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  • 1
    ISSN: 1420-9136
    Keywords: Continental extension ; crustal shortening ; metamorphic core complex ; Basin and Range
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract This paper examines the first-order dynamic interactions between crustal shortening, extension, and volcanism in tectonic evolution in the North American Cordillera. The protracted crustal compression in the Mesozoic and early Cenozoic (110−55 Ma) contributed to the subsequent Tertiary extension by thermally weakening the lithosphere and producing an overthickened (〉50 km) and gravitationally unstable crust. In addition to post-kinematic burial heating, synkinematic thermal processes including conduction are shown significantly because of the long period of crustal contraction and the slow shortening rates (〈4 mm/yr). The effects of shear heating were probably limited for the same reasons. Localized delamination of the lithospheric mantle may have contributed to the abundant plutonism and high crustal temperature in the southeastern Canadian Cordillera at the end of the orogeny. Most early-stage extension in the Cordillera, characterized by formation of metamorphic core complexes, resulted from gravitational collapse of the overthickened crust. Plutionism may have facilitated strain localization, causing widespread crustal extension at relatively low stress levels. Crustal collapse, however, was unlikely the direct cause of the Basin-Range extension, because the gravitational stresses induced by crustal thickening are limited to the crust; only a small fraction of the gravitational stresses may be transmitted to the lithospheric mantle. Nor could core complex formation induce the voluminous mid-Tertiary volcanism, which requires major upwelling of the asthenosphere. While the causes of the asthenospheric upwelling are not clear, such processes could provide the necessary conditions for the Basin-Range extension: the driving force from thermally induced gravitational potential and a thermally weakened lithosphere. The complicated spatial and temporal patterns of volcanism and extension in the Basin and Range province may be partially due to the time-dependent competing effects of thermal weakening and rheological hardening associated with intrusion and underplating of mantle-derived magmas.
    Type of Medium: Electronic Resource
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  • 2
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    Copernicus Publications (EGU)
    In:  Ocean Science Discussions . pp. 1-43.
    Publication Date: 2019-01-17
    Description: he characteristics of the main water masses in the Atlantic Ocean are investigated and defined as Source Water Types (SWTs) from their formation area by six key properties based on the GLODAPv2 observational data. These include both conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate) variables. For this we divided the Atlantic Ocean into four vertical layers by distinct potential densities in the shallow and intermediate water column, and additionally by concentration of silicate in the deep waters. The SWTs in the upper/central water layer originates from subduction during winter and are defined as central waters, formed in four distinct areas; East North Atlantic Central water (ENACW), West North Atlantic Central Water (WNACW), East South Atlantic Central Water (ESACW) and West South Atlantic Central Water (WSACW). Below the upper/central layer the intermediate layer consist of three main SWTs; Antarctic Intermediate Water (AAIW), Subarctic Intermediate Water (SAIW) and Mediterranean Overflow Water (MOW). The North Atlantic Deep Water (NADW) is the dominating SWT in the deep and overflow layer, and is divided into upper and lower NADW based on the different origins and properties. The origin of both the upper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland Overflow Water (ISOW) and Denmark Strait Overflow Water (DSOW). Antarctic Bottom Water (AABW) is the only natural SWT in the bottom layer and this SWT is redefined as North East Atlantic Bottom Water (NEABW) in the north of equator due to the change of key properties, especial silicate. Similar with NADW, two additional SWTS, Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are defined in the Weddell Sea in order to understand the origin of AABW. The definition of water masses in biogeochemical space is useful for, in particular, chemical and biological oceanography to understand the origin and mixing history of water samples.
    Type: Article , NonPeerReviewed
    Format: text
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  • 3
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    Copernicus Publications (EGU)
    In:  Ocean Science Discussions . pp. 1-32.
    Publication Date: 2019-01-17
    Description: The distribution of the main water masses in the Atlantic Ocean are investigated with the Optimal Multi-Parameter (OMP) method. The properties of the main water masses in the Atlantic Ocean are described in a companion article; here these definitions are used to map out the general distribution of those water masses. Six key properties, including conservative (potential temperature and salinity) and non-conservative (oxygen, silicate, phosphate and nitrate), are incorporated into the OMP analysis to determine the contribution of the water masses in the Atlantic Ocean based on the GLODAP v2 observational data. To facilitate the analysis the Atlantic Ocean is divided into four vertical layers based on potential density. Due to the high seasonal variability in the mixed layer, this layer is excluded from the analysis. Central waters are the main water masses in the upper/central layer, generally featuring high potential temperature and salinity and low nutrient concentrations and are easily distinguished from the intermediate water masses. In the intermediate layer, the Antarctic Intermediate Water (AAIW) from the south can be detected to ~30°N, whereas the Subarctic Intermediate Water (SAIW), having similarly low salinity to the AAIW flows from the north. Mediterranean Overflow Water (MOW) flows from the Strait of Gibraltar as a high salinity water. NADW dominates the deep and overflow layer both in the North and South Atlantic. In the bottom layer, AABW is the only natural water mass with high silicate signature spreading from the Antarctic to the North Atlantic. Due to the change of water mass properties, in this work we renamed to North East Antarctic Bottom Water NEABW north of the equator. Similarly, the distributions of Labrador Sea Water (LSW), Iceland Scotland Overflow Water (ISOW), and Denmark Strait Overflow Water (DSOW) forms upper and lower portion of NADW, respectively roughly south of the Grand Banks between ~50 and 66°N. In the far south the distributions of Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW) are of significance to understand the formation of the AABW.
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2013-08-31
    Description: An analytic model of axisymmetric mantle plumes driven by either thermal diffusion or combined diffusion of both heat and chemical species from a point source is presented. The governing equations are solved numerically in cylindrical coordinates for a Newtonian fluid with constant viscosity. Instead of starting from an assumed plume source, constraints on the source parameters, such as the depth of the source regions and the total heat input from the plume sources, are deduced using the geophysical characteristics of mantle plumes inferred from modelling of hotspot swells. The Hawaiian hotspot and the Bermuda hotspot are used as examples. Narrow mantle plumes are expected for likely mantle viscosities. The temperature anomaly and the size of thermal plumes underneath the lithosphere can be sensitive indicators of plume depth. The Hawaiian plume is likely to originate at a much greater depth than the Bermuda plume. One suggestive result puts the Hawaiian plume source at a depth near the core-mantle boundary and the source of the Bermuda plume in the upper mantle, close to the 700 km discontinuity. The total thermal energy input by the source region to the Hawaiian plume is about 5 x 10(10) watts. The corresponding diameter of the source region is about 100 to 150 km. Chemical diffusion from the same source does not affect the thermal structure of the plume.
    Keywords: GEOPHYSICS
    Type: NAS 1.26:186461 , NASA-CR-186461
    Format: application/pdf
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  • 5
    Publication Date: 2013-08-31
    Description: The evolution of midplate hotspot swells on an oceanic plate moving over a hot, upwelling mantle plume is numerically simulated. The plume supplies a Gaussian-shaped thermal perturbation and thermally-induced dynamic support. The lithosphere is treated as a thermal boundary layer with a strongly temperature-dependent viscosity. The two fundamental mechanisms of transferring heat, conduction and convection, during the interaction of the lithosphere with the mantle plume are considered. The transient heat transfer equations, with boundary conditions varying in both time and space, are solved in cylindrical coordinates using the finite difference ADI (alternating direction implicit) method on a 100 x 100 grid. The topography, geoid anomaly, and heat flow anomaly of the Hawaiian swell and the Bermuda rise are used to constrain the models. Results confirm the conclusion of previous works that the Hawaiian swell can not be explained by conductive heating alone, even if extremely high thermal perturbation is allowed. On the other hand, the model of convective thinning predicts successfully the topography, geoid anomaly, and the heat flow anomaly around the Hawaiian islands, as well as the changes in the topography and anomalous heat flow along the Hawaiian volcanic chain.
    Keywords: GEOPHYSICS
    Type: NASA-CR-186462 , NAS 1.26:186462
    Format: application/pdf
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  • 6
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    Elsevier
    In:  Journal of Marine Systems, 151 . pp. 57-70.
    Publication Date: 2017-04-11
    Description: Transient tracer data (CFC-12 and SF6) from three oceanographic field campaigns to the Mauritanian Upwelling area conducted during winter, spring and summer from 2005 to 2007 is presented. The transient tracers are used to constrain a possible solution to the transient time distribution (TTD) along 18°N and to quantify the mean ages in vertical sections perpendicular to the coast. We found that an Inverse Gaussian distribution where the ratio of the moments δ and Γ equals 1.2 is a possible solution (δ/Γ=1.2) of the TTD. The transient tracers further show considerable under-saturation in the mixed layer during the winter and spring cruises that can only be maintained by mixing or upwelling by tracer-poor water from below the mixed layer. We use dissipation data from microstructure measurements and the tracer depth distribution to quantify the flux of tracers to the mixed layer by vertical diffusivity and wind data from the ship to quantify the air-sea flux. We then use the magnitude of the under-saturation in the mixed layer to estimate the advective upwelling velocity which is the balance the first two processes, in a steady state assumption. We find that the upwelling velocities range from less than 1 to 5.6×10-5ms-1 (〈0.8-4.8md-1), with generally higher values close to the coast, but with comparable upwelling velocities during spring and winter. During the summer cruise the transient tracers were close to equilibrium with the atmosphere, suggesting no upwelling. We have shown the use of CFC-12 and SF6 transient tracer data for calculating upwelling velocity, and found an overall uncertainty of roughly ±50%.
    Type: Article , PeerReviewed
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: We present a boundary-layer model for mantle plumes driven by thermal and chemical diffusion and buoyancy. The problem is solved for a Boussinesq, Newtonian fluid with infinite Prandtl number and constant physical properties. We focus on axisymmetric mantle plumes, but also solve 2-D plumes due to line-sources for comparison. The results show that chemical plumes are much thinner than thermal plumes because of small chemical diffusivity in the mantle. When pressure-release partial melting occurs in a thermal-chemical plume, at least two mantle components may be involved: one from the chemical plume and one from the ambient mantle. A buoyant chemical boundary layer in the plume source region tends to cause narrow and strong plumes. A dense chemical source would have the opposite effect. The effects of chemical buoyancy diminish as the Lewis number, the ratio of thermal to chemical diffusivity, increases. For fully developed mantle plumes, the effects of chemical buoyancy may be insignificant. The physical parameters of mantle plumes may be estimated using surface information deduced from swell models. The total heat input from the Hawaiian plume source is about 1.3 times 1011 W, nearly 5–10 per cent of the total heat loss from the core. The depth of the Hawaiian plume source is constrained to be near the core-mantle boundary. Our results show that 2-D plumes are generally stronger than axisymmetric plumes.
    Type of Medium: Electronic Resource
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  • 8
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    In:  (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 45 pp
    Publication Date: 2016-12-13
    Keywords: Course of study: MSc Climate Physics
    Type: Thesis , NonPeerReviewed
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  • 9
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    In:  [Poster] In: SOLAS Open Science Conference, 07.-11.09.2015, Kiel, Germany .
    Publication Date: 2015-12-14
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 10
    Publication Date: 2019-07-13
    Description: The main objective of this project was to better understand the geodynamics controlling the mountain building and topographic evolution in the central Andes using an integrated approach that combines GPS, seismological, and numerical studies.
    Keywords: Geophysics
    Type: SENSH99-0060-0029
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