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  • 1
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    Full waveform tomographic images of the peak ring at the Chicxulub impact crater (2011)
    Wiley
    Details
    Publication Date: 2011-06-16
    Description: Peak rings are a feature of large impact craters on the terrestrial planets and are generally believed to be formed from deeply buried rocks that are uplifted during crater formation. The precise lithology and kinematics of peak ring formation, however, remains unclear. Previous work has revealed a suite of bright inward dipping reflectors beneath the peak ring at the Chicxulub impact crater and that the peak ring was formed from rocks with a relatively low seismic velocity. New two-dimensional, full waveform tomographic velocity images show that the uppermost lithology of the peak ring is formed from a thin (∼100–200 m thick) layer of low-velocity (∼3000–3200 m/s) rocks. This low-velocity layer is most likely composed of highly porous, allogenic impact breccias. Our models also show that the change in velocity between lithologies within and outside the peak ring is more abrupt than previously realized and occurs close to the location of the dipping reflectors. Across the peak ring, velocity appears to correlate well with predicted shock pressures from a dynamic model of crater formation, where the rocks that form the peak ring originate from an uplifted basement that has been subjected to high shock pressures (10–50 GPa) and lie above downthrown sedimentary rocks that have been subjected to shock pressures of
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Synthesis of Oceanic Crustal Structure From Two‐Dimensional Seismic Profiles (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract We present a new synthesis of oceanic crustal structure from two‐dimensional seismic profiles to explore differences related to spreading rate and age. Primary results are as follows: (1) Layer 2 has an average thickness of 1.84 km but is thicker for young slow‐spreading crust and thinner for young superfast‐spreading crust. At faster‐spreading rates the layer 2/3 boundary likely corresponds to the lithologic boundary between dikes and gabbros. At slow‐spreading centers, the layer 2/3 boundary is interpreted to mark a change in porosity with depth within the dikes. (2) Total crustal thickness averages 6.15 km and is similar across all spreading rates. (3) Velocities at the top of layer 2 increase rapidly from 3.0 km/s at 0 Ma to 4.6 km/s at 10.5 Ma, with a slower increase to 5.0 km/s at 170 Ma. The rapid increase in velocity at young ages is attributed to crack closure by precipitation of hydrothermal alteration products; the increase at older ages suggests that this process persists as the oceanic crust evolves. (4) There is a correlation between velocities at the top of layer 2 and sediment thickness, with velocities of 5.8–5.9 km/s associated with a sediment thickness of 4.0–4.3 km. The thick sediment may collapse large‐scale features such as lava tubes and fractures. (5) Average velocities at the top of layer 3 are lower for young slow‐spreading and intermediate‐spreading oceanic crust (6.1–6.2 km/s) than for older or faster‐spreading oceanic crust (6.5–6.7 km/s). These low velocities are likely associated with faults penetrating into the sheeted dikes.
    Print ISSN: 8755-1209
    Electronic ISSN: 1944-9208
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary (2010)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2010-03-06
    Description: The Cretaceous-Paleogene boundary approximately 65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The extinction event coincided with a large asteroid impact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism in India. Here, we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction. Notably, a single ejecta-rich deposit compositionally linked to the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary. The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Schulte, Peter -- Alegret, Laia -- Arenillas, Ignacio -- Arz, Jose A -- Barton, Penny J -- Bown, Paul R -- Bralower, Timothy J -- Christeson, Gail L -- Claeys, Philippe -- Cockell, Charles S -- Collins, Gareth S -- Deutsch, Alexander -- Goldin, Tamara J -- Goto, Kazuhisa -- Grajales-Nishimura, Jose M -- Grieve, Richard A F -- Gulick, Sean P S -- Johnson, Kirk R -- Kiessling, Wolfgang -- Koeberl, Christian -- Kring, David A -- MacLeod, Kenneth G -- Matsui, Takafumi -- Melosh, Jay -- Montanari, Alessandro -- Morgan, Joanna V -- Neal, Clive R -- Nichols, Douglas J -- Norris, Richard D -- Pierazzo, Elisabetta -- Ravizza, Greg -- Rebolledo-Vieyra, Mario -- Reimold, Wolf Uwe -- Robin, Eric -- Salge, Tobias -- Speijer, Robert P -- Sweet, Arthur R -- Urrutia-Fucugauchi, Jaime -- Vajda, Vivi -- Whalen, Michael T -- Willumsen, Pi S -- New York, N.Y. -- Science. 2010 Mar 5;327(5970):1214-8. doi: 10.1126/science.1177265.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉GeoZentrum Nordbayern, Universitat Erlangen-Nurnberg, Schlossgarten 5, D-91054 Erlangen, Germany. schulte@geol.uni-erlangen.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20203042" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; *Extinction, Biological ; *Fossils ; Geologic Sediments ; Mexico ; *Minor Planets
    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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  • 4
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    Deep Crustal Structure in the Eastern Gulf of Mexico (2014)
    Wiley
    Details
    Publication Date: 2014-08-01
    Description: We use air gun data recorded by ocean bottom seismometers to constrain the velocity structure along GUMBO 4, a profile extending from the northwestern Florida peninsula across the Florida Escarpment to the central Gulf of Mexico. Moderately thinned continental crust with a Moho depth of 32-33 km, average sediment thickness of 6 km, and an average crustal thickness of 27 km is interpreted on the northeast end of the profile offshore Florida. Thinned and intruded continental crust is identified over a horizontal distance of 225 km where the crustal layer thins from 25 km to 6-7 km; mean seismic velocities of the crust in this region increase from 6.55 km/s to 6.95 km/s from northeast to southwest, and are evidence for increased magmatic input as rifting developed. Oceanic crust with an average thickness of 5.6-5.7 km is observed over a distance of 175 km on the southwest end of the profile, with an extinct spreading ridge with an axial valley morphology imaged on a coincident seismic reflection profile. Anomalously high upper oceanic crust velocities of 6.0-6.7 km/s are interpreted as massive basalt flows, and could reflect increased temperatures during emplacement. Integrating well, seismic reflection, and our seismic refraction data allows us to estimate a full spreading rate of 2.2 cm/yr for seafloor spreading along the profile; this indicates oceanic crust was emplaced at a slow spreading center.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Electronic Resource
    Electronic Resource
    Structure of the Northern Symmetrical Segment of the Juan de Fuca Ridge (1993)
    Springer
    Marine geophysical researches 15 (1993), S. 219-240 
    Details
    ISSN: 1573-0581
    Keywords: Mid-Ocean Ridge ; Juan de Fuca Ridge ; seismic refraction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A seismic refraction profile was shot along the axis of the Northern Symmetrical Segment of the Juan de Fuca Ridge system. Three models of the along-axis crustal structure fit the observed data equally well. One model includes a low-velocity zone, the top of which is at a depth below the seafloor of approximately 3 km, that is continuous along-axis for at least 30 km. A second model includes a low-Q layer, the top of which is also at a depth of approximately 3 km below the seafloor and is continuous along-axis for at least 30 km. Both the low-Q layer and low-velocity zone can be explained geologically by a region of elevated temperatures. The third model is characterized by a homogeneous seismic layer 3. All models contain an ~1 km s−1 discontinuity at the seismic layer 2/3 boundary; a wide-angle reflection from this boundary is seen on all record sections. Kappel and Ryan (1986) had previously proposed that the Northern Symmetrical Segment was in a stage of volcanic inactivity, and this theory is supported by the seismic observations. Two-dimensional modelling of travel times to ocean bottom hydrophone instruments shows that the amplitude variations in the along-axis depth to intracrustal seismic layers (a few hundred meters) is on the order of the lateral changes in topographic relief. It is suggested that the crustal emplacement processes reflect the deeper style of 3-D mantle upwelling beneath the ridge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01204234
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  • 6
    Electronic Resource
    Electronic Resource
    Relationship between spreading rate and the seismic structure of mid-ocean ridges (1992)
    [s.l.] : Nature Publishing Group
    Nature 355 (1992), S. 815-817 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The existence of substantial zones of elevated temperature and/or partial melt beneath mid-ocean ridges is inferred when seismic velocities are observed to decrease with depth beneath the axes of active mid-ocean ridge segments. Until recently, almost all the robust determinations of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/355815a0
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  • 7
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    Continental rifting and sediment infill in the northwestern Gulf of Mexico (2015)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2015-06-23
    Description: The opening of the Gulf of Mexico was an important Mesozoic tectonic event that provides new insight in the role of magmatism and lithospheric stresses in the initiation of continental rifting. A new seismic velocity profile based on seismic refraction data in the northwestern Gulf of Mexico offshore Texas, where the basin started opening in the Early Jurassic, shows a rifted margin with strong lateral heterogeneity beneath the shelf and slope. The structure of the thinned crust is consistent with large-scale extensional faulting and moderate amounts of synrift magmatism before continental breakup. These new seismic constraints do not indicate the presence of a volcanic margin along the Texas coast, as has sometimes been proposed based on magnetic data. The Laurentian continental lithosphere of central Texas may have been too thick at the onset of rifting (〉100 km) to let magmatic diking control the extension. In contrast, the continental lithosphere of the northeastern Gulf of Mexico may have been thinner, such that magma-assisted rifting formed a volcanic margin there later in the Jurassic.
    Print ISSN: 0091-7613
    Electronic ISSN: 1943-2682
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 8
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    Dynamic response to strike-slip tectonic control on the deposition and evolution of the Baranof Fan, Gulf of Alaska (2014)
    Geological Society of America (GSA)
    In: Geosphere
    Details
    Publication Date: 2014-07-30
    Description: The Baranof Fan is one of three large deep-sea fans in the Gulf of Alaska, and is a key component in understanding large-scale erosion and sedimentation patterns for southeast Alaska and western Canada. We integrate new and existing seismic reflection profiles to provide new constraints on the Baranof Fan area, geometry, volume, and channel development. We estimate the fan’s area and total sediment volume to be ~323,000 km 2 and ~301,000 km 3 , respectively, making it among the largest deep-sea fans in the world. We show that the Baranof Fan consists of channel-levee deposits from at least three distinct aggradational channel systems: the currently active Horizon and Mukluk channels, and the waning system we call the Baranof channel. The oldest sedimentary deposits are in the northern fan, and the youngest deposits at the fan’s southern extent; in addition, the channels seem to avulse southward consistently through time. We suggest that Baranof Fan sediment is sourced from the Coast Mountains in southeastern Alaska, transported offshore most recently via fjord to glacial sea valley conduits. Because of the translation of the Pacific plate northwest past sediment sources on the North American plate along the Queen Charlotte strike-slip fault, we suggest that new channel formation, channel beheadings, and southward-migrating channel avulsions have been influenced by regional tectonics. Using a simplified tectonic reconstruction assuming a constant Pacific plate motion of 4.4 cm/yr, we estimate that Baranof Fan deposition initiated ca. 7 Ma.
    Electronic ISSN: 1553-040X
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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  • 9
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    Seismic images of the Transition fault and the unstable Yakutat-Pacific-North American triple junction (2013)
    Geological Society of America (GSA)
    In: Geology
    Details
    Publication Date: 2013-04-19
    Description: In southern Alaska, the Pacific plate and Yakutat terrane subduct beneath the North American plate along the Aleutian Trench and Pamplona zone, respectively, and are sliding past each other at minimal rates along the Transition fault. As the deformation front of the Pamplona zone stepped eastward during the Pliocene–Pleistocene, the Pacific–North American–Yakutat triple junction became unstable. Four recent seismic images reveal that the Transition fault changes from a single strike-slip boundary east of the deformation front to three strands that step increasingly seaward between the deformation front and the Aleutian Trench. The southern two strands deform the Pacific crust, and the outermost of these became increasingly convergent sometime since 1 Ma, as demonstrated by young growth strata. We propose that this internal deformation of the Pacific plate is an attempt to re-attain stability, which can only be reached by creating a tectonic boundary collinear with the Pamplona zone. The plate reorganization will result in initiation of subduction such that a portion of former Pacific crust will become accreted to the North American plate. Such accretion events caused by triple-junction instability may be an important mechanism for transferring oceanic crust to continental margins.
    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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    Structure of the Northern Symmetrical Segment of the Juan de Fuca Ridge (1993)
    Springer
    Details
    Publication Date: 1993-08-01
    Print ISSN: 0025-3235
    Electronic ISSN: 1573-0581
    Topics: Geosciences , Physics
    Published by Springer
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