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  • 1
    Online Resource
    Online Resource
    Sedimentology and tectonic setting of devonian-carboniferous turbidites and debris flow deposits in the variscan Vosges Mountains (Markstein Group, NE-France) (2007)
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    In: Deutsche Gesellschaft für Geowissenschaften, Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, Stuttgart : Schweizerbart, 1866, 158(2007), 4, Seite 1063-1087, 1861-4094
    In: volume:158
    In: year:2007
    In: number:4
    In: pages:1063-1087
    Type of Medium: Online Resource
    ISSN: 1861-4094
    DOI: 10.1127/1860-1804/2007/0158-1063
    Language: English
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  • 2
    Electronic Resource
    Electronic Resource
    Microstructure and fabric transitions in calcite tectonites from the Sierra Alhamilla (Spain) (1983)
    Springer
    International journal of earth sciences 72 (1983), S. 605-618 
    Details
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract A suite of marble specimens from the Sierra Alhamilla (Spain), deformed to large strains under natural conditions at about 300° C shows distinct variations in microstructure and fabrics. It can be demonstrated that the development of crystallographic preferred orientations and grain shape fabrics are strongly dependent on recrystallized grain size. This is interpreted to reflect the relative importance of various deformational mechanisms. Superplasticity seems to have a sharp upper grain size limit at 10–15 /smm. Within the power law creep regime, deformation in fine grained aggregates is probably dominated by diffusional, in coarser ones by dislocation mechanisms. The transition is a gradual one, and may span a grain size range of 30 /sm.
    Abstract: Résumé Une série d'échantillons de marbres de la Sierra Alhamilla (Espagne), fortement déformés sous des conditions naturelles de 300° C, montre des variations distinctes de microstructure et de texture. On peut démontrer que la formation des orientations préférentielles cristallographiques et de l'aplatissement des grains dépend clairement des dimensions des grains recristallisés. Ceci est interpreté a comme le reflet de l'importance relative de plusieurs mécanismes de déformation. Il apparaît, que le domaine de superplasticité a une limite bien definie a 10–15 /smm. Dans le domaine du fluage en σn, la déformation des aggrégats fins semble être dominée par des mécanismes de diffusion, et des aggregats de grande taille par des mećanismes de dislocation. La transition est graduelle, et peut comprendre un intervalle dimensionel des grains de 30 /smm.
    Notes: Zusammenfassung Eine Anzahl von Marmoren aus der Sierra Alhamilla (Spanien), intensiv deformiert unter natürlichen Bedingungen bei ca. 300° C, zeigt ausgeprägte Variationen in Mikrostruktur und Gefüge. Es kann gezeigt werden, daß die Entwicklung von bevorzugten Kristallorientierungen und Formanisotropien im Korngefüge erheblich von der rekristallisierten Korngröße abhängt. Dies wird als Ausdruck der relativen Aktivität verschiedener Deformationsmechanismen interpretiert. Superplastizität scheint eine relativ scharf definierte Obergrenze für Korngrößen von 10–15 /sm zu besitzen. Im Bereich des Potenzgesetz-Fließens wird die Verformung feinkörniger Aggregate wahrscheinlich von Diffusion, die von grobkörnigen von Dislokationsmechanismen bestimmt. Der Übergangsbereich zwischen beiden Mechanismen umfaßt einen Korngrößenunterschied von etwa 30 µ.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01822084
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  • 3
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    The onset of Walvis Ridge: Plume influence at the continental margin (2017)
    Elsevier
    In:  Tectonophysics, 716 . pp. 90-107.
    Details
    Publication Date: 2020-02-06
    Description: Highlights • Crustal structure of Walvis Ridge reveals high seismic velocities in the lower crust intruding the African continent. • This modified crust is localized to approx. 100 × 100 km within the continent. • No indication for a large plume head observed The opening of the South Atlantic is a classical example for a plume related continental breakup. Flood basalts are present on both conjugate margins as well as aseismic ridges connecting them with the current plume location at Tristan da Cunha. To determine the effect of the proposed plume head on the continental crust, we acquired wide-angle seismic data at the junction of the Walvis Ridge with the African continent and modelled the P-wave velocity structure in a forward approach. The profile extends 430. km along the ridge and continues onshore to a length of 720. km. Crustal velocities beneath the Walvis Ridge vary between 5.5. km/s and 7.0. km/s, a typical range for oceanic crust. The crustal thickness of 22. km, however, is approximately three times larger than of normal oceanic crust. The continent-ocean transition is characterized by 30. km thick crust with strong lateral velocity variations in the upper crust and a high-velocity lower crust (HVLC), where velocities reach up to 7.5. km/s. The HVLC is 100 to 130. km wider at the Walvis Ridge than it is farther south, and impinges onto the continental crust of the Kaoko fold belt. Such high seismic velocities indicate Mg-rich igneous material intruded into the continental crust during the initial rifting stage. However, the remaining continental crust seems unaffected by intrusions and the root of the 40. km-thick crust of the Kaoko belt is not thermally abraded. We conclude that the plume head did not modify the continental crust on a large scale, but caused rather local effects. Thus, it seems unlikely that a plume drove or initiated the breakup process. We further propose that the plume already existed underneath the continent prior to the breakup, and ponded melt erupted at emerging rift structures providing the magma for continental flood basalts.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.tecto.2017.03.011
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  • 4
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    Textures of eclogites and blueschists from Syros island, Greece: inferences for elastic anisotropy of subducted oceanic crust (2017)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 122 (7). 5306-5324 .
    Details
    Publication Date: 2020-02-06
    Description: Many blueschists and eclogites are inferred to have formed from oceanic basalts in subducted slabs. Knowledge of their elastic behaviour is essential for reconstructing the internal structure of subduction zones. The Cycladic Blueschist Unit, exposed on Syros Island (Greece), contains rocks belonging to an exhumed Tertiary subduction complex. They were possibly part of a subduction channel, a shear zone above the subducting slab in which exhumation is possible during subduction. Intense plastic deformation, forming crystallographic preferred orientations (CPO), accompanied blueschist and eclogite metamorphism. CPO of the constituent minerals in the collected samples was determined by time-of-flight neutron diffraction. Two samples are foliated fine-grained blueschists with strong CPO, rich in glaucophane, zoisite and phengite. Two coarser-grained eclogite samples rich in omphacite and clinozoisite, or glaucophane, have weaker CPO. Vp and Vs anisotropies were computed from the orientation distribution function and single-crystal elastic constants. All samples show velocity maxima parallel to the mineral lineation, and minima normal to the foliation, providing important constraints on orientations of seismic anisotropy in subduction channels. Vp anisotropies are up to three times higher (6.5-12%) in the blueschists than in the eclogites (3-4%), pointing to a potentially important lithological control of elastic anisotropy in subducted oceanic crust.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2017JB014181
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  • 5
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    Extrapolation of bulk rock elastic moduli of different rock types to high pressure conditions and comparison with texture-derived elastic moduli (2018)
    Elsevier
    In:  Physics of the Earth and Planetary Interiors, 275 . pp. 32-43.
    Details
    Publication Date: 2021-02-08
    Description: Highlights • Bulk rock elastic moduli of gneiss, amphibolite and marble using different techniques. • Neutron diffraction texture analysis and modeling of rock physical properties. • Measurement of seismic velocity anisotropy under pressures of up to 600 MPa. • Extrapolation of experimental data to higher pressures of 1000 MPa (crack free rock). • Comparison of modeled, experimental and extrapolated elastic anisotropy data. Abstract In this study elastic moduli of three different rock types of simple (calcite marble) and more complex (amphibolite, micaschist) mineralogical compositions were determined by modeling of elastic moduli using texture (crystallographic preferred orientation; CPO) data, experimental investigation and extrapolation. 3D models were calculated using single crystal elastic moduli, and CPO measured using time-of-flight neutron diffraction at the SKAT diffractometer in Dubna (Russia) and subsequently analyzed using Rietveld Texture Analysis. To define extrinsic factors influencing elastic behaviour, P-wave and S-wave velocity anisotropies were experimentally determined at 200, 400 and 600 MPa confining pressure. Functions describing variations of the elastic moduli with confining pressure were then used to predict elastic properties at 1000 MPa, revealing anisotropies in a supposedly crack-free medium. In the calcite marble elastic anisotropy is dominated by the CPO. Velocities continuously increase, while anisotropies decrease from measured, over extrapolated to CPO derived data. Differences in velocity patterns with sample orientation suggest that the foliation forms an important mechanical anisotropy. The amphibolite sample shows similar magnitudes of extrapolated and CPO derived velocities, however the pattern of CPO derived velocity is closer to that measured at 200 MPa. Anisotropy decreases from the extrapolated to the CPO derived data. In the micaschist, velocities are higher and anisotropies are lower in the extrapolated data, in comparison to the data from measurements at lower pressures. Generally our results show that predictions for the elastic behavior of rocks at great depths are possible based on experimental data and those computed from CPO. The elastic properties of the lower crust can, thus, be characterized with an improved degree of confidence using extrapolations. Anisotropically distributed spherical micro-pores are likely to be preserved, affecting seismic velocity distributions. Compositional variations in the polyphase rock samples do not significantly change the velocity patterns, allowing the use of RTA-derived volume percentages for the modeling of elastic moduli.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.pepi.2018.01.001
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  • 6
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    The Seno Otway pockmark field and its relationship to thermogenic gas occurrence at the western margin of the Magallanes Basin (Chile) (2018)
    Springer
    In:  Geo-Marine Letters, 38 (3). pp. 227-240.
    Details
    Publication Date: 2021-02-08
    Description: Pockmarks are variably sized crater-like structures that occur in young continental margin sediments. They are formed by gas eruptions and/or long-term release of fluid or gas. So far no pockmarks were known from the Pacific coast of South America between 51°S and 55°S. This article documents an extensive and previously unknown pockmark field in the Seno Otway (Otway Sound, 52°S) with multibeam bathymetry and parametric echosounding as well as sediment drill cores. Up to 31 pockmarks per square kilometer occur in water depths of 50 to 〉100 m in late glacial and Holocene sediments. They are up to 150 m wide and 10 m deep. Below and near the pockmarks, echosounder profiles image acoustic blanking as well as gas chimneys often crosscutting the 20 to 〉30 m thick glacial sediments above the acoustic basement, in particular along fault zones. Upward-migrating gas is trapped within the sediment strata, forming dome-like features. Two 5 m long piston cores from inside and outside a typical pockmark give no evidence for gas storage within the uppermost sediments. The inside core recovered poorly sorted glacial sediment, indicating reworking and re-deposition after several explosive events. The outside core documents an undisturbed stratigraphic sequence since ~15 ka. Many buried paleo-pockmarks occur directly below a prominent seismic reflector marking the mega-outflow event of the Seno Otway at 14.3 ka, lowering the proglacial lake level by about 80 m. This decompression would have led to frequent eruptions of gas trapped in reservoirs below the glacial sediments. However, the sediment fill of pockmarks formed after this event suggests recurrent events throughout the Holocene until today. Most pockmarks occur above folded hydrocarbon-bearing Upper Cretaceous and Paleogene rocks near the western margin of the Magallanes Basin, constraining them as likely source rocks for thermogenic gas.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00367-017-0530-6
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  • 7
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    A first estimation of gas hydrates offshore Patagonia (Chile) (2018)
    Elsevier
    In:  Marine and Petroleum Geology, 96 . pp. 232-239.
    Details
    Publication Date: 2021-02-08
    Description: In many places along the central and southern Chilean active continental margin sedimentary successions covering the forearc contain methane hydrate, resulting from a mixture of biogenic and thermogenic processes. Here, we report the spatial distribution of gas hydrate in the accretionary prism and forearc sediments offshore western Patagonia (50°S and 57°S), landward of the Antarctica-South America plate boundary. Knowledge of the forearc structure here is limited, owing to the small number of reflection seismic profiles available, lack of high-resolution bathymetry data and the absence of scientific drillholes. However bottom-simulating reflectors (BSR) indicative of gas hydrate occur regionally extensive below about one third of the forearc slope, between about 280 and 630 m below sea floor. BSR-derived heat flow was calculated at about 30 and 70 mWm−2. These are typical values above subduction zones of oceanic crust older than 10 Ma, where vigorous fluid flow above young and hot subducting oceanic crust has leveled off. To move towards an estimate of gas hydrate present in the sediments, the velocity model was converted into a gas-phase concentration model using data from one of the seismic sections. Average thickness of gas hydrate is about 290 m, and average concentrations estimated are in a range of 3.4%–10%. If we use the minimum value of 3.4%, the amount of methane present in the region is about 3.0 × 1013 m3 at standard pressure-temperature conditions. We conclude that the Pacific forearc of Patagonia area is an important reservoir of methane hydrates and we propose this area be considered as a potential methane hydrate concentrated zone and a key area to be investigated in the future.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.marpetgeo.2018.06.002
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  • 8
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    Does permanent extensional deformation in lower forearc slopes indicate shallow plate-boundary rupture? (2018)
    Elsevier
    In:  Earth and Planetary Science Letters, 489 . pp. 17-27.
    Details
    Publication Date: 2021-03-18
    Description: Highlights • We document marine forearc deformation in the Northern Chile seismic gap. • Upper-plate normal faulting off Northern Chile locally extends close to the trench. • Normal faults indicate that past earthquakes may reached the shallow plate-boundary. Abstract Seismic rupture of the shallow plate-boundary can result in large tsunamis with tragic socio-economic consequences, as exemplified by the 2011 Tohoku-Oki earthquake. To better understand the processes involved in shallow earthquake rupture in seismic gaps (where megathrust earthquakes are expected), and investigate the tsunami hazard, it is important to assess whether the region experienced shallow earthquake rupture in the past. However, there are currently no established methods to elucidate whether a margin segment has repeatedly experienced shallow earthquake rupture, with the exception of mechanical studies on subducted fault-rocks. Here we combine new swath bathymetric data, unpublished seismic reflection images, and inter-seismic seismicity to evaluate if the pattern of permanent deformation in the marine forearc of the Northern Chile seismic gap allows inferences on past earthquake behavior. While the tectonic configuration of the middle and upper slope remains similar over hundreds of kilometers along the North Chilean margin, we document permanent extensional deformation of the lower slope localized to the region 20.8°S–22°S. Critical taper analyses, the comparison of permanent deformation to inter-seismic seismicity and plate-coupling models, as well as recent observations from other subduction-zones, including the area that ruptured during the 2011 Tohoku-Oki earthquake, suggest that the normal faults at the lower slope may have resulted from shallow, possibly near-trench breaking earthquake ruptures in the past. In the adjacent margin segments, the 1995 Antofagasta, 2007 Tocopilla, and 2014 Iquique earthquakes were limited to the middle and upper-slope and the terrestrial forearc, and so are upper-plate normal faults. Our findings suggest a seismo-tectonic segmentation of the North Chilean margin that seems to be stable over multiple earthquake cycles. If our interpretations are correct, they indicate a high tsunami hazard posed by the yet un-ruptured southern segment of the seismic gap.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2018.02.030
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  • 9
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    Active tectonics of the North Chilean marine forearc and adjacent oceanic Nazca Plate (2018)
    AGU (American Geophysical Union) | Wiley
    In:  Tectonics, 37 (11). pp. 4194-4211.
    Details
    Publication Date: 2021-02-08
    Description: Key Points: Multibeam bathymetric and seismic reflection data image the structure of the North Chilean marine forearc and the oceanic Nazca plate The structural character and tectonic configuration of the offshore forearc and the oceanic plate change significantly along the margin The derived pattern of permanent deformation may hold information for studying seismicity or other types of short term deformation New multibeam bathymetry allows an unprecedented view of the tectonic regime and its along‐strike heterogeneity of the North Chilean marine forearc and the oceanic Nazca Plate between 19‐22.75°S. Combining bathymetric and backscatter information from the multibeam data with sub‐bottom profiler and published and previously unpublished legacy seismic reflection lines, we derive a tectonic map. The new map reveals a middle and upper‐slope configuration dominated by pervasive extensional faulting, with some faults outlining a 〉500 km long ridge that may represent the remnants of a Jurassic or pre‐Jurassic magmatic arc. Lower slope deformation is more variable and includes slope‐failures, normal faulting, re‐entrant embayments, and NW‐SE trending anticlines and synclines. This complex pattern likely results from the combination of subducting lower‐plate topography, gravitational forearc collapse, and the accumulation of permanent deformation over multiple earthquake cycles. We find little evidence for widespread fluid seepage despite a highly faulted upper‐plate. An explanation could be a lack of fluid sources due to the sediment starved nature of the trench and most of the upper‐plate in vicinity of the hyper‐arid Atacama Desert. Changes in forearc architecture partly correlate to structural variations of the oceanic Nazca Plate, which is dominated by the spreading‐related abyssal hill fabric and is regionally overprinted by the Iquique Ridge. The ridge collides with the forearc around 20‐21°S. South of the ridge‐forearc intersection, bending‐related horst‐and‐grabens result in vertical seafloor offsets of hundreds of meters. To the north, plate‐bending is accommodated by reactivation of the paleo‐spreading fabric and new horst‐and‐grabens do not develop.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2018TC005087
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  • 10
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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
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