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  • 1
    Electronic Resource
    Electronic Resource
    Isostatic Consequences of Giant Landslides on the Hawaiian Ridge (2000)
    Springer
    Pure and applied geophysics 157 (2000), S. 1097-1114 
    Details
    ISSN: 1420-9136
    Keywords: Key Words: Isostasy, flexure, landslide, Hawaii.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —Giant landslides, like melting glaciers, lead to a redistribution of mass which will have isostatic consequences. Three-dimensional numerical modeling experiments were devised to examine how this mass redistribution affects the isostatic flexural curve. A debris avalanche of 10–40% of pre-slide Oahu is required to account for the 1200–5000 km3 Nuuanu deposit, while only ∼ 1% of pre-slide Hawaii Island is necessary to generate the 200–800 km3 Alika I and II avalanche deposits. Trials were run using 25, 30, and 40 km elastic plate thicknesses (T e ). The island uplift resulting from the Nuuanu slide was calculated to be 23 m and 109 m for 10% and 40% volume slides, respectively, both using T e = 25 km. A rebound of 10 m and 49 m was calculated for the same volumes, respectively, using T e = 40 km. A greater amount of uplift is expressed direct lyover the failed flank, causing the edifice to tilt away from the calved-off portion. The landslide deposit depresses the plate several meters beneath the debris field itself. Smaller slides (e.g., Alika I and II) do not produce as much flexural response, with 17 m and 7 m uplift for T e = 25 and 40 km, respectively. The effects of slow moving, intact slumps where the failed blocks remain relatively close to the island pedestal were examined for the case of the Hilina slump, making up approximately 10% of the Hawaii Island edifice. Perhaps more significant than the uplift for the Hilina slump, comparable to that for the 10% Nuuanu debris avalanche, is the 114 m and 56 m of downwarp beneath its massive slumped foot (T e = 25 and 40 km, respectively). The landslide rebound process, in the case of a relatively large landslide, should be considered as an added component to the evolutionary course of oceanic islands.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000240050019
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  • 2
    Electronic Resource
    Electronic Resource
    Flexure across a continent–ocean fracture zone: the northern Falkland/Malvinas Plateau, South Atlantic (1997)
    Springer
    Geo-marine letters 17 (1997), S. 110-118 
    Details
    ISSN: 1432-1157
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Bathymetry, satellite-derived gravity, and interpreted seismic reflection data across the northern Falkland/Malvinas Plateau fossil continent–ocean transform rim may record the degree of mechanical coupling across the boundary after ridge–transform intersection time. The rim comprises a broad microcontinental block in the east and a continental marginal fracture ridge 50–100 km wide elsewhere. Free-air gravity anomalies tentatively suggest that the fracture ridge is locked against oceanic elastic lithosphere both to the north (Argentine Basin) and south (Central Falkland Basin).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003670050015
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  • 3
    Electronic Resource
    Electronic Resource
    Literatur (1939)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 118 (1939), S. 102-106 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01547094
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  • 4
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    Motion of the Ontong Java Plateau in the hot-spot frame of reference: 122 Ma-present (2007)
    In:  Geological Society Special Publication 229: 9-20.
    Details
    Publication Date: 2007-10-08
    Description: A new model of Pacific absolute plate motion between 140 and 0 Ma, generated in the fixed hot-spot frame of reference, has been used to track palaeogeographic positions of the Ontong Java Plateau (OJP) from the time (c. 122 Ma) and location (c. 43{degrees}S) of its formation to its present location north of the Solomon Islands. The resulting OJP seafloor flow-line suggests that changes in Pacific plate motion, passage over hot spots and Pacific Rim tectonism all have influenced the continuing structural development and deformation of the plateau. Satellite-derived gravity, bathymetry and Rayleigh-wave tomography potentially reveal the structural fabric of the OJP and adjoining Nauru Basin, including the orientation of probable fracture zones, location of possible relict spreading centres and the presence of a thick lithospheric root, as well as possible later hot-spot-related modification of the fabric. The most recent phase of OJP deformation, which began about 6 Ma, accelerated at 2.6 Ma and continues today, has resulted in the uplift of the islands of Malaita and Santa Isabel, and the formation of the Malaita Anticlinorium, with slip along the old fracture zones possibly triggering submarine canyon formation on the NE side of the OJP. This collision-related deformation also is probably responsible for the ongoing uplift and tilting of the islands of Nauru and Banaba NE of the OJP high plateau.
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  • 5
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    Analysis of Ontong Java Plateau palaeolatitudes: evidence for large-scale rotation since 123 Ma? (2013)
    Oxford University Press
    Details
    Publication Date: 2013-06-11
    Description: We have discovered evidence of a previously unrecognized, large-scale rotation of the Ontong Java Plateau (OJP) recorded in its basement palaeolatitudes. When palaeolatitude differences computed among Ocean Drilling Program Sites 807 and 1183–1187 are plotted versus their present-day site latitude differences, a systematic 2:1 slope bias is evident. While it is possible to resolve this bias by introducing ad hoc tilt corrections at all six sites, drilling records indicate relatively undisturbed conditions at Sites 1183 and 1185–1187. Of the possible causes of the bias, only whole plateau rotation resolves it while honouring the majority of published palaeolatitudes. This implies that only Sites 807 and 1184 palaeolatitudes, both questioned in the literature, are erroneous. A 9° northward dip previously reported at Site 1184 appears to stem from inclined deposition rather than post-emplacement deformation. We also estimate an 8° southward tilt correction at Site 807 to make the data set self-consistent. Based on the six sites analysed, we find that OJP may have experienced ~40° of clockwise rotation since its formation at ~123 Ma. In contrast, available Pacific absolute plate motion (APM) models predict less than 10° of rotation. If our analysis is correct, it suggests that the plateau moved independently of the Pacific Plate early in its history or that Pacific APM models for the Lower Cretaceous are unreliable. While our corrections to Sites 807 and 1184 combined with ~40° rotation resolve the internal inconsistencies, the mean palaeolatitude value of Ontong Java remains largely unchanged and is still anomalous with respect to the Pacific apparent polar wander path at ~123 Ma.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 6
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    Absolute plate motion of Africa around Hawaii-Emperor bend time (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-17
    Description: Numerous regional plate reorganizations and the coeval ages of the Hawaiian Emperor bend (HEB) and Louisville bend of 50–47 Ma have been interpreted as a possible global tectonic plate reorganization at ~chron 21 (47.9 Ma). Yet for a truly global event we would expect a contemporaneous change in Africa absolute plate motion (APM) reflected by physical evidence distributed on the Africa Plate. This evidence has been postulated to take the form of the Réunion-Mascarene bend which exhibits many HEB-like features, such as a large angular change close to ~chron 21. However, the Réunion hotspot trail has recently been interpreted as a sequence of continental fragments with incidental hotspot volcanism. Here we show that the alternative Réunion-Mascarene Plateau trail can also satisfy the age progressions and geometry of other hotspot trails on the Africa Plate. The implied motion, suggesting a pivoting of Africa from 67 to 50 Ma, could explain the apparent bifurcation of the Tristan hotspot chain, the age reversals seen along the Walvis Ridge, the sharp curve of the Canary trail, and the diffuse nature of the St. Helena chain. To test this hypothesis further we made a new Africa APM model that extends back to ~80 Ma using a modified version of the Hybrid Polygonal Finite Rotation Method. This method uses seamount chains and their associated hotspots as geometric constraints for the model, and seamount age dates to determine APM through time. While this model successfully explains many of the volcanic features, it implies an unrealistically fast global lithospheric net rotation, as well as improbable APM trajectories for many other plates, including the Americas, Eurasia and Australia. We contrast this speculative model with a more conventional model in which the Mascarene Plateau is excluded in favour of the Chagos-Laccadive Ridge rotated into the Africa reference frame. This second model implies more realistic net lithospheric rotation and far-field APMs, but fails to explain key details of the Atlantic Ocean volcanic chains. Both models predict a Canary plume influence beneath the Madeiras. Neither model, when projected via the global plate circuit into the Pacific, predicts any significant change in plate motion around chron 21. Consequently, Africa APM models do not appear to provide independent support for a chron 21 global reorganization.
    Keywords: Geodynamics and Tectonics
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 7
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    Regional-residual separation of bathymetry and revised estimates of Hawaii plume flux (2015)
    Oxford University Press
    Details
    Publication Date: 2015-12-17
    Description: Observations of the temporal variations in the volume flux of a plume can provide useful constraints on geodynamic models of plumes and plume-plate interactions. Furthermore, they can be compared with observations at other plumes and may be analysed further to understand the nature and cause of the variations. The volume plume flux is typically derived from a sum of edifice and compensation root volumes. The former can be obtained via the application of regional–residual separation procedures that split the observed relief into regional (swell) and residual (edifice) components, while the latter is generally inferred from the former using local (Airy) or regional (flexural) compensation models. Most regional–residual techniques used in past studies give non-unique results and provide no estimates of the uncertainty in the separation, which impacts the significance of the results. Here, the optimal robust separator (ORS) method achieves a unique separation for the swell and edifice components of the Hawaiian Ridge and furthermore obtain confidence bounds on the total volume flux. A fast spectral method for plate flexure with different edifice and infill densities is used to determine compensation volumes. Although my flux estimates have assigned confidence bounds, these are much smaller than the flux estimates themselves. A comparison of my new results to published volume flux curves shows that my revised flux estimates are lower by a factor of 2–3. Reproducing the prior higher results demonstrates that these discrepancies appear to be related to shortcomings in the implementation of the methodology used in the separation. The variability in the Hawaiian plume flux occurs at two different time scales: A short (1–2 Myr) periodicity related to the spacing of islands and seamounts, which ultimately is related to plume-plate flexural interactions, and a much longer (10–15 Myr) periodicity that may be related to plate kinematic changes. Superimposed on these trends may be an exponential increase towards more recent times, but this trend may also be explained by a higher flux level during the period when the plume was positioned beneath the relatively younger lithospheric segment bracketed by the Murray and Molokai fracture zones. Landslides and erosion of the edifice may imply an underestimation of total volumes by 5–10 per cent. The main uncertainty facing studies of plume flux is related to the unknown quantity of magmatic underplating.
    Keywords: Geodynamics and Tectonics
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 8
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    Chronology and Geochemistry of Lavas from the Nazca Ridge and Easter Seamount Chain: an ~30 Myr Hotspot Record (2012)
    Oxford University Press
    Details
    Publication Date: 2012-06-22
    Description: The Easter Seamount Chain and Nazca Ridge are two of the most conspicuous volcanic features on the Nazca plate. Many questions about their nature and origin have remained unresolved because of a lack of geochronological and geochemical data for large portions of both chains. New 40 Ar– 39 Ar incremental heating age determinations for dredged rocks from volcanoes east of Salas y Gomez Island show that, with very few exceptions, ages increase steadily to the east from 1·4 to 30 Ma, confirming that the two chains are parts of the same hotspot trail and indicating a hotspot location near Salas y Gomez rather than beneath Easter Island some 400 km farther west. Most of the volcanoes appear to have been erupted onto seafloor that was 5–13 Myr old, and no systematic variation in seafloor age at the time of seamount formation is apparent. At about 23 Ma, the formation of the Nazca Ridge ceased and that of the Easter Seamount Chain began, corresponding to a change in the direction of motion of the Nazca plate. Most of the studied rocks are moderately alkalic to transitional basalts. Their geochemical characteristics suggest that they represent relatively small mean amounts of partial melting initiating in garnet-bearing mantle and ending in the spinel facies. Nd–Sr–Pb isotopic compositions are within the range of values previously observed for volcanoes of the Easter Seamount Chain, west of Easter Island; moreover, most of our data cluster in a rather small part of this range [e.g. Nd (t) is between +6·0 and +4·0]. The results indicate that the mantle source has consisted of the same two principal components, a C/FOZO-type component and a high- Nd , incompatible-element-depleted Pacific mid-ocean ridge basalt-source-type component, since at least 30 Ma. The lack of any geochemical gradient along the chain east of Salas y Gomez implies that no systematic change over time has occurred in the proportions of these end-members.
    Print ISSN: 0022-3530
    Electronic ISSN: 1460-2415
    Topics: Geosciences
    Published by Oxford University Press
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  • 9
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    Mid-Cenozoic Pacific plate motion change: Implications for the Northwest Hawaiian Ridge and circum-Pacific (2018)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2018
    Description: 〈span〉〈div〉Abstract〈/div〉The alignment and age progression of volcanoes produced as a tectonic plate moves over a mantle plume can be used to reconstruct both the direction and rate of past plate motion assuming the plume remains in a fixed location. New 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar dates for lavas from 15 volcanoes spanning the entire length (∼2800 km) of the Northwest Hawaiian Ridge (NWHR) facilitate improved age-distance relationships. These are used to constrain a significant kink in the NWHR at 25.3 ± 0.5 Ma as the Pacific plate experienced a brief episode of more northerly motion and rotated counter-clockwise. The age progression (i.e., velocity of the Pacific plate) increased markedly from 57 to 87 km/Ma following the plate motion change. This mid-Cenozoic tectonic reorganization has been previously identified in plate motion models, but has been poorly constrained temporally. We demonstrate that this event affected four seamount trails within the Pacific Basin, and had a significant impact on all circum-Pacific volcanic arcs.〈/span〉
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 10
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    Toward 1-mGal accuracy in global marine gravity from CryoSat-2, Envisat, and Jason-1 (2013)
    Society of Exploration Geophysicists (SEG)
    Details
    Publication Date: 2013-08-07
    Description: More than 60% of the Earth's land and shallow marine areas are covered by 〉 2 km of sediments and sedimentary rocks, with the thickest accumulations on rifted continental margins (Figure 1). Free-air marine gravity anomalies derived from Geosat and ERS-1 satellite altimetry (Fairhead et al., 2001; Sandwell and Smith, 2009; Andersen et al., 2009) outline most of these major basins with remarkable precision. Moreover, gravity and bathymetry data derived from altimetry are used to identify current and paleo-submarine canyons, faults, and local recent uplifts. These geomorphic features provide clues to where to look for large deposits of sediments. While current altimeter data delineate large offshore basins and major structures, they do not resolve some of the smaller geomorphic features and basins (Yale et al., 1998; Fairhead et al., 2001). Improved accuracy and resolution is desirable: to facilitate comparisons between continental margins; as an exploration tool and to permit extrapolation of known structures from well-surveyed areas; to follow fracture zones out of the deep-ocean basin into antecedent continental structures, to define and compare segmentation of margins along strike and identify the position of the continent-ocean boundary; and to study mass anomalies (e.g., sediment type and distribution) and isostatic compensation at continental margins. In this article, we assess the accuracy of a new global marine gravity model based on a wealth of new radar altimetry data and demonstrate that these gravity data are superior in quality to the majority of publicly available academic and government ship gravity data.
    Print ISSN: 1070-485X
    Electronic ISSN: 1938-3789
    Topics: Geosciences
    Published by Society of Exploration Geophysicists (SEG)
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