140 research outputs found
Melt extraction and crustal thickness variations at segmented mid-ocean ridges
Mid-ocean ridges are underwater volcanic mountains extending more than 55,000 km in ocean basins worldwide, accounting for nearly 80% of the Earth’s volcanism. They are the birthplace of new seafloor, resurfacing two thirds of the planet over about 100 million years. At mid-ocean ridges, tectonic plates move away from each other, a phenomenon known as seafloor spreading, at rates ranging from slow (~10 cm/yr) to fast (~100 cm/yr). Plate divergence induces the underlying mantle to rise and melt. Buoyant melts segregate from the mantle and collect toward axes of mid-ocean ridges, where they are extracted and solidify into new oceanic crust. The thickness of oceanic crust, the final product of ridge magmatism, contains integrated information about plate motion, mantle flow, mantle temperature, melt generation, melt extraction and crustal accretion. In this dissertation, I investigate three types of crustal thickness variations at mid-ocean ridges to provide insights into the Earth’s deep, less accessible interior.
Mid-ocean ridges are broken into segments bounded by transform faults. At fast-spreading ridges, transform faults exhibit thicker crust than adjacent ridge segments, while the crust along transform faults at slow-spreading ridges is thinner. I show that these observations are compatible with melt being extracted along fast-slipping transform faults, but not at the slow-slipping ones.
The plates on either side of a ridge axis may move away from the ridge at different rates. I reveal a discrepancy between the expected and observed topography at such asymmetrically spreading ridges, and argue that the discrepancy is best explained by asymmetric crustal thickness, with thicker crust on the slower-moving plate and thinner crust on the faster-moving plate.
Crustal thickness may differ between ridge segments separated by a transform fault, in a way that correlates with the relative motion between the ridge and the underlying mantle. I study the three-dimensional effects of background mantle flow, and demonstrate that the pattern of along-axis crustal thickness variations is controlled by the relative angle between ridge and background mantle flow.
This dissertation systematically examines the origins of crustal thickness variations at mid-ocean ridges, and provides constraints on mantle and melt dynamics
Duality Regularization for Unsupervised Bilingual Lexicon Induction
Unsupervised bilingual lexicon induction naturally exhibits duality, which
results from symmetry in back-translation. For example, EN-IT and IT-EN
induction can be mutually primal and dual problems. Current state-of-the-art
methods, however, consider the two tasks independently. In this paper, we
propose to train primal and dual models jointly, using regularizers to
encourage consistency in back translation cycles. Experiments across 6 language
pairs show that the proposed method significantly outperforms competitive
baselines, obtaining the best-published results on a standard benchmark
MeltMigrator : a MATLAB-based software for modeling three-dimensional melt migration and crustal thickness variations at mid-ocean ridges following a rules-based approach
Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 18 (2017): 445–456, doi:10.1002/2016GC006686.MeltMigrator is a MATLAB®-based melt migration software developed to process three-dimensional mantle temperature and velocity data from user-supplied numerical models of mid-ocean ridges, calculate melt production and melt migration trajectories in the mantle, estimate melt flux along plate boundaries, and predict crustal thickness distribution on the seafloor. MeltMigrator is also capable of calculating compositional evolution depending on the choice of petrologic melting model. Programmed in modules, MeltMigrator is highly customizable and can be expanded to a wide range of applications. We have applied it to complex mid-ocean ridge model settings, including transform faults, oblique segments, ridge migration, asymmetrical spreading, background mantle flow, and ridge-plume interaction. In this technical report, we include an example application to a segmented mid-ocean ridge. MeltMigrator is available as a supplement to this paper, and it is also available from GitHub and the University of Maryland Geodynamics Group website.National Science Foundation Grant Number: OCE-0937277 and OCE-14582012017-07-2
ELM of ELM-WD: An extremely low mass hot donor star discovered in LAMOST survey
The Extremely Low Mass White Dwarfs (ELM WDs) and pre-ELM WDs are helium core
white dwarfs with mass . They are formed in close binaries
and have lost over half of their initial masses via Common Envelope (CE)
ejection or stable Roche Lobe Over Flow (RLOF). Both evolution simulations and
observations show that a lower mass limit for ELM WDs exists at
. Here we report the discovery of an extremely low mass
ELM WD, ID70904216 in LAMOST survey, that may be lower than the ELM WD mass
limit. Based on LAMOST and P200 spectroscopic observations, ID70904216 shows
orbital period 0.219658 days and radial velocity semi-amplitude
, which gives the mass function of 0.73, indicating
the companion is a compact star. The low resolution spectra shows a F type star
with without emission features. The temperature is
consistent with that derived from SED fitting() and multi-color light
curve solution(). The optical light curves, in ZTF g, r and i bands and
Catalina V band, show ellipsoidal variability with amplitudes ,
suggesting that the visible companion is heavily tidal distorted. Combining
with the distance from Gaia survey, the WD code modeling estimates that the
mass of the visible star is , and the mass of
the invisible star is . The radius of the
visible donor is . The inclination angle is constrained
between 60 and 90. The observations indicate the system is
a pre-ELM WD + WD/NS binary system with an extremely low mass hot donor below
the theoretical limit.Comment: 16 pages, 10 figure
Orbital parameters for an ELM white dwarf with a white dwarf companion: LAMOST J033847.06+413424.2
Double white dwarf systems are of great astrophysical importance in the field
of gravitational wave and Type Ia supernova. While the binary fraction of CO
core white dwarf is about a few percents, the extremely low mass white dwarfs
are all thought to be within binary systems. In this work, we report the
orbital solution of a double degenerate system: J033847.06+413424.24, an
extremely low mass He core white dwarf orbiting a CO core white dwarf. With
LAMOST and P200, time domain spectroscopic observations have been made and
spectral atmosphere parameters are estimated to be K and
log dex. Combining Gaia parallax, 3D extinction, and evolution
tracks, we estimate a radius of and a mass of
. With the 37 single exposure spectra, the radial velocities are
measured and the orbital parameters are estimated to be days,
km/s and km/s. The radial velocity based system
ephemeris is also provided. The light curves from several photometric surveys
show no orbital modulation. The orbital solution suggests that the invisible
companion has a minimum mass of about 0.60 and is
for an inclination of , indicating most probably a CO
core white dwarf. The system is expected to merge in about 1 Gyr. With present
period and distance ( pc) it can not irradiate strong enough
gravitational wave for LISA. More double degenerate systems are expected to be
discovered and parameterized as the LAMOST survey goes on.Comment: 12 pages, 11 figure
Sedimentation rates test models of oceanic detachment faulting
This is the accepted manuscript version.The final version is available from Wiley at http://onlinelibrary.wiley.com/doi/10.1002/2014GL061555/full.Long-lived detachment faults play an important role in the construction of new oceanic
crust at slow-spreading mid-oceanic ridges. Although the corrugated surfaces of exposed
low-angle faults demonstrate past slip, it is difficult to determine whether a given fault is
currently active. If inactive, it is unclear when slip ceased. This judgment is crucial for
tectonic reconstructions where detachment faults are present, and for models of plate
spreading. We quantify variation in sediment thickness over two corrugated surfaces
near 16.5°N at the Mid-Atlantic Ridge using near-bottom CHIRP data. We show that the
distribution of sediment and tectonic features at one detachment fault is consistent with
slip occurring today. In contrast, another corrugated surface 20 km to the south shows a
sediment distribution suggesting that slip ceased ~150,000 years ago. Data presented here
provide new evidence for active detachment faulting, and suggest along-axis variations in
fault activity occur over tens of kilometers.This work was supported by the National Science Foundation grant number OCE-1155650
Serum CA72-4 is specifically elevated in gout patients and predicts flares
Objectives Serum CA72-4 levels are elevated in some gout patients but this has not been comprehensively described. The present study profiled serum CA72-4 expression in gout patients and verified the hypothesis that CA72-4 is a predictor of future flares in a prospective gout cohort. Methods To profile CA72-4 expression, a cross-sectional study was conducted in subjects with gouty arthritis, asymptomatic hyperuricaemia, four major arthritis types (OA, RA, SpA, septic arthritis) and healthy controls. A prospective gout cohort study was initiated to test the value of CA72-4 for predicting gout flares. During a 6-month follow-up, gout flares, CA72-4 levels and other gout-related clinical variables were observed at 1, 3 and 6 months. Results CA72-4 was highly expressed in patients with gouty arthritis [median (interquartile range) 4.55 (1.56, 32.64) U/ml] compared with hyperuricaemia patients [1.47 (0.87, 3.29) U/ml], healthy subjects [1.59 (0.99, 3.39) U/ml] and other arthritis patients [septic arthritis, 1.38 (0.99, 2.66) U/ml; RA, 1.58 (0.95, 3.37) U/ml; SpA, 1.56 (0.98, 2.85) U/ml; OA, 1.54 (0.94, 3.34) U/ml; P 6.9 U/ml) was the strongest predictor of gout flares (hazard ratio = 3.889). Prophylactic colchicine was effective, especially for patients with high CA72-4 levels (P = 0.014). Conclusion CA72-4 levels were upregulated in gout patients who experienced frequent flares and CA72-4 was a useful biomarker to predict future flares
- …