Crustal growth: Some major problems

Fundamental problems with models currently used to explain the genesis and evolution of continental crust were raised. These problems focus around the difficulty of generating the upper continental crust from a lower crustal or mantle protolith without leaving a very large, and so far undetected, volume of restite. No conclusive resolution to the problems was achieved

SHRIMP ion probe zircon geochronology and Sr and Nd isotope geochemistry for southern Longwood Range and Bluff Peninsula intrusive rocks of Southland, New Zealand

Permian–Jurassic ultramafic to felsic intrusive complexes at Bluff Peninsula and in the southern Longwood Range along the Southland coast represent a series of intraoceanic magmatic arcs with ages spanning a time interval of 110 m.y. New SHRIMP U-Pb zircon data for a quartz diorite from the Flat Hill complex, Bluff Peninsula, yield an age of 259 ± 4 Ma, consistent with other geochronological and paleontological evidence confirming a Late Permian age. The new data are consistent with an age of c. 260 Ma for the intrusive rocks of the Brook Street Terrane. SHRIMP U-Pb zircon ages for the southern Longwood Range confirm that intrusions become progressively younger from east to west across the complex. A gabbro at Oraka Point (eastern end of coastal section) has an age of 245 ± 4 Ma and shows virtually no evidence of zircon inheritance. The age is significantly different from that of the Brook Street Terrane intrusives. Zircon ages from the western parts of the section are younger and more varied (203–227 Ma), indicating more complex magmatic histories. A leucogabbro dike from Pahia Point gives the youngest emplacement age of 142 Ma, which is similar to published U-Pb zircon ages for the Anglem Complex and Paterson Group on Stewart Island

The alkali basalt andesite association of Grenada Lesser Antilles

Grenada is the southernmost volcanic island of the Lesser Antilles. A series of volcanic centres ranging from Pliocene to Recent in age are present overlying a folded Lower to Middle Tertiary volcano-sedimentary formation. Eruptions of silica-undersaturated alkali basalt and picrite magmas have occurred repeatedly during the evolution of these centres. Calc-alkaline andesites and dacites show a close field association with the basalts and picrites. Recent activity on the island has been explosive in nature. A model of variable volumes of Upper Mantle partial melting is proposed to account for the diversity of major, trace and Rare Earth element compositions and strontium isotope ratios of the basalts and picrites. Geochemical, petrographic and mineralogical criteria suggest that the andesites and dacites are related to these basic melts by fractional crystallisation processes. In addition the chemical compositions and strontium isotope ratios of the andesites and dacites reflect the diverse compositions of the parental basalt magmas. The petrography and mineralogy of the andesites and dacites is similar to calc-alkaline suites elsewhere in the arc. Some of the basalts and picrites contain abundant olivine and sector and oscillatory zoned clinopyroxene phenocrysts. In some basalts, phenocryst amphibole is present. An origin by partial melting of an Upper Mantle pericotite source is proposed. Alternative sources are examiner: but partial melting of a subducted lithospheric plate does not appear to be a significant petrogenetic process in Grenada, Fractional crystallisation of olivine, clinopyroxene and spinel is mainly responsible for the development of a normal calc-alkaline trend towards increasing silica-saturation in the magmas. Subsequent crystallisation of plagioclase feldspar and then amphibole is also important in the development of a trend towards silica- rather than alkali-enrichment in the residual melts. The significant feature of the Grenada vulcanicity is the occurrence within a restricted geographic range of magmas of contrasted geochemical characteristics. The local volcanic and tectonic history of the southern part of the Lesser Antilles island arc are probably the most important factors in the development of these unusual characteristics

Complicité: Resisting the Tyranny of Talk

This article is based video data from a project called SALTMusic, for young children diagnosed as having “language delay.” The interdisciplinary action-research project was co-delivered by speech and language therapists and early childhood arts practitioners, with children and their parents. Addressing a concern that children’s lack of words places anxiety, guilt, and stress upon families, SALTMusic explored ways of engaging with children using minimum words, by focusing on playful encounters of bodies responding to a range of materials, objects, and sounds.  In this paper, we consider two filmed events from this project. We explore these events through the theme of this special issue, with its emphasis on the “complex intermingling of knowledges” between children, their families, early years’ arts practitioners, and speech therapists. We wish to think more deeply about what happens when adults talk less, and instead use space, sound, materials, and bodies to converse with toddlers.  In particular, we turn to the dramaturgical notion of complicité in order to enlarge our understanding of communication and conversation towards a mutually transformative sense of unfolding collective action. In particular, we ask what the potential of the concept of complicité might offer early years’ practice in an era of accountability, where the professionalisation discourses of early childhood education are creeping into and infecting parenting discourses. We ask if the concept of complicité might help adults working with young children to resist the domination of word-oriented discourses that eclipse implicit, bodily, and materially attuned ways of relating to the young child

Quantifying brine assimilation by submarine magmas: Examples from the Galápagos Spreading Centre and Lau Basin

Volatiles are critically important in controlling the chemical and physical properties of the mantle. However, determining mantle volatile abundances via the preferred proxy of submarine volcanic glass can be hampered by seawater assimilation. This study shows how combined Cl, Br, I, K and H2O abundances can be used to unambiguously constrain the dominant mechanism by which melts assimilate seawater-derived components, and provide an improved method for determining mantle H2O and Cl abundances. We demonstrate that melts from the northwest part of the Lau Basin, the Galápagos Spreading Centre and melts from other locations previously shown to have anomalously high Cl contents, all assimilated excess Cl and H2O from ultra-saline brines with estimated salinities of 55±15wt.% salts. Assimilation probably occurs at depths of ~3-6km in the crust when seawater-derived fluids come into direct contact with deep magmas. In addition to their ultra-high salinity, the brines are characterised by K/Cl of <0.2, I/Cl of close to the seawater value (~3×10-6) and distinctive Br/Cl ratios of 3.7-3.9×10-3, that are higher than both the seawater value of 3.5×10-3 and the range of Br/Cl in 43 pristine E-MORB and OIB glasses that are considered representative of diverse mantle reservoirs [Br/Clmantle=(2.8±0.6)×10-3 and I/Clmantle=(60±30)×10-6 (2σ)]. The ultra-saline brines, with characteristically elevated Br/Cl ratios, are produced by a combination of fluid-rock reactions during crustal hydration and hydrothermal boiling. The relative importance of these processes is unknown; however, it is envisaged that a vapour phase will be boiled off when crustal fluids are heated to magmatic temperatures during assimilation. Furthermore, the ultra-high salinity of the residual brine that is assimilated may be partly determined by the relative solubilities of H2O and Cl in basaltic melts. The most contaminated glasses from the Galápagos Spreading Centre and Lau Basin have assimilated ~95% of their total Cl and up to 35-40% of their total H2O, equivalent to the melts assimilating 1000-2000ppm brine at an early stage of their evolution. Dacite glasses from Galapagos contain even higher concentrations of brine components (e.g. 12,000ppm), but the H2O and Cl in these melts was probably concentrated by fractional crystallisation after assimilation. The Cl, Br, I and K data presented here confirm the proportion of seawater-derived volatiles assimilated by submarine magmas can vary from zero to nearly 100%, and that assimilation is closely related to hydrothermal activity. Assimilation of seawater components has previously been recognised as a possible source of atmospheric noble gases in basalt glasses. However, hydrothermal brines have metal and helium concentrations up to hundreds of times greater than seawater, and brine assimilation could also influence the helium isotope systematics of some submarine glasse

Landforms predict phylogenetic structure on one of the world's most ancient surfaces

<p>Abstract</p> <p>Background</p> <p>The iconic Pilbara in northwestern Australia is an ancient geological and biophysical region that is an important zone of biodiversity, endemism and refugia. It also is overlain by some of the oldest erosion surfaces on Earth, but very little is known about the patterns of biotic diversity within the Pilbara or how they relate to the landscape. We combined phylogenetic and spatial-autocorrelation genetic analyses of mitochondrial DNA data on populations of the gekkotan lizard <it>Lucasium stenodactylum </it>within the Pilbara with geological, distributional and habitat data to test the hypothesis that ancient surface geology predicts current clade-habitat associations in saxicoline animals.</p> <p>Results</p> <p>This is the first detailed phylogenetic examination of a vertebrate organism across the Pilbara region. Our phylogeny provides strong support for a deep and ancient phylogenetic split within <it>L. stenodactylum </it>that distinguishes populations within the Pilbara region from those outside the Pilbara. Within the Pilbara region itself, our phylogeny has identified five major clades whose distribution closely matches different surface geologies of this ancient landscape. Each clade shows strong affinities with particular terrain types and topographic regions, which are directly related to different geological bedrock.</p> <p>Conclusion</p> <p>Together our phylogenetic, distributional, geological and habitat data provide a clear example of ecological diversification across an ancient and heterogeneous landscape. Our favoured hypothesis is that ancestors of the Pilbara lineages radiated into the region at the onset of aridity in Australia approximately 5 mya and locally adapted to the various ancient and highly stable terrain types and the micro-habitats derived from them. In terms of specimen recovery and analysis, we are only beginning to reconstruct the biotic history of this ancient landscape. Our results show the geological history and the habitats derived from them will form an important part of this emerging story.</p

Boninite and Harzburgite from Leg 125 (Bonin-Mariana Forearc): A Case Study of Magma Genesis during the Initial Stages of Subduction

Holes drilled into the volcanic and ultrabasic basement of the Izu-Ogasawara and Mariana forearc terranes during Leg 125 provide data on some of the earliest lithosphere created after the start of Eocene subduction in the Western Pacific. The volcanic basement contains three boninite series and one tholeiite series. (1) Eocene low-Ca boninite and low-Ca bronzite andesite pillow lavas and dikes dominate the lowermost part of the deep crustal section through the outer-arc high at Site 786. (2) Eocene intermediate-Ca boninite and its fractionation products (bronzite andesite, andesite, dacite, and rhyolite) make up the main part of the boninitic edifice at Site 786. (3) Early Oligocene intermediate-Ca to high-Ca boninite sills or dikes intrude the edifice and perhaps feed an uppermost breccia unit at Site 786. (4) Eocene or Early Oligocene tholeiitic andesite, dacite, and rhyolite form the uppermost part of the outer-arc high at Site 782. All four groups can be explained by remelting above a subduction zone of oceanic mantle lithosphere that has been depleted by its previous episode of partial melting at an ocean ridge. We estimate that the average boninite source had lost 10-15 wt% of melt at the ridge before undergoing further melting (5-10%) shortly after subduction started. The composition of the harzburgite (<2% clinopyroxene, Fo content of about 92%) indicates that it underwent a total of about 25% melting with respect to a fertile MORB mantle. The low concentration of Nb in the boninite indicates that the oceanic lithosphere prior to subduction was not enriched by any asthenospheric (OIB) component. The subduction component is characterized by (1) high Zr and Hf contents relative to Sm, Ti, Y, and middle-heavy REE, (2) light REE-enrichment, (3) low contents of Nb and Ta relative to Th, Rb, or La, (4) high contents of Na and Al, and (5) Pb isotopes on the Northern Hemisphere Reference Line. This component is unlike any subduction component from active arc volcanoes in the Izu-Mariana region or elsewhere. Modeling suggests that these characteristics fit a trondhjemitic melt from slab fusion in amphibolite facies. The resulting metasomatized mantle may have contained about 0.15 wt% water. The overall melting regime is constrained by experimental data to shallow depths and high temperatures (1250°C and 1.5 kb for an average boninite) of boninite segregation. We thus envisage that boninites were generated by decompression melting of a diapir of metasomatized residual MORB mantle leaving the harzburgites as the uppermost, most depleted residue from this second stage of melting. Thermal constraints require that both subducted lithosphere and overlying oceanic lithosphere of the mantle wedge be very young at the time of boninite genesis. This conclusion is consistent with models in which an active transform fault offsetting two ridge axes is placed under compression or transpression following the Eocene plate reorganization in the Pacific. Comparison between Leg 125 boninites and boninites and related rocks elsewhere in the Western Pacific highlights large regional differences in petrogenesis in terms of mantle mineralogy, degree of partial melting, composition of subduction components, and the nature of pre-subduction lithosphere. It is likely that, on a regional scale, the initiation of subduction involved subducted crust and lithospheric mantle wedge of a range of ages and compositions, as might be expected in this type of tectonic setting

More-than-words: Reconceptualising Two-year-old Children’s Onto-epistemologies Through Improvisation and the Temporal Arts

This thesis project takes place at a time of increasing focus upon two-year-old children and the words they speak. On the one hand there is a mounting pressure, driven by the school readiness agenda, to make children talk as early as possible. On the other hand, there is an increased interest in understanding children’s communication in order to create effective pedagogies. More-than-words (MTW) examines an improvised art-education practice that combines heterogenous elements: sound, movement and materials (such as silk, string, light) to create encounters for young children, educators and practitioners from diverse backgrounds. During these encounters, adults adopt a practice of stripping back their words in order to tune into the polyphonic ways that children are becoming-with the world. For this research-creation, two MTW sessions for two-year-old children and their carers took place in a specially created installation. These sessions were filmed on a 360˚ camera, nursery school iPad and on a specially made child-friendly Toddler-cam (Tcam) that rolled around in the installation-event with the children. Through using the frameless technology of 360˚ film, I hoped to make tangible the relation and movement of an emergent and improvised happening and the way in which young children operate fluidly through multiple modes. Travelling with posthuman, Deleuzio-Guattarian and feminist vital material philosophy, I wander and wonder speculatively through practice, memory, and film data as a bag lady, a Haraway-ian writer/artist/researcher-creator who resists the story of the wordless child as lacking and tragic; the story that positions the word as heroic. Instead, through returning to the uncertainty of improvisation, I attempt to tune into the savage, untamed and wild music of young children’s animistic onto-epistemologies