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  • 1
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    A sea-floor spreading event captured by seismometers (2006)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2006-11-25
    Description: Two-thirds of Earth's surface is formed at mid-ocean ridges, yet sea-floor spreading events are poorly understood because they occur far beneath the ocean surface. At 9 degrees 50'N on the East Pacific Rise, ocean-bottom seismometers recently recorded the microearthquake character of a mid-ocean ridge eruption, including precursory activity. A gradual ramp-up in activity rates since seismic monitoring began at this site in October 2003 suggests that eruptions may be forecast in the fast-spreading environment. The pattern culminates in an intense but brief (approximately 6-hour) inferred diking event on 22 January 2006, followed by rapid tapering to markedly decreased levels of seismicity.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tolstoy, M -- Cowen, J P -- Baker, E T -- Fornari, D J -- Rubin, K H -- Shank, T M -- Waldhauser, F -- Bohnenstiehl, D R -- Forsyth, D W -- Holmes, R C -- Love, B -- Perfit, M R -- Weekly, R T -- Soule, S A -- Glazer, B -- New York, N.Y. -- Science. 2006 Dec 22;314(5807):1920-2. Epub 2006 Nov 23.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lamont-Doherty Earth Observatory (LDEO) of Columbia University, Palisades, NY 10964, USA. tolstoy@ldeo.columbia.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17124289" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
    Electronic Resource
    Electronic Resource
    Minimum speed limit for ocean ridge magmatism from 210 Pb– 226 Ra– 230 Th disequilibria (2005)
    [s.l.] : Nature Publishing Group
    Nature 437 (2005), S. 534-538 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Although 70 per cent of global crustal magmatism occurs at mid-ocean ridges—where the heat budget controls crustal structure, hydrothermal activity and a vibrant biosphere—the tempo of magmatic inputs in these regions remains poorly understood. Such timescales can be assessed, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature03993
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Cryptic striations in the upper mantle revealed by hafnium isotopes in southeast Indian ridge basalts (2006)
    [s.l.] : Nature Publishing Group
    Nature 440 (2006), S. 199-202 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Earth's mantle is isotopically heterogeneous on length scales ranging from centimetres to more than 104 kilometres. This heterogeneity originates from partial melt extraction and plate tectonic recycling, whereas stirring during mantle convection tends to reduce it. Here ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature04582
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  • 4
    Electronic Resource
    Electronic Resource
    226 Ra excesses in mid-ocean-ridge basalts and mantle melting (1988)
    [s.l.] : Nature Publishing Group
    Nature 335 (1988), S. 158-161 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In the 238U decay chain each isotope except 238U and 206Pb is both radiogenic and radioactive. In the state of secular equilibrium, which exists in the absence of chemical fractionation of decay-series elements, the activity of each isotope is the same (activity = \iNi where A; is the decay ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/335158a0
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  • 5
    Electronic Resource
    Electronic Resource
    210 Po– 210 Pb dating of recent volcanic eruptions on the sea floor (1994)
    [s.l.] : Nature Publishing Group
    Nature 368 (1994), S. 841-844 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] 210Po is a member of the 238U decay chain and has the same activity as all other nuclides in the chain in an undisturbed system (that is, at secular, or radioactive, equilibrium). Polonium is, however, moderately volatile and in volcanic emissions is completely gaseous at 400 °C (ref. 6). ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/368841a0
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  • 6
    Electronic Resource
    Electronic Resource
    Submarine magma degassing and explosive magmatism at Macdonald (Tamarii) seamount (1989)
    [s.l.] : Nature Publishing Group
    Nature 341 (1989), S. 50-52 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Macdonald seamount sits on Eocene age Pacific lithosphere3. Based on a regression of ages for the Austral-Cook islands, Macdonald seems to be the current active site of that linear hotspot chain4'5. The volcano rises ~ 1,800 m from the sea floor and has a small summit plateau (100 mx 150m) about ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/341050a0
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  • 7
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    Simulating the carbon footprint of galactic haloes (2016)
    Oxford University Press
    Details
    Publication Date: 2016-08-03
    Description: We compare simulations, including the Illustris simulations, to observations of C iv and C ii absorption at z  = 2–4. These are the C iv column density distribution function in the column density range 10 12 –10 15 cm –2 , the C iv equivalent width distribution at 0.1–2 Å, and the covering fractions and equivalent widths of C iv 1548 Å and C ii 1337 Å around damped Lyman α systems (DLAs). In the context of the feedback models that we investigate, all C iv observations favour the use of more energetic wind models, which are better able to enrich the gas surrounding haloes. We propose two ways to achieve this: an increased wind velocity and an increase in wind thermal energy. However, even our most energetic wind models do not produce enough absorbers with C iv equivalent width 〉0.6 Å, which in our simulations are associated with the most massive haloes. All simulations are in reasonable agreement with the C ii covering fraction and equivalent widths around damped Lyman α absorbers, although there is a moderate deficit in one bin 10–100 kpc from the DLA. Finally, we show that the C iv in our simulations is predominantly photoionized.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 8
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    Resolving discordant U-Th-Ra ages: constraints on petrogenetic processes of recent effusive eruptions at Tatun Volcano Group, northern Taiwan (2015)
    Geological Society (of London)
    Details
    Publication Date: 2015-05-16
    Description: U–Th–Ra isotope analyses of whole rocks and mineral separates were conducted in order to perform isochron dating of three morphologically young lavas from Tatun volcano, northern Taiwan (from Mt Cising, the Shamao dome and the Huangzuei volcano). The data do not yield tight U–Th isochrons, indicating open-system magmatic processes. However, crystallization ages of two samples can be constrained: namely, less than about 1370 years for the Shamao dome, based on 226 Ra– 230 Th disequilibrium in magnetite, and less than approximately 70 ka (but potentially Holocene) for a Huangzuei flow, based on 238 U– 230 Th disequilibrium in plagioclase. Discordant Ar–Ar, 238 U– 230 Th and 226 Ra– 230 Th ages are best explained by young lavas having inherited some crystals from older lithologies (crystal mushes or rocks), and indicate that the above ages represent maxima. Our study provides the first evidence of effusive volcanism at the Tatun Volcano Group in Late Holocene times. All separates from the Shamao dome and Huangzuei volcano are in 234 U– 238 U equilibrium. Minerals in the Mt Cising sample are in 234 U– 238 U disequilibrium, despite the 234 U– 238 U equilibrium of the whole rock. We interpret this as uptake of a hydrothermally altered, old crystal cargo into fresh melt prior to eruption. A different dating approach will thus be required to constrain the eruption age of Mt Cising. Supplementary material: Ar–Ar plateaus from Mt Cising and the Shamao dome, reproduced from Lee (1996), are available at www.geolsoc.org.uk/SUP18817
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 9
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    Magmatic Processes at Variable Magma Supply along the Galapagos Spreading Center: Constraints from Single Eruptive Units (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-01
    Description: Petrological study of eruptive units in two locations along the Galápagos Spreading Center provides insight into how the rate of magma supply affects mid-ocean ridge magmatic systems. Study areas with lower magma supply (95°W) and higher magma supply (92°W) have similar spreading rates (53 and 55 mm a –1 ), but differ by 30% in the time-averaged rate of magma supply (0·3 x 10 6 and 0·4 x 10 6 m 3 km –1 a –1 ) as a result of varying proximity to the Galápagos hotspot. We use major and trace element compositions of glass and whole-rock samples, chemistry of mineral phases, and petrography to characterize parental magma variability, fractional crystallization and magma mixing in crustal reservoirs, and timescales of magmatic recharge relative to eruption. At the low magma supply study area, eruptible magma appears to be present only intermittently within the crust; magma recharge is probably infrequent, occurring with a periodicity of several hundred to one thousand years. The shallowest magma body in the crust is thought to be at ~3 km below the seafloor, and lavas are restricted to a relatively limited compositional range (6·2–9·1 wt % MgO). Magmatic evolution at this location is probably dominated by processes occurring within a crystal-rich mush, with limited subsequent residence in melt-dominated magma reservoirs. Eruptions here appear to be closely coupled to magmatic recharge events; lower MgO lavas have compositional trends controlled by mixing of low- and high-MgO magmas from compositionally distinct parents, and commonly contain both normally and reversely zoned crystals. In contrast, at the high magma supply study area, where a seismically imaged melt lens is located ~1·7 km below the seafloor, fractional crystallization within a melt-rich magma reservoir results in a larger range in major element compositions of the erupted magmas (2·7–8·2 wt % MgO) with less variation in trace element concentrations or ratios. Temperatures within the melt lens over the last several hundred years have varied by at least 100°C (1070–1170°C); cooling rates within the melt lens are estimated to be greater than 0·5°C per year. Relatively low-MgO lavas have over-enrichments in Cl that are best explained by assimilation of brine associated with hydrothermal circulation within the overlying crust. Between magmatic recharge events, resident magma fractionates and feeds one or more low-volume fissure eruptions. Small bodies of magma may become isolated from the larger magmatic system in the crust, allowing more extreme degrees of fractionation, locally reaching basaltic andesite. This study demonstrates that persistent melt lenses at intermediate rates of magma supply need not be ‘steady state’. The variations in magma composition among eruptive episodes at each location allow us to assess the temporal variability in magma reservoir properties at ridge segments along the Galápagos Spreading Center, in the context of regional variations in magma supply.
    Print ISSN: 0022-3530
    Electronic ISSN: 1460-2415
    Topics: Geosciences
    Published by Oxford University Press
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  • 10
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    On the cosmic evolution of Fe/Mg in QSO absorption line systems (2015)
    Oxford University Press
    Details
    Publication Date: 2015-06-11
    Description: We investigate the variation of the ratio of the equivalent widths of the Fe ii 2600 line to the Mg ii 2796, 2803 doublet as a function of redshift in a large sample of absorption lines drawn from the Johns Hopkins University - Sloan Digital Sky Survey Absorption Line Catalog. We find that despite large scatter, the observed ratio shows a trend where the equivalent width ratio $\mathcal {R}\equiv W_{\rm Fe\,\small {II}}/W_{\rm Mg\,\small {II}}$ decreases monotonically with increasing redshift z over the range 0.55 ≤  z  ≤ 1.90. Selecting the subset of absorbers where the signal-to-noise ratio of the Mg ii equivalent width $W_{\rm Mg\,\small {II}}\ {\rm is} \ge 3$ and modelling the equivalent width ratio distribution as a Gaussian, we find that the mean of the Gaussian distribution varies as $\mathcal {R}\propto (-0.045\pm 0.005)z$ . We discuss various possible reasons for the trend. A monotonic trend in the Fe/Mg abundance ratio is predicted by a simple model where the abundances of Mg and Fe in the absorbing clouds are assumed to be the result of supernova (SN) ejecta and where the cosmic evolution in the SNIa and core-collapse SN rates is related to the cosmic star formation rate. If the trend in $\mathcal {R}$ reflects the evolution in the abundances, then it is consistent with the predictions of the simple model.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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