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  • AGU (American Geophysical Union)  (5)
  • Kiel : GEOMAR  (1)
  • 1
    Book
    Book
    CONGO Compilation of seismic wide-angle data : RV METEOR Cruise M56 Congo 2002, Gashydrate Research - GEOMAR Data Report (2003)
    Kiel : GEOMAR
    Details Availability
    Keywords: Forschungsbericht
    Type of Medium: Book
    Pages: 43 Seiten
    Language: English
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  • 2
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    Lower plate structure and upper plate deformational segmentation at the Sunda-Banda arc transition, Indonesia (2010)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 115 (B8). B08107.
    Details
    Publication Date: 2018-02-27
    Description: The Sunda‐Banda arc transition at the eastern termination of the Sunda margin (Indonesia) represents a unique natural laboratory to study the effects of lower plate variability on upper plate deformational segmentation. Neighboring margin segments display a high degree of structural diversity of the incoming plate (transition from an oceanic to a continental lower plate, presence/absence of an oceanic plateau, variability of subducting seafloor morphology) as well as a wide range of corresponding fore‐arc structures, including a large sedimentary basin and an accretionary prism/outer arc high of variable size and shape. Here, we present results of a combined analysis of seismic wide‐angle refraction, multichannel streamer and gravity data recorded in two trench normal corridors located offshore the islands of Lombok (116°E) and Sumba (119°E). On the incoming plate, the results reveal a 8.6–9.0 km thick oceanic crust, which is progressively faulted and altered when approaching the trench, where upper mantle velocities are reduced to ∼7.5 km/s. The outer arc high, located between the trench and the fore‐arc basin, is characterized by sedimentary‐type velocities (Vp 〈 5.5 km/s) down to the top of the subducting slab (∼13 km depth). The oceanic slab can be traced over 70–100 km distance beneath the fore arc. A shallow serpentinized mantle wedge at ∼16 km depth offshore Lombok is absent offshore Sumba, where our models reveal the transition to the collisional regime farther to the east and to the Sumba block in the north. Our results allow a detailed view into the complex structure of both the deeper and shallower portions of the eastern Sunda margin.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2009JB006713
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Fore-arc deformation and underplating at the northern Hikurangi margin, New Zealand (2010)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 115 (B6). B06408.
    Details
    Publication Date: 2018-01-19
    Description: Geophysical investigations of the northern Hikurangi subduction zone northeast of New Zealand, image fore‐arc and surrounding upper lithospheric structures. A seismic velocity (Vp) field is determined from seismic wide‐angle data, and our structural interpretation is supported by multichannel seismic reflection stratigraphy and gravity and magnetic modeling. We found that the subducting Hikurangi Plateau carries about 2 km of sediments above a 2 km mixed layer of volcaniclastics, limestone, and chert. The upper plateau crust is characterized by Vp = 4.9–6.7 km/s overlying the lower crust with Vp 〉 7.1 km/s. Gravity modeling yields a plateau thickness around 10 km. The reactivated Raukumara fore‐arc basin is 〉10 km deep, deposited on 5–10 km thick Australian crust. The fore‐arc mantle of Vp 〉 8 km/s appears unaffected by subduction hydration processes. The East Cape Ridge fore‐arc high is underlain by a 3.5 km deep strongly magnetic (3.3 A/m) high‐velocity zone, interpreted as part of the onshore Matakaoa volcanic allochthon and/or uplifted Raukumara Basin basement of probable oceanic crustal origin. Beneath the trench slope, we interpret low‐seismic‐velocity, high‐attenuation, low‐density fore‐arc material as accreted and recycled, suggesting that underplating and uplift destabilizes East Cape Ridge, triggering two‐sided mass wasting. Mass balance calculations indicate that the proposed accreted and recycled material represents 25–100% of all incoming sediment, and any remainder could be accounted for through erosion of older accreted material into surrounding basins. We suggest that continental mass flux into the mantle at subduction zones may be significantly overestimated because crustal underplating beneath fore‐arc highs have not properly been accounted for.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2009JB006645
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Microearthquake seismicity of the Mid-Atlantic Ridge at 5°S: A view of tectonic extension (2004)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 109 . B06102.
    Details
    Publication Date: 2018-04-25
    Description: We report measurements made with an ocean bottom array which was operated for 10 days on the Mid-Atlantic Ridge just south of the 5°S transform fault/fracture zone. A total of 148 locatable earthquakes with magnitudes ∼0.5–2.8 were recorded; seismic activity appears to be concentrated within the western half of the median valley. The median valley seismic zone is bounded in along-axis direction by the transform fault to the north and the tip of the axial volcanic ridge to the south. A few scattered events occurred within the inside corner high, on the transform fault, and in the western sidewall close to the segment center. Earthquakes reach a maximum depth of 8 km below the median valley floor and appear to be predominantly in the mantle, although a few crustal earthquakes also occurred. The presence of earthquakes in the mantle indicates that it is not strongly serpentinized. We infer the median valley seismic activity to primarily arise from normal faulting.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2003JB002827
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Sunda-Banda arc transition: incipient continent-island arc collision (Northwest Australia) (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 . L10304.
    Details
    Publication Date: 2017-10-12
    Description: The eastern Sunda arc represents one of the few regions globally where the early stages of continent-arc collision can be studied. We studied along the western limit of the collision zone at the Sunda-Banda arc transition, where the Australian margin collides with the Banda island arc, causing widespread back arc thrusting. We present integrated results of a refraction/wide-angle reflection tomography, gravity modeling, and multichannel reflection seismic imaging using data acquired in 2006 southeast of Sumba Island. The composite structural model reveals the previously unresolved deep geometry of the collision zone. Changes in crustal structure encompass the 10 - 12 km thick Australian basement in the south and the 22 - 24 kmthick Sumba ridge in the north, where backthrusting of the 130 km wide accretionary prism is documented. The structural diversity along this transect could be characteristic of young collisional systems at the transition from oceanic subduction to continent-arc collision. Citation: Shulgin, A., H. Kopp, C. Mueller, E. Lueschen, L. Planert, M. Engels, E. R. Flueh, A. Krabbenhoeft, and Y. Djajadihardja (2009), Sunda-Banda arc transition: Incipient continent-island arc collision (northwest Australia), Geophys. Res. Lett., 36, L10304, doi: 10.1029/2009GL037533.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2009GL037533
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  • 6
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    Along- and across-axis variations in crustal thickness and structure at the Mid-Atlantic Ridge at 5°S obtained from wide-angle seismic tomography: implications for ridge segmentation (2009)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2022-03-07
    Description: Two end‐member styles of crustal accretion are observed at two adjacent spreading segments at the Mid‐Atlantic Ridge at 5°S: focused accretion to the segment center with rapid crustal thinning toward the transform in the northern segment and crustal thickening toward the transform at an oceanic core complex in the southern segment. Our results were obtained by tomographic inversion of wide‐angle seismic reflection and refraction data collected along three intersecting profiles. The segment north of the 5°S fracture zone is characterized by a well‐developed median valley with a pronounced seafloor bulge in the segment center. A discrete portion of anomalously low velocities (−0.4 to −0.5 km/s relative to average off‐axis structure) at depths of ∼2.5 km beneath this bulge is possibly related to the presence of elevated temperatures and perhaps small portions of partial melt. This suggests that this segment is currently in a magmatically active period, which is confirmed by the observation of fresh lava flows and ongoing high‐temperature hydrothermal activity at the seafloor. Close to the current spreading axis, the crust thins rapidly from 8.5 km beneath the segment center to less than 3 km beneath the transform fault which indicates that melt supply here is strongly focused to the segment center. The reduction in crustal thickness is almost exclusively accommodated by the thinning of velocity portions indicative of seismic layer 3. The transform fault is characterized by more uniform velocity gradients throughout the entire crustal section and very low upper mantle velocities of 7.2–7.3 km/s indicating that serpentinization could be as much as 25% at 3.5 km depth. In contrast, ∼4.1 Ma old crust of the northern segment shows only minor thinning from the segment center toward the segment end. Here, the transform is characterized by a normal seismic layer 2/3 transition suggesting robust melt supply to the segment end at those times. In the adjacent southern segment, the crust thickens from ∼2.5 km beneath the flank of an oceanic core complex to ∼5.0 km at the segment boundary. The observed changes in crustal thickness show a significant temporal and lateral variability in melt supply and suggest a more complex crustal emplacement process than predicted by models of focused melt supply to the segment centers.
    Type: Article , PeerReviewed
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