2,449 research outputs found
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
Late time tails from momentarily stationary, compact initial data in Schwarzschild spacetimes
An L-pole perturbation in Schwarzschild spacetime generally falls off at late
times t as t^{-2L-3}. It has recently been pointed out by Karkowski,
Swierczynski and Malec, that for initial data that is of compact support, and
is initially momentarily static, the late-time behavior is different, going as
t^{-2L-4}. By considering the Laplace transforms of the fields, we show here
why the momentarily stationary case is exceptional. We also explain, using a
time-domain description, the special features of the time development in this
exceptional case.Comment: 7 pages, 5 figure
In an expanding universe, what doesn't expand?
The expansion of the universe is often viewed as a uniform stretching of
space that would affect compact objects, atoms and stars, as well as the
separation of galaxies. One usually hears that bound systems do not take part
in the general expansion, but a much more subtle question is whether bound
systems expand partially. In this paper, a very definitive answer is given for
a very simple system: a classical "atom" bound by electrical attraction. With a
mathemical description appropriate for undergraduate physics majors, we show
that this bound system either completely follows the cosmological expansion, or
-- after initial transients -- completely ignores it. This "all or nothing"
behavior can be understood with techniques of junior-level mechanics. Lastly,
the simple description is shown to be a justifiable approximation of the
relativistically correct formulation of the problem.Comment: 8 pages, 9 eps figure
Designing and testing inflationary models with Bayesian networks
Even simple inflationary scenarios have many free parameters. Beyond the
variables appearing in the inflationary action, these include dynamical initial
conditions, the number of fields, and couplings to other sectors. These
quantities are often ignored but cosmological observables can depend on the
unknown parameters. We use Bayesian networks to account for a large set of
inflationary parameters, deriving generative models for the primordial spectra
that are conditioned on a hierarchical set of prior probabilities describing
the initial conditions, reheating physics, and other free parameters. We use
--quadratic inflation as an illustrative example, finding that the number
of -folds between horizon exit for the pivot scale and the end of
inflation is typically the most important parameter, even when the number of
fields, their masses and initial conditions are unknown, along with possible
conditional dependencies between these parameters.Comment: 24 pages, 9 figures, 1 table; discussion update
The Knotted Sky II: Does BICEP2 require a nontrivial primordial power spectrum?
An inflationary gravitational wave background consistent with BICEP2 is
difficult to reconcile with a simple power-law spectrum of primordial scalar
perturbations. Tensor modes contribute to the temperature anisotropies at
multipoles with , and this effect --- together with a prior on
the form of the scalar perturbations --- was the source of previous bounds on
the tensor-to-scalar ratio. We compute Bayesian evidence for combined fits to
BICEP2 and Planck for three nontrivial primordial spectra: a) a running
spectral index, b) a cutoff at fixed wavenumber, and c) a spectrum described by
a linear spline with a single internal knot. We find no evidence for a cutoff,
weak evidence for a running index, and significant evidence for a "broken"
spectrum. Taken at face-value, the BICEP2 results require two new inflationary
parameters in order to describe both the broken scale invariance in the
perturbation spectrum and the observed tensor-to-scalar ratio. Alternatively,
this tension may be resolved by additional data and more detailed analyses.Comment: 14 pages, 5 figures, 4 tables; v2: references added, discussion
updated, matches published versio
An assessment of the mantle and slab components in the magmas of an oceanic arc volcano: Raoul Volcano, Kermadec arc
Raoul Volcano occupies a simple oceanic subduction setting in the northern part of the Kermadec arc on the Pacific–Australian convergent plate boundary. The primary inputs to the magmatic system that feeds the volcano are a subduction component derived from the subducting old Pacific oceanic lithosphere and its veneer of pelagic sediment, and the overlying peridotitic mantle wedge. Conservative trace elements that are very incompatible during mantle melting are relatively depleted in Raoul lavas indicating a source that has been depleted during an earlier melting event. Major element co-variations indicate magma genesis by 25% near fractional melting of a mantle source that is weakly depleted (2% melt extraction) relative to a fertile MORB source. An important influence on the composition of the mantle component is progressive melt extraction coupled with minimal advection of fresh material into the sub-arc zone followed by melt extraction from a melting column beneath the spreading centre of an adjacent back arc basin. High field strength element and rare earth element systematics indicate involvement of a subduction-related component of constant composition. Two fluid components can be distinguished, one enriched in large ion lithophile elements inferred to be an aqueous fluid that is continuously added to the ascending melt column and the other a less mobile fluid that transfers Th. A homogeneous subduction-related component of constant composition and magnitude arises if the slab-derived flux migrates from the slab–mantle interface to the sub-arc melting column by repeated episodes of amphibole formation and decomposition its composition is then governed by the distribution coefficients of pyroxene and its magnitude by the degree of amphibole saturation of mantle peridotite. The results from Raoul Volcano are comparable to those from other oceanic subduction-related arcs such as South Sandwich and Marianas suggesting that this is a general model for oceanic arcs
Testing for New Physics: Neutrinos and the Primordial Power Spectrum
We test the sensitivity of neutrino parameter constraints from combinations
of CMB and LSS data sets to the assumed form of the primordial power spectrum
(PPS) using Bayesian model selection. Significantly, none of the tested
combinations, including recent high-precision local measurements of
and cluster abundances, indicate a signal for massive neutrinos
or extra relativistic degrees of freedom. For PPS models with a large, but
fixed number of degrees of freedom, neutrino parameter constraints do not
change significantly if the location of any features in the PPS are allowed to
vary, although neutrino constraints are more sensitive to PPS features if they
are known a priori to exist at fixed intervals in . Although there is
no support for a non-standard neutrino sector from constraints on both neutrino
mass and relativistic energy density, we see surprisingly strong evidence for
features in the PPS when it is constrained with data from Planck 2015, SZ
cluster counts, and recent high-precision local measurements of .
Conversely combining Planck with matter power spectrum and BAO measurements
yields a much weaker constraint. Given that this result is sensitive to the
choice of data this tension between SZ cluster counts, Planck and
measurements is likely an indication of unmodeled systematic
bias that mimics PPS features, rather than new physics in the PPS or neutrino
sector.Comment: 23 pages, 9 figures, 8 tables; matches version published in JCA
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