure estimates for the DHC relative to the LRI (400 MPa vs 500–800 MPa). The DHC forms a link between Grenvillian rocks of the northern Long Range of Newfoundland and those of Cape Breton Island. The structural position of these massifs suggests that their emplacement was a post-Taconic event.
Geochemistry and original nature of Precambrian khondalites in the Eastern Ghats, Orissa: a discussion
Authors: Nanda J. K. , Pati U. C.
Published: November 2011

While congratulating the authors for the wealth of geochemical data on a very important Precambrian lithological assemblage of India, known commonly as khondalites, which constitute a major part of the Eastern Ghats mobile belt bordering the eastern fringes of the Indian Peninsula, we have a few comments to offer on the hypothesis propounded by the authors (Dash et al. 1987).
Origin of sulphur in metamorphosed stratabound mineralisation from the Argyll Group Dalradian of Scotland
Authors: Scott R. A. , Pattrick R. A. D. , Polya D. A.
Published: November 2011

Sulphur isotopic data are presented for the four horizons of stratabound mineralisation in the Argyll Group Dalradian (Vendian) of the Central Highlands of Scotland. The styles of mineralisation reflect the stratigraphic and tectonic evolution of the Dalradian basin. The SEDEX-type Ba + (Zn + Pb) Loch Lyon Horizon has δ34S values for pyrite of +17% and for baryte of +27%. The baryte sulphur source was Dalradian sea-water although the values were modified by isotopic exchange with an H2S-rich metamorphic fluid derived from the surrounding graphitic schists. The sulphur source for sulphide in the horizon was probably the underlying strata; sulphide values were only slightly affected by metamorphism. Sulphides in the Pyrite Horizon are isotopically indistinguishable from those in the remainder of the volcanogenic Ben Lawers Schist Formation (0 ± 4%); these values suggest that, at least in the Tyndrum area, sulphides in the Pyrite Horizon are of igneous origin. VMS-type Cu + Zn + Pb mineralisation in the Ben Challum Quartzite Formation has a narrow range of values around + ll%. The likely source of this sulphide sulphur is reduced sea-water sulphate, the isotopic values remaining consistent owing to the buffering effect of anhydrite in the underlying calcium-rich rocks.
The perforated trilobiteLaethoprusiagen. nov., and the phylogeny ofKoneprusiaandIsoprusia(Odontopleuridae, Koneprusiinae)
Authors: Ramsköld Lars
Published: November 2011

The subfamily Koneprusiinae is revised as part of a larger study of the Odontopleuridae, andLaethoprusiagen. nov. is described. The type speciesL. salaxsp. nov. is from the Wenlock of Gotland, Sweden, and the genus is known also from the Wenlock of the Montagne Noire in south France, and from the Lower Devonian of Australia. The type species is most unusual among trilobites in possessing large fenestrae perforating the exoskeleton on segmental boundaries from the cephalic posterior margin to within the pygidium. The fenestrae were probably covered with soft tissues. Their function is enigmatic.Laethoprusiagen. nov. is the sister taxon toIsoprusiaand/orKoneprusia. These genera are revised, and a review of all species assigned to them is given. A cladistic analysis of the best known taxa ofLaethoprusia, Isoprusia, andKoneprusiais presented.Laethoprusiais the most derived genus of the subfamily, although stratigraphically it is the earliest.
Calymenid trilobites from the Wenlock Series (Silurian) of Britain
Authors: Siveter Derek J.
Published: November 2011

Most species of calymenid trilobite from the Wenlock Series of Britain are revised. In total, British trilobites of this family and epoch comprise nine species and three genera, with a further six species being referred to under open nomenclature:Calymeneis represented by five species,Tapinocalymeneby three andDiacalymeneby one. One new subspecies,C. neotuberculata ludicra, and one new species,C. fuliginata, from the lower and upper Wenlock, respectively, are established. The previously monotypicD. allportiana(Salter, 1865) is now known from about 50 specimens. The upper Wenlock Much Wenlock Limestone Formation yields five species, the most for any formation.Calymeneoccurs mostly in the shallower water facies on the western edge of the Midland Platform and eastern and southern margins of the Welsh Basin,Tapinocalymeneessentially in the more offshore carbonate muds of this basin andD. allportianaon the fringe of the Midland Platform and more offshore carbonate muds. British Wenlock calymenids show some affinity with those of the Scandinavia-Baltic area.C. tuberculosaDalman, 1827 is recorded with certaintyin situoutside Gotland for the first time.
Partially melted granodiorite and related rocks ejected from Crater Lake caldera, Oregon
Authors: Bacon Charles R.
Published: November 2011

Blocks of medium-grained granodiorite to 4 m, and minor diabase, quartz diorite, granite, aplite and granophyre, are common in ejecta of the ∼6,900 yrBP calderaforming eruption of Mount Mazama. The blocks show degrees of melting from 0–50 vol%. Because very few have adhering juvenile magma, it is thought that the blocks are fragments of the Holocene magma chamber's walls. Primary crystallisation of granodiorite produced phenocrystic pl + hyp + aug + mt + il + ap + zc, followed by qz + hb + bt + alkali feldspar (af). Presence of fluid inclusions in all samples implies complete crystallisation before melting. Subsolidus exchange with meteoric hydrothermal fluids before melting is evident in δ18O values of −3·4+4·9‰ for quartz and plagioclase in partially melted granodiorites (fresh lavas from the region have δ18O values of +5·8−+7·0‰); δ18O values of unmelted granodiorites from preclimatic eruptive units suggest hydrothermal exchange began between ∼70 and 24 ka. Before eruption, the granitic rocks equilibrated at temperatures, estimated from Fe-Ti oxide compositions, of up to ∼1000°C for c. 102–104 years at a minimum pressure of 100-180 MPa. Heating caused progressive breakdown or dissolution of hb, af, bt, and qz, so that samples with the highest melt fractions have residual pl + qz and new or re-equilibrated af + hyp + aug + mt + il in high-silica rhyolitic glass (75-77% SiO2). Mineral compositions vary systematically with increasing temperature. Hornblende is absent in rocks with Fe-Ti oxide temperatures >870°C, and bt above 970°C. Oxygen isotope fractionation between qz, pl, and glass in partially fused granodiorite also is consistent with equilibration at T≥900°C (Δ18Oqz.pl = +0·7 ± 0·5‰). Element partitioning between glass and crystals reflects the large fraction of refractory pl, re-equilibration of af and isolation or incomplete dissolution of accessory phases. Ba and REE contents of analysed glass separates can be successfully modelled by observed degrees of partial melting of granodiorite, but Rb, Sr and Sc concentrations cannot. Several samples have veins of microlite-free glass 1–5 mm thick that are compositionally and physically continuous with intergranular melt and which apparently formed after the climactic eruption began. Whole-rock H2O content, microprobe glass analysis sums near 100% and evidence for high temperature suggest liquids in the hotter samples were nearly anhydrous. The occurrence of similar granodiorite blocks at all azimuths around the 8 × 10 km caldera implies derivation from one pluton. Compositional similarity between granodiorite and pre-Mazama rhyodacites suggests that the pluton may have crystallised as recently as 0·4 Ma; compositional data preclude crystallisation from the Holocene chamber. The history of crystallisation, hydrothermal alteration, and remelting of the granitic rocks may be characteristic of shallow igneous systems in which the balance between hydrothermal cooling and magmatic input changes repeatedly over intervals of 104-106 years.
Granites and rhyolites from the northwestern U.S.A.: temporal variation in magmatic processes and relations to tectonic setting
Authors: Norman Marc D. , Leeman William P. , Mertzman Stanley A.
Published: November 2011

Cretaceous and Cainozoic granites and rhyolites in the northwestern U.S.A. provide a record of silicic magmatism related to diverse tectonic settings and large-scale variations in crustal structure. The Late Cretaceous Idaho Batholith is a tonalitic to granitic Cordilleran batholith that was produced during plate convergence. Rocks of the batholith tend to be sodic (Na2O > K2O), with fractionated HREE, negligible Eu anomalies, and high Sr contents, suggesting their generation from relatively mafic sources at a depth sufficient to stabilise garnet. In contrast, Neogene rhyolites of the Snake River Plain, which erupted in an extensional environment, are potassic (K2O > Na2O), with unfractionated HREE patterns, negative Eu anomalies, and low Sr contents, suggesting a shallower, more feldspathic source with abundant plagioclase. Eocene age volcanic and plutonic rocks have compositions transi- tional between those of the Cretaceous batholith and the Neogene rhyolites. These data are consistent with a progressively shallowing locus of silicic magma generation as the tectonic regime changed from convergence to extension.
Migmatite and melt segregation at Cooma, New South Wales
Authors: Ellis D. J. , Obata M.
Published: November 2011

The Cooma Complex of southeastern New South Wales comprises an andalusite-bearing S-type granodiorite surrounded by migmatites and low-pressure metamorphosed pelitic and psammitic sediments. The migmatite formed by the melting reaction:

Biotite + Andalusite + K-feldspar + Quartz + V = Cordierite + Liquid

at about 350–400 MPa , 670-730°C.

The melanosome consists of biotite + cordierite + andalusite + K-feldspar + plagioclase + quartz + ilmenite, whereas the leucosome consists of cordierite + K-feldspar + quartz with extremely rare biotite and plagioclase. In a closed system, freezing of the leucosome melt patches should have resulted in cordierite back-reaction with melt to produce biotite and andalusite. The virtually anhydrous mineralogy of the leucosome patches, lack of cordierite reaction and the absence of biotite selvedges at the leucosome-melanosome contacts, indicates that the melt did not completely solidify in situ. These observations can be explained by an initial peritectic melting reaction in the migmatite being arrested from back-reaction upon cooling because of the removal of hydrous melt, enabling leucosome cordierite to escape back-reaction. We propose that the melanosome is the residue of partial melting but that the leucosome patches do not represent frozen melt segregations but rather the liquidus minerals (cumulates) which precipitated from the melt.

In the restite-rich granodiorite from the core of the Cooma Complex, cordierite of similar composition to that in the migmatite has reaction rims of biotite and andalusite and there are coexisting biotite and andalusite in the matrix. The granodiorite consisted of about 50 wt% melt together with resite biotite, quartz and plagioclase, which can possibly be identified in the surrounding migmatite. Previous work suggested that the Cooma Granodiorite can be derived from a mixture of the surrounding metasediments which are of similar composition in the high and low-grade areas surrounding the granodiorite. Re-examinatibn of those data shows that the high-grade metasediments are more An-rich than the low-grade rocks. The Cooma Granodiorite is very similar to the high-grade rocks in terms of Or-Ab-An ratio. This suggests derivation of the Cooma Granodiorite from the high-grade rocks and not from the relatively An-poor low-grade rocks which are typical of exposed sediments in the Lachlan Fold Belt. It is most likely that the granodiorite and envelope of high-grade rocks have been emplaced into the compositionally different lower grade rocks from slightly greater depths.
Using granite to image the thermal state of the source terrane
Authors: Zen E-an
Published: November 2011

It should be possible to infer the thermal state of the source terrane for granitic bodies, provided we have independent means to establish the chemical nature of this terrane. The chemical nature of the granitic rocks, including their degree of hydration, implies the solidus temperature. The concentration of the heat-producing radioactive elements in the granite (K, U, and Th) probably provides an upper estimate of their concentration in the source rock, which is an important thermal parameter. The depth and ambient temperature of the country rock into which the granite magma intruded provide useful boundary conditions for the thermal regime at the crustal level of anatexis. These constraints in turn form the bases for estimating the subcrustal thermal flux as well as the effective thermal interface for enhanced heat flow from below that resulted in anatexis. These inferences, in combination with other field-based parameters such as uplift rates and permissible time lapses for the geological events, permit realistic thermal modelling for the formation of granitic batholiths. The procedure is applied to the Late Cretaceous Pioneer and Boulder batholiths in southwestern Montana, U.S.A. The modelling results suggest that mantle upwelling, not subduction or thrust loading, caused anatexis. The isotopic chemistry of the granitic rocks rules out direct mixing of mantle magma, and field relations rule out crustal thinning as causes for partial melting.
C-type magmas: igneous charnockites and their extrusive equivalents
Authors: Kilpatrick Jonathan A. , Ellis David J.
Published: November 2011

Igneous charnockites are characterised by distinctively high abundances of K2O, TiO2, P2O5 and LIL elements and low CaO at a given SiO2 level compared to metamorphic charnockites, and I-, S- and A-type granites. They form a distinctive type of intrusive igneous rocks, the Charnockite Magma Type (CMT or C-type), which generally lack hornblende and consist of pyroxene, alkali feldspar, plagioclase, quartz, biotite, apatite, ilmenite and titanomagnetite. Although this mineral assemblage superficially resembles that of metamorphic charnockites, magmatic charnockites are characterised by inverted pigeonite, exceptionally calcic alkali feldspar, potassic plagioclase, and coexisting opaque oxides, all with crystallisation temperatures of 950-1050°C. Apatite is a ubiquitous phase which, together with the very high concentrations of Zr and TiO2 over a wide silica range, is consistent with the derivation of the Charnockite Magma Type by very high temperature partial melting and fractionation.

The credibility of intrusive charnockites as a magmatic type has historically foundered because of their apparent restriction to granulite belts and the absence of any reported extrusive equivalents. We report examples of volcanic rocks, of various ages, with the same distinctive major and trace element compositions, mineral assemblages and high temperatures of crystallisation as intrusive chamockites.

The Charnockite Magma Type is considered to be derived by melting of a hornblende-free or poor, LILE-enriched fertile granulite source which had not been geochemically depleted by a previous partial melting event but which was dehydrated in an earlier metamorphism. Whereas H2O-saturated melting produces migmatites or "failed" granites, and vapour-absent melting of an amphibolite can produce I-type granites, according to this model the vapour-absent melting of a hornblende-free or hornblende-poor granulite at even higher temperatures produces charnockites.
A nested diapir model for the reversely zoned Turtle Pluton, southeastern California
Authors: Allen Charlotte M.
Published: November 2011

Most zoned plutons described in the geological literature have mafic rims and felsic cores and are referred to as “normally zoned”, whereas relatively few “reversely zoned” intrusions (felsic rims and mafic cores) have been described. That unusual zonation pattern has been variously attributed to in situ processes or to the reordering of an underlying, vertically stratified, magma chamber either by intrusion through an orifice or by emplacement of composite diapirs. The Turtle Pluton is an early Cretaceous, reversely zoned, intrusion that is divided into four facies: a Rim Sequence that is graditionally zoned from bt + ilm + muse monzogranite to hb + bt + mt + sph granodiorite; a Core Facies of more homogeneous hb + bt + mt + sph granodiorite to quartz monzodiorite; between these two facies, a structural discontinuity termed the Schlieren Zone; and an Eastern Facies of monzogranite to granodiorite. Field relationships, distribution of strain, and geochemical and isotopic studies (including a range of initial87Sr/86Sr from 0·7085–0·7065) suggest that the reverse zonation of the Turtle Pluton is the result of sequential emplacement of two diapirs each derived from the same underlying, vertically stratified, magma chamber, and that the Rim Sequence zonation is chiefly the result of mixing of intermediate and felsic magmas from distinct sources accompanied by minor fractional crystallisation.