Lateral magma flow in mafic sill complexes

We benefitted from discussions with many Earth scientists in different disciplines over the years; we particularly thank Ken Thomson, Donny Hutton, Brian O’Driscoll, Mike Petronis, Ken McDermott, Derek Keir, Ben van Wyk de Vries, and Davie Brown for their insights. We thank Schlumberger for software and data provision, and Department of Communications, Energy, and Natural Resources (Petroleum Affairs Division) in Ireland, Geoscience Australia, and PGS (Petroleum Geo-Services) for provision of seismic data. This work was completed as part of Magee’s Junior Research Fellowship funded by Imperial College London. Muirhead acknowledges support from Fulbright New Zealand and the Ministry of Science and Innovation. We thank Shan de Silva for his editorial handling of the manuscript and Tyrone Rooney, Agust Gudmundsson, and Mattia Pistone for the time and effort they put in to their constructive reviews

Life and letters of John Bacchus Dykes, M.A., MUS. DOC., vicar of St. Oswald's, Durham.

"The work of a sister and niece of Dr. Dykes, who do not wish their names to be published." Appendix I: The bishop of Durham and the vicar of S. Oswald's. From the Durham county advertiser of Friday, July 25, 1873. App. II. Dr. Dykes' published hymn-tunes.

Characteristics and petrogenesis of Alaskan-type ultramafic-mafic intrusions, southeastern Alaska /

Mode of access: Internet.

Petrology and geochemistry of early cretaceous bimodal continental flood volcanism of the NW Etendeka, Namibia. Part 1: Introduction, mafic lavas and re-evaluation of mantle source components

The bimodal NW Etendeka province is located at the continental end of the Tristan plume trace in coastal Namibia. It comprises a high-Ti (Khumib type) and three low-Ti basalt (Tafelberg, Kuidas and Esmeralda types) suites, with, at stratigraphically higher level, interstratified high-Ti latites (three units) and quartz latites (five units), and one low-Ti quartz latite. Khumib basalts are enriched in high field strength elements and light rare earth elements relative to low-Ti types and exhibit trace element affinities with Tristan da Cunha lavas. The unradiogenic Pb-206/Pb-204 ratios of Khumib basalts are distinctive, most plotting to the left of the 132 Ma Geochron, together with elevated Pb-207/Pb-204 ratios, and Sr-Nd isotopic compositions plotting in the lower Nd-143/Nd-144 part of mantle array (EM1-like). The low-Ti basalts have less coherent trace element patterns and variable, radiogenic initial Sr (similar to0.707-0.717) and Pb isotope compositions, implying crustal contamination. Four samples, however, have less radiogenic Pb and Sr that we suggest approximate their uncontaminated source. All basalt types, but particularly the low-Ti types, contain samples with trace element characteristics (e.g. Nb/Nb-*) suggesting metasediment input, considered source-related. Radiogenic isotope compositions of these samples require long-term isolation of the source in the mantle and depletions (relative to unmodified sediment) in certain elements (e.g. Cs, Pb, U), which are possibly subduction-related. A geodynamic model is proposed in which the emerging Tristan plume entrained subducted material in the Transition Zone region, and further entrained asthenosphere during plume head expansion. Mixing calculations suggest that the main features of the Etendeka basalt types can be explained without sub-continental lithospheric mantle input. Crustal contamination is evident in most low-Ti basalts, but is distinct from the incorporation of a metasedimentary source component at mantle depths.

The geochemistry and petrogenesis of the minor intrusive suite associated with the late Caledonian Criffell-Dalbeattie pluton, SW Scotland

The Criffell-Dalbeattie pluton from SW Scotland is one of a suite of late Caledonian granitoids which are associated with extensive, contemporaneous and compositionally diverse suits of minor intrusions. The minor intrusive suite associated with the Criffell-Dalbeattie pluton is dominantly composed of a series of porphyritic microdiorites, microgranodiorites and microgranites known collectively as the porphyrite-porphyry series. This series can be divided into two groups, the porphyrites and the quartz porphyries, on the basis of petrography and geochemistry although there is some compositional overlap between the two. Compositionally, the porphyrites and quartz porphyries appear to correspond to the granodiorites and granites, respectively, which comprise the Criffell-Dalbeattie pluton, suggesting that the porphyrite-porphyry series of dykes represent magmas which were tapped from the evolving granitic magma chamber. The most mafic component of the minor intrusive suite is represented by calc-alkaline hornblende- and mica bearing lamprophyres. Geochemical studies, including fractional crystallisation, combine assimilation-fractional crystallisation (AFC) show that these are mafic, LILE and LREE enriched melts derived by low degrees of partial melting of a subduction-modified mantle source. It is suggested that the source of the lamprophyres is "Lake District" lithosphere, metasomatised by Lower Palaeozoic subduction, and thrust under the southern part of the Southern Uplands. AFC modelling using chemical and isotopic data further suggest that there is a close genetic link between the lamprophyres and the Criffell-Dalbeattie granitoids and that lamprophyres represent the mantle derived precursors of the Criffell-Dalbeattie granitoids.

Representative analyses of garnet, plagioclase, orthopyroxene, ilmenite, hornblende and biotite for pre-tectonic mafic and metapelitic rocks in Gjelsvikfjella

A metamorphic petrological study, in conjunction with recent precise geochronometric data, revealed a complex P-T-t path for high-grade gneisses in a hitherto poorly understood sector of the Mesoproterozoic Maud Belt in East Antarctica. The Maud Belt is an extensive high-grade, polydeformed, metamorphic belt, which records two significant tectono-thermal episodes, once towards the end of the Mesoproterozoic and again towards the late Neoproterozoic/Cambrian. In contrast to previous models, most of the metamorphic mineral assemblages are related to a Pan-African tectono-thermal overprint, with only very few relics of late Mesoproterozoic granulite-facies mineral assemblages (M1) left in strain-protected domains. Petrological and mineral chemical evidence indicates a clockwise P-T-t path for the Pan-African orogeny. Peak metamorphic (M2b) conditions recorded by most rocks in the area (T = 709-785 °C and P = 7.0-9.5 kbar) during the Pan-African orogeny were attained subsequent to decompression from probably eclogite-facies metamorphic conditions (M2a). The new data acquired in this study, together with recent geochronological and geochemical data, permit the development of a geodynamic model for the Maud Belt that involves volcanic arc formation during the late Mesoproterozoic followed by extension at 1100 Ma and subsequent high-grade tectono-thermal reworking once during continent-continent collision at the end of the Mesoproterozoic (M1; 1090-1030 Ma) and again during the Pan-African orogeny (M2a, M2b) between 565 and 530 Ma. Post-peak metamorphic K-metasomatism under amphibolite-facies conditions (M2c) followed and is ascribed to post-orogenic bimodal magmatism between 500 and 480 Ma.

Mafic and felsic plutonism in the Elvas region (SW Iberia, Portugal): two distinct Nd isotope sources and geodynamics

The occurrence of mafic (mainly gabbros and diorites) and felsic (syenites and granites) rocks, in close spatial association, in the Elvas region, at the northern part of the Ossa-Morena Zone, could be interpreted as a single bimodal (alkaline) plutonic complex. However, in spite of scarce isotopic (Sm-Nd) data, the co-magmatic origin of both rock groups (mafic and felsic) has already been questioned [1]. Based on the mineral chemistry of primary clinopyroxenes (Di–Hd, %En: 45.5 – 27.2) and representative whole-rock analyses, gabbros and diorites of the Elvas massif show a transitional character between alkaline and non-alkaline fields and wide compositions: SiO2 (42.47 – 58.00 wt%); TiO2 (0.24 – 1.68 wt%); Y/Nb (4.0 – 10.7); Th (0.1 – 6.8 ppm); Zr (18.6 – 576.9 ppm). The felsic group is composed by highly differentiated rocks which correspond to distinct levels of silica saturation and alkalinity. Peralkaline syenites usually present sodic (riebeckite) and sodic-calcic (aegirine-augite, ferrowinchite) inosilicates and reveal quite variable compositions: SiO2 (57.50 – 72.07 wt%); TiO2 (0.10 – 1.45 wt%); Th (1.7 – 67.0 ppm); Zr (133.0 – 4800.0 ppm). The alkaline granites show hedenbergite as the characteristic inosilicate, presenting relatively common compositions: SiO2 (61.85 – 78.06 wt%); TiO2 (0.21 – 0.58 wt%); Th (11.8 – 38.4 ppm); Zr (317.3 – 1234.6 ppm) [2]. Recent Sm-Nd isotopic results, on a total of 18 whole-rock samples (6 mafites and 12 felsites), allow new and more consistent interpretation concerning the petrogenesis of these plutonic rocks. Assuming an age of 490 Ma [3], the felsic rocks provide (0.6 < Nd490 < 4.3), similar to other contemporary (per)alkaline rocks of this region [4], reflecting magmatic extractions from time-integrated depleted mantle sources followed by variable and incomplete mixing (and/or AFC-type) processes with enriched, probably crustal sources. This alkaline/peralkaline magmatism is thought to represent the main regional record of the rifting event which presumably led to the opening of the Rheic Ocean. On the other hand, the mafic plutonic rocks of the Elvas massif cannot represent the magmatic precursors of these syenites and granites as they show completely distinct Nd isotopic ratios (3.7 < Nd490 < 1.2) indicating important contribution of long-term enriched (crustal) sources. Instead, considering the age and the Nd isotopic signature of other mafic plutonic unit emplaced nearby (the Campo Maior massif: ca. 370 Ma; 6.0 < Nd370 < 5.2) [5], and recalculating the isotopic ratios of the Elvas massif for the same age (4.3 < Nd370 < 1.6), it is plausible to consider that these plutons (Campo Maior and Elvas) can be coeval and representative of the Variscan magmatism in this region. In such hypothesis, the differences between these isotopic values could be explained, on a time-integrated basis, either by magmatic sources for the Elvas massif less enriched in LREE than the sources involved in the Campo Maior massif, or, if both plutonites share similar depleted mantle sources, by magmatic differentiation paths considerably affected by crustal contamination processes, which reached higher degrees in the Campo Maior massif.

Validation of the impact of Health Information Technology (I-HIT) scale : an international collaborative

In 2005, the Healthcare Information Management Systems Society (HIMSS) Nursing Informatics Community developed a survey to measure the impact of health information technology (HIT), the IHIT Scale, on the role of nurses and interdisciplinary communication in hospital settings. In 2007, nursing informatics colleagues from Australia, England, Finland, Ireland, New Zealand, Scotland and the United States formed a research collaborative to validate the IHIT across countries. All teams have completed construct and face validation in their countries. Five out of six teams have initiated reliability testing by practicing nurses. This paper reports the international collaborative’s validation of the IHIT Scale completed to date.

Volcanic stratigraphy, alteration zoning, and vein paragenesis of the Sascha-Pelligrini low-sulphidation epithermal system, Santa Cruz, Argentina

The Sascha-Pelligrini low-sulphidation epithermal system is located on the western edge of the Deseado Massif, Santa Cruz Province, Argentina. Outcrop sampling has returned values of up to 160g/t gold and 796g/t silver, with Mirasol Resources and Coeur D.Alene Mines currently exploring the property. Detailed mapping of the volcanic stratigraphy has defined three units that comprise the middle Jurassic Chon Aike Formation and two units that comprise the upper Jurassic La Matilde Formation. The Chon Aike Formation consists of rhyodacite ignimbrites and tuffs, with the La Matilde Formation including rhyolite ash and lithic tuffs. The volcanic sequence is intruded by a large flow-banded rhyolite dome, with small, spatially restricted granodiorite dykes and sills cropping out across the study area. ASTER multispectral mineral mapping, combined with PIMA (Portable Infrared Mineral Analyser) and XRD (X-ray diffraction) analysis defines an alteration pattern that zones from laumontite-montmorillonite, to illite-pyritechlorite, followed by a quartz-illite-smectite-pyrite-adularia vein selvage. Supergene kaolinite and steam-heated acid-sulphate kaolinite-alunite-opal alteration horizons crop out along the Sascha Vein trend and Pelligrini respectively. Paragenetically, epithermal veining varies from chalcedonic to saccharoidal with minor bladed textures, colloform/crustiform-banded with visible electrum and acanthite, crustiform-banded grey chalcedonic to jasperoidal with fine pyrite, and crystalline comb quartz. Geothermometry of mineralised veins constrains formation temperatures from 174.8 to 205.1¡ÆC and correlates with the stability field for the interstratified illite-smectite vein selvage. Vein morphology, mineralogy and associated alteration are controlled by host rock rheology, permeability, and depth of the palaeo-water table. Mineralisation within ginguro banded veins resulted from fluctuating fluid pH associated with selenide-rich magmatic pulses, pressure release boiling and wall-rock silicate buffering. The study of the Sascha-Pelligrini epithermal system will form the basis for a deposit-specific model helping to clarify the current understanding of epithermal deposits, and may serve as a template for exploration of similar epithermal deposits throughout Santa Cruz.

Pre-eruptive uplift in the Emeishan? [Correspondence]

In their correspondence, He and colleagues question our conclusion of little or no uplift preceding Emeishan volcanism that we reported in our letter1. Debate concerns the nature of the contact between the Maokou limestone and Emeishan volcanics, the depositional environment and volumetric significance of mafic hydromagmatic deposits (MHDs), and evidence for symmetrical domal thinning. MHDs in the Daqiao section are separated from the Maokou limestone by 100 m of subaerial basaltic lavas, but elsewhere MHDs — previously interpreted as basal conglomerates2, 3 — directly overlie the Maokou2, 3. MHDs thus feature strongly in basal sections of the Emeishan lava succession, as also recently shown4 elsewhere in the Emeishan. An irregular surface at the top of the Maokou limestone has been interpreted as an erosional unconformity2, 3, but clastic deposits presented as evidence of this erosion2, 3 are MHDs produced by explosive magma–water interaction1. A clear demonstration that this irregular top surface is an erosional truncation of limestone reef facies (slope/rim, flat, lagoonal) is currently lacking, but is critical because reefs and carbonate platforms show considerable natural relief of tens of metres. The persistent hot, wet climate since the Oligocene has produced well-developed weathering profiles on exposed Palaeozoic marine sedimentary sequences5, but weathering and karst relief of the uppermost Maokou limestone underlying the flood basalts have not been properly documented, nor shown to be of middle Permian age and immediately preceding emplacement of the large igneous province.