ESC Publications - Cambridge Univesity
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Quantitative morphology, recent evolution, and future activity of the Kameni islands volcano, Santorini, Greece
No full textPetrology igneous metamorphic and volcanic studies
Wide dispersal and deposition of distal tephra during the Pleistocene ‘Campanian Ignimbrite/Y5’ eruption, Italy
No full textA trachytic volcanic ash layer is widely distributed across south-western Russia, where it is found both in well-characterised archaeological contexts close to the Don River (the Paleolithic sites of Kostenki-Borschevo (51.4°N, 39.0°E), and in undisturbed geological contexts. This ash layer has all of the characteristics of a distal tephra fall deposit: it is fine grained and unimodal with a grain size of 60–170μm, dominated by strongly elongate glass shard fragments.
Chemical analysis confirms that this ash layer is a distal equivalent of the deposits of the ca 39.3ka Campanian Ignimbrite eruption of the Phlegrean Fields, Italy, and correlates with the widely recognised Y5 ash layer in marine cores in the south-eastern Mediterranean. This work shows that ash particles can be dispersed over considerable distances (>2500km) and areas (>1.5–3×106km2) during large-magnitude explosive eruptions. The volume of the products associated with this event (31–50km3 of magma erupted as fallout tephra, and a total volume of 105–210km3 of magma, or 2.5–5×1014kg) confirms the Campanian Ignimbrite/Y5 eruption as the most significant known volcanic eruption in Europe of the past 100ka. This correlation places tight constraints on the absolute ages of a number of important archaeological horizons in southern Russia
Quantitative textural analysis of packings of elongate crystals
No full textThe spatial distribution of grains in a solidifying igneous rock controls the physical properties of the crystal mush, and in turn is controlled by the rate of crystal growth and accumulation. A predominant non-spherical habit for igneous minerals brings into question the use of spherical particles in reference packings used for quantification of spatial distribution. Furthermore, variations of crystal clustering/ordering with length scale require spatial statistics which take into account the distribution of particles beyond nearest neighbours. Using random close packings of spherocylinders, we demonstrate the importance of aspect ratio for the aggregation index (usually known as R) and show that packings of spherical particles have more structure than packings of rods. The spatial distribution functions demonstrate that the plagioclase grains in the colonnade from the Holyoke basalt are clustered on a length scale of 0.5 mm. Understanding the controls on grain spatial distribution in igneous rocks will depend on the application of these techniques to well-understood environments
A Plume Model of Transient Diachronous Uplift at the Earth's Surface
No full textConvection in the Earth's mantle appears to be strongly time-dependent on geological time scales. However, we lack direct observations which would help constrain the temporal variation of convection on time scales of 1–10 Ma. Recently, it has been demonstrated that transient uplift events punctuated the otherwise uniform thermal subsidence of sedimentary basins which fringe the Icelandic plume. In the Faroe–Shetland basin, three-dimensional seismic reflection surveys calibrated by well logs have been used to reconstruct a not, vert, similar 55 million year old transient event. The minimum amount of uplift is 490 m, which grew and decayed within 2 Ma. This event has also been mapped 400 km further east in the North Sea basin, where peak uplift with an amplitude of 300 m occurred 0.3–1.6 Ma later. Neither observation can be explained by glacio-eustatic sea-level changes or by crustal shortening. We describe a simple fluid dynamical model which accounts for these transient and diachronous observations. In this model, we assume that the Icelandic plume was already in existence and that it had an axisymmetric geometry in which hot (e.g. 1400 °C) asthenospheric material flows away from a central conduit within a horizontal layer. A transient temperature anomaly introduced at the plume centre flows outward as an expanding annulus. Its geometry is calculated using radial flow between two parallel plates with a Poiseuille cross-stream velocity profile. The expanding annulus of hot asthenosphere generates transient isostatic uplift at the Earth's surface. Stratigraphic observations from both basins can be accounted for using a plume flux of 1.3 × 108 km3 Ma− 1 for a layer thickness of 100 km. Plume flux is broadly consistent with that required to account for Neogene (0–20 Ma) V-shaped ridges south of Iceland, although our transient temperature anomalies are larger. We suspect that the stratigraphic expression of transient convective behaviour is common and that a careful examination of appropriate records could yield important insights
Morphological Control of Polar Orientation in Single-Crystal Ferroelectric Nanowires
No full textIn an attempt to explore and understand domain configurations that occur in idealized ferroelectric nanowires, a focused ion beam microscope has been used to directly cut columns in a variety of sizes from single-crystal barium titanate. The scanning transmission electron microscope has then been used to image the ferroelectric domain patterns evident after cooling through the Curie temperature in the vacuum environment of the electron microscope. As the overall length of the wires is physically constrained, the observed length-conserving packets of 90° domains with {110}pseudocubic domain-wall orientations can easily be rationalized. Such domain structures necessarily dictate that although half of the domains can be such that their polarization direction lies parallel to the axis of the wire, the other half of the domains will have polarization directions approximately perpendicular to the wire axis (nonaxial). This situation introduces a depolarizing field and associated energy, which is minimized when the nonaxial polarization is oriented perpendicular to the smallest dimension of the column. Locally changing the aspect ratio of the column dimensions therefore allows local variations in the direction of polarization to be introduced. This was demonstrated by fabricating wire structures in which dimensions were varied along their length. Such wires did indeed show morphologically controlled polar reorientation. The study suggests that shape engineering alone could be used to create complex heterogeneous dipole configurations in ferroelectrics at the nanoscale without the need for externally applied poling electric fields. Possibilities for the further development of this observation might include introducing chiral variations in wire thickness, for example, to create dipole helices
Transport of terrestrial organic matter to the deep North Atlantic Ocean by ice rafting.
No full textTotal organic carbon (TOC), d13C values of TOC (d13Corg) and glycerol dialkyl glycerol tetraethers (GDGTs) were analysed
for a sediment core from the North Atlantic covering the last 30 kyr to investigate organic matter deposition due to
ice rafting. TOC content was low in sediments representing glacial times (0.2–0.4%) and even lower in Holocene sediments
(< 0.2%). The d13Corg values varied from 24& in glacial times to 20& at the start of the Holocene (8 ky cal BP), with
negative excursions to 26& during Heinrich events. The d13Corg values correlated non-linearly with % ice rafted debris in
the sediments, suggestive of supply of continental organic matter by ice rafting. GDGT analysis revealed varying amounts
of soil-derived branched GDGTs and the marine isoprenoid GDGT, crenarchaeol, which is expressed in the branched isoprenoid
tetraether (BIT) index. The BIT index was relatively high (0.3) in sediments deposited during the glacial compared
to those laid down at the start of the Holocene (0.1), suggesting enhanced delivery of terrestrial OM to the North Atlantic
by ice rafting, in agreement with the d13Corg results. This was confirmed by analysis of the 14C content of TOC, which
indicated substantially older ages (1–9 kyr) than the sediment age inferred from planktonic foraminifera. BIT indices
and d13Corg values show phase offsets during Heinrich events, suggestive of differences either in timing of supply or of different
sources of organic matter, i.e. soil organic matter and ancient mature sedimentary organic matter. Alternatively it
may reflect changing contributions of source areas
Layered functional ceramics via misted chemical solution deposition
No full textA review is given of "misted" CSD deposition. This technique uses stoichiometrically
correct sol-gel solutions but is not a spin-on process. Instead a monodisperse mist of droplets as
large as 3 microns in diameter or as small as 0.3 microns is deposited on a substrate. This
technique has the great advantage over sol-gel spin-on processing in that it is suitable for nonplanar
structures, including nanotubes and nano-wires. One could coat a variety of objects with this
technique, including anything from non-planar flash-goggles to a parabolic mirror or focal-plane
array of pyroelectric detectors. Yet it is much simpler and less expensive than conventional
chemical vapour deposition (CVD). We illustrate its use with functionally graded layers on
platinised silicon wafers, on nanotubes of piezoelectrics, and most recently [Pollard, Gregg, et al.]
on 100 Gbit/cm2 arrays of Pt nanowires on Si substrates (the latter are 30-nm diameter, spaced 50
nm apart, embedded in porous alumina and capped with lead zirconate titanate capacitors)
The deep crust beneath island arcs: Inherited zircons reveal a Gondwana continental fragment beneath East Java, Indonesia
No full textPost-emplacement serpentinization and related hydrothermal metamorphism in a kimberlite from Venetia, South Africa
No full textPetrology igneous metamorphic and volcanic studies
Synchrotron radiation, neutron, and mass spectrometry techniques at user facilities
No full textUser research facilities around the world offer tremendous opportunities
for scientific experimentation by members of the Earth science community.
Synchrotron radiation sources, neutron sources, mass spectrometers,
and others represent a powerful force in tackling complex scientific
problems. In these techniques, Earth materials are bombarded with
beams of ions, subatomic particles and/or photons to learn the secrets of
their properties and histories. Some of these methods can be applied to
nanoscale materials with “desktop” instruments while others require macroscopic
samples and utilize large-scale devices residing in multiple buildings;
and there is everything in between