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  • 1
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    Crustal structure of northwest Namibia: Evidence for plume-rift-continent interaction (2015)
    GSA, Geological Society of America
    In:  Geology, 43 (8). pp. 739-742.
    Details
    Publication Date: 2017-05-17
    Description: The causes for the formation of large igneous provinces and hotspot trails are still a matter of considerable dispute. Seismic tomography and other studies suggest that hot mantle material rising from the core-mantle boundary (CMB) might play a significant role in the formation of such hotspot trails. An important area to verify this concept is the South Atlantic region, with hotspot trails that spatially coincide with one of the largest low-velocity regions at the CMB, the African large low shear-wave velocity province. The Walvis Ridge started to form during the separation of the South American and African continents at ca. 130 Ma as a consequence of Gondwana breakup. Here, we present the first deep-seismic sounding images of the crustal structure from the landfall area of the Walvis Ridge at the Namibian coast to constrain processes of plume-lithosphere interaction and the formation of continental flood basalts (Paraná and Etendeka continental flood basalts) and associated intrusive rocks. Our study identified a narrow region (〈100 km) of high-seismic-velocity anomalies in the middle and lower crust, which we interpret as a massive mafic intrusion into the northern Namibian continental crust. Seismic crustal reflection imaging shows a flat Moho as well as reflectors connecting the high-velocity body with shallow crustal structures that we speculate to mark potential feeder channels of the Etendeka continental flood basalt. We suggest that the observed massive but localized mafic intrusion into the lower crust results from similar-sized variations in the lithosphere (i.e., lithosphere thickness or preexisting structures)
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/G36768.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    The thickness of subduction plate boundary faults from the seafloor into the seismogenic zone (2013)
    GSA, Geological Society of America
    In:  Geology, 41 (9). pp. 991-994.
    Details
    Publication Date: 2017-05-17
    Description: The thickness of an active plate boundary fault is an important parameter for understanding the strength and spatial heterogeneity of fault behavior. We have compiled direct measurements of the thickness of subduction thrust faults from active and ancient examples observed by ocean drilling and fi eld studies in accretionary wedges. We describe a general geometric model for subduction thrust décollements, which includes multiple simultaneously active, anastomosing fault strands tens of meters thick. The total thickness encompassing all simultaneously active strands increases to ~100–350 m at ~1–2 km below seafl oor, and this thickness is maintained down to a depth of ~15 km. Thin sharp faults representing earthquake slip surfaces or other discrete slip events are found within and along the edges of the tens-ofmeters- thick fault strands. Although fl attening, primary inherited chaotic fabrics, and fault migration through subducting sediments or the frontal prism may build mélange sections that are much thicker (to several kilometers), this thickness does not describe the active fault at any depth. These observations suggest that models should treat the subduction thrust plate boundary fault as 〈1–20 cm thick during earthquakes, with a concentration of postseismic and interseismic creep in single to several strands 5–35 m thick, with lesser distributed interseismic deformation in stratally disrupted rocks surrounding the fault strands.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1130/G34556.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Back-scattered electron imagery of the tectonic fabrics of some fine-grained sediments : implications for fabric nomenclature and deformation processes (1989)
    GSA, Geological Society of America
    In:  Geology, 17 . pp. 901-904.
    Details
    Publication Date: 2018-01-17
    Description: Back-scattered electron investigations of Argille Scagliose, mudstones from the Barbados forearc sampled during Ocean Drilling Program Leg 110, and the matrix of the Okitsu melange, southwest Japan, indicate a variety of microfabric geometries and deformation mechanisms despite the similarity of their mesoscopic scaly fabrics. In the Okitsu melange, the scaly fabric is the mesoscopic expression of an anastomosing microfabric, whereas the detailed geometry of scaly fabrics is unrelated to the microfabric in the Argille Scagliose and Leg 110 mudstones. Care must be taken in the classification and interpretation of scaly fabrics in light of these data, and future studies should focus on microstructural investigations.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/0091-7613(1989)017〈0901:BSEIOT〉2.3.CO;2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    South Atlantic opening: A plume-induced breakup? (2015)
    GSA, Geological Society of America
    In:  Geology, 43 (10). pp. 931-934.
    Details
    Publication Date: 2017-05-17
    Description: Upwelling hot mantle plumes are thought to disintegrate continental lithosphere and are considered to be drivers of active continental breakup. The formation of the Walvis Ridge during the opening of the South Atlantic is related to a putative plume-induced breakup. We investigated the crustal structure of the Walvis Ridge (southeast Atlantic Ocean) at its intersection with the continental margin and searched for anomalies related to the possible plume head. The overall structure we identify suggests that no broad plume head existed during opening of the South Atlantic and anomalous mantle melting occurred only locally. We therefore question the importance of a plume head as a driver of continental breakup and further speculate that the hotspot was present before the rifting, leaving a track of kimberlites in the African craton.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1130/G36936.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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