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  • 1
    Electronic Resource
    Electronic Resource
    Constraints on melt production rate beneath the mid-ocean ridges based on passive flow models (1996)
    Springer
    Pure and applied geophysics 146 (1996), S. 589-620 
    Details
    ISSN: 1420-9136
    Keywords: Melt production rate ; fractional melting ; melt depletion ; crustal thickness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We present a model for computing the total melt production rate from the decompression partial melting region beneath a mid-ocean ridge, and the maximum oceanic crustal thickness created at the ridge axis assuming an ideal melt migration mechanism. The calculations are based on a self-consistent numerical model for the thermal structure and steady-state mantle flow field at a mid-ocean ridge. The model includes the effect of decreasing the melt production rate within the partial melting region by melt extraction as the residual mantle matrix becomes increasingly difficult to melt. Thus the melt fraction depends not only on temperature and pressure determined by the location beneath the ridge axis (the Eulerian description) but also on the accumulated melt extraction since the upwelling mantle matrix enters the partial melting region determined by the location along the flow-line path (the Langrangian description). This effect has been neglected by previous models. The model can predict the size of the melting region and the locations of the boundaries between mantle, residual mantle, and the partial melting region for a given spreading rate, also the distribution of the melt depletion and the mean melting depth. Given the observed average thickness of oceanic crust (∼6 km), which is relatively independent of spreading rate, the model results also provide a constraint on the overall efficiency of melt migration to the ridge axis; the efficiency must decrease from 100% at 10 mm/yr to about 60% at fast spreading rates (〉50 mm/yr). Although this reduction may be partially due to the increasing size of the melting region with increasing spreading rate, it still requires less efficient melt migration near the ridge axis at fast spreading rate. We found that the calculated crustal thickness is very sensitive to the mantle temperature. For a normal mantle temperature of 1350°C, the model can generate the observed 6 km oceanic crust over the global range of spreading rates, while the anomalous thicker crusts of the Iceland hotspot and the Reykjanes Ridge are related to higher mantle temperatures associated with the hotspot. Finally, by comparing our model results with previous ones we found that neglecting variations of the melting relations of the residual mantle matrix with melt removal will overestimate the crustal thickness by at least a factor of 1.7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00874735
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamics of the mid-ocean ridge plate boundary: Recent observations and theory (1996)
    Springer
    Pure and applied geophysics 146 (1996), S. 621-648 
    Details
    ISSN: 1420-9136
    Keywords: Oceanic spreading center ; mantle upwelling ; rift valley to no-rift valley transition ; ridge segmentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The global mid-ocean ridge system is one of the most active plate boundaries on the earth and understanding the dynamic processes at this plate boundary is one of the most important problems in geodynamics. In this paper I present recent results of several aspects of mid-ocean ridge studies concerning the dynamics of oceanic lithosphere at these diverging plate boundaries. I show that the observed rift valley to no-rift valley transition (globally due to the increase of spreading rate or locally due to the crustal thickness variations and/or thermal anomalies) can be explained by the strong temperature dependence of the power law rheology of the oceanic lithosphere, and most importantly, by the difference in the rheological behavior of the oceanic crust from the underlying mantle. The effect of this weaker lower crust on ridge dynamics is mainly influenced by spreading rate and crustal thickness variations. The accumulated strain pattern from a recently developed lens model, based on recent seismic observations, was proposed as an appealing mechanism for the observed gabbro layering sequence in the Oman Ophiolite. It is now known that the mid-ocean ridges at all spreading rates are offset into individual spreading segments by both transform and nontransform discontinuities. The tectonics of ridge segmentation are also spreading-rate dependent: the slow-spreading Mid-Atlantic Ridge is characterized by distinct “bulls-eye” shaped gravity lows, suggesting large along-axis variations in melt production and crustal thickness, whereas the fast-spreading East-Pacific Rise is associated with much smaller along-axis variations. These spreading-rate dependent changes have been attributed to a fundamental differences in ridge segmentation mechanisms and mantle upwelling at mid-ocean ridges: the mantle upwelling may be intrinsically plume-like (3-D) beneath a slow-spreading ridge but more sheet-like (2-D) beneath a fast-spreading ridge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00874736
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  • 3
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    Crustal thickness anomalies in the North Atlantic Ocean basin from gravity analysis (2011)
    American Geophysical Union and the Geochemical Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. 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 12 (2011): Q0AE02, doi:10.1029/2010GC003402.
    Description: Gravity-derived crustal thickness models were calculated for the North Atlantic Ocean between 76°N and the Chain Fracture Zone and calibrated using seismically determined crustal thickness. About 7% of the ocean crust is 〈4 km thick (designated as thin crust), and 58% is 4–7 km thick (normal crust); the remaining 35% is 〉7 km thick and is interpreted to have been affected by excess magmatism. Thin crust probably reflects reduced melt production from relatively cold or refractory mantle at scales of up to hundreds of kilometers along the spreading axis. By far the most prominent thick crust anomaly is associated with Iceland and adjacent areas, which accounts for 57% of total crustal volume in excess of 7 km. Much smaller anomalies include the Azores (8%), Cape Verde Islands (6%), Canary Islands (5%), Madeira (〈4%), and New England–Great Meteor Seamount chain (2%), all of which appear to be associated with hot spots. Hot spot–related crustal thickening is largely intermittent, suggesting that melt production is episodic on time scales of tens of millions of years. Thickened crust shows both symmetrical and asymmetrical patterns about the Mid-Atlantic Ridge (MAR) axis, reflecting whether melt anomalies were or were not centered on the MAR axis, respectively. Thickened crust at the Bermuda and Cape Verde rises appears to have been formed by isolated melt anomalies over periods of only ∼20–25 Myr. Crustal thickness anomalies on the African plate generally are larger than those on the North American plate; this most likely results from slower absolute plate speed of the African plate over relatively fixed hot spots.
    Description: Supported by a fellowship from the China Scholarship Council. Additional support for this research was provided by the Charles D. Hollister Endowed Fund for Support of Innovative Research at WHOI (JL) and NSF China grants 40676023 and 40821062 (YJC).
    Keywords: Crustal thickness ; Gravity ; Hot spot ; North Atlantic
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: text/plain
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  • 4
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    A reduced crustal magnetization zone near the first observed active hydrothermal vent field on the Southwest Indian Ridge (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 37 (2010): L18303, doi:10.1029/2010GL043542.
    Description: Inversion of near-bottom magnetic data reveals a well-defined low crustal magnetization zone (LMZ) near a local topographic high (37°47′S, 49°39′E) on the ultraslow-spreading Southwest Indian Ridge (SWIR). The magnetic data were collected by the autonomous underwater vehicle ABE on board R/V DaYangYiHao in February-March 2007. The first active hydrothermal vent field observed on the SWIR is located in Area A within and adjacent to the LMZ at the local topographic high, implying that this LMZ may be the result of hydrothermal alteration of magnetic minerals. The maximum reduction in crustal magnetization is 3 A/M. The spatial extent of the LMZ is estimated to be at least 6.7 × 104 m2, which is larger than that of the LMZs at the TAG vent field on the Mid-Atlantic Ridge (MAR), as well as the Relict Field, Bastille, Dante-Grotto, and New Field vent-sites on the Juan de Fuca Ridge (JdF). The calculated magnetic moment, i.e., the product of the spatial extent and amplitude of crustal magnetization reduction is at least −3 × 107 Am2 for the LMZ on the SWIR, while that for the TAG field on the MAR is −8 × 107 Am2 and that for the four individual vent fields on the JdF range from −5 × 107 to −3 × 107 Am2. Together these results indicate that crustal demagnetization is a common feature of basalt-hosted hydrothermal vent fields at mid-ocean ridges of all spreading rates. Furthermore, the crustal demagnetization of the Area A on the ultraslow-spreading SWIR is comparable in strength to that of the TAG area on the slow-spreading MAR.
    Description: This work was supported by NSF‐China and COMRA Projects 40676023 and DYXM‐115‐02‐03‐02 (JZ and YJC), the Charles D. Hollister Endowed Fund for Support of Innovative Research at WHOI (JL), and the ChEss Program of the Census of Marine Life (CRG).
    Keywords: Reduced magnetization zone ; Southwest Indian Ridge ; Hydrothermal vent
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Imaging Poisson's Ratio of the Uppermost Mantle beneath China (2011)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2011-06-01
    Description: We have obtained a Poisson's ratio image of the uppermost mantle beneath China by performing tomographic inversion of travel-time differences between Sn and Pn. The arrival pairs were selected from the Annual Bulletin of Chinese Earthquakes from 1985 to 2007 and from the International Seismological Center (ISC) data set between 1985 and 2005. The data include 58,663 arrival pairs from 10,486 earthquakes recorded at 204 stations. The average Poisson's ratio is 0.266. The preliminary tomographic results show that (1) the pseudowave velocity is high and the velocity ratio (VP/VS) and Poisson's ratio are low in the stable cratons around the Tibetan Plateau such as the Tarim and Junggar basins, the Ordos craton, and the southern region of the Sichuan basin; (2) a low pseudowave velocity and high velocity ratio and Poisson's ratio exist in the central and northern Tibetan Plateau, the North-South Seismic Zone, and north China; and (3) the high velocity ratio and Poisson's ratio region in the Tibetan Plateau extends to the surrounding cratons, suggesting that the uplift of the Tibetan Plateau results from a high Poisson's ratio or partially melted rocks beneath the plateau and that the softer rocks have intruded into the upper mantle of surrounding cratons.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 6
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    Link between Seismic Velocity Structure and the 2010 Ms 7.1 Yushu Earthquake, Qinghai, China: Evidence from Aftershock Tomography (2012)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2012-02-01
    Description: A high-resolution 2D (horizontal) seismic velocity model is presented for the upper crust around the epicenter of the 14 April 2010 Ms 7.1 Yushu earthquake from aftershock tomography. The velocity model is obtained using a simple Pn-like tomography method including both station and event depth corrections. The most striking result is a fast-velocity anomaly at the epicenter on the Yushu–Garze fault (YGF). The main rupture originated within this fast-velocity anomaly and propagated southeastward into a slow-velocity anomaly at Yushu. The second largest aftershock on 29 May 2010 on a nearby fault also occurred within this fast-velocity anomaly. These results demonstrate a clear example that lateral variation in seismic velocity structures of the upper crust controlled the origination (stress accumulation) and rupture propagation of the 2010 Yushu earthquake and distribution of aftershocks as well. The simple 2D Pg wave travel-time tomography method presented here introduces a new approach utilizing abundant aftershocks data for investigating the rupturing process of a major earthquake.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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  • 7
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    Revisit the K-segment of the Southeast Indian Ridge for new evidence of hydrothermal plumes (2011)
    Springer
    Details
    Publication Date: 2011-09-12
    Print ISSN: 1001-6538
    Electronic ISSN: 1861-9541
    Topics: Natural Sciences in General
    Published by Springer
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  • 8
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    First active hydrothermal vents on an ultraslow-spreading center: Southwest Indian Ridge (2012)
    Geological Society of America (GSA)
    Details
    Publication Date: 2012-01-01
    Description: The ultraslow-spreading Southwest Indian Ridge is a major tectonic province, representing one of the important end-member mid-ocean-ridge types for its very slow and oblique spreading, and providing the only known route for migration of chemosynthetic deep-sea vent fauna between the Atlantic and Indian Oceans. We report the investigation of the first active high-temperature hydrothermal field found on any ultraslow mid-ocean ridge worldwide. Located on Southwest Indian Ridge at 37°47'S, 49°39'E, it consists of three zones extending ~1000 m laterally, and it is one of four recently discovered active and inactive vent sites within a 250-km-long magmatically robust section. Our results provide the first direct evidence for potentially widespread distribution of hydrothermal activity along ultraslow-spreading ridges—at least along magmatically robust segments. This implies that the segment sections with excess heat from enhanced magmatism and suitable crustal permeability along slow and ultraslow ridges might be the most promising areas for searching for hydrothermal activities. It is surprising that the special vent fauna appear to indicate some complex affinity to those on the Central Indian Ridge, southern Mid-Atlantic Ridge, and the southwest Pacific Ocean.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 9
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    Optimization of the microwave-assisted extraction of phlorotannins from Saccharina japonica Aresch and evaluation of the inhibitory effects of phlorotannin-containing extracts on HepG2 cancer cells (2013)
    Springer
    Details
    Publication Date: 2013-09-01
    Print ISSN: 0254-4059
    Electronic ISSN: 1993-5005
    Topics: Biology , Geosciences
    Published by Springer
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  • 10
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    Hydrothermal plume anomalies along the Central Indian Ridge (2008)
    Elsevier
    Details
    Publication Date: 2008-08-01
    Print ISSN: 2095-9273
    Electronic ISSN: 2095-9281
    Topics: Natural Sciences in General
    Published by Elsevier
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