657 research outputs found
Pre-breakup magmatism on the Vøring margin: Insight from new sub-basalt imaging and results from Ocean Drilling program hole 642E
Highlights
• Sub-basalt imaging improvement on the Vøring Margin
• Definition of a new seismic facies unit: the Lower Series Flows
• Significant organic carbon content within the melting crustal segment
• Apectodinium augustum marker for the PETM is reworked into the Lower Series Flows
• The Lower Series Flows, early Eocene in age, predate the Vøring Margin breakup
Abstract
Improvements in sub-basalt imaging combined with petrological and geochemical observations from the Ocean Drilling Program (ODP) Hole 642E core provide new constraints on the initial breakup processes at the Vøring Margin. New and reprocessed high quality seismic data allow us to identify a new seismic facies unit which we define as the Lower Series Flows. This facies unit is seismically characterized by wavy to continuous subparallel reflections with an internal disrupted and hummocky shape. Drilled lithologies, which we correlate to this facies unit, have been interpreted as subaqueous flows extruding and intruding into wet sediments. Locally, the top boundary of this facies unit is defined as a negative in polarity reflection, and referred as the K-Reflection. This reflection can be correlated with the spatial extent of pyroclastic deposits, emplaced during transitional shallow marine to subaerial volcanic activities during the rift to drift transition. The drilled Lower Series Flows consist of peraluminous, cordierite bearing peperitic basaltic andesitic to dacitic flows interbedded with thick volcano-sedimentary deposits and intruded sills. The peraluminous geochemistry combined with available C (from calcite which fills vesicles and fractures), Sr, Nd, and Pb isotopes data point towards upper crustal rock-mantle magma interactions with a significant contribution of organic carbon rich pelagic sedimentary material during crustal anatexis. From biostratigraphic analyses, Apectodinium augustum was found in the The Lower Series Flows. This species is a marker for the Paleocene – Eocene Thermal Maximum (PETM). However, the absence of very low carbon isotope values (from bulk organic matter), that characterize the PETM, imply that A.augustum was reworked into the early Eocene sediments of this facies unit which predate the breakup time of the Vøring Margin.
Finally, a plausible conceptual emplacement model for the Lower Series Flows facies unit is proposed. This model comprises several stages: (1) the emplacement of subaqueous peperitic basaltic andesitic flows intruding and/or extruding wet sediments; (2) a subaerial to shallow marine volcanism and extrusion of dacitic flows; (3) a proto-breakup phase with intense shallow marine to subaerial explosive volcanism responsible for pyroclastic flow deposits which can be correlated with the seismic K-Reflection and (4) the main breakup stage with intense transitional tholeiitic MORB-type volcanism and large subsidence concomitant with the buildup of the Seaward Dipping Reflector wedge
Tectonic evolution and extension at the Møre Margin – Offshore mid-Norway
Highlights
• New and reprocessed seismic data improved structural mapping at the Møre Margin.
• Time-structure and thickness maps of the Cretaceous units have been constructed.
• Stratigraphy reconstruction of a transect reveals 188 km extension.
• Average stretching factor is 2.2–3.6 depending on assumed initial crustal thickness.
Abstract
Lithospheric stretching is the key process in forming extensional sedimentary basins at passive rifted margins. This study explores the stretching factors, resulting extension, and structural evolution of the Møre segment on the Mid-Norwegian continental margin. Based on the interpretation of new and reprocessed high-quality seismic, we present updated structural maps of the Møre margin that show very thick post-rift sediments in the central Møre Basin and extensive sill intrusion into the Cretaceous sediments. A major shift in subsidence and deposition occurred during mid-Cretaceous. One transect across the Møre continental margin from the Slørebotn Subbasin to the continent-ocean boundary is reconstructed using the basin modelling software TecMod. We test different initial crustal configurations and rifting events and compare our structural reconstruction results to stretching factors derived both from crustal thinning and the classical backstripping/decompaction approach. Seismic interpretation in combination with structural reconstruction modelling does not support the lower crustal bodies as exhumed and serpentinised mantle. Our extension estimate along this transect is ~ 188 ± 28 km for initial crustal thickness varying between 30 and 40 km
The Ultracool SpeXtroscopic Survey. I. Volume-Limited Spectroscopic Sample and Luminosity Function of M7L5 Ultracool Dwarfs
We present a volume-limited, spectroscopically-verified sample of M7L5
ultracool dwarfs within 25\,pc. The sample contains 410 sources, of which
have trigonometric distance measurements ( from \textit{Gaia}
DR2), and have low-resolution (), near-infrared (NIR)
spectroscopy. We also present an additional list of 60 sources which may be
M7L5 dwarfs within 25\,pc when distance or spectral type uncertainties are
taken into account. The spectra provide NIR spectral and gravity
classifications, and we use these to identify young sources, red and blue
color outliers, and spectral binaries. We measure very low gravity and
intermediate gravity fractions of and
, respectively; fractions of red and blue color outliers
of \% and \%, respectively; and a
spectral binary fraction of . We present an updated
luminosity function for M7L5 dwarfs continuous across the hydrogen burning
limit that agrees with previous studies. We estimate our completeness to range
between when compared to an isotropic model. However, we find that
the literature late-M sample is severely incomplete compared to L dwarfs, with
completeness of and , respectively. This
incompleteness can be addressed with astrometric-based searches of ultracool
dwarfs with \textit{Gaia} to identify objects previously missed by color- and
magnitude-limited surveys.Comment: 71 pages, 27 figures, and 18 table
Lattice Boltzmann Simulations of Liquid Crystal Hydrodynamics
We describe a lattice Boltzmann algorithm to simulate liquid crystal
hydrodynamics. The equations of motion are written in terms of a tensor order
parameter. This allows both the isotropic and the nematic phases to be
considered. Backflow effects and the hydrodynamics of topological defects are
naturally included in the simulations, as are viscoelastic properties such as
shear-thinning and shear-banding.Comment: 14 pages, 5 figures, Revte
Hydrogen-poor superluminous stellar explosions
Supernovae (SNe) are stellar explosions driven by gravitational or
thermonuclear energy, observed as electromagnetic radiation emitted over weeks
or more. In all known SNe, this radiation comes from internal energy deposited
in the outflowing ejecta by either radioactive decay of freshly-synthesized
elements (typically 56Ni), stored heat deposited by the explosion shock in the
envelope of a supergiant star, or interaction between the SN debris and
slowly-moving, hydrogen-rich circumstellar material. Here we report on a new
class of luminous SNe whose observed properties cannot be explained by any of
these known processes. These include four new SNe we have discovered, and two
previously unexplained events (SN 2005ap; SCP 06F6) that we can now identify as
members. These SNe are all ~10 times brighter than SNe Ia, do not show any
trace of hydrogen, emit significant ultra-violet (UV) flux for extended periods
of time, and have late-time decay rates which are inconsistent with
radioactivity. Our data require that the observed radiation is emitted by
hydrogen-free material distributed over a large radius (~10^15 cm) and
expanding at high velocities (>10^4 km s^-1). These long-lived, UV-luminous
events can be observed out to redshifts z>4 and offer an excellent opportunity
to study star formation in, and the interstellar medium of, primitive distant
galaxies.Comment: Accepted to Nature. Press embargoed until 2011 June 8, 18:00 U
Early-time Spectropolarimetry of the Asymmetric Type II Supernova SN 2023ixf
We present six epochs of optical spectropolarimetry of the Type II supernova
(SN) 2023ixf ranging from 2 to 15 days after the explosion. Polarimetry
was obtained with the Kast double spectrograph on the Shane 3 m telescope at
Lick Observatory, representing the earliest such observations ever captured for
an SN. We observe a high continuum polarization %
on days +1.4 and +2.5 before dropping to 0.5 % on day +3.5, persisting at that
level up to day +14.5. Remarkably, this change coincides temporally with the
disappearance of highly ionized "flash" features. The decrease of the continuum
polarization is accompanied by a rotation of the polarization
position angle () as seen across the continuum. The early evolution of the
polarization may indicate different geometric configurations of the
electron-scattering atmosphere as seen before and after the disappearance of
the emission lines associated with highly-ionized species (e.g., He II, C IV, N
III), which are likely produced by elevated mass loss shortly prior to the SN
explosion. We interpret the rapid change of polarization and from days
+2.5 to +4.5 as the time when the SN ejecta emerge from the dense asymmetric
circumstellar material (CSM). The temporal evolution of the continuum
polarization and the is consistent with an aspherical SN explosion that
exhibits a distinct geometry compared to the CSM. The rapid follow-up
spectropolarimetry of SN 2023ixf during the shock ionization phase reveals an
exceptionally asymmetric mass-loss process leading up to the explosion.Comment: Submitted to Ap
Evolving a photosynthetic organelle
The evolution of plastids from cyanobacteria is believed to represent a singularity in the history of life. The enigmatic amoeba Paulinella and its 'recently' acquired photosynthetic inclusions provide a fascinating system through which to gain fresh insight into how endosymbionts become organelles
A method for selecting M dwarfs with an increased likelihood of unresolved ultracool companionship
This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record [N. J, Cook, et al, 'A method for selecting M dwarfs with an increased likelihood of unresolved ultracool companionship', MNRAS, Vol. 457(2): 2192-2208, February 2016] is available online at: https://doi.org/10.1093/mnras/stw061. Published by Oxford University Press on behalf of the Royal Astronomical Society.Locating ultracool companions to M dwarfs is important for constraining low-mass formation models, the measurement of substellar dynamical masses and radii, and for testing ultracool evolutionary models. We present an optimized method for identifying M dwarfs which may have unresolved ultracool companions. We construct a catalogue of 440 694 M dwarf candidates, from Wide-Field Infrared Survey Explorer, Two Micron All-Sky Survey and Sloan Digital Sky Survey, based on optical- and near-infrared colours and reduced proper motion. With strict reddening, photometric and quality constraints we isolate a subsample of 36 898 M dwarfs and search for possible mid-infrared M dwarf + ultracool dwarf candidates by comparing M dwarfs which have similar optical/near-infrared colours (chosen for their sensitivity to effective temperature and metallicity). We present 1082 M dwarf + ultracool dwarf candidates for follow-up. Using simulated ultracool dwarf companions to M dwarfs, we estimate that the occurrence of unresolved ultracool companions amongst our M dwarf + ultracool dwarf candidates should be at least four times the average for our full M dwarf catalogue. We discuss possible contamination and bias and predict yields of candidates based on our simulations.Peer reviewe
Pleosporales
One hundred and five generic types of Pleosporales are described and illustrated. A brief introduction and detailed history with short notes on morphology, molecular phylogeny as well as a general conclusion of each genus are provided. For those genera where the type or a representative specimen is unavailable, a brief note is given. Altogether 174 genera of Pleosporales are treated. Phaeotrichaceae as well as Kriegeriella, Zeuctomorpha and Muroia are excluded from Pleosporales. Based on the multigene phylogenetic analysis, the suborder Massarineae is emended to accommodate five families, viz. Lentitheciaceae, Massarinaceae, Montagnulaceae, Morosphaeriaceae and Trematosphaeriaceae
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