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Integrated petrological and geophysical constraints on magma system architecture in the western Galápagos Archipelago: insights from Wolf volcano
Get PDFThe 2015 eruption of Wolf volcano was one of the largest eruptions in the Galápagos Islands since the onset of routine satellite-based volcano monitoring. It therefore provides an excellent opportunity to combine geophysical and petrological data, to place detailed constraints on the architecture and dynamics of sub-volcanic systems in the western archipelago. We present new geodetic models which show that pre-eruptive inflation at Wolf was caused by magma accumulation in a shallow flat-topped reservoir at ~1.1 km, whereas edifice-scale deformation during the eruption was related to a deflationary source at 6.1–8.8 km. Petrological observations suggest that the erupted material was derived from both a sub-volcanic mush and a liquid-rich magma body. Using a combination of olivine-plagioclase-augite-melt (OPAM) and clinopyroxene-melt barometry, we show that the majority of magma equilibration, crystallisation and mush entrainment occurred at a depth equal to or greater than the deep geodetic source, with little petrological evidence of material sourced from shallower levels. Hence, our multidisciplinary study does not support a fully trans-crustal magmatic system beneath Wolf volcano before the 2015 eruption, but instead indicates two discrete storage regions, with a small magma lens at shallow levels and the major zone of magma storage in the lower crust, from which most of the erupted material was sourced. A predominance of lower crustal magma storage has previously been thought typical of sub-volcanic systems in the eastern Galápagos Archipelago, but our new data suggest that this may also occur beneath the more active volcanoes of the western archipelago
Some fluid mechanical constraints on crystallization and recharge within sills
No full textThe injection of hot magma into a sill can lead to heating and melting of the walls and roof of the reservoir while the injected magma cools and crystallizes. If the crystals are relatively dense, they will try to sediment from the injected magma to form a cumulate layer. In this cumulate layer, the crystals form a porous framework which traps the melt as it is built up. As the melt within the sill continually cools and precipitates dense crystals, there will be a gradual reduction in the density of the remaining silicate liquid. As a result, the melt which is progressively trapped in the pore space of the cumulate layer will become stably stratified in density. Using an idealized model of the fluid mechanical and thermodynamical principles, we explore some of the controls on the thickness and density stratification of cumulate layers following replenishment of a sill-like magma chamber. We show the balance between jamming of the crystal laden melt to form a homogeneous layer and the formation of a stratified cumulate zone depends on the cooling time scale compared to the sedimentation time scale. A key finding is that the composition and stratification in a packed crystal–melt suspension and the associated cumulate layer formed by cooling an intrusion of hot melt injected into the crust may have considerable variability, depending on the properties of the overlying roof melt and the size and hence fall speed of crystals which form in the melt
Rare helium-bearing compound FeO2He stabilized at deep-earth conditions
No full textThere is compelling geochemical evidence for primordial helium trapped in Earth’s lower mantle, but the origin and nature of the helium source remain elusive due to scarce knowledge on viable helium-bearing compounds that are extremely rare. Here we explore materials physics underlying this prominent challenge. Our structure searches in conjunction with first-principles energetic and thermodynamic calculations uncover a remarkable helium-bearing compound FeO2He at high pressure-temperature conditions relevant to the core-mantle boundary. Calculated sound velocities consistent with seismic data validate FeO2He as a feasible constituent in ultralow velocity zones at the lowermost mantle. These mutually corroborating findings establish the first and hitherto only helium-bearing compound viable at pertinent geophysical conditions, thus providing vital physics mechanisms and materials insights for elucidating the enigmatic helium reservoir in deep Earth
Microstructural evidence for crystallization regimes in mafic intrusions: a case study from the Little Minch Sill Complex, Scotland
Get PDFThe magma forming the 20 m thick crinanitic/picrodoleritic Dun Raisburgh sill, part of the Little Minch Sill Complex of NW Scotland, comprised a mafic carrier liquid with a crystal cargo of plagioclase and olivine (1 vol%). The olivine component of the cargo settled on the floor of the intrusion while the more buoyant plagioclase component remained suspended during solidification, resulting in a relatively high plagioclase content in the centre of the sill. The settled olivine grains form a lower fining-upwards sequence overlain by a poorly sorted accumulation formed of grains that grew within the convecting magma. The accumulation of olivine on the sill floor occurred over 5–10 weeks, synchronous with the upwards-propagation of a solidification front comprising a porous (~ 70 vol% interstitial liquid) plagioclase-rich crystal mush
The Calcium Isotope Systematics of the Late Quaternary Dead Sea Basin Lakes
Get PDFWe report the calcium isotopic composition (δ44Ca) of primary aragonite laminae, primary gypsum, and secondary gypsum in sediments deposited from Lake Lisan, the last glacial cycle of the Dead Sea (70–14.5 ka). The δ44Ca of primary gypsum varies between 0.17‰ and 0.71‰ versus bulk silicate earth, with an average of 0.29‰, whereas the aragonite δ44Ca varies between −0.68‰ and −0.16‰ with an average of −0.4‰. The secondary gypsum δ44Ca is close to the calcium isotope composition of the aragonite, averaging at −0.3‰. The aragonite δ44Ca shows small variations temporally in sync with lake level fluctuations, suggesting the aragonite δ44Ca reflects changes in the lake calcium balance, which in turn reflects changes in the local hydrological cycle. The secondary gypsum calcium isotope composition (−0.3‰) overlaps with that of coeval aragonite, suggesting the calcium for secondary gypsum was derived from the aragonite through quantitative, or near‐isotopic equilibrium, recrystallization of the aragonite to gypsum after the lake desiccation and exposure of sediments during the Holocene. A numerical box model is used to explore the effect of changing lake water levels on the calcium isotope composition of the aragonite and gypsum in the lake. The relatively low variability in the δ44Ca over the lake's history suggests that a high‐concentration calcium‐rich brine buffers the calcium cycle
Large-area ultrathin Te films with substrate-tunable orientation
Get PDFAnisotropy in a crystal structure can lead to large orientation-dependent variations of mechanical, optical, and electronic properties. Material orientation control can thus provide a handle to manipulate properties. Here, a novel sputtering approach for 2D materials enables growth of ultrathin (2.5-10 nm) tellurium films with rational control of the crystalline orientation templated by the substrate. The anisotropic Te helical chains align in the plane of the substrate on highly oriented pyrolytic graphite (HOPG) and orthogonally to MgO(100) substrates, as shown by polarized Raman spectroscopy and high-resolution electron microscopy. Furthermore, the films are shown to grow in a textured fashion on HOPG, in contrast with previous reports. These ultrathin Te films cover exceptionally large areas (>1 cm2) and are grown at low temperature (25 oC) affording the ability to accommodate a variety of substrates including flexible electronics. They are robust toward oxidation over a period of days and exhibit the non-centrosymmetric P3121 Te structure. Raman signals are acutely dependent on film thickness, suggesting that optical anisotropy persists and is even enhanced at the ultrathin limit. Hall effect measurements indicate orientation-dependent carrier mobility up to 19 cm2V-1s-1. These large-area, ultrathin Te films grown by a truly scalable, physical vapor deposition technique with rational control of orientation/thickness open avenues for controlled orientation-dependent properties in semiconducting thin films for applications in electronic and optoelectronic devices
Bedrock geology, Barnes Ice Cap northwest, Baffin Island, Nunavut, NTS 37-E west 1:100,000 Map
No full textThis map presents the field observations and initial geological interpretations for the Barnes Ice Cap northwest area (NTS 37-E west), Baffin Island, Nunavut. The regional bedrock geology depicted on CGM maps 402 to 406 comprises Archean tonalitic to monzogranitic gneiss that includes mafic to intermediate components, and relatively homogeneous monzogranite-granodiorite intrusions. The Archean Mary River Group forms discontinuous volcano-sedimentary belts, consisting of mafic volcanic rocks interlayered with siliciclastic strata, banded iron-formation, and felsic to intermediate and ultramafic volcanic units. The supracrustal rocks are intruded by monzogranite-granodiorite plutons. Pelitic to psammitic units, marble, and calc-silicate of the middle Paleoproterozoic Piling Group unconformably overlie the Archean units. Archean units are also unconformably overlain by Mesoproterozoic clastic and carbonate platform sequences of the Bylot Supergroup. These strata were deposited within a graben that forms part of the larger Borden Basin. Paleozoic (Cambrian to Ordovician) strata lie unconformably upon Archean and Paleoproterozoic felsic plutonic rocks in the western portion of northern Baffin Island
Bedrock geology, Rowley River-Isortoq River, Baffin Island, Nunavut, NTS 37-F east 1:100,000 Map
No full textThis map presents the field observations and initial geological interpretations for the Rowley River-Isortoq River area (NTS 37-F east) Baffin Island, Nunavut. The regional bedrock geology depicted on CGM maps 402 to 406 comprises Archean tonalitic to monzogranitic gneiss that includes mafic to intermediate components, and relatively homogeneous monzogranite-granodiorite intrusions. The Archean Mary River Group forms discontinuous volcano-sedimentary belts, consisting of mafic volcanic rocks interlayered with siliciclastic strata, banded iron-formation, and felsic to intermediate and ultramafic volcanic units. The supracrustal rocks are intruded by monzogranite-granodiorite plutons. Pelitic to psammitic units, marble, and calc-silicate of the middle Paleoproterozoic Piling Group unconformably overlie the Archean units. Archean units are also unconformably overlain by Mesoproterozoic clastic and carbonate platform sequences of the Bylot Supergroup. These strata were deposited within a graben that forms part of the larger Borden Basin. Paleozoic (Cambrian to Ordovician) strata lie unconformably upon Archean and Paleoproterozoic felsic plutonic rocks in the western portion of northern Baffin Island
Genome‐wide insights into introgression and its consequences for genome‐wide heterozygosity in the Mytilus species complex across Europe
Get PDFThe three mussel species comprising the Mytilus complex are widespread across Europe and readily hybridize when they occur in sympatry, resulting in a mosaic of populations with varying genomic backgrounds. Two of these species, M. edulis and M. galloprovincialis, are extensively cultivated across Europe, with annual production exceeding 230,000 tonnes. The third species, M. trossulus, is considered commercially damaging as hybridization with this species results in weaker shells and poor meat quality. We therefore used restriction site associated DNA sequencing to generate high‐resolution insights into the structure of the Mytilus complex across Europe and to resolve patterns of introgression. Inferred species distributions were concordant with the results of previous studies based on smaller numbers of genetic markers, with M. edulis and M. galloprovincialis predominating in northern and southern Europe respectively, while introgression between these species was most pronounced in northern France and the Shetland Islands. We also detected traces of M. trossulus ancestry in several northern European populations, especially around the Baltic and in northern Scotland. Finally, genome‐wide heterozygosity, whether quantified at the population or individual level, was lowest in M. edulis, intermediate in M. galloprovincialis, and highest in M. trossulus, while introgression was positively associated with heterozygosity in M. edulis but negatively associated with heterozygosity in M. galloprovincialis. Our study will help to inform mussel aquaculture by providing baseline information on the genomic backgrounds of different Mytilus populations across Europe and by elucidating the effects of introgression on genome‐wide heterozygosity, which is known to influence commercially important traits such as growth, viability, and fecundity in mussels
Coupled evolution of stable carbon isotopes between the Southern Ocean and the atmosphere over the last 260 ka
No full textThe oceanic thermocline circulation provides a route of communication between the surface and deep ocean and could have played an important role in the global carbon cycle, but studies on reconstructing past thermocline water properties are limited. Here we explore the potential use of left-coiling Globorotalia truncatulinoides as a recorder of thermocline conditions by measuring the stable oxygen and carbon isotopic compositions of this species from 28 surface sediments in the southwest Pacific near New Zealand. Our data show that G. truncatulinoides (sinistral) calcify mainly in the range of subsurface/thermocline depths in this study region between 100 and 850 m with their carbon isotopes largely corresponding to the surrounding seawater values. To understand the controlling factors of the thermocline δ13C evolution in the South Pacific, a 260 ka downcore δ13C record on this species (δ13CG.trunc) from core site ODP1123 is presented and compared with other δ13C records. The convergence of δ13C from thermocline, upper and lower circumpolar deep waters (UCDW/LCDW) during glacial terminations indicates that the deep ocean is the predominant source of increased atmospheric pCO2 and the δ13C anomalies in the upper ocean and atmosphere during the deglacials. This is evident in both the South Pacific and South Atlantic. A quantitative calculation of predicted surface ocean δ13C based on thermodynamic air-sea equilibrium implies this process has a significant control on the temporal thermocline water δ13C variation over the last glacial-interglacial (G-I) cycle. The lower deglacial δ13CG.trunc values in the South Atlantic compared to the Pacific further suggest a stronger upwelling in the Atlantic sector of the Southern Ocean, indicating that this was a major ventilation route with an important stock of light δ13C from the deep waters of this region. This study demonstrates the deep water influence (via upwelling) and atmospheric carbon isotope imprint (via air-sea exchange) on thermocline water δ13C evolution. It also provides important evidence for the rapid exchange of carbon between the Southern Ocean and atmosphere over multiple G-I cycles